1 ACPI ACPI support is enabled. 2 AGP AGP (Accelerated Graphics Port) is enabled. 3 ALSA ALSA sound support is enabled. 4 APIC APIC support is enabled. 5 APM Advanced Power Management support is enabled. 6 APPARMOR AppArmor support is enabled. 7 ARM ARM architecture is enabled. 8 ARM64 ARM64 architecture is enabled. 9 CLK Common clock infrastructure is enabled. 10 CMA Contiguous Memory Area support is enabled. 11 CPU_FREQ CPU frequency scaling is enabled. 12 CPU_IDLE CPU idle time management is enabled. 13 DRM Direct Rendering Management support is enabled. 14 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 15 EARLY Parameter processed too early to be embedded in initrd. 16 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 17 EFI EFI Partitioning (GPT) is enabled 18 EVM Extended Verification Module 19 FB The frame buffer device is enabled. 20 FTRACE Function tracing enabled. 21 GCOV GCOV profiling is enabled. 22 HIBERNATION HIBERNATION is enabled. 23 HW Appropriate hardware is enabled. 24 HYPER_V HYPERV support is enabled. 25 IMA Integrity measurement architecture is enabled. 26 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 27 IPV6 IPv6 support is enabled. 28 ISAPNP ISA PnP code is enabled. 29 ISOL CPU Isolation is enabled. 30 JOY Appropriate joystick support is enabled. 31 KGDB Kernel debugger support is enabled. 32 KVM Kernel Virtual Machine support is enabled. 33 LIBATA Libata driver is enabled 34 LOONGARCH LoongArch architecture is enabled. 35 LOOP Loopback device support is enabled. 36 LP Printer support is enabled. 37 M68k M68k architecture is enabled. 38 These options have more detailed description inside of 39 Documentation/arch/m68k/kernel-options.rst. 40 MIPS MIPS architecture is enabled. 41 MOUSE Appropriate mouse support is enabled. 42 MSI Message Signaled Interrupts (PCI). 43 MTD MTD (Memory Technology Device) support is enabled. 44 NET Appropriate network support is enabled. 45 NFS Appropriate NFS support is enabled. 46 NUMA NUMA support is enabled. 47 OF Devicetree is enabled. 48 PARISC The PA-RISC architecture is enabled. 49 PCI PCI bus support is enabled. 50 PCIE PCI Express support is enabled. 51 PCMCIA The PCMCIA subsystem is enabled. 52 PM Power Management support is enabled. 53 PNP Plug & Play support is enabled. 54 PPC PowerPC architecture is enabled. 55 PPT Parallel port support is enabled. 56 PS2 Appropriate PS/2 support is enabled. 57 PV_OPS A paravirtualized kernel is enabled. 58 RAM RAM disk support is enabled. 59 RDT Intel Resource Director Technology. 60 RISCV RISCV architecture is enabled. 61 S390 S390 architecture is enabled. 62 SCSI Appropriate SCSI support is enabled. 63 A lot of drivers have their options described inside 64 the Documentation/scsi/ sub-directory. 65 SDW SoundWire support is enabled. 66 SECURITY Different security models are enabled. 67 SELINUX SELinux support is enabled. 68 SERIAL Serial support is enabled. 69 SH SuperH architecture is enabled. 70 SMP The kernel is an SMP kernel. 71 SPARC Sparc architecture is enabled. 72 SUSPEND System suspend states are enabled. 73 SWSUSP Software suspend (hibernation) is enabled. 74 TPM TPM drivers are enabled. 75 UMS USB Mass Storage support is enabled. 76 USB USB support is enabled. 77 NVME NVMe support is enabled 78 USBHID USB Human Interface Device support is enabled. 79 V4L Video For Linux support is enabled. 80 VGA The VGA console has been enabled. 81 VMMIO Driver for memory mapped virtio devices is enabled. 82 VT Virtual terminal support is enabled. 83 WDT Watchdog support is enabled. 84 X86-32 X86-32, aka i386 architecture is enabled. 85 X86-64 X86-64 architecture is enabled. 86 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 87 X86_UV SGI UV support is enabled. 88 XEN Xen support is enabled 89 XTENSA xtensa architecture is enabled. 90 91In addition, the following text indicates that the option 92 93 BOOT Is a boot loader parameter. 94 BUGS= Relates to possible processor bugs on the said processor. 95 KNL Is a kernel start-up parameter. 96 97 98Kernel parameters 99 100 accept_memory= [MM] 101 Format: { eager | lazy } 102 default: lazy 103 By default, unaccepted memory is accepted lazily to 104 avoid prolonged boot times. The lazy option will add 105 some runtime overhead until all memory is eventually 106 accepted. In most cases the overhead is negligible. 107 For some workloads or for debugging purposes 108 accept_memory=eager can be used to accept all memory 109 at once during boot. 110 111 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 112 Advanced Configuration and Power Interface 113 Format: { force | on | off | strict | noirq | rsdt | 114 copy_dsdt | nospcr } 115 force -- enable ACPI if default was off 116 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 117 off -- disable ACPI if default was on 118 noirq -- do not use ACPI for IRQ routing 119 strict -- Be less tolerant of platforms that are not 120 strictly ACPI specification compliant. 121 rsdt -- prefer RSDT over (default) XSDT 122 copy_dsdt -- copy DSDT to memory 123 nocmcff -- Disable firmware first mode for corrected 124 errors. This disables parsing the HEST CMC error 125 source to check if firmware has set the FF flag. This 126 may result in duplicate corrected error reports. 127 nospcr -- disable console in ACPI SPCR table as 128 default _serial_ console on ARM64 129 spcr -- enable console in ACPI SPCR table as 130 default _serial_ console on x86 131 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 132 "acpi=nospcr" are available 133 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 134 are available 135 136 See also Documentation/power/runtime_pm.rst, pci=noacpi 137 138 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 139 Format: <int> 140 2: use 2nd APIC table, if available 141 1,0: use 1st APIC table 142 default: 0 143 144 acpi_backlight= [HW,ACPI] 145 { vendor | video | native | none } 146 If set to vendor, prefer vendor-specific driver 147 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 148 of the ACPI video.ko driver. 149 If set to video, use the ACPI video.ko driver. 150 If set to native, use the device's native backlight mode. 151 If set to none, disable the ACPI backlight interface. 152 153 acpi_force_32bit_fadt_addr [ACPI,EARLY] 154 force FADT to use 32 bit addresses rather than the 155 64 bit X_* addresses. Some firmware have broken 64 156 bit addresses for force ACPI ignore these and use 157 the older legacy 32 bit addresses. 158 159 acpica_no_return_repair [HW, ACPI] 160 Disable AML predefined validation mechanism 161 This mechanism can repair the evaluation result to make 162 the return objects more ACPI specification compliant. 163 This option is useful for developers to identify the 164 root cause of an AML interpreter issue when the issue 165 has something to do with the repair mechanism. 166 167 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 168 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 169 Format: <int> 170 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 171 debug output. Bits in debug_layer correspond to a 172 _COMPONENT in an ACPI source file, e.g., 173 #define _COMPONENT ACPI_EVENTS 174 Bits in debug_level correspond to a level in 175 ACPI_DEBUG_PRINT statements, e.g., 176 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 177 The debug_level mask defaults to "info". See 178 Documentation/firmware-guide/acpi/debug.rst for more information about 179 debug layers and levels. 180 181 Enable processor driver info messages: 182 acpi.debug_layer=0x20000000 183 Enable AML "Debug" output, i.e., stores to the Debug 184 object while interpreting AML: 185 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 186 Enable all messages related to ACPI hardware: 187 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 188 189 Some values produce so much output that the system is 190 unusable. The "log_buf_len" parameter may be useful 191 if you need to capture more output. 192 193 acpi.poweroff_on_fatal= [ACPI] 194 {0 | 1} 195 Causes the system to poweroff when the ACPI bytecode signals 196 a fatal error. The default value of this setting is 1. 197 Overriding this value should only be done for diagnosing 198 ACPI firmware problems, as the system might behave erratically 199 after having encountered a fatal ACPI error. 200 201 acpi_enforce_resources= [ACPI] 202 { strict | lax | no } 203 Check for resource conflicts between native drivers 204 and ACPI OperationRegions (SystemIO and SystemMemory 205 only). IO ports and memory declared in ACPI might be 206 used by the ACPI subsystem in arbitrary AML code and 207 can interfere with legacy drivers. 208 strict (default): access to resources claimed by ACPI 209 is denied; legacy drivers trying to access reserved 210 resources will fail to bind to device using them. 211 lax: access to resources claimed by ACPI is allowed; 212 legacy drivers trying to access reserved resources 213 will bind successfully but a warning message is logged. 214 no: ACPI OperationRegions are not marked as reserved, 215 no further checks are performed. 216 217 acpi_force_table_verification [HW,ACPI,EARLY] 218 Enable table checksum verification during early stage. 219 By default, this is disabled due to x86 early mapping 220 size limitation. 221 222 acpi_irq_balance [HW,ACPI] 223 ACPI will balance active IRQs 224 default in APIC mode 225 226 acpi_irq_nobalance [HW,ACPI] 227 ACPI will not move active IRQs (default) 228 default in PIC mode 229 230 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 231 Format: <irq>,<irq>... 232 233 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 234 use by PCI 235 Format: <irq>,<irq>... 236 237 acpi_mask_gpe= [HW,ACPI] 238 Due to the existence of _Lxx/_Exx, some GPEs triggered 239 by unsupported hardware/firmware features can result in 240 GPE floodings that cannot be automatically disabled by 241 the GPE dispatcher. 242 This facility can be used to prevent such uncontrolled 243 GPE floodings. 244 Format: <byte> or <bitmap-list> 245 246 acpi_no_auto_serialize [HW,ACPI] 247 Disable auto-serialization of AML methods 248 AML control methods that contain the opcodes to create 249 named objects will be marked as "Serialized" by the 250 auto-serialization feature. 251 This feature is enabled by default. 252 This option allows to turn off the feature. 253 254 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 255 kernels. 256 257 acpi_no_static_ssdt [HW,ACPI,EARLY] 258 Disable installation of static SSDTs at early boot time 259 By default, SSDTs contained in the RSDT/XSDT will be 260 installed automatically and they will appear under 261 /sys/firmware/acpi/tables. 262 This option turns off this feature. 263 Note that specifying this option does not affect 264 dynamic table installation which will install SSDT 265 tables to /sys/firmware/acpi/tables/dynamic. 266 267 acpi_no_watchdog [HW,ACPI,WDT] 268 Ignore the ACPI-based watchdog interface (WDAT) and let 269 a native driver control the watchdog device instead. 270 271 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 272 Pass the RSDP address to the kernel, mostly used 273 on machines running EFI runtime service to boot the 274 second kernel for kdump. 275 276 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 277 Format: To spoof as Windows 98: ="Microsoft Windows" 278 279 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 280 of 2 which is mandated by ACPI 6) as the supported ACPI 281 specification revision (when using this switch, it may 282 be necessary to carry out a cold reboot _twice_ in a 283 row to make it take effect on the platform firmware). 284 285 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 286 acpi_osi="string1" # add string1 287 acpi_osi="!string2" # remove string2 288 acpi_osi=!* # remove all strings 289 acpi_osi=! # disable all built-in OS vendor 290 strings 291 acpi_osi=!! # enable all built-in OS vendor 292 strings 293 acpi_osi= # disable all strings 294 295 'acpi_osi=!' can be used in combination with single or 296 multiple 'acpi_osi="string1"' to support specific OS 297 vendor string(s). Note that such command can only 298 affect the default state of the OS vendor strings, thus 299 it cannot affect the default state of the feature group 300 strings and the current state of the OS vendor strings, 301 specifying it multiple times through kernel command line 302 is meaningless. This command is useful when one do not 303 care about the state of the feature group strings which 304 should be controlled by the OSPM. 305 Examples: 306 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 307 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 308 can make '_OSI("Windows 2000")' TRUE. 309 310 'acpi_osi=' cannot be used in combination with other 311 'acpi_osi=' command lines, the _OSI method will not 312 exist in the ACPI namespace. NOTE that such command can 313 only affect the _OSI support state, thus specifying it 314 multiple times through kernel command line is also 315 meaningless. 316 Examples: 317 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 318 FALSE. 319 320 'acpi_osi=!*' can be used in combination with single or 321 multiple 'acpi_osi="string1"' to support specific 322 string(s). Note that such command can affect the 323 current state of both the OS vendor strings and the 324 feature group strings, thus specifying it multiple times 325 through kernel command line is meaningful. But it may 326 still not able to affect the final state of a string if 327 there are quirks related to this string. This command 328 is useful when one want to control the state of the 329 feature group strings to debug BIOS issues related to 330 the OSPM features. 331 Examples: 332 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 333 '_OSI("Module Device")' FALSE. 334 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 335 '_OSI("Module Device")' TRUE. 336 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 337 equivalent to 338 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 339 and 340 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 341 they all will make '_OSI("Windows 2000")' TRUE. 342 343 acpi_pm_good [X86] 344 Override the pmtimer bug detection: force the kernel 345 to assume that this machine's pmtimer latches its value 346 and always returns good values. 347 348 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 349 Format: { level | edge | high | low } 350 351 acpi_skip_timer_override [HW,ACPI,EARLY] 352 Recognize and ignore IRQ0/pin2 Interrupt Override. 353 For broken nForce2 BIOS resulting in XT-PIC timer. 354 355 acpi_sleep= [HW,ACPI] Sleep options 356 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 357 s4_nohwsig, old_ordering, nonvs, 358 sci_force_enable, nobl } 359 See Documentation/power/video.rst for information on 360 s3_bios and s3_mode. 361 s3_beep is for debugging; it makes the PC's speaker beep 362 as soon as the kernel's real-mode entry point is called. 363 s4_hwsig causes the kernel to check the ACPI hardware 364 signature during resume from hibernation, and gracefully 365 refuse to resume if it has changed. This complies with 366 the ACPI specification but not with reality, since 367 Windows does not do this and many laptops do change it 368 on docking. So the default behaviour is to allow resume 369 and simply warn when the signature changes, unless the 370 s4_hwsig option is enabled. 371 s4_nohwsig prevents ACPI hardware signature from being 372 used (or even warned about) during resume. 373 old_ordering causes the ACPI 1.0 ordering of the _PTS 374 control method, with respect to putting devices into 375 low power states, to be enforced (the ACPI 2.0 ordering 376 of _PTS is used by default). 377 nonvs prevents the kernel from saving/restoring the 378 ACPI NVS memory during suspend/hibernation and resume. 379 sci_force_enable causes the kernel to set SCI_EN directly 380 on resume from S1/S3 (which is against the ACPI spec, 381 but some broken systems don't work without it). 382 nobl causes the internal blacklist of systems known to 383 behave incorrectly in some ways with respect to system 384 suspend and resume to be ignored (use wisely). 385 386 acpi_use_timer_override [HW,ACPI,EARLY] 387 Use timer override. For some broken Nvidia NF5 boards 388 that require a timer override, but don't have HPET 389 390 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 391 kernel's map of available physical RAM. 392 393 agp= [AGP] 394 { off | try_unsupported } 395 off: disable AGP support 396 try_unsupported: try to drive unsupported chipsets 397 (may crash computer or cause data corruption) 398 399 ALSA [HW,ALSA] 400 See Documentation/sound/alsa-configuration.rst 401 402 alignment= [KNL,ARM] 403 Allow the default userspace alignment fault handler 404 behaviour to be specified. Bit 0 enables warnings, 405 bit 1 enables fixups, and bit 2 sends a segfault. 406 407 align_va_addr= [X86-64] 408 Align virtual addresses by clearing slice [14:12] when 409 allocating a VMA at process creation time. This option 410 gives you up to 3% performance improvement on AMD F15h 411 machines (where it is enabled by default) for a 412 CPU-intensive style benchmark, and it can vary highly in 413 a microbenchmark depending on workload and compiler. 414 415 32: only for 32-bit processes 416 64: only for 64-bit processes 417 on: enable for both 32- and 64-bit processes 418 off: disable for both 32- and 64-bit processes 419 420 alloc_snapshot [FTRACE] 421 Allocate the ftrace snapshot buffer on boot up when the 422 main buffer is allocated. This is handy if debugging 423 and you need to use tracing_snapshot() on boot up, and 424 do not want to use tracing_snapshot_alloc() as it needs 425 to be done where GFP_KERNEL allocations are allowed. 426 427 allow_mismatched_32bit_el0 [ARM64,EARLY] 428 Allow execve() of 32-bit applications and setting of the 429 PER_LINUX32 personality on systems where only a strict 430 subset of the CPUs support 32-bit EL0. When this 431 parameter is present, the set of CPUs supporting 32-bit 432 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 433 and hot-unplug operations may be restricted. 434 435 See Documentation/arch/arm64/asymmetric-32bit.rst for more 436 information. 437 438 amd_iommu= [HW,X86-64] 439 Pass parameters to the AMD IOMMU driver in the system. 440 Possible values are: 441 fullflush - Deprecated, equivalent to iommu.strict=1 442 off - do not initialize any AMD IOMMU found in 443 the system 444 force_isolation - Force device isolation for all 445 devices. The IOMMU driver is not 446 allowed anymore to lift isolation 447 requirements as needed. This option 448 does not override iommu=pt 449 force_enable - Force enable the IOMMU on platforms known 450 to be buggy with IOMMU enabled. Use this 451 option with care. 452 pgtbl_v1 - Use v1 page table for DMA-API (Default). 453 pgtbl_v2 - Use v2 page table for DMA-API. 454 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 455 nohugepages - Limit page-sizes used for v1 page-tables 456 to 4 KiB. 457 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 458 to 4KiB/2Mib/1GiB. 459 460 461 amd_iommu_dump= [HW,X86-64] 462 Enable AMD IOMMU driver option to dump the ACPI table 463 for AMD IOMMU. With this option enabled, AMD IOMMU 464 driver will print ACPI tables for AMD IOMMU during 465 IOMMU initialization. 466 467 amd_iommu_intr= [HW,X86-64] 468 Specifies one of the following AMD IOMMU interrupt 469 remapping modes: 470 legacy - Use legacy interrupt remapping mode. 471 vapic - Use virtual APIC mode, which allows IOMMU 472 to inject interrupts directly into guest. 473 This mode requires kvm-amd.avic=1. 474 (Default when IOMMU HW support is present.) 475 476 amd_pstate= [X86,EARLY] 477 disable 478 Do not enable amd_pstate as the default 479 scaling driver for the supported processors 480 passive 481 Use amd_pstate with passive mode as a scaling driver. 482 In this mode autonomous selection is disabled. 483 Driver requests a desired performance level and platform 484 tries to match the same performance level if it is 485 satisfied by guaranteed performance level. 486 active 487 Use amd_pstate_epp driver instance as the scaling driver, 488 driver provides a hint to the hardware if software wants 489 to bias toward performance (0x0) or energy efficiency (0xff) 490 to the CPPC firmware. then CPPC power algorithm will 491 calculate the runtime workload and adjust the realtime cores 492 frequency. 493 guided 494 Activate guided autonomous mode. Driver requests minimum and 495 maximum performance level and the platform autonomously 496 selects a performance level in this range and appropriate 497 to the current workload. 498 499 amd_prefcore= 500 [X86] 501 disable 502 Disable amd-pstate preferred core. 503 504 amd_dynamic_epp= 505 [X86] 506 disable 507 Disable amd-pstate dynamic EPP. 508 enable 509 Enable amd-pstate dynamic EPP. 510 511 amijoy.map= [HW,JOY] Amiga joystick support 512 Map of devices attached to JOY0DAT and JOY1DAT 513 Format: <a>,<b> 514 See also Documentation/input/joydev/joystick.rst 515 516 analog.map= [HW,JOY] Analog joystick and gamepad support 517 Specifies type or capabilities of an analog joystick 518 connected to one of 16 gameports 519 Format: <type1>,<type2>,..<type16> 520 521 apc= [HW,SPARC] 522 Power management functions (SPARCstation-4/5 + deriv.) 523 Format: noidle 524 Disable APC CPU standby support. SPARCstation-Fox does 525 not play well with APC CPU idle - disable it if you have 526 APC and your system crashes randomly. 527 528 apic [APIC,X86-64] Use IO-APIC. Default. 529 530 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 531 Change the output verbosity while booting 532 Format: { quiet (default) | verbose | debug } 533 Change the amount of debugging information output 534 when initialising the APIC and IO-APIC components. 535 536 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 537 Format: { bsp (default) | all | none } 538 bsp: External NMI is delivered only to CPU 0 539 all: External NMIs are broadcast to all CPUs as a 540 backup of CPU 0 541 none: External NMI is masked for all CPUs. This is 542 useful so that a dump capture kernel won't be 543 shot down by NMI 544 545 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 546 apicmaintimer. Useful when your PIT timer is totally 547 broken. 548 549 autoconf= [IPV6] 550 See Documentation/networking/ipv6.rst. 551 552 apm= [APM] Advanced Power Management 553 See header of arch/x86/kernel/apm_32.c. 554 555 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 556 Format: { "0" | "1" } 557 See security/apparmor/Kconfig help text 558 0 -- disable. 559 1 -- enable. 560 Default value is set via kernel config option. 561 562 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 563 32 bit applications. 564 565 arm64.nobti [ARM64] Unconditionally disable Branch Target 566 Identification support 567 568 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 569 support 570 571 arm64.nohaft [ARM64] Unconditionally disable Hardware managed Access 572 Flag for Table descriptors support 573 574 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 575 Set instructions support 576 577 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 578 Monitoring support. Only for a machine that does not 579 boot without it. See Documentation/arch/arm64/mpam.rst 580 581 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 582 support 583 584 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 585 support 586 587 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 588 Extension support 589 590 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 591 Extension support 592 593 arm64.nowfxt [ARM64] Unconditionally disable Wait For Event with 594 Timeout and Wait For Interrupt with Timeout support 595 596 ataflop= [HW,M68k] 597 598 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 599 EzKey and similar keyboards 600 601 atkbd.reset= [HW] Reset keyboard during initialization 602 603 atkbd.set= [HW] Select keyboard code set 604 Format: <int> (2 = AT (default), 3 = PS/2) 605 606 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 607 keyboards 608 609 atkbd.softraw= [HW] Choose between synthetic and real raw mode 610 Format: <bool> (0 = real, 1 = synthetic (default)) 611 612 atkbd.softrepeat= [HW] 613 Use software keyboard repeat 614 615 audit= [KNL] Enable the audit sub-system 616 Format: { "0" | "1" | "off" | "on" } 617 0 | off - kernel audit is disabled and can not be 618 enabled until the next reboot 619 unset - kernel audit is initialized but disabled and 620 will be fully enabled by the userspace auditd. 621 1 | on - kernel audit is initialized and partially 622 enabled, storing at most audit_backlog_limit 623 messages in RAM until it is fully enabled by the 624 userspace auditd. 625 Default: unset 626 627 audit_backlog_limit= [KNL] Set the audit queue size limit. 628 Format: <int> (must be >=0) 629 Default: 64 630 631 bdev_allow_write_mounted= 632 Format: <bool> 633 Control the ability to open a mounted block device 634 for writing, i.e., allow / disallow writes that bypass 635 the FS. This was implemented as a means to prevent 636 fuzzers from crashing the kernel by overwriting the 637 metadata underneath a mounted FS without its awareness. 638 This also prevents destructive formatting of mounted 639 filesystems by naive storage tooling that don't use 640 O_EXCL. Default is Y and can be changed through the 641 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 642 643 bert_disable [ACPI] 644 Disable BERT OS support on buggy BIOSes. 645 646 bgrt_disable [ACPI,X86,EARLY] 647 Disable BGRT to avoid flickering OEM logo. 648 649 blkdevparts= Manual partition parsing of block device(s) for 650 embedded devices based on command line input. 651 See Documentation/block/cmdline-partition.rst 652 653 boot_delay= [KNL,EARLY] 654 Milliseconds to delay each printk during boot. 655 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 656 and you may also have to specify "lpj=". Boot_delay 657 values larger than 10 seconds (10000) are assumed 658 erroneous and ignored. 659 Format: integer 660 661 bootconfig [KNL,EARLY] 662 Extended command line options can be added to an initrd 663 and this will cause the kernel to look for it. 664 665 See Documentation/admin-guide/bootconfig.rst 666 667 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 668 bttv.radio= Most important insmod options are available as 669 kernel args too. 670 bttv.pll= See Documentation/admin-guide/media/bttv.rst 671 bttv.tuner= 672 673 bulk_remove=off [PPC] This parameter disables the use of the pSeries 674 firmware feature for flushing multiple hpte entries 675 at a time. 676 677 c101= [NET] Moxa C101 synchronous serial card 678 679 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 680 Sometimes CPU hardware bugs make them report the cache 681 size incorrectly. The kernel will attempt work arounds 682 to fix known problems, but for some CPUs it is not 683 possible to determine what the correct size should be. 684 This option provides an override for these situations. 685 686 carrier_timeout= 687 [NET] Specifies amount of time (in seconds) that 688 the kernel should wait for a network carrier. By default 689 it waits 120 seconds. 690 691 ca_keys= [KEYS] This parameter identifies a specific key(s) on 692 the system trusted keyring to be used for certificate 693 trust validation. 694 format: { id:<keyid> | builtin } 695 696 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 697 algorithm. Accepted values range from 0 to 7 698 inclusive. See arch/mips/include/asm/pgtable-bits.h 699 for platform specific values (SB1, Loongson3 and 700 others). 701 702 ccw_timeout_log [S390] 703 See Documentation/arch/s390/common_io.rst for details. 704 705 cfi= [X86-64] Set Control Flow Integrity checking features 706 when CONFIG_FINEIBT is enabled. 707 Format: feature[,feature...] 708 Default: auto 709 710 auto: Use FineIBT if IBT available, otherwise kCFI. 711 Under FineIBT, enable "paranoid" mode when 712 FRED is not available. 713 off: Turn off CFI checking. 714 kcfi: Use kCFI (disable FineIBT). 715 fineibt: Use FineIBT (even if IBT not available). 716 norand: Do not re-randomize CFI hashes. 717 paranoid: Add caller hash checking under FineIBT. 718 bhi: Enable register poisoning to stop speculation 719 across FineIBT. (Disabled by default.) 720 warn: Do not enforce CFI checking: warn only. 721 debug: Report CFI initialization details. 722 723 cgroup_disable= [KNL] Disable a particular controller or optional feature 724 Format: {name of the controller(s) or feature(s) to disable} 725 The effects of cgroup_disable=foo are: 726 - foo isn't auto-mounted if you mount all cgroups in 727 a single hierarchy 728 - foo isn't visible as an individually mountable 729 subsystem 730 - if foo is an optional feature then the feature is 731 disabled and corresponding cgroup files are not 732 created 733 {Currently only "memory" controller deal with this and 734 cut the overhead, others just disable the usage. So 735 only cgroup_disable=memory is actually worthy} 736 Specifying "pressure" disables per-cgroup pressure 737 stall information accounting feature 738 739 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 740 Format: { { controller | "all" | "named" } 741 [,{ controller | "all" | "named" }...] } 742 Like cgroup_disable, but only applies to cgroup v1; 743 the blacklisted controllers remain available in cgroup2. 744 "all" blacklists all controllers and "named" disables 745 named mounts. Specifying both "all" and "named" disables 746 all v1 hierarchies. 747 748 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 749 Format: { "true" | "false" } 750 /proc/cgroups lists only v1 controllers by default. 751 This compatibility option enables listing also v2 752 controllers (whose v1 code is not compiled!), so that 753 semi-legacy software can check this file to decide 754 about usage of v2 (sic) controllers. 755 756 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 757 Format: { "true" | "false" } 758 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 759 760 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 761 Format: <string> 762 nosocket -- Disable socket memory accounting. 763 nokmem -- Disable kernel memory accounting. 764 nobpf -- Disable BPF memory accounting. 765 766 check_pages= [MM,EARLY] Enable sanity checking of pages after 767 allocations / before freeing. This adds checks to catch 768 double-frees, use-after-frees, and other sources of 769 page corruption by inspecting page internals (flags, 770 mapcount/refcount, memcg_data, etc.). 771 Format: { "0" | "1" } 772 Default: 0 (1 if CONFIG_DEBUG_VM is set) 773 774 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 775 Format: { "0" | "1" } 776 See security/selinux/Kconfig help text. 777 0 -- check protection applied by kernel (includes 778 any implied execute protection). 779 1 -- check protection requested by application. 780 Default value is set via a kernel config option. 781 Value can be changed at runtime via 782 /sys/fs/selinux/checkreqprot. 783 Setting checkreqprot to 1 is deprecated. 784 785 cio_ignore= [S390] 786 See Documentation/arch/s390/common_io.rst for details. 787 788 clk_ignore_unused 789 [CLK] 790 Prevents the clock framework from automatically gating 791 clocks that have not been explicitly enabled by a Linux 792 device driver but are enabled in hardware at reset or 793 by the bootloader/firmware. Note that this does not 794 force such clocks to be always-on nor does it reserve 795 those clocks in any way. This parameter is useful for 796 debug and development, but should not be needed on a 797 platform with proper driver support. For more 798 information, see Documentation/driver-api/clk.rst. 799 800 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 801 [Deprecated] 802 Forces specified clocksource (if available) to be used 803 when calculating gettimeofday(). If specified 804 clocksource is not available, it defaults to PIT. 805 Format: { pit | tsc | cyclone | pmtmr } 806 807 clocksource= Override the default clocksource 808 Format: <string> 809 Override the default clocksource and use the clocksource 810 with the name specified. 811 Some clocksource names to choose from, depending on 812 the platform: 813 [all] jiffies (this is the base, fallback clocksource) 814 [ACPI] acpi_pm 815 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 816 pxa_timer,timer3,32k_counter,timer0_1 817 [X86-32] pit,hpet,tsc; 818 scx200_hrt on Geode; cyclone on IBM x440 819 [MIPS] MIPS 820 [PARISC] cr16 821 [S390] tod 822 [SH] SuperH 823 [SPARC64] tick 824 [X86-64] hpet,tsc 825 826 clocksource.arm_arch_timer.evtstrm= 827 [ARM,ARM64,EARLY] 828 Format: <bool> 829 Enable/disable the eventstream feature of the ARM 830 architected timer so that code using WFE-based polling 831 loops can be debugged more effectively on production 832 systems. 833 834 clocksource.verify_n_cpus= [KNL] 835 Limit the number of CPUs checked for clocksources 836 marked with CLOCK_SOURCE_VERIFY_PERCPU that 837 are marked unstable due to excessive skew. 838 A negative value says to check all CPUs, while 839 zero says not to check any. Values larger than 840 nr_cpu_ids are silently truncated to nr_cpu_ids. 841 The actual CPUs are chosen randomly, with 842 no replacement if the same CPU is chosen twice. 843 844 clocksource-wdtest.holdoff= [KNL] 845 Set the time in seconds that the clocksource 846 watchdog test waits before commencing its tests. 847 Defaults to zero when built as a module and to 848 10 seconds when built into the kernel. 849 850 cma=nn[MG]@[start[MG][-end[MG]]] 851 [KNL,CMA,EARLY] 852 Sets the size of kernel global memory area for 853 contiguous memory allocations and optionally the 854 placement constraint by the physical address range of 855 memory allocations. A value of 0 disables CMA 856 altogether. For more information, see 857 kernel/dma/contiguous.c 858 859 cma_pernuma=nn[MG] 860 [KNL,CMA,EARLY] 861 Sets the size of kernel per-numa memory area for 862 contiguous memory allocations. A value of 0 disables 863 per-numa CMA altogether. And If this option is not 864 specified, the default value is 0. 865 With per-numa CMA enabled, DMA users on node nid will 866 first try to allocate buffer from the pernuma area 867 which is located in node nid, if the allocation fails, 868 they will fallback to the global default memory area. 869 870 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 871 [KNL,CMA,EARLY] 872 Sets the size of kernel numa memory area for 873 contiguous memory allocations. It will reserve CMA 874 area for the specified node. 875 876 If it is setup together with upper 'cmd_pernuma=' 877 (unlikely), its size setting takes priority for the 878 specified numa nodes. 879 880 With numa CMA enabled, DMA users on node nid will 881 first try to allocate buffer from the numa area 882 which is located in node nid, if the allocation fails, 883 they will fallback to the global default memory area. 884 885 cmo_free_hint= [PPC] Format: { yes | no } 886 Specify whether pages are marked as being inactive 887 when they are freed. This is used in CMO environments 888 to determine OS memory pressure for page stealing by 889 a hypervisor. 890 Default: yes 891 892 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 893 Sets the size of memory pool for coherent, atomic dma 894 allocations, by default set to 256K. 895 896 condev= [HW,S390] console device 897 conmode= 898 899 con3215_drop= [S390,EARLY] 3215 console drop mode. 900 Format: y|n|Y|N|1|0 901 When set to true, drop data on the 3215 console when 902 the console buffer is full. In this case the 903 operator using a 3270 terminal emulator (for example 904 x3270) does not have to enter the clear key for the 905 console output to advance and the kernel to continue. 906 This leads to a much faster boot time when a 3270 907 terminal emulator is active. If no 3270 terminal 908 emulator is used, this parameter has no effect. 909 910 console= [KNL] Output console device and options. 911 912 tty<n> Use the virtual console device <n>. 913 914 ttyS<n>[,options] 915 ttyUSB0[,options] 916 Use the specified serial port. The options are of 917 the form "bbbbpnf", where "bbbb" is the baud rate, 918 "p" is parity ("n", "o", or "e"), "n" is number of 919 bits, and "f" is flow control ("r" for RTS or 920 omit it). Default is "9600n8". 921 922 See Documentation/admin-guide/serial-console.rst for more 923 information. See 924 Documentation/networking/netconsole.rst for an 925 alternative. 926 927 <DEVNAME>:<n>.<n>[,options] 928 Use the specified serial port on the serial core bus. 929 The addressing uses DEVNAME of the physical serial port 930 device, followed by the serial core controller instance, 931 and the serial port instance. The options are the same 932 as documented for the ttyS addressing above. 933 934 The mapping of the serial ports to the tty instances 935 can be viewed with: 936 937 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 938 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 939 940 In the above example, the console can be addressed with 941 console=00:04:0.0. Note that a console addressed this 942 way will only get added when the related device driver 943 is ready. The use of an earlycon parameter in addition to 944 the console may be desired for console output early on. 945 946 uart[8250],io,<addr>[,options] 947 uart[8250],mmio,<addr>[,options] 948 uart[8250],mmio16,<addr>[,options] 949 uart[8250],mmio32,<addr>[,options] 950 uart[8250],0x<addr>[,options] 951 Start an early, polled-mode console on the 8250/16550 952 UART at the specified I/O port or MMIO address, 953 switching to the matching ttyS device later. 954 MMIO inter-register address stride is either 8-bit 955 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 956 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 957 to be equivalent to 'mmio'. 'options' are specified in 958 the same format described for ttyS above; if unspecified, 959 the h/w is not re-initialized. 960 961 hvc<n> Use the hypervisor console device <n>. This is for 962 both Xen and PowerPC hypervisors. 963 964 { null | "" } 965 Use to disable console output, i.e., to have kernel 966 console messages discarded. 967 This must be the only console= parameter used on the 968 kernel command line. 969 970 If the device connected to the port is not a TTY but a braille 971 device, prepend "brl," before the device type, for instance 972 console=brl,ttyS0 973 For now, only VisioBraille is supported. 974 975 console_msg_format= 976 [KNL] Change console messages format 977 default 978 By default we print messages on consoles in 979 "[time stamp] text\n" format (time stamp may not be 980 printed, depending on CONFIG_PRINTK_TIME or 981 `printk_time' param). 982 syslog 983 Switch to syslog format: "<%u>[time stamp] text\n" 984 IOW, each message will have a facility and loglevel 985 prefix. The format is similar to one used by syslog() 986 syscall, or to executing "dmesg -S --raw" or to reading 987 from /proc/kmsg. 988 989 consoleblank= [KNL] The console blank (screen saver) timeout in 990 seconds. A value of 0 disables the blank timer. 991 Defaults to 0. 992 993 coredump_filter= 994 [KNL] Change the default value for 995 /proc/<pid>/coredump_filter. 996 See also Documentation/filesystems/proc.rst. 997 998 coresight_cpu_debug.enable 999 [ARM,ARM64] 1000 Format: <bool> 1001 Enable/disable the CPU sampling based debugging. 1002 0: default value, disable debugging 1003 1: enable debugging at boot time 1004 1005 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1006 Format: 1007 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1008 1009 cpuidle.off=1 [CPU_IDLE] 1010 disable the cpuidle sub-system 1011 1012 cpuidle.governor= 1013 [CPU_IDLE] Name of the cpuidle governor to use. 1014 1015 cpufreq.off=1 [CPU_FREQ] 1016 disable the cpufreq sub-system 1017 1018 cpufreq.default_governor= 1019 [CPU_FREQ] Name of the default cpufreq governor or 1020 policy to use. This governor must be registered in the 1021 kernel before the cpufreq driver probes. 1022 1023 cpu_init_udelay=N 1024 [X86,EARLY] Delay for N microsec between assert and de-assert 1025 of APIC INIT to start processors. This delay occurs 1026 on every CPU online, such as boot, and resume from suspend. 1027 Default: 10000 1028 1029 cpuhp.parallel= 1030 [SMP] Enable/disable parallel bringup of secondary CPUs 1031 Format: <bool> 1032 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1033 the parameter has no effect. 1034 1035 crash_kexec_post_notifiers 1036 Only jump to kdump kernel after running the panic 1037 notifiers and dumping kmsg. This option increases 1038 the risks of a kdump failure, since some panic 1039 notifiers can make the crashed kernel more unstable. 1040 In configurations where kdump may not be reliable, 1041 running the panic notifiers could allow collecting 1042 more data on dmesg, like stack traces from other CPUS 1043 or extra data dumped by panic_print. Note that some 1044 configurations enable this option unconditionally, 1045 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1046 1047 crashkernel=size[KMG][@offset[KMG]] 1048 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1049 upon panic. This parameter reserves the physical 1050 memory region [offset, offset + size] for that kernel 1051 image. If '@offset' is omitted, then a suitable offset 1052 is selected automatically. 1053 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1054 under 4G first, and fall back to reserve region above 1055 4G when '@offset' hasn't been specified. 1056 See Documentation/admin-guide/kdump/kdump.rst for further details. 1057 1058 crashkernel=range1:size1[,range2:size2,...][@offset] 1059 [KNL] Same as above, but depends on the memory 1060 in the running system. The syntax of range is 1061 start-[end] where start and end are both 1062 a memory unit (amount[KMG]). See also 1063 Documentation/admin-guide/kdump/kdump.rst for an example. 1064 1065 crashkernel=size[KMG],high 1066 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1067 above 4G. 1068 Allow kernel to allocate physical memory region from top, 1069 so could be above 4G if system have more than 4G ram 1070 installed. Otherwise memory region will be allocated 1071 below 4G, if available. 1072 It will be ignored if crashkernel=X is specified. 1073 crashkernel=size[KMG],low 1074 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1075 When crashkernel=X,high is passed, kernel could allocate 1076 physical memory region above 4G, that cause second kernel 1077 crash on system that require some amount of low memory, 1078 e.g. swiotlb requires at least 64M+32K low memory, also 1079 enough extra low memory is needed to make sure DMA buffers 1080 for 32-bit devices won't run out. Kernel would try to allocate 1081 default size of memory below 4G automatically. The default 1082 size is platform dependent. 1083 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1084 --> arm64: 128MiB 1085 --> riscv: 128MiB 1086 --> loongarch: 128MiB 1087 This one lets the user specify own low range under 4G 1088 for second kernel instead. 1089 0: to disable low allocation. 1090 It will be ignored when crashkernel=X,high is not used 1091 or memory reserved is below 4G. 1092 crashkernel=size[KMG],cma 1093 [KNL, X86, ARM64, RISCV, PPC] Reserve additional crash 1094 kernel memory from CMA. This reservation is usable by 1095 the first system's userspace memory and kernel movable 1096 allocations (memory balloon, zswap). Pages allocated 1097 from this memory range will not be included in the vmcore 1098 so this should not be used if dumping of userspace memory 1099 is intended and it has to be expected that some movable 1100 kernel pages may be missing from the dump. 1101 1102 A standard crashkernel reservation, as described above, 1103 is still needed to hold the crash kernel and initrd. 1104 1105 This option increases the risk of a kdump failure: DMA 1106 transfers configured by the first kernel may end up 1107 corrupting the second kernel's memory. 1108 1109 This reservation method is intended for systems that 1110 can't afford to sacrifice enough memory for standard 1111 crashkernel reservation and where less reliable and 1112 possibly incomplete kdump is preferable to no kdump at 1113 all. 1114 1115 cryptomgr.notests 1116 [KNL] Disable crypto self-tests 1117 1118 cs89x0_dma= [HW,NET] 1119 Format: <dma> 1120 1121 cs89x0_media= [HW,NET] 1122 Format: { rj45 | aui | bnc } 1123 1124 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1125 function call handling. When switched on, 1126 additional debug data is printed to the console 1127 in case a hanging CPU is detected, and that 1128 CPU is pinged again in order to try to resolve 1129 the hang situation. The default value of this 1130 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1131 Kconfig option. 1132 1133 dasd= [HW,NET] 1134 See header of drivers/s390/block/dasd_devmap.c. 1135 1136 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1137 (one device per port) 1138 Format: <port#>,<type> 1139 See also Documentation/input/devices/joystick-parport.rst 1140 1141 debug [KNL,EARLY] Enable kernel debugging (events log level). 1142 1143 debug_boot_weak_hash 1144 [KNL,EARLY] Enable printing [hashed] pointers early in the 1145 boot sequence. If enabled, we use a weak hash instead 1146 of siphash to hash pointers. Use this option if you are 1147 seeing instances of '(___ptrval___)') and need to see a 1148 value (hashed pointer) instead. Cryptographically 1149 insecure, please do not use on production kernels. 1150 1151 debug_locks_verbose= 1152 [KNL] verbose locking self-tests 1153 Format: <int> 1154 Print debugging info while doing the locking API 1155 self-tests. 1156 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1157 (no extra messages), setting it to -1 (all bits set) 1158 will print _a_lot_ more information - normally only 1159 useful to lockdep developers. 1160 1161 debug_objects [KNL,EARLY] Enable object debugging 1162 1163 debug_guardpage_minorder= 1164 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1165 parameter allows control of the order of pages that will 1166 be intentionally kept free (and hence protected) by the 1167 buddy allocator. Bigger value increase the probability 1168 of catching random memory corruption, but reduce the 1169 amount of memory for normal system use. The maximum 1170 possible value is MAX_PAGE_ORDER/2. Setting this 1171 parameter to 1 or 2 should be enough to identify most 1172 random memory corruption problems caused by bugs in 1173 kernel or driver code when a CPU writes to (or reads 1174 from) a random memory location. Note that there exists 1175 a class of memory corruptions problems caused by buggy 1176 H/W or F/W or by drivers badly programming DMA 1177 (basically when memory is written at bus level and the 1178 CPU MMU is bypassed) which are not detectable by 1179 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1180 help tracking down these problems. 1181 1182 debug_pagealloc= 1183 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1184 enables the feature at boot time. By default, it is 1185 disabled and the system will work mostly the same as a 1186 kernel built without CONFIG_DEBUG_PAGEALLOC. 1187 Note: to get most of debug_pagealloc error reports, it's 1188 useful to also enable the page_owner functionality. 1189 on: enable the feature 1190 1191 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1192 userspace and debugfs internal clients. 1193 Format: { on, off } 1194 on: All functions are enabled. 1195 off: Filesystem is not registered and clients 1196 get a -EPERM as result when trying to register files 1197 or directories within debugfs. 1198 This is equivalent of the runtime functionality if 1199 debugfs was not enabled in the kernel at all. 1200 Default value is set in build-time with a kernel configuration. 1201 1202 debugpat [X86] Enable PAT debugging 1203 1204 default_hugepagesz= 1205 [HW] The size of the default HugeTLB page. This is 1206 the size represented by the legacy /proc/ hugepages 1207 APIs. In addition, this is the default hugetlb size 1208 used for shmget(), mmap() and mounting hugetlbfs 1209 filesystems. If not specified, defaults to the 1210 architecture's default huge page size. Huge page 1211 sizes are architecture dependent. See also 1212 Documentation/admin-guide/mm/hugetlbpage.rst. 1213 Format: size[KMG] 1214 1215 deferred_probe_timeout= 1216 [KNL] Debugging option to set a timeout in seconds for 1217 deferred probe to give up waiting on dependencies to 1218 probe. Only specific dependencies (subsystems or 1219 drivers) that have opted in will be ignored. A timeout 1220 of 0 will timeout at the end of initcalls; a negative 1221 value is treated as an infinite timeout value. If the 1222 timeout hasn't expired, it'll be restarted by each 1223 successful driver registration. This option will also 1224 dump out devices still on the deferred probe list after 1225 retrying. 1226 1227 delayacct [KNL] Enable per-task delay accounting 1228 1229 dell_smm_hwmon.ignore_dmi= 1230 [HW] Continue probing hardware even if DMI data 1231 indicates that the driver is running on unsupported 1232 hardware. 1233 1234 dell_smm_hwmon.force= 1235 [HW] Activate driver even if SMM BIOS signature does 1236 not match list of supported models and enable otherwise 1237 blacklisted features. 1238 1239 dell_smm_hwmon.power_status= 1240 [HW] Report power status in /proc/i8k 1241 (disabled by default). 1242 1243 dell_smm_hwmon.restricted= 1244 [HW] Allow controlling fans only if SYS_ADMIN 1245 capability is set. 1246 1247 dell_smm_hwmon.fan_mult= 1248 [HW] Factor to multiply fan speed with. 1249 1250 dell_smm_hwmon.fan_max= 1251 [HW] Maximum configurable fan speed. 1252 1253 dfltcc= [HW,S390] 1254 Format: { on | off | def_only | inf_only | always } 1255 on: s390 zlib hardware support for compression on 1256 level 1 and decompression (default) 1257 off: No s390 zlib hardware support 1258 def_only: s390 zlib hardware support for deflate 1259 only (compression on level 1) 1260 inf_only: s390 zlib hardware support for inflate 1261 only (decompression) 1262 always: Same as 'on' but ignores the selected compression 1263 level always using hardware support (used for debugging) 1264 1265 dhash_entries= [KNL] 1266 Set number of hash buckets for dentry cache. 1267 1268 disable_1tb_segments [PPC,EARLY] 1269 Disables the use of 1TB hash page table segments. This 1270 causes the kernel to fall back to 256MB segments which 1271 can be useful when debugging issues that require an SLB 1272 miss to occur. 1273 1274 disable= [IPV6] 1275 See Documentation/networking/ipv6.rst. 1276 1277 disable_radix [PPC,EARLY] 1278 Disable RADIX MMU mode on POWER9 1279 1280 disable_tlbie [PPC] 1281 Disable TLBIE instruction. Currently does not work 1282 with KVM, with HASH MMU, or with coherent accelerators. 1283 1284 disable_ddw [PPC/PSERIES,EARLY] 1285 Disable Dynamic DMA Window support. Use this 1286 to workaround buggy firmware. 1287 1288 disable_ipv6= [IPV6] 1289 See Documentation/networking/ipv6.rst. 1290 1291 disable_mtrr_cleanup [X86,EARLY] 1292 The kernel tries to adjust MTRR layout from continuous 1293 to discrete, to make X server driver able to add WB 1294 entry later. This parameter disables that. 1295 1296 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1297 By default the kernel will trim any uncacheable 1298 memory out of your available memory pool based on 1299 MTRR settings. This parameter disables that behavior, 1300 possibly causing your machine to run very slowly. 1301 1302 disable_timer_pin_1 [X86,EARLY] 1303 Disable PIN 1 of APIC timer 1304 Can be useful to work around chipset bugs. 1305 1306 dis_ucode_ldr [X86] Disable the microcode loader. 1307 1308 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1309 this option disables the debugging code at boot. 1310 1311 dma_debug_entries=<number> 1312 This option allows to tune the number of preallocated 1313 entries for DMA-API debugging code. One entry is 1314 required per DMA-API allocation. Use this if the 1315 DMA-API debugging code disables itself because the 1316 architectural default is too low. 1317 1318 dma_debug_driver=<driver_name> 1319 With this option the DMA-API debugging driver 1320 filter feature can be enabled at boot time. Just 1321 pass the driver to filter for as the parameter. 1322 The filter can be disabled or changed to another 1323 driver later using sysfs. 1324 1325 reg_file_data_sampling= 1326 [X86] Controls mitigation for Register File Data 1327 Sampling (RFDS) vulnerability. RFDS is a CPU 1328 vulnerability which may allow userspace to infer 1329 kernel data values previously stored in floating point 1330 registers, vector registers, or integer registers. 1331 RFDS only affects Intel Atom processors. 1332 1333 on: Turns ON the mitigation. 1334 off: Turns OFF the mitigation. 1335 1336 This parameter overrides the compile time default set 1337 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1338 disabled when other VERW based mitigations (like MDS) 1339 are enabled. In order to disable RFDS mitigation all 1340 VERW based mitigations need to be disabled. 1341 1342 For details see: 1343 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1344 1345 dm_verity.keyring_unsealed= 1346 [KNL] When set to 1, leave the dm-verity keyring 1347 unsealed after initialization so userspace can 1348 provision keys. Once the keyring is restricted 1349 it becomes active and is searched during signature 1350 verification. 1351 1352 driver_async_probe= [KNL] 1353 List of driver names to be probed asynchronously. * 1354 matches with all driver names. If * is specified, the 1355 rest of the listed driver names are those that will NOT 1356 match the *. 1357 Format: <driver_name1>,<driver_name2>... 1358 1359 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1360 Broken monitors, graphic adapters, KVMs and EDIDless 1361 panels may send no or incorrect EDID data sets. 1362 This parameter allows to specify an EDID data sets 1363 in the /lib/firmware directory that are used instead. 1364 An EDID data set will only be used for a particular 1365 connector, if its name and a colon are prepended to 1366 the EDID name. Each connector may use a unique EDID 1367 data set by separating the files with a comma. An EDID 1368 data set with no connector name will be used for 1369 any connectors not explicitly specified. 1370 1371 dscc4.setup= [NET] 1372 1373 dt_cpu_ftrs= [PPC,EARLY] 1374 Format: {"off" | "known"} 1375 Control how the dt_cpu_ftrs device-tree binding is 1376 used for CPU feature discovery and setup (if it 1377 exists). 1378 off: Do not use it, fall back to legacy cpu table. 1379 known: Do not pass through unknown features to guests 1380 or userspace, only those that the kernel is aware of. 1381 1382 dump_apple_properties [X86] 1383 Dump name and content of EFI device properties on 1384 x86 Macs. Useful for driver authors to determine 1385 what data is available or for reverse-engineering. 1386 1387 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1388 <module>.dyndbg[="val"] 1389 Enable debug messages at boot time. See 1390 Documentation/admin-guide/dynamic-debug-howto.rst 1391 for details. 1392 1393 early_ioremap_debug [KNL,EARLY] 1394 Enable debug messages in early_ioremap support. This 1395 is useful for tracking down temporary early mappings 1396 which are not unmapped. 1397 1398 earlycon= [KNL,EARLY] Output early console device and options. 1399 1400 When used with no options, the early console is 1401 determined by stdout-path property in device tree's 1402 chosen node or the ACPI SPCR table if supported by 1403 the platform. 1404 1405 cdns,<addr>[,options] 1406 Start an early, polled-mode console on a Cadence 1407 (xuartps) serial port at the specified address. Only 1408 supported option is baud rate. If baud rate is not 1409 specified, the serial port must already be setup and 1410 configured. 1411 1412 uart[8250],io,<addr>[,options[,uartclk]] 1413 uart[8250],mmio,<addr>[,options[,uartclk]] 1414 uart[8250],mmio32,<addr>[,options[,uartclk]] 1415 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1416 uart[8250],0x<addr>[,options] 1417 Start an early, polled-mode console on the 8250/16550 1418 UART at the specified I/O port or MMIO address. 1419 MMIO inter-register address stride is either 8-bit 1420 (mmio) or 32-bit (mmio32 or mmio32be). 1421 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1422 to be equivalent to 'mmio'. 'options' are specified 1423 in the same format described for "console=ttyS<n>"; if 1424 unspecified, the h/w is not initialized. 'uartclk' is 1425 the uart clock frequency; if unspecified, it is set 1426 to 'BASE_BAUD' * 16. 1427 1428 pl011,<addr> 1429 pl011,mmio32,<addr> 1430 Start an early, polled-mode console on a pl011 serial 1431 port at the specified address. The pl011 serial port 1432 must already be setup and configured. Options are not 1433 yet supported. If 'mmio32' is specified, then only 1434 the driver will use only 32-bit accessors to read/write 1435 the device registers. 1436 1437 liteuart,<addr> 1438 Start an early console on a litex serial port at the 1439 specified address. The serial port must already be 1440 setup and configured. Options are not yet supported. 1441 1442 meson,<addr> 1443 Start an early, polled-mode console on a meson serial 1444 port at the specified address. The serial port must 1445 already be setup and configured. Options are not yet 1446 supported. 1447 1448 msm_serial,<addr> 1449 Start an early, polled-mode console on an msm serial 1450 port at the specified address. The serial port 1451 must already be setup and configured. Options are not 1452 yet supported. 1453 1454 msm_serial_dm,<addr> 1455 Start an early, polled-mode console on an msm serial 1456 dm port at the specified address. The serial port 1457 must already be setup and configured. Options are not 1458 yet supported. 1459 1460 owl,<addr> 1461 Start an early, polled-mode console on a serial port 1462 of an Actions Semi SoC, such as S500 or S900, at the 1463 specified address. The serial port must already be 1464 setup and configured. Options are not yet supported. 1465 1466 rda,<addr> 1467 Start an early, polled-mode console on a serial port 1468 of an RDA Micro SoC, such as RDA8810PL, at the 1469 specified address. The serial port must already be 1470 setup and configured. Options are not yet supported. 1471 1472 sbi 1473 Use RISC-V SBI (Supervisor Binary Interface) for early 1474 console. 1475 1476 smh Use ARM semihosting calls for early console. 1477 1478 s3c2410,<addr> 1479 s3c2412,<addr> 1480 s3c2440,<addr> 1481 s3c6400,<addr> 1482 s5pv210,<addr> 1483 exynos4210,<addr> 1484 Use early console provided by serial driver available 1485 on Samsung SoCs, requires selecting proper type and 1486 a correct base address of the selected UART port. The 1487 serial port must already be setup and configured. 1488 Options are not yet supported. 1489 1490 lantiq,<addr> 1491 Start an early, polled-mode console on a lantiq serial 1492 (lqasc) port at the specified address. The serial port 1493 must already be setup and configured. Options are not 1494 yet supported. 1495 1496 lpuart,<addr> 1497 lpuart32,<addr> 1498 Use early console provided by Freescale LP UART driver 1499 found on Freescale Vybrid and QorIQ LS1021A processors. 1500 A valid base address must be provided, and the serial 1501 port must already be setup and configured. 1502 1503 ec_imx21,<addr> 1504 ec_imx6q,<addr> 1505 Start an early, polled-mode, output-only console on the 1506 Freescale i.MX UART at the specified address. The UART 1507 must already be setup and configured. 1508 1509 ar3700_uart,<addr> 1510 Start an early, polled-mode console on the 1511 Armada 3700 serial port at the specified 1512 address. The serial port must already be setup 1513 and configured. Options are not yet supported. 1514 1515 qcom_geni,<addr> 1516 Start an early, polled-mode console on a Qualcomm 1517 Generic Interface (GENI) based serial port at the 1518 specified address. The serial port must already be 1519 setup and configured. Options are not yet supported. 1520 1521 efifb,[options] 1522 Start an early, unaccelerated console on the EFI 1523 memory mapped framebuffer (if available). On cache 1524 coherent non-x86 systems that use system memory for 1525 the framebuffer, pass the 'ram' option so that it is 1526 mapped with the correct attributes. 1527 1528 linflex,<addr> 1529 Use early console provided by Freescale LINFlexD UART 1530 serial driver for NXP S32V234 SoCs. A valid base 1531 address must be provided, and the serial port must 1532 already be setup and configured. 1533 1534 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1535 earlyprintk=vga 1536 earlyprintk=sclp 1537 earlyprintk=xen 1538 earlyprintk=serial[,ttySn[,baudrate]] 1539 earlyprintk=serial[,0x...[,baudrate]] 1540 earlyprintk=ttySn[,baudrate] 1541 earlyprintk=dbgp[debugController#] 1542 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1543 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1544 earlyprintk=xdbc[xhciController#] 1545 earlyprintk=bios 1546 1547 earlyprintk is useful when the kernel crashes before 1548 the normal console is initialized. It is not enabled by 1549 default because it has some cosmetic problems. 1550 1551 Use "nocfg" to skip UART configuration, assume 1552 BIOS/firmware has configured UART correctly. 1553 1554 Append ",keep" to not disable it when the real console 1555 takes over. 1556 1557 Only one of vga, serial, or usb debug port can 1558 be used at a time. 1559 1560 Currently only ttyS0 and ttyS1 may be specified by 1561 name. Other I/O ports may be explicitly specified 1562 on some architectures (x86 and arm at least) by 1563 replacing ttySn with an I/O port address, like this: 1564 earlyprintk=serial,0x1008,115200 1565 You can find the port for a given device in 1566 /proc/tty/driver/serial: 1567 2: uart:ST16650V2 port:00001008 irq:18 ... 1568 1569 Interaction with the standard serial driver is not 1570 very good. 1571 1572 The VGA output is eventually overwritten by 1573 the real console. 1574 1575 The xen option can only be used in Xen domains. 1576 1577 The sclp output can only be used on s390. 1578 1579 The bios output can only be used on SuperH. 1580 1581 The optional "force" to "pciserial" enables use of a 1582 PCI device even when its classcode is not of the 1583 UART class. 1584 1585 edd= [EDD] 1586 Format: {"off" | "on" | "skip[mbr]"} 1587 1588 efi= [EFI,EARLY] 1589 Format: { "debug", "disable_early_pci_dma", 1590 "nochunk", "noruntime", "nosoftreserve", 1591 "novamap", "no_disable_early_pci_dma" } 1592 debug: enable misc debug output. 1593 disable_early_pci_dma: disable the busmaster bit on all 1594 PCI bridges while in the EFI boot stub. 1595 nochunk: disable reading files in "chunks" in the EFI 1596 boot stub, as chunking can cause problems with some 1597 firmware implementations. 1598 noruntime : disable EFI runtime services support 1599 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1600 attribute may cause the kernel to reserve the 1601 memory range for a memory mapping driver to 1602 claim. Specify efi=nosoftreserve to disable this 1603 reservation and treat the memory by its base type 1604 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1605 novamap: do not call SetVirtualAddressMap(). 1606 no_disable_early_pci_dma: Leave the busmaster bit set 1607 on all PCI bridges while in the EFI boot stub 1608 1609 efi_no_storage_paranoia [EFI,X86,EARLY] 1610 The kernel reserves 5KB of EFI variable storage for 1611 safety, because some UEFI implementation may fail to 1612 boot if there's insufficient space in the EFI variable 1613 storage. 1614 1615 Using this parameter, you can use the 5KB reservation 1616 in the EFI variable storage. 1617 1618 However, Use this parameter only if you are really 1619 sure that your UEFI does sane gc and fulfills the spec 1620 otherwise your board may brick. 1621 1622 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1623 that is to be dynamically loaded by Linux. If there are 1624 multiple variables with the same name but with different 1625 vendor GUIDs, all of them will be loaded. See 1626 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1627 1628 1629 eisa_irq_edge= [PARISC,HW] 1630 See header of drivers/parisc/eisa.c. 1631 1632 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1633 Format: ekgdboc=kbd 1634 1635 This is designed to be used in conjunction with 1636 the boot argument: earlyprintk=vga 1637 1638 This parameter works in place of the kgdboc parameter 1639 but can only be used if the backing tty is available 1640 very early in the boot process. For early debugging 1641 via a serial port see kgdboc_earlycon instead. 1642 1643 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1644 Specifies physical address of start of kernel core 1645 image elf header and optionally the size. Generally 1646 kexec loader will pass this option to capture kernel. 1647 See Documentation/admin-guide/kdump/kdump.rst for details. 1648 1649 enable_mtrr_cleanup [X86,EARLY] 1650 The kernel tries to adjust MTRR layout from continuous 1651 to discrete, to make X server driver able to add WB 1652 entry later. This parameter enables that. 1653 1654 enforcing= [SELINUX] Set initial enforcing status. 1655 Format: {"0" | "1"} 1656 See security/selinux/Kconfig help text. 1657 0 -- permissive (log only, no denials). 1658 1 -- enforcing (deny and log). 1659 Default value is 0. 1660 Value can be changed at runtime via 1661 /sys/fs/selinux/enforce. 1662 1663 erst_disable [ACPI] 1664 Disable Error Record Serialization Table (ERST) 1665 support. 1666 1667 ether= [HW,NET] Ethernet cards parameters 1668 This option is obsoleted by the "netdev=" option, which 1669 has equivalent usage. See its documentation for details. 1670 1671 evm= [EVM] 1672 Format: { "fix" } 1673 Permit 'security.evm' to be updated regardless of 1674 current integrity status. 1675 1676 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1677 stages so cover more early boot allocations. 1678 Please note that as side effect some optimizations 1679 might be disabled to achieve that (e.g. parallelized 1680 memory initialization is disabled) so the boot process 1681 might take longer, especially on systems with a lot of 1682 memory. Available with CONFIG_PAGE_EXTENSION=y. 1683 1684 failslab= 1685 fail_usercopy= 1686 fail_page_alloc= 1687 fail_skb_realloc= 1688 fail_make_request=[KNL] 1689 General fault injection mechanism. 1690 Format: <interval>,<probability>,<space>,<times> 1691 See also Documentation/fault-injection/. 1692 1693 fb_tunnels= [NET] 1694 Format: { initns | none } 1695 See Documentation/admin-guide/sysctl/net.rst for 1696 fb_tunnels_only_for_init_ns 1697 1698 floppy= [HW] 1699 See Documentation/admin-guide/blockdev/floppy.rst. 1700 1701 forcepae [X86-32] 1702 Forcefully enable Physical Address Extension (PAE). 1703 Many Pentium M systems disable PAE but may have a 1704 functionally usable PAE implementation. 1705 Warning: use of this parameter will taint the kernel 1706 and may cause unknown problems. 1707 1708 fred= [X86-64] 1709 Enable/disable Flexible Return and Event Delivery. 1710 Format: { on | off } 1711 on: enable FRED when it's present, the default setting. 1712 off: disable FRED. 1713 1714 ftrace=[tracer] 1715 [FTRACE] will set and start the specified tracer 1716 as early as possible in order to facilitate early 1717 boot debugging. 1718 1719 ftrace_boot_snapshot 1720 [FTRACE] On boot up, a snapshot will be taken of the 1721 ftrace ring buffer that can be read at: 1722 /sys/kernel/tracing/snapshot. 1723 This is useful if you need tracing information from kernel 1724 boot up that is likely to be overridden by user space 1725 start up functionality. 1726 1727 Optionally, the snapshot can also be defined for a tracing 1728 instance that was created by the trace_instance= command 1729 line parameter. 1730 1731 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1732 1733 The above will cause the "foo" tracing instance to trigger 1734 a snapshot at the end of boot up. 1735 1736 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1737 ,<instance>=2(orig_cpu)] 1738 [FTRACE] will dump the trace buffers on oops. 1739 If no parameter is passed, ftrace will dump global 1740 buffers of all CPUs, if you pass 2 or orig_cpu, it 1741 will dump only the buffer of the CPU that triggered 1742 the oops, or the specific instance will be dumped if 1743 its name is passed. Multiple instance dump is also 1744 supported, and instances are separated by commas. Each 1745 instance supports only dump on CPU that triggered the 1746 oops by passing 2 or orig_cpu to it. 1747 1748 ftrace_dump_on_oops=foo=orig_cpu 1749 1750 The above will dump only the buffer of "foo" instance 1751 on CPU that triggered the oops. 1752 1753 ftrace_dump_on_oops,foo,bar=orig_cpu 1754 1755 The above will dump global buffer on all CPUs, the 1756 buffer of "foo" instance on all CPUs and the buffer 1757 of "bar" instance on CPU that triggered the oops. 1758 1759 ftrace_filter=[function-list] 1760 [FTRACE] Limit the functions traced by the function 1761 tracer at boot up. function-list is a comma-separated 1762 list of functions. This list can be changed at run 1763 time by the set_ftrace_filter file in the debugfs 1764 tracing directory. 1765 1766 ftrace_notrace=[function-list] 1767 [FTRACE] Do not trace the functions specified in 1768 function-list. This list can be changed at run time 1769 by the set_ftrace_notrace file in the debugfs 1770 tracing directory. 1771 1772 ftrace_graph_filter=[function-list] 1773 [FTRACE] Limit the top level callers functions traced 1774 by the function graph tracer at boot up. 1775 function-list is a comma-separated list of functions 1776 that can be changed at run time by the 1777 set_graph_function file in the debugfs tracing directory. 1778 1779 ftrace_graph_notrace=[function-list] 1780 [FTRACE] Do not trace from the functions specified in 1781 function-list. This list is a comma-separated list of 1782 functions that can be changed at run time by the 1783 set_graph_notrace file in the debugfs tracing directory. 1784 1785 ftrace_graph_max_depth=<uint> 1786 [FTRACE] Used with the function graph tracer. This is 1787 the max depth it will trace into a function. This value 1788 can be changed at run time by the max_graph_depth file 1789 in the tracefs tracing directory. default: 0 (no limit) 1790 1791 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1792 devices by scanning the firmware to infer the 1793 consumer/supplier relationships. This feature is 1794 especially useful when drivers are loaded as modules as 1795 it ensures proper ordering of tasks like device probing 1796 (suppliers first, then consumers), supplier boot state 1797 clean up (only after all consumers have probed), 1798 suspend/resume & runtime PM (consumers first, then 1799 suppliers). 1800 Format: { off | permissive | on | rpm } 1801 off -- Don't create device links from firmware info. 1802 permissive -- Create device links from firmware info 1803 but use it only for ordering boot state clean 1804 up (sync_state() calls). 1805 on -- Create device links from firmware info and use it 1806 to enforce probe and suspend/resume ordering. 1807 rpm -- Like "on", but also use to order runtime PM. 1808 1809 fw_devlink.strict=<bool> 1810 [KNL,EARLY] Treat all inferred dependencies as mandatory 1811 dependencies. This only applies for fw_devlink=on|rpm. 1812 Format: <bool> 1813 1814 fw_devlink.sync_state = 1815 [KNL,EARLY] When all devices that could probe have finished 1816 probing, this parameter controls what to do with 1817 devices that haven't yet received their sync_state() 1818 calls. 1819 Format: { strict | timeout } 1820 strict -- Default. Continue waiting on consumers to 1821 probe successfully. 1822 timeout -- Give up waiting on consumers and call 1823 sync_state() on any devices that haven't yet 1824 received their sync_state() calls after 1825 deferred_probe_timeout has expired or by 1826 late_initcall() if !CONFIG_MODULES. 1827 1828 gamecon.map[2|3]= 1829 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1830 support via parallel port (up to 5 devices per port) 1831 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1832 See also Documentation/input/devices/joystick-parport.rst 1833 1834 gamma= [HW,DRM] 1835 1836 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1837 Format: off | on 1838 default: on 1839 1840 gather_data_sampling= 1841 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1842 mitigation. 1843 1844 Gather Data Sampling is a hardware vulnerability which 1845 allows unprivileged speculative access to data which was 1846 previously stored in vector registers. 1847 1848 This issue is mitigated by default in updated microcode. 1849 The mitigation may have a performance impact but can be 1850 disabled. On systems without the microcode mitigation 1851 disabling AVX serves as a mitigation. 1852 1853 force: Disable AVX to mitigate systems without 1854 microcode mitigation. No effect if the microcode 1855 mitigation is present. Known to cause crashes in 1856 userspace with buggy AVX enumeration. 1857 1858 off: Disable GDS mitigation. 1859 1860 gbpages [X86] Use GB pages for kernel direct mappings. 1861 1862 gcov_persist= [GCOV] When non-zero (default), profiling data for 1863 kernel modules is saved and remains accessible via 1864 debugfs, even when the module is unloaded/reloaded. 1865 When zero, profiling data is discarded and associated 1866 debugfs files are removed at module unload time. 1867 1868 goldfish [X86] Enable the goldfish android emulator platform. 1869 Don't use this when you are not running on the 1870 android emulator 1871 1872 gpio-mockup.gpio_mockup_ranges 1873 [HW] Sets the ranges of gpiochip of for this device. 1874 Format: <start1>,<end1>,<start2>,<end2>... 1875 gpio-mockup.gpio_mockup_named_lines 1876 [HW] Let the driver know GPIO lines should be named. 1877 1878 gpt [EFI] Forces disk with valid GPT signature but 1879 invalid Protective MBR to be treated as GPT. If the 1880 primary GPT is corrupted, it enables the backup/alternate 1881 GPT to be used instead. 1882 1883 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1884 the "Enable 0" bit of the configuration register. 1885 Format: 0 | 1 1886 Default: 0 1887 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1888 the "Enable 0" bit of the configuration register. 1889 Format: 0 | 1 1890 Default: 0 1891 grcan.select= [HW] Select which physical interface to use. 1892 Format: 0 | 1 1893 Default: 0 1894 grcan.txsize= [HW] Sets the size of the tx buffer. 1895 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1896 Default: 1024 1897 grcan.rxsize= [HW] Sets the size of the rx buffer. 1898 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1899 Default: 1024 1900 1901 hardened_usercopy= 1902 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1903 hardening is enabled for this boot. Hardened 1904 usercopy checking is used to protect the kernel 1905 from reading or writing beyond known memory 1906 allocation boundaries as a proactive defense 1907 against bounds-checking flaws in the kernel's 1908 copy_to_user()/copy_from_user() interface. 1909 The default is determined by 1910 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1911 on Perform hardened usercopy checks. 1912 off Disable hardened usercopy checks. 1913 1914 hardlockup_all_cpu_backtrace= 1915 [KNL] Should the hard-lockup detector generate 1916 backtraces on all cpus. 1917 Format: 0 | 1 1918 1919 hash_pointers= 1920 [KNL,EARLY] 1921 By default, when pointers are printed to the console 1922 or buffers via the %p format string, that pointer is 1923 "hashed", i.e. obscured by hashing the pointer value. 1924 This is a security feature that hides actual kernel 1925 addresses from unprivileged users, but it also makes 1926 debugging the kernel more difficult since unequal 1927 pointers can no longer be compared. The choices are: 1928 Format: { auto | always | never } 1929 Default: auto 1930 1931 auto - Hash pointers unless slab_debug is enabled. 1932 always - Always hash pointers (even if slab_debug is 1933 enabled). 1934 never - Never hash pointers. This option should only 1935 be specified when debugging the kernel. Do 1936 not use on production kernels. The boot 1937 param "no_hash_pointers" is an alias for 1938 this mode. 1939 1940 For controlling hashing dynamically at runtime, 1941 use the "kernel.kptr_restrict" sysctl instead. 1942 1943 hashdist= [KNL,NUMA] Large hashes allocated during boot 1944 are distributed across NUMA nodes. Defaults on 1945 for 64-bit NUMA, off otherwise. 1946 Format: 0 | 1 (for off | on) 1947 1948 hd= [EIDE] (E)IDE hard drive subsystem geometry 1949 Format: <cyl>,<head>,<sect> 1950 1951 hest_disable [ACPI] 1952 Disable Hardware Error Source Table (HEST) support; 1953 corresponding firmware-first mode error processing 1954 logic will be disabled. 1955 1956 hibernate= [HIBERNATION] 1957 noresume Don't check if there's a hibernation image 1958 present during boot. 1959 nocompress Don't compress/decompress hibernation images. 1960 no Disable hibernation and resume. 1961 protect_image Turn on image protection during restoration 1962 (that will set all pages holding image data 1963 during restoration read-only). 1964 1965 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1966 used with hibernation. 1967 Format: { lzo | lz4 } 1968 Default: lzo 1969 1970 lzo: Select LZO compression algorithm to 1971 compress/decompress hibernation image. 1972 1973 lz4: Select LZ4 compression algorithm to 1974 compress/decompress hibernation image. 1975 1976 hibernate.pm_test_delay= 1977 [HIBERNATION] 1978 Sets the number of seconds to remain in a hibernation test 1979 mode before resuming the system (see 1980 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 1981 is set. Default value is 5. 1982 1983 hibernate_compression_threads= 1984 [HIBERNATION] 1985 Set the number of threads used for compressing or decompressing 1986 hibernation images. 1987 1988 Format: <integer> 1989 Default: 3 1990 Minimum: 1 1991 Example: hibernate_compression_threads=4 1992 1993 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 1994 size of <nn>. This works even on boxes that have no 1995 highmem otherwise. This also works to reduce highmem 1996 size on bigger boxes. 1997 1998 highres= [KNL] Enable/disable high resolution timer mode. 1999 Valid parameters: "on", "off" 2000 Default: "on" 2001 2002 hlt [BUGS=ARM,SH] 2003 2004 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2005 Format: <string> 2006 This allows setting the system's hostname during early 2007 startup. This sets the name returned by gethostname. 2008 Using this parameter to set the hostname makes it 2009 possible to ensure the hostname is correctly set before 2010 any userspace processes run, avoiding the possibility 2011 that a process may call gethostname before the hostname 2012 has been explicitly set, resulting in the calling 2013 process getting an incorrect result. The string must 2014 not exceed the maximum allowed hostname length (usually 2015 64 characters) and will be truncated otherwise. 2016 2017 hpet= [X86-32,HPET] option to control HPET usage 2018 Format: { enable (default) | disable | force | 2019 verbose } 2020 disable: disable HPET and use PIT instead 2021 force: allow force enabled of undocumented chips (ICH4, 2022 VIA, nVidia) 2023 verbose: show contents of HPET registers during setup 2024 2025 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2026 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2027 2028 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2029 If this follows hugepagesz (below), it specifies 2030 the number of pages of hugepagesz to be allocated. 2031 If this is the first HugeTLB parameter on the command 2032 line, it specifies the number of pages to allocate for 2033 the default huge page size. If using node format, the 2034 number of pages to allocate per-node can be specified. 2035 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2036 Format: <integer> or (node format) 2037 <node>:<integer>[,<node>:<integer>] 2038 2039 hugepagesz= 2040 [HW,EARLY] The size of the HugeTLB pages. This is 2041 used in conjunction with hugepages (above) to 2042 allocate huge pages of a specific size at boot. The 2043 pair hugepagesz=X hugepages=Y can be specified once 2044 for each supported huge page size. Huge page sizes 2045 are architecture dependent. See also 2046 Documentation/admin-guide/mm/hugetlbpage.rst. 2047 Format: size[KMG] 2048 2049 hugepage_alloc_threads= 2050 [HW] The number of threads that should be used to 2051 allocate hugepages during boot. This option can be 2052 used to improve system bootup time when allocating 2053 a large amount of huge pages. 2054 The default value is 25% of the available hardware threads. 2055 2056 Note that this parameter only applies to non-gigantic huge pages. 2057 2058 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2059 of gigantic hugepages. Or using node format, the size 2060 of a CMA area per node can be specified. 2061 The size can be an absolute value (e.g., 2G) or a 2062 percentage of the total memory or node memory (e.g., 20%). 2063 Percentage-derived sizes are rounded down to a multiple of 2064 the architecture's gigantic hugepage size and may become 2065 zero. 2066 Format: nn[KMGTPE] or nn% or (node format) 2067 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] or 2068 <node>:nn%[,<node>:nn%] 2069 2070 The size must be a multiple of the gigantic page size. 2071 When using node format, this applies to each per-node size. 2072 Missaligned values are dropped with a warning. 2073 2074 Reserve a CMA area of given size and allocate gigantic 2075 hugepages using the CMA allocator. If enabled, the 2076 boot-time allocation of gigantic hugepages is skipped. 2077 2078 hugetlb_cma_only= 2079 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2080 try to allocate from the CMA areas. 2081 2082 This option does nothing if hugetlb_cma= is not also 2083 specified. 2084 2085 hugetlb_free_vmemmap= 2086 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2087 enabled. 2088 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2089 Allows heavy hugetlb users to free up some more 2090 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2091 Format: { on | off (default) } 2092 2093 on: enable HVO 2094 off: disable HVO 2095 2096 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2097 the default is on. 2098 2099 Note that the vmemmap pages may be allocated from the added 2100 memory block itself when memory_hotplug.memmap_on_memory is 2101 enabled, those vmemmap pages cannot be optimized even if this 2102 feature is enabled. Other vmemmap pages not allocated from 2103 the added memory block itself do not be affected. 2104 2105 hung_task_panic= 2106 [KNL] Number of hung tasks to trigger kernel panic. 2107 Format: <int> 2108 2109 When set to a non-zero value, a kernel panic will be triggered if 2110 the number of detected hung tasks reaches this value. 2111 2112 0: don't panic 2113 1: panic immediately on first hung task 2114 N: panic after N hung tasks are detected in a single scan 2115 2116 The default value is controlled by the 2117 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2118 selected by this boot parameter can be changed later by the 2119 kernel.hung_task_panic sysctl. 2120 2121 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2122 terminal devices. Valid values: 0..8 2123 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2124 If specified, z/VM IUCV HVC accepts connections 2125 from listed z/VM user IDs only. 2126 2127 hv_nopvspin [X86,HYPER_V,EARLY] 2128 Disables the paravirt spinlock optimizations 2129 which allow the hypervisor to 'idle' the guest 2130 on lock contention. 2131 2132 hw_protection= [HW] 2133 Format: reboot | shutdown 2134 2135 Hardware protection action taken on critical events like 2136 overtemperature or imminent voltage loss. 2137 2138 i2c_bus= [HW] Override the default board specific I2C bus speed 2139 or register an additional I2C bus that is not 2140 registered from board initialization code. 2141 Format: 2142 <bus_id>,<clkrate> 2143 2144 i2c_touchscreen_props= [HW,ACPI,X86] 2145 Set device-properties for ACPI-enumerated I2C-attached 2146 touchscreen, to e.g. fix coordinates of upside-down 2147 mounted touchscreens. If you need this option please 2148 submit a drivers/platform/x86/touchscreen_dmi.c patch 2149 adding a DMI quirk for this. 2150 2151 Format: 2152 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2153 Where <val> is one of: 2154 Omit "=<val>" entirely Set a boolean device-property 2155 Unsigned number Set a u32 device-property 2156 Anything else Set a string device-property 2157 2158 Examples (split over multiple lines): 2159 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2160 touchscreen-inverted-y 2161 2162 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2163 touchscreen-size-y=1080:touchscreen-inverted-y: 2164 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2165 2166 i8042.debug [HW] Toggle i8042 debug mode 2167 i8042.unmask_kbd_data 2168 [HW] Enable printing of interrupt data from the KBD port 2169 (disabled by default, and as a pre-condition 2170 requires that i8042.debug=1 be enabled) 2171 i8042.direct [HW] Put keyboard port into non-translated mode 2172 i8042.dumbkbd [HW] Pretend that controller can only read data from 2173 keyboard and cannot control its state 2174 (Don't attempt to blink the leds) 2175 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2176 i8042.nokbd [HW] Don't check/create keyboard port 2177 i8042.noloop [HW] Disable the AUX Loopback command while probing 2178 for the AUX port 2179 i8042.nomux [HW] Don't check presence of an active multiplexing 2180 controller 2181 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2182 controllers 2183 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2184 i8042.reset [HW] Reset the controller during init, cleanup and 2185 suspend-to-ram transitions, only during s2r 2186 transitions, or never reset 2187 Format: { 1 | Y | y | 0 | N | n } 2188 1, Y, y: always reset controller 2189 0, N, n: don't ever reset controller 2190 Default: only on s2r transitions on x86; most other 2191 architectures force reset to be always executed 2192 i8042.unlock [HW] Unlock (ignore) the keylock 2193 i8042.kbdreset [HW] Reset device connected to KBD port 2194 i8042.probe_defer 2195 [HW] Allow deferred probing upon i8042 probe errors 2196 2197 i810= [HW,DRM] 2198 2199 i915.invert_brightness= 2200 [DRM] Invert the sense of the variable that is used to 2201 set the brightness of the panel backlight. Normally a 2202 brightness value of 0 indicates backlight switched off, 2203 and the maximum of the brightness value sets the backlight 2204 to maximum brightness. If this parameter is set to 0 2205 (default) and the machine requires it, or this parameter 2206 is set to 1, a brightness value of 0 sets the backlight 2207 to maximum brightness, and the maximum of the brightness 2208 value switches the backlight off. 2209 -1 -- never invert brightness 2210 0 -- machine default 2211 1 -- force brightness inversion 2212 2213 ia32_emulation= [X86-64] 2214 Format: <bool> 2215 When true, allows loading 32-bit programs and executing 32-bit 2216 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2217 boot time. When false, unconditionally disables IA32 emulation. 2218 2219 2220 idle= [X86,EARLY] 2221 Format: idle=poll, idle=halt, idle=nomwait 2222 2223 idle=poll: Don't do power saving in the idle loop 2224 using HLT, but poll for rescheduling event. This will 2225 make the CPUs eat a lot more power, but may be useful 2226 to get slightly better performance in multiprocessor 2227 benchmarks. It also makes some profiling using 2228 performance counters more accurate. Please note that 2229 on systems with MONITOR/MWAIT support (like Intel 2230 EM64T CPUs) this option has no performance advantage 2231 over the normal idle loop. It may also interact badly 2232 with hyperthreading. 2233 2234 idle=halt: Halt is forced to be used for CPU idle. 2235 In such case C2/C3 won't be used again. 2236 2237 idle=nomwait: Disable mwait for CPU C-states 2238 2239 [ARM64,EARLY] 2240 Format: idle=wfi, idle=yield, idle=nop 2241 2242 idle=wfi: Use the WFI (Wait For Interrupt) hint 2243 instruction in the idle loop. This is the default and 2244 allows the CPU to enter a low-power state until an 2245 interrupt arrives. 2246 2247 idle=yield: Use the YIELD hint instruction instead of 2248 WFI. CPUs supporting simultaneous multi-threading (SMT), 2249 can continue executing another thread when the current 2250 thread reaches the idle loop. This will make the CPUs 2251 eat more power, but may be useful to get slightly better 2252 performance in some applications, since the CPUs will 2253 not enter a low-power state. 2254 2255 idle=nop: Do not execute any idle instruction in the 2256 idle loop. This is useful on platforms where WFI 2257 misbehaves, leading to system instability or loss of CPU 2258 state. This will make the CPUs eat more power, but may 2259 give slightly better performance in some applications, 2260 since the CPUs will not enter a low-power state. 2261 2262 idxd.sva= [HW] 2263 Format: <bool> 2264 Allow force disabling of Shared Virtual Memory (SVA) 2265 support for the idxd driver. By default it is set to 2266 true (1). 2267 2268 idxd.tc_override= [HW] 2269 Format: <bool> 2270 Allow override of default traffic class configuration 2271 for the device. By default it is set to false (0). 2272 2273 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2274 Format: { strict | legacy | 2008 | relaxed | emulated } 2275 Default: strict 2276 2277 Choose which programs will be accepted for execution 2278 based on the IEEE 754 NaN encoding(s) supported by 2279 the FPU and the NaN encoding requested with the value 2280 of an ELF file header flag individually set by each 2281 binary. Hardware implementations are permitted to 2282 support either or both of the legacy and the 2008 NaN 2283 encoding mode. 2284 2285 Available settings are as follows: 2286 strict accept binaries that request a NaN encoding 2287 supported by the FPU 2288 legacy only accept legacy-NaN binaries, if supported 2289 by the FPU 2290 2008 only accept 2008-NaN binaries, if supported 2291 by the FPU 2292 relaxed accept any binaries regardless of whether 2293 supported by the FPU 2294 emulated accept any binaries but enable FPU emulator 2295 if binary mode is unsupported by the FPU. 2296 2297 The FPU emulator is always able to support both NaN 2298 encodings, so if no FPU hardware is present or it has 2299 been disabled with 'nofpu', then the settings of 2300 'legacy' and '2008' strap the emulator accordingly, 2301 'relaxed' straps the emulator for both legacy-NaN and 2302 2008-NaN, whereas 'strict' enables legacy-NaN only on 2303 legacy processors and both NaN encodings on MIPS32 or 2304 MIPS64 CPUs. 2305 2306 The setting for ABS.fmt/NEG.fmt instruction execution 2307 mode generally follows that for the NaN encoding, 2308 except where unsupported by hardware. 2309 2310 ignore_loglevel [KNL,EARLY] 2311 Ignore loglevel setting - this will print /all/ 2312 kernel messages to the console. Useful for debugging. 2313 We also add it as printk module parameter, so users 2314 could change it dynamically, usually by 2315 /sys/module/printk/parameters/ignore_loglevel. 2316 2317 ignore_rlimit_data 2318 Ignore RLIMIT_DATA setting for data mappings, 2319 print warning at first misuse. Can be changed via 2320 /sys/module/kernel/parameters/ignore_rlimit_data. 2321 2322 ihash_entries= [KNL] 2323 Set number of hash buckets for inode cache. 2324 2325 ima_appraise= [IMA] appraise integrity measurements 2326 Format: { "off" | "enforce" | "fix" | "log" } 2327 default: "enforce" 2328 2329 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2330 The builtin appraise policy appraises all files 2331 owned by uid=0. 2332 2333 ima_canonical_fmt [IMA] 2334 Use the canonical format for the binary runtime 2335 measurements, instead of host native format. 2336 2337 ima_flush_htable [IMA] 2338 Flush the IMA hash table when deleting all the 2339 staged measurement records, to achieve maximum 2340 memory saving at the cost of having duplicate 2341 records across the staged measurement lists. 2342 2343 ima_hash= [IMA] 2344 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2345 | sha512 | ... } 2346 default: "sha1" 2347 2348 The list of supported hash algorithms is defined 2349 in crypto/hash_info.h. 2350 2351 ima_policy= [IMA] 2352 The builtin policies to load during IMA setup. 2353 Format: "tcb | appraise_tcb | secure_boot | 2354 fail_securely | critical_data" 2355 2356 The "tcb" policy measures all programs exec'd, files 2357 mmap'd for exec, and all files opened with the read 2358 mode bit set by either the effective uid (euid=0) or 2359 uid=0. 2360 2361 The "appraise_tcb" policy appraises the integrity of 2362 all files owned by root. 2363 2364 The "secure_boot" policy appraises the integrity 2365 of files (eg. kexec kernel image, kernel modules, 2366 firmware, policy, etc) based on file signatures. 2367 2368 The "fail_securely" policy forces file signature 2369 verification failure also on privileged mounted 2370 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2371 flag. 2372 2373 The "critical_data" policy measures kernel integrity 2374 critical data. 2375 2376 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2377 Load a policy which meets the needs of the Trusted 2378 Computing Base. This means IMA will measure all 2379 programs exec'd, files mmap'd for exec, and all files 2380 opened for read by uid=0. 2381 2382 ima_template= [IMA] 2383 Select one of defined IMA measurements template formats. 2384 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2385 "ima-sigv2" } 2386 Default: "ima-ng" 2387 2388 ima_template_fmt= 2389 [IMA] Define a custom template format. 2390 Format: { "field1|...|fieldN" } 2391 2392 ima= [IMA] Enable or disable IMA 2393 Format: { "off" | "on" } 2394 Default: "on" 2395 Note that disabling IMA is limited to kdump kernel. 2396 2397 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2398 Target Selection(ITS) bug in Intel CPUs. Updated 2399 microcode is also required for a fix in IBPB. 2400 2401 on: Enable mitigation (default). 2402 off: Disable mitigation. 2403 force: Force the ITS bug and deploy default 2404 mitigation. 2405 vmexit: Only deploy mitigation if CPU is affected by 2406 guest/host isolation part of ITS. 2407 stuff: Deploy RSB-fill mitigation when retpoline is 2408 also deployed. Otherwise, deploy the default 2409 mitigation. 2410 2411 For details see: 2412 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2413 2414 init= [KNL] 2415 Format: <full_path> 2416 Run specified binary instead of /sbin/init as init 2417 process. 2418 2419 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2420 for working out where the kernel is dying during 2421 startup. 2422 2423 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2424 initcall functions. Useful for debugging built-in 2425 modules and initcalls. 2426 2427 initramfs_async= [KNL] 2428 Format: <bool> 2429 Default: 1 2430 This parameter controls whether the initramfs 2431 image is unpacked asynchronously, concurrently 2432 with devices being probed and 2433 initialized. This should normally just work, 2434 but as a debugging aid, one can get the 2435 historical behaviour of the initramfs 2436 unpacking being completed before device_ and 2437 late_ initcalls. 2438 2439 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2440 2441 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2442 load the initrd. If an initrd is compiled in or 2443 specified in the bootparams, it takes priority over this 2444 setting. 2445 Format: ss[KMG],nn[KMG] 2446 Default is 0, 0 2447 2448 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2449 zeroes. 2450 Format: 0 | 1 2451 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2452 2453 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2454 Format: 0 | 1 2455 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2456 2457 init_pkru= [X86] Specify the default memory protection keys rights 2458 register contents for all processes. 0x55555554 by 2459 default (disallow access to all but pkey 0). Can 2460 override in debugfs after boot. 2461 2462 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2463 Format: <irq> 2464 2465 int_pln_enable [X86] Enable power limit notification interrupt 2466 2467 integrity_audit=[IMA] 2468 Format: { "0" | "1" } 2469 0 -- basic integrity auditing messages. (Default) 2470 1 -- additional integrity auditing messages. 2471 2472 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2473 on 2474 Enable intel iommu driver. 2475 off 2476 Disable intel iommu driver. 2477 igfx_off [Default Off] 2478 By default, gfx is mapped as normal device. If a gfx 2479 device has a dedicated DMAR unit, the DMAR unit is 2480 bypassed by not enabling DMAR with this option. In 2481 this case, gfx device will use physical address for 2482 DMA. 2483 strict [Default Off] 2484 Deprecated, equivalent to iommu.strict=1. 2485 sp_off [Default Off] 2486 By default, super page will be supported if Intel IOMMU 2487 has the capability. With this option, super page will 2488 not be supported. 2489 sm_on 2490 Enable the Intel IOMMU scalable mode if the hardware 2491 advertises that it has support for the scalable mode 2492 translation. 2493 sm_off 2494 Disallow use of the Intel IOMMU scalable mode. 2495 tboot_noforce [Default Off] 2496 Do not force the Intel IOMMU enabled under tboot. 2497 By default, tboot will force Intel IOMMU on, which 2498 could harm performance of some high-throughput 2499 devices like 40GBit network cards, even if identity 2500 mapping is enabled. 2501 Note that using this option lowers the security 2502 provided by tboot because it makes the system 2503 vulnerable to DMA attacks. 2504 2505 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2506 0 disables intel_idle and fall back on acpi_idle. 2507 1 to 9 specify maximum depth of C-state. 2508 2509 intel_pstate= [X86,EARLY] 2510 disable 2511 Do not enable intel_pstate as the default 2512 scaling driver for the supported processors 2513 active 2514 Use intel_pstate driver to bypass the scaling 2515 governors layer of cpufreq and provides it own 2516 algorithms for p-state selection. There are two 2517 P-state selection algorithms provided by 2518 intel_pstate in the active mode: powersave and 2519 performance. The way they both operate depends 2520 on whether or not the hardware managed P-states 2521 (HWP) feature has been enabled in the processor 2522 and possibly on the processor model. 2523 passive 2524 Use intel_pstate as a scaling driver, but configure it 2525 to work with generic cpufreq governors (instead of 2526 enabling its internal governor). This mode cannot be 2527 used along with the hardware-managed P-states (HWP) 2528 feature. 2529 force 2530 Enable intel_pstate on systems that prohibit it by default 2531 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2532 instead of acpi-cpufreq may disable platform features, such 2533 as thermal controls and power capping, that rely on ACPI 2534 P-States information being indicated to OSPM and therefore 2535 should be used with caution. This option does not work with 2536 processors that aren't supported by the intel_pstate driver 2537 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2538 no_hwp 2539 Do not enable hardware P state control (HWP) 2540 if available. 2541 hwp_only 2542 Only load intel_pstate on systems which support 2543 hardware P state control (HWP) if available. 2544 support_acpi_ppc 2545 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2546 Description Table, specifies preferred power management 2547 profile as "Enterprise Server" or "Performance Server", 2548 then this feature is turned on by default. 2549 per_cpu_perf_limits 2550 Allow per-logical-CPU P-State performance control limits using 2551 cpufreq sysfs interface 2552 no_cas 2553 Do not enable capacity-aware scheduling (CAS) on 2554 hybrid systems 2555 2556 intremap= [X86-64,Intel-IOMMU,EARLY] 2557 on enable Interrupt Remapping (default) 2558 off disable Interrupt Remapping 2559 nosid disable Source ID checking 2560 no_x2apic_optout 2561 BIOS x2APIC opt-out request will be ignored 2562 nopost disable Interrupt Posting 2563 posted_msi 2564 enable MSIs delivered as posted interrupts 2565 2566 iomem= Disable strict checking of access to MMIO memory 2567 strict regions from userspace. 2568 relaxed 2569 2570 iommu= [X86,EARLY] 2571 2572 off 2573 Don't initialize and use any kind of IOMMU. 2574 2575 force 2576 Force the use of the hardware IOMMU even when 2577 it is not actually needed (e.g. because < 3 GB 2578 memory). 2579 2580 noforce 2581 Don't force hardware IOMMU usage when it is not 2582 needed. (default). 2583 2584 merge 2585 Do scatter-gather (SG) merging. Implies "force" 2586 (experimental). 2587 2588 nomerge 2589 Don't do scatter-gather (SG) merging. 2590 2591 biomerge 2592 Do scatter-gather (SG) merging. Implies "force" 2593 (experimental). [same as "merge"] 2594 2595 panic 2596 Always panic when IOMMU overflows. 2597 2598 nopanic 2599 Don't panic on IOMMU overflows. 2600 2601 pt 2602 Use passththrough mode by default 2603 (Equivalent to iommu.passthrough=1) 2604 2605 nopt 2606 Use translated mode for DMA by default 2607 (Equivalent to iommu.passthrough=0) 2608 2609 soft 2610 Use software bounce buffering (SWIOTLB) (default for 2611 Intel machines). This can be used to prevent the usage 2612 of an available hardware IOMMU. 2613 2614 usedac 2615 Use the DAC on VIA PCI bridge 2616 (default: disable the VIA PCI bridge DAC) 2617 2618 AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU) 2619 2620 <size> 2621 Set the size of the remapping area in bytes. 2622 2623 allowed 2624 Overwrite iommu off workarounds for specific chipsets 2625 2626 force 2627 Overwrite iommu off workarounds for specific chipsets 2628 2629 fullflush 2630 Flush IOMMU on each allocation (default). 2631 2632 nofullflush 2633 Don't use IOMMU fullflush. 2634 2635 memaper[=<order>] 2636 Allocate an own aperture over RAM with size 2637 32MB<<order. (default: order=1, i.e. 64MB) 2638 2639 noaperture 2640 Ask the IOMMU not to touch the aperture for AGP. 2641 2642 noagp 2643 Don't initialize the AGP driver and use full aperture. 2644 2645 iommu= [PPC/POWERNV] 2646 2647 nobypass 2648 Disable IOMMU bypass, using IOMMU for PCI devices. 2649 2650 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2651 Format: { "0" | "1" } 2652 0 - Try to allocate a 32-bit DMA address first, before 2653 falling back to the full range if needed. 2654 1 - Allocate directly from the full usable range, 2655 forcing Dual Address Cycle for PCI cards supporting 2656 greater than 32-bit addressing. 2657 2658 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2659 Format: { "0" | "1" } 2660 0 - Lazy mode. 2661 Request that DMA unmap operations use deferred 2662 invalidation of hardware TLBs, for increased 2663 throughput at the cost of reduced device isolation. 2664 Will fall back to strict mode if not supported by 2665 the relevant IOMMU driver. 2666 1 - Strict mode. 2667 DMA unmap operations invalidate IOMMU hardware TLBs 2668 synchronously. 2669 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2670 Note: on x86, strict mode specified via one of the 2671 legacy driver-specific options takes precedence. 2672 2673 iommu.passthrough= 2674 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2675 Format: { "0" | "1" } 2676 0 - Use IOMMU translation for DMA. 2677 1 - Bypass the IOMMU for DMA. 2678 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2679 2680 iommu.debug_pagealloc= 2681 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2682 parameter enables the feature at boot time. By default, it 2683 is disabled and the system behaves the same way as a kernel 2684 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2685 Format: { "0" | "1" } 2686 0 - Sanitizer disabled. 2687 1 - Sanitizer enabled, expect runtime overhead. 2688 2689 io7= [HW] IO7 for Marvel-based Alpha systems 2690 See comment before marvel_specify_io7 in 2691 arch/alpha/kernel/core_marvel.c. 2692 2693 io_delay= [X86,EARLY] I/O delay method 2694 0x80 2695 Standard port 0x80 based delay 2696 0xed 2697 Alternate port 0xed based delay (needed on some systems) 2698 udelay 2699 Simple two microseconds delay 2700 none 2701 No delay 2702 2703 ip= [IP_PNP] 2704 See Documentation/admin-guide/nfs/nfsroot.rst. 2705 2706 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2707 IPC identifiers from 32,768 to 16,777,216. 2708 2709 ipe.enforce= [IPE] 2710 Format: <bool> 2711 Determine whether IPE starts in permissive (0) or 2712 enforce (1) mode. The default is enforce. 2713 2714 ipe.success_audit= 2715 [IPE] 2716 Format: <bool> 2717 Start IPE with success auditing enabled, emitting 2718 an audit event when a binary is allowed. The default 2719 is 0. 2720 2721 irqaffinity= [SMP] Set the default irq affinity mask 2722 The argument is a cpu list, as described above. 2723 2724 irqchip.gicv2_force_probe= 2725 [ARM,ARM64,EARLY] 2726 Format: <bool> 2727 Force the kernel to look for the second 4kB page 2728 of a GICv2 controller even if the memory range 2729 exposed by the device tree is too small. 2730 2731 irqchip.gicv3_nolpi= 2732 [ARM,ARM64,EARLY] 2733 Force the kernel to ignore the availability of 2734 LPIs (and by consequence ITSs). Intended for system 2735 that use the kernel as a bootloader, and thus want 2736 to let secondary kernels in charge of setting up 2737 LPIs. 2738 2739 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2740 Enables support for pseudo-NMIs in the kernel. This 2741 requires the kernel to be built with 2742 CONFIG_ARM64_PSEUDO_NMI. 2743 2744 irqchip.riscv_imsic_noipi 2745 [RISC-V,EARLY] 2746 Force the kernel to not use IMSIC software injected MSIs 2747 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2748 and thus want to reduce MMIO traps when triggering IPIs 2749 to multiple harts. 2750 2751 irqfixup [HW] 2752 When an interrupt is not handled search all handlers 2753 for it. Intended to get systems with badly broken 2754 firmware running. 2755 2756 irqhandler.duration_warn_us= [KNL] 2757 Warn if an IRQ handler exceeds the specified duration 2758 threshold in microseconds. Useful for identifying 2759 long-running IRQs in the system. 2760 2761 irqpoll [HW] 2762 When an interrupt is not handled search all handlers 2763 for it. Also check all handlers each timer 2764 interrupt. Intended to get systems with badly broken 2765 firmware running. 2766 2767 isapnp= [ISAPNP] 2768 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2769 2770 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2771 Format: [flag-list,]<cpu-list> 2772 2773 Specify one or more CPUs to isolate from disturbances 2774 specified in the flag list (default: domain): 2775 2776 nohz 2777 Disable the tick when a single task runs as well as 2778 disabling other kernel noises like having RCU callbacks 2779 offloaded. This is equivalent to the nohz_full parameter. 2780 2781 A residual 1Hz tick is offloaded to workqueues, which you 2782 need to affine to housekeeping through the global 2783 workqueue's affinity configured via the 2784 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2785 by using the 'domain' flag described below. 2786 2787 NOTE: by default the global workqueue runs on all CPUs, 2788 so to protect individual CPUs the 'cpumask' file has to 2789 be configured manually after bootup. 2790 2791 domain 2792 Isolate from the general SMP balancing and scheduling 2793 algorithms. Note that performing domain isolation this way 2794 is irreversible: it's not possible to bring back a CPU to 2795 the domains once isolated through this boot time 2796 configuration. Use cpusets for a dynamic configuration 2797 which can be altered at runtime. For details see 2798 Documentation/admin-guide/cpu-isolation.rst. 2799 2800 You can move a process onto or off an "isolated" CPU via 2801 the CPU affinity syscalls or cpuset. 2802 <cpu number> begins at 0 and the maximum value is 2803 "number of CPUs in system - 1". 2804 2805 managed_irq 2806 2807 Isolate from being targeted by managed interrupts 2808 which have an interrupt mask containing isolated 2809 CPUs. The affinity of managed interrupts is 2810 handled by the kernel and cannot be changed via 2811 the /proc/irq/* interfaces. 2812 2813 This isolation is best effort and only effective 2814 if the automatically assigned interrupt mask of a 2815 device queue contains isolated and housekeeping 2816 CPUs. If housekeeping CPUs are online then such 2817 interrupts are directed to the housekeeping CPU 2818 so that IO submitted on the housekeeping CPU 2819 cannot disturb the isolated CPU. 2820 2821 If a queue's affinity mask contains only isolated 2822 CPUs then this parameter has no effect on the 2823 interrupt routing decision, though interrupts are 2824 only delivered when tasks running on those 2825 isolated CPUs submit IO. IO submitted on 2826 housekeeping CPUs has no influence on those 2827 queues. 2828 2829 The format of <cpu-list> is described above. 2830 2831 iucv= [HW,NET] 2832 2833 ivrs_ioapic [HW,X86-64] 2834 Provide an override to the IOAPIC-ID<->DEVICE-ID 2835 mapping provided in the IVRS ACPI table. 2836 By default, PCI segment is 0, and can be omitted. 2837 2838 For example, to map IOAPIC-ID decimal 10 to 2839 PCI segment 0x1 and PCI device 00:14.0, 2840 write the parameter as: 2841 ivrs_ioapic=10@0001:00:14.0 2842 2843 Deprecated formats: 2844 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2845 write the parameter as: 2846 ivrs_ioapic[10]=00:14.0 2847 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2848 PCI device 00:14.0 write the parameter as: 2849 ivrs_ioapic[10]=0001:00:14.0 2850 2851 ivrs_hpet [HW,X86-64] 2852 Provide an override to the HPET-ID<->DEVICE-ID 2853 mapping provided in the IVRS ACPI table. 2854 By default, PCI segment is 0, and can be omitted. 2855 2856 For example, to map HPET-ID decimal 10 to 2857 PCI segment 0x1 and PCI device 00:14.0, 2858 write the parameter as: 2859 ivrs_hpet=10@0001:00:14.0 2860 2861 Deprecated formats: 2862 * To map HPET-ID decimal 0 to PCI device 00:14.0 2863 write the parameter as: 2864 ivrs_hpet[0]=00:14.0 2865 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2866 PCI device 00:14.0 write the parameter as: 2867 ivrs_ioapic[10]=0001:00:14.0 2868 2869 ivrs_acpihid [HW,X86-64] 2870 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2871 mapping provided in the IVRS ACPI table. 2872 By default, PCI segment is 0, and can be omitted. 2873 2874 For example, to map UART-HID:UID AMD0020:0 to 2875 PCI segment 0x1 and PCI device ID 00:14.5, 2876 write the parameter as: 2877 ivrs_acpihid=AMD0020:0@0001:00:14.5 2878 2879 Deprecated formats: 2880 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2881 PCI device ID 00:14.5, write the parameter as: 2882 ivrs_acpihid[00:14.5]=AMD0020:0 2883 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2884 PCI device ID 00:14.5, write the parameter as: 2885 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2886 2887 js= [HW,JOY] Analog joystick 2888 See Documentation/input/joydev/joystick.rst. 2889 2890 kasan_multi_shot 2891 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2892 report on every invalid memory access. Without this 2893 parameter KASAN will print report only for the first 2894 invalid access. 2895 2896 keep_bootcon [KNL,EARLY] 2897 Do not unregister boot console at start. This is only 2898 useful for debugging when something happens in the window 2899 between unregistering the boot console and initializing 2900 the real console. 2901 2902 keepinitrd [HW,ARM] See retain_initrd. 2903 2904 kernelcore= [KNL,X86,PPC,EARLY] 2905 Format: nn[KMGTPE] | nn% | "mirror" 2906 This parameter specifies the amount of memory usable by 2907 the kernel for non-movable allocations. The requested 2908 amount is spread evenly throughout all nodes in the 2909 system as ZONE_NORMAL. The remaining memory is used for 2910 movable memory in its own zone, ZONE_MOVABLE. In the 2911 event, a node is too small to have both ZONE_NORMAL and 2912 ZONE_MOVABLE, kernelcore memory will take priority and 2913 other nodes will have a larger ZONE_MOVABLE. 2914 2915 ZONE_MOVABLE is used for the allocation of pages that 2916 may be reclaimed or moved by the page migration 2917 subsystem. Note that allocations like PTEs-from-HighMem 2918 still use the HighMem zone if it exists, and the Normal 2919 zone if it does not. 2920 2921 It is possible to specify the exact amount of memory in 2922 the form of "nn[KMGTPE]", a percentage of total system 2923 memory in the form of "nn%", or "mirror". If "mirror" 2924 option is specified, mirrored (reliable) memory is used 2925 for non-movable allocations and remaining memory is used 2926 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2927 are exclusive, so you cannot specify multiple forms. 2928 2929 kfence.burst= [MM,KFENCE] The number of additional successive 2930 allocations to be attempted through KFENCE for each 2931 sample interval. 2932 Format: <unsigned integer> 2933 Default: 0 2934 2935 kfence.check_on_panic= 2936 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2937 canaries on panic. 2938 Format: <bool> 2939 Default: false 2940 2941 kfence.deferrable= 2942 [MM,KFENCE] Whether to use a deferrable timer to trigger 2943 allocations. This avoids forcing CPU wake-ups if the 2944 system is idle, at the risk of a less predictable 2945 sample interval. 2946 Format: <bool> 2947 Default: CONFIG_KFENCE_DEFERRABLE 2948 2949 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2950 error is detected. 2951 report - print the error report and continue (default). 2952 oops - print the error report and oops. 2953 panic - print the error report and panic. 2954 2955 kfence.sample_interval= 2956 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2957 Format: <unsigned integer> 2958 0 - Disable KFENCE. 2959 >0 - Enabled KFENCE with given sample interval. 2960 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2961 2962 kfence.skip_covered_thresh= 2963 [MM,KFENCE] If pool utilization reaches this threshold 2964 (pool usage%), KFENCE limits currently covered 2965 allocations of the same source from further filling 2966 up the pool. 2967 Format: <unsigned integer> 2968 Default: 75 2969 2970 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2971 Format: <Controller#>[,poll interval] 2972 The controller # is the number of the ehci usb debug 2973 port as it is probed via PCI. The poll interval is 2974 optional and is the number seconds in between 2975 each poll cycle to the debug port in case you need 2976 the functionality for interrupting the kernel with 2977 gdb or control-c on the dbgp connection. When 2978 not using this parameter you use sysrq-g to break into 2979 the kernel debugger. 2980 2981 kgdboc= [KGDB,HW] kgdb over consoles. 2982 Requires a tty driver that supports console polling, 2983 or a supported polling keyboard driver (non-usb). 2984 Serial only format: <serial_device>[,baud] 2985 keyboard only format: kbd 2986 keyboard and serial format: kbd,<serial_device>[,baud] 2987 Optional Kernel mode setting: 2988 kms, kbd format: kms,kbd 2989 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2990 2991 kgdboc_earlycon= [KGDB,HW,EARLY] 2992 If the boot console provides the ability to read 2993 characters and can work in polling mode, you can use 2994 this parameter to tell kgdb to use it as a backend 2995 until the normal console is registered. Intended to 2996 be used together with the kgdboc parameter which 2997 specifies the normal console to transition to. 2998 2999 The name of the early console should be specified 3000 as the value of this parameter. Note that the name of 3001 the early console might be different than the tty 3002 name passed to kgdboc. It's OK to leave the value 3003 blank and the first boot console that implements 3004 read() will be picked. 3005 3006 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3007 kernel debugger at the earliest opportunity. 3008 3009 kho= [KEXEC,EARLY] 3010 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3011 Enables or disables Kexec HandOver. 3012 "0" | "off" | "n" - kexec handover is disabled 3013 "1" | "on" | "y" - kexec handover is enabled 3014 3015 kho_scratch= [KEXEC,EARLY] 3016 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3017 Defines the size of the KHO scratch region. The KHO 3018 scratch regions are physically contiguous memory 3019 ranges that can only be used for non-kernel 3020 allocations. That way, even when memory is heavily 3021 fragmented with handed over memory, the kexeced 3022 kernel will always have enough contiguous ranges to 3023 bootstrap itself. 3024 3025 It is possible to specify the exact amount of 3026 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3027 where the first parameter defines the size of a low 3028 memory scratch area, the second parameter defines 3029 the size of a global scratch area and the third 3030 parameter defines the size of additional per-node 3031 scratch areas. The form "nn%" defines scale factor 3032 (in percents) of memory that was used during boot. 3033 3034 kmac= [MIPS] Korina ethernet MAC address. 3035 Configure the RouterBoard 532 series on-chip 3036 Ethernet adapter MAC address. 3037 3038 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3039 Valid arguments: on, off 3040 Default: on 3041 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3042 the default is off. 3043 3044 kprobe_event=[probe-list] 3045 [FTRACE] Add kprobe events and enable at boot time. 3046 The probe-list is a semicolon delimited list of probe 3047 definitions. Each definition is same as kprobe_events 3048 interface, but the parameters are comma delimited. 3049 For example, to add a kprobe event on vfs_read with 3050 arg1 and arg2, add to the command line; 3051 3052 kprobe_event=p,vfs_read,$arg1,$arg2 3053 3054 See also Documentation/trace/kprobetrace.rst "Kernel 3055 Boot Parameter" section. 3056 3057 kpti= [ARM64,EARLY] Control page table isolation of 3058 user and kernel address spaces. 3059 Default: enabled on cores which need mitigation. 3060 0: force disabled 3061 1: force enabled 3062 3063 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3064 CONFIG_KUNIT to be set to be fully enabled. The 3065 default value can be overridden via 3066 KUNIT_DEFAULT_ENABLED. 3067 Default is 1 (enabled) 3068 3069 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3070 Default is 0 (don't ignore, but inject #GP) 3071 3072 kvm.eager_page_split= 3073 [KVM,X86,RISCV] Controls whether or not KVM will try to 3074 proactively split all huge pages during dirty logging. 3075 Eager page splitting reduces interruptions to vCPU 3076 execution by eliminating the write-protection faults 3077 and MMU lock contention that would otherwise be 3078 required to split huge pages lazily. 3079 3080 VM workloads that rarely perform writes or that write 3081 only to a small region of VM memory may benefit from 3082 disabling eager page splitting to allow huge pages to 3083 still be used for reads. 3084 3085 The behavior of eager page splitting depends on whether 3086 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3087 disabled, all huge pages in a memslot will be eagerly 3088 split when dirty logging is enabled on that memslot. If 3089 enabled, eager page splitting will be performed during 3090 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3091 cleared. 3092 3093 On x86, eager page splitting is only supported when 3094 kvm.tdp_mmu=Y. 3095 3096 On RISCV, eager page splitting is supported by default. 3097 3098 Default is Y (on). 3099 3100 kvm.enable_pmu=[KVM,X86] 3101 If enabled, KVM will virtualize PMU functionality based 3102 on the virtual CPU model defined by userspace. This 3103 can be overridden on a per-VM basis via 3104 KVM_CAP_PMU_CAPABILITY. 3105 3106 If disabled, KVM will not virtualize PMU functionality, 3107 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3108 a virtual CPU model that contains PMU assets. 3109 3110 Note, KVM's vPMU support implicitly requires running 3111 with an in-kernel local APIC, e.g. to deliver PMIs to 3112 the guest. Running without an in-kernel local APIC is 3113 not supported, though KVM will allow such a combination 3114 (with severely degraded functionality). 3115 3116 See also enable_mediated_pmu. 3117 3118 Default is Y (on). 3119 3120 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3121 If enabled, KVM will enable virtualization in hardware 3122 when KVM is loaded, and disable virtualization when KVM 3123 is unloaded (if KVM is built as a module). 3124 3125 If disabled, KVM will dynamically enable and disable 3126 virtualization on-demand when creating and destroying 3127 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3128 number of VMs. 3129 3130 Enabling virtualization at module load avoids potential 3131 latency for creation of the 0=>1 VM, as KVM serializes 3132 virtualization enabling across all online CPUs. The 3133 "cost" of enabling virtualization when KVM is loaded, 3134 is that doing so may interfere with using out-of-tree 3135 hypervisors that want to "own" virtualization hardware. 3136 3137 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3138 Default is false (don't support). 3139 3140 kvm.nx_huge_pages= 3141 [KVM] Controls the software workaround for the 3142 X86_BUG_ITLB_MULTIHIT bug. 3143 force : Always deploy workaround. 3144 off : Never deploy workaround. 3145 auto : Deploy workaround based on the presence of 3146 X86_BUG_ITLB_MULTIHIT. 3147 3148 Default is 'auto'. 3149 3150 If the software workaround is enabled for the host, 3151 guests do need not to enable it for nested guests. 3152 3153 kvm.nx_huge_pages_recovery_ratio= 3154 [KVM] Controls how many 4KiB pages are periodically zapped 3155 back to huge pages. 0 disables the recovery, otherwise if 3156 the value is N KVM will zap 1/Nth of the 4KiB pages every 3157 period (see below). The default is 60. 3158 3159 kvm.nx_huge_pages_recovery_period_ms= 3160 [KVM] Controls the time period at which KVM zaps 4KiB pages 3161 back to huge pages. If the value is a non-zero N, KVM will 3162 zap a portion (see ratio above) of the pages every N msecs. 3163 If the value is 0 (the default), KVM will pick a period based 3164 on the ratio, such that a page is zapped after 1 hour on average. 3165 3166 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3167 If enabled, KVM will provide a mediated virtual PMU, 3168 instead of the default perf-based virtual PMU (if 3169 kvm.enable_pmu is true and PMU is enumerated via the 3170 virtual CPU model). 3171 3172 With a perf-based vPMU, KVM operates as a user of perf, 3173 i.e. emulates guest PMU counters using perf events. 3174 KVM-created perf events are managed by perf as regular 3175 (guest-only) events, e.g. are scheduled in/out, contend 3176 for hardware resources, etc. Using a perf-based vPMU 3177 allows guest and host usage of the PMU to co-exist, but 3178 incurs non-trivial overhead and can result in silently 3179 dropped guest events (due to resource contention). 3180 3181 With a mediated vPMU, hardware PMU state is context 3182 switched around the world switch to/from the guest. 3183 KVM mediates which events the guest can utilize, but 3184 gives the guest direct access to all other PMU assets 3185 when possible (KVM may intercept some accesses if the 3186 virtual CPU model provides a subset of hardware PMU 3187 functionality). Using a mediated vPMU significantly 3188 reduces PMU virtualization overhead and eliminates lost 3189 guest events, but is mutually exclusive with using perf 3190 to profile KVM guests and adds latency to most VM-Exits 3191 (to context switch PMU state). 3192 3193 Default is N (off). 3194 3195 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3196 KVM/SVM. Default is 1 (enabled). 3197 3198 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3199 a.k.a. Two-Dimensional Page Tables. Default is 1 3200 (enabled). Disable by KVM if hardware lacks support 3201 for NPT. 3202 3203 kvm-amd.ciphertext_hiding_asids= 3204 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3205 to SNP private memory from reading ciphertext. Instead, 3206 reads will see constant default values (0xff). 3207 3208 If ciphertext hiding is enabled, the joint SEV-ES and 3209 SEV-SNP ASID space is partitioned into separate SEV-ES 3210 and SEV-SNP ASID ranges, with the SEV-SNP range being 3211 [1..max_snp_asid] and the SEV-ES range being 3212 (max_snp_asid..min_sev_asid), where min_sev_asid is 3213 enumerated by CPUID.0x.8000_001F[EDX]. 3214 3215 A non-zero value enables SEV-SNP ciphertext hiding and 3216 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3217 KVM caps the number of SEV-SNP ASIDs at the maximum 3218 possible value, e.g. specifying -1u will assign all 3219 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3220 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3221 max_snp_asid == min_sev_asid-1, will effectively make 3222 SEV-ES unusable. 3223 3224 kvm-arm.mode= 3225 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3226 operation. 3227 3228 none: Forcefully disable KVM. 3229 3230 nvhe: Standard nVHE-based mode, without support for 3231 protected guests. 3232 3233 protected: Mode with support for guests whose state is 3234 kept private from the host, using VHE or 3235 nVHE depending on HW support. 3236 3237 nested: VHE-based mode with support for nested 3238 virtualization. Requires at least ARMv8.4 3239 hardware (with FEAT_NV2). 3240 3241 Defaults to VHE/nVHE based on hardware support. Setting 3242 mode to "protected" will disable kexec and hibernation 3243 for the host. To force nVHE on VHE hardware, add 3244 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3245 command-line. 3246 "nested" and "protected" are experimental and should be 3247 used with extreme caution. 3248 3249 kvm-arm.vgic_v3_group0_trap= 3250 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3251 system registers 3252 3253 kvm-arm.vgic_v3_group1_trap= 3254 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3255 system registers 3256 3257 kvm-arm.vgic_v3_common_trap= 3258 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3259 system registers 3260 3261 kvm-arm.vgic_v4_enable= 3262 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3263 injection of LPIs. 3264 3265 kvm-arm.wfe_trap_policy= 3266 [KVM,ARM] Control when to set WFE instruction trap for 3267 KVM VMs. Traps are allowed but not guaranteed by the 3268 CPU architecture. 3269 3270 trap: set WFE instruction trap 3271 3272 notrap: clear WFE instruction trap 3273 3274 kvm-arm.wfi_trap_policy= 3275 [KVM,ARM] Control when to set WFI instruction trap for 3276 KVM VMs. Traps are allowed but not guaranteed by the 3277 CPU architecture. 3278 3279 trap: set WFI instruction trap 3280 3281 notrap: clear WFI instruction trap 3282 3283 kvm_cma_resv_ratio=n [PPC,EARLY] 3284 Reserves given percentage from system memory area for 3285 contiguous memory allocation for KVM hash pagetable 3286 allocation. 3287 By default it reserves 5% of total system memory. 3288 Format: <integer> 3289 Default: 5 3290 3291 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3292 a.k.a. Two-Dimensional Page Tables. Default is 1 3293 (enabled). Disable by KVM if hardware lacks support 3294 for EPT. 3295 3296 kvm-intel.emulate_invalid_guest_state= 3297 [KVM,Intel] Control whether to emulate invalid guest 3298 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3299 as guest state is never invalid for unrestricted 3300 guests. This param doesn't apply to nested guests (L2), 3301 as KVM never emulates invalid L2 guest state. 3302 Default is 1 (enabled). 3303 3304 kvm-intel.flexpriority= 3305 [KVM,Intel] Control KVM's use of FlexPriority feature 3306 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3307 hardware lacks support for it. 3308 3309 kvm-intel.nested= 3310 [KVM,Intel] Control nested virtualization feature in 3311 KVM/VMX. Default is 1 (enabled). 3312 3313 kvm-intel.unrestricted_guest= 3314 [KVM,Intel] Control KVM's use of unrestricted guest 3315 feature (virtualized real and unpaged mode). Default 3316 is 1 (enabled). Disable by KVM if EPT is disabled or 3317 hardware lacks support for it. 3318 3319 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3320 CVE-2018-3620. 3321 3322 Valid arguments: never, cond, always 3323 3324 always: L1D cache flush on every VMENTER. 3325 cond: Flush L1D on VMENTER only when the code between 3326 VMEXIT and VMENTER can leak host memory. 3327 never: Disables the mitigation 3328 3329 Default is cond (do L1 cache flush in specific instances) 3330 3331 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3332 Identification feature (tagged TLBs). Default is 1 3333 (enabled). Disable by KVM if hardware lacks support 3334 for it. 3335 3336 l1d_flush= [X86,INTEL,EARLY] 3337 Control mitigation for L1D based snooping vulnerability. 3338 3339 Certain CPUs are vulnerable to an exploit against CPU 3340 internal buffers which can forward information to a 3341 disclosure gadget under certain conditions. 3342 3343 In vulnerable processors, the speculatively 3344 forwarded data can be used in a cache side channel 3345 attack, to access data to which the attacker does 3346 not have direct access. 3347 3348 This parameter controls the mitigation. The 3349 options are: 3350 3351 on - enable the interface for the mitigation 3352 3353 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3354 affected CPUs 3355 3356 The kernel PTE inversion protection is unconditionally 3357 enabled and cannot be disabled. 3358 3359 full 3360 Provides all available mitigations for the 3361 L1TF vulnerability. Disables SMT and 3362 enables all mitigations in the 3363 hypervisors, i.e. unconditional L1D flush. 3364 3365 SMT control and L1D flush control via the 3366 sysfs interface is still possible after 3367 boot. Hypervisors will issue a warning 3368 when the first VM is started in a 3369 potentially insecure configuration, 3370 i.e. SMT enabled or L1D flush disabled. 3371 3372 full,force 3373 Same as 'full', but disables SMT and L1D 3374 flush runtime control. Implies the 3375 'nosmt=force' command line option. 3376 (i.e. sysfs control of SMT is disabled.) 3377 3378 flush 3379 Leaves SMT enabled and enables the default 3380 hypervisor mitigation, i.e. conditional 3381 L1D flush. 3382 3383 SMT control and L1D flush control via the 3384 sysfs interface is still possible after 3385 boot. Hypervisors will issue a warning 3386 when the first VM is started in a 3387 potentially insecure configuration, 3388 i.e. SMT enabled or L1D flush disabled. 3389 3390 flush,nosmt 3391 3392 Disables SMT and enables the default 3393 hypervisor mitigation. 3394 3395 SMT control and L1D flush control via the 3396 sysfs interface is still possible after 3397 boot. Hypervisors will issue a warning 3398 when the first VM is started in a 3399 potentially insecure configuration, 3400 i.e. SMT enabled or L1D flush disabled. 3401 3402 flush,nowarn 3403 Same as 'flush', but hypervisors will not 3404 warn when a VM is started in a potentially 3405 insecure configuration. 3406 3407 off 3408 Disables hypervisor mitigations and doesn't 3409 emit any warnings. 3410 It also drops the swap size and available 3411 RAM limit restriction on both hypervisor and 3412 bare metal. 3413 3414 Default is 'flush'. 3415 3416 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3417 3418 l2cr= [PPC] 3419 3420 l3cr= [PPC] 3421 3422 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3423 disabled it. 3424 3425 lapic= [X86,APIC] Do not use TSC deadline 3426 value for LAPIC timer one-shot implementation. Default 3427 back to the programmable timer unit in the LAPIC. 3428 Format: notscdeadline 3429 3430 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3431 in C2 power state. 3432 3433 libata.dma= [LIBATA] DMA control 3434 libata.dma=0 Disable all PATA and SATA DMA 3435 libata.dma=1 PATA and SATA Disk DMA only 3436 libata.dma=2 ATAPI (CDROM) DMA only 3437 libata.dma=4 Compact Flash DMA only 3438 Combinations also work, so libata.dma=3 enables DMA 3439 for disks and CDROMs, but not CFs. 3440 3441 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3442 libata.ignore_hpa=0 keep BIOS limits (default) 3443 libata.ignore_hpa=1 ignore limits, using full disk 3444 3445 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3446 when set. 3447 Format: <int> 3448 3449 libata.force= [LIBATA] Force configurations. The format is a comma- 3450 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3451 PORT and DEVICE are decimal numbers matching port, link 3452 or device. Basically, it matches the ATA ID string 3453 printed on console by libata. If the whole ID part is 3454 omitted, the last PORT and DEVICE values are used. If 3455 ID hasn't been specified yet, the configuration applies 3456 to all ports, links and devices. 3457 3458 If only DEVICE is omitted, the parameter applies to 3459 the port and all links and devices behind it. DEVICE 3460 number of 0 either selects the first device or the 3461 first fan-out link behind PMP device. It does not 3462 select the host link. DEVICE number of 15 selects the 3463 host link and device attached to it. 3464 3465 The VAL specifies the configuration to force. As long 3466 as there is no ambiguity, shortcut notation is allowed. 3467 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3468 The following configurations can be forced. 3469 3470 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3471 Any ID with matching PORT is used. 3472 3473 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3474 3475 * Transfer mode: pio[0-6], mwdma[0-4] and udma[0-7]. 3476 udma[/][16,25,33,44,66,100,133] notation is also 3477 allowed. 3478 3479 * nohrst, nosrst, norst: suppress hard, soft and both 3480 resets. 3481 3482 * rstonce: only attempt one reset during hot-unplug 3483 link recovery. 3484 3485 * [no]dbdelay: Enable or disable the extra 200ms delay 3486 before debouncing a link PHY and device presence 3487 detection. 3488 3489 * [no]ncq: Turn on or off NCQ. 3490 3491 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3492 3493 * [no]ncqati: Enable or disable NCQ on ATI chipsets. 3494 3495 * [no]trim: Enable or disable (unqueued) TRIM. 3496 3497 * trim_zero: Indicate that TRIM command zeroes data. 3498 3499 * max_trim_128m: Set 128M maximum trim size limit. 3500 3501 * [no]dma: Turn on or off DMA transfers. 3502 3503 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3504 3505 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3506 commands that are not a multiple of 16 bytes. 3507 3508 * [no]dmalog: Enable or disable the use of the 3509 READ LOG DMA EXT command to access logs. 3510 3511 * [no]iddevlog: Enable or disable access to the 3512 identify device data log. 3513 3514 * [no]logdir: Enable or disable access to the general 3515 purpose log directory. 3516 3517 * max_sec=<sectors>: Set the transfer size limit, in 3518 number of 512-byte sectors, to the value specified in 3519 <sectors>. The value specified in <sectors> has to be 3520 a non-zero positive integer. 3521 3522 * max_sec_128: Set transfer size limit to 128 sectors. 3523 3524 * max_sec_1024: Set transfer size limit to 1024 sectors. 3525 3526 * max_sec_lba48: Set transfer size limit to 65535 sectors. 3527 3528 * external: Mark port as external (hotplug-capable). 3529 3530 * [no]lpm: Enable or disable link power management. 3531 3532 * [no]setxfer: Indicate if transfer speed mode setting 3533 should be skipped. 3534 3535 * [no]fua: Disable or enable FUA (Force Unit Access) 3536 support for devices supporting this feature. 3537 3538 * dump_id: Dump IDENTIFY data. 3539 3540 * disable: Disable this device. 3541 3542 If there are multiple matching configurations changing 3543 the same attribute, the last one is used. 3544 3545 liveupdate= [KNL,EARLY] 3546 Format: <bool> 3547 Enable Live Update Orchestrator (LUO). 3548 Default: off. 3549 3550 lockd.nlm_grace_period=P [NFS] Assign grace period. 3551 Format: <integer> 3552 3553 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3554 Format: <integer> 3555 3556 lockd.nlm_timeout=T [NFS] Assign timeout value. 3557 Format: <integer> 3558 3559 lockd.nlm_udpport=M [NFS] Assign UDP port. 3560 Format: <integer> 3561 3562 lockdown= [SECURITY,EARLY] 3563 { integrity | confidentiality } 3564 Enable the kernel lockdown feature. If set to 3565 integrity, kernel features that allow userland to 3566 modify the running kernel are disabled. If set to 3567 confidentiality, kernel features that allow userland 3568 to extract confidential information from the kernel 3569 are also disabled. 3570 3571 locktorture.acq_writer_lim= [KNL] 3572 Set the time limit in jiffies for a lock 3573 acquisition. Acquisitions exceeding this limit 3574 will result in a splat once they do complete. 3575 3576 locktorture.bind_readers= [KNL] 3577 Specify the list of CPUs to which the readers are 3578 to be bound. 3579 3580 locktorture.bind_writers= [KNL] 3581 Specify the list of CPUs to which the writers are 3582 to be bound. 3583 3584 locktorture.call_rcu_chains= [KNL] 3585 Specify the number of self-propagating call_rcu() 3586 chains to set up. These are used to ensure that 3587 there is a high probability of an RCU grace period 3588 in progress at any given time. Defaults to 0, 3589 which disables these call_rcu() chains. 3590 3591 locktorture.long_hold= [KNL] 3592 Specify the duration in milliseconds for the 3593 occasional long-duration lock hold time. Defaults 3594 to 100 milliseconds. Select 0 to disable. 3595 3596 locktorture.nested_locks= [KNL] 3597 Specify the maximum lock nesting depth that 3598 locktorture is to exercise, up to a limit of 8 3599 (MAX_NESTED_LOCKS). Specify zero to disable. 3600 Note that this parameter is ineffective on types 3601 of locks that do not support nested acquisition. 3602 3603 locktorture.nreaders_stress= [KNL] 3604 Set the number of locking read-acquisition kthreads. 3605 Defaults to being automatically set based on the 3606 number of online CPUs. 3607 3608 locktorture.nwriters_stress= [KNL] 3609 Set the number of locking write-acquisition kthreads. 3610 3611 locktorture.onoff_holdoff= [KNL] 3612 Set time (s) after boot for CPU-hotplug testing. 3613 3614 locktorture.onoff_interval= [KNL] 3615 Set time (s) between CPU-hotplug operations, or 3616 zero to disable CPU-hotplug testing. 3617 3618 locktorture.rt_boost= [KNL] 3619 Do periodic testing of real-time lock priority 3620 boosting. Select 0 to disable, 1 to boost 3621 only rt_mutex, and 2 to boost unconditionally. 3622 Defaults to 2, which might seem to be an 3623 odd choice, but which should be harmless for 3624 non-real-time spinlocks, due to their disabling 3625 of preemption. Note that non-realtime mutexes 3626 disable boosting. 3627 3628 locktorture.rt_boost_factor= [KNL] 3629 Number that determines how often and for how 3630 long priority boosting is exercised. This is 3631 scaled down by the number of writers, so that the 3632 number of boosts per unit time remains roughly 3633 constant as the number of writers increases. 3634 On the other hand, the duration of each boost 3635 increases with the number of writers. 3636 3637 locktorture.shuffle_interval= [KNL] 3638 Set task-shuffle interval (jiffies). Shuffling 3639 tasks allows some CPUs to go into dyntick-idle 3640 mode during the locktorture test. 3641 3642 locktorture.shutdown_secs= [KNL] 3643 Set time (s) after boot system shutdown. This 3644 is useful for hands-off automated testing. 3645 3646 locktorture.stat_interval= [KNL] 3647 Time (s) between statistics printk()s. 3648 3649 locktorture.stutter= [KNL] 3650 Time (s) to stutter testing, for example, 3651 specifying five seconds causes the test to run for 3652 five seconds, wait for five seconds, and so on. 3653 This tests the locking primitive's ability to 3654 transition abruptly to and from idle. 3655 3656 locktorture.torture_type= [KNL] 3657 Specify the locking implementation to test. 3658 3659 locktorture.verbose= [KNL] 3660 Enable additional printk() statements. 3661 3662 locktorture.writer_fifo= [KNL] 3663 Run the write-side locktorture kthreads at 3664 sched_set_fifo() real-time priority. 3665 3666 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3667 Format: <irq> 3668 3669 loglevel= [KNL,EARLY] 3670 All Kernel Messages with a loglevel smaller than the 3671 console loglevel will be printed to the console. It can 3672 also be changed with klogd or other programs. The 3673 loglevels are defined as follows: 3674 3675 0 (KERN_EMERG) system is unusable 3676 1 (KERN_ALERT) action must be taken immediately 3677 2 (KERN_CRIT) critical conditions 3678 3 (KERN_ERR) error conditions 3679 4 (KERN_WARNING) warning conditions 3680 5 (KERN_NOTICE) normal but significant condition 3681 6 (KERN_INFO) informational 3682 7 (KERN_DEBUG) debug-level messages 3683 3684 log_buf_len=n[KMG] [KNL,EARLY] 3685 Sets the size of the printk ring buffer, in bytes. 3686 n must be a power of two and greater than the 3687 minimal size. The minimal size is defined by 3688 LOG_BUF_SHIFT kernel config parameter. There 3689 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3690 parameter that allows to increase the default size 3691 depending on the number of CPUs. See init/Kconfig 3692 for more details. 3693 3694 logo.nologo [FB] Disables display of the built-in Linux logo. 3695 This may be used to provide more screen space for 3696 kernel log messages and is useful when debugging 3697 kernel boot problems. 3698 3699 lp=0 [LP] Specify parallel ports to use, e.g, 3700 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3701 lp=reset first parallel port). 'lp=0' disables the 3702 lp=auto printer driver. 'lp=reset' (which can be 3703 specified in addition to the ports) causes 3704 attached printers to be reset. Using 3705 lp=port1,port2,... specifies the parallel ports 3706 to associate lp devices with, starting with 3707 lp0. A port specification may be 'none' to skip 3708 that lp device, or a parport name such as 3709 'parport0'. Specifying 'lp=auto' instead of a 3710 port specification list means that device IDs 3711 from each port should be examined, to see if 3712 an IEEE 1284-compliant printer is attached; if 3713 so, the driver will manage that printer. 3714 See also header of drivers/char/lp.c. 3715 3716 lpj=n [KNL] 3717 Sets loops_per_jiffy to given constant, thus avoiding 3718 time-consuming boot-time autodetection (up to 250 ms per 3719 CPU). 0 enables autodetection (default). To determine 3720 the correct value for your kernel, boot with normal 3721 autodetection and see what value is printed. Note that 3722 on SMP systems the preset will be applied to all CPUs, 3723 which is likely to cause problems if your CPUs need 3724 significantly divergent settings. An incorrect value 3725 will cause delays in the kernel to be wrong, leading to 3726 unpredictable I/O errors and other breakage. Although 3727 unlikely, in the extreme case this might damage your 3728 hardware. 3729 3730 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3731 3732 lsm=lsm1,...,lsmN 3733 [SECURITY] Choose order of LSM initialization. This 3734 overrides CONFIG_LSM, and the "security=" parameter. 3735 3736 machtype= [Loongson] Share the same kernel image file between 3737 different yeeloong laptops. 3738 Example: machtype=lemote-yeeloong-2f-7inch 3739 3740 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3741 will bring up during bootup. maxcpus=n : n >= 0 limits 3742 the kernel to bring up 'n' processors. Surely after 3743 bootup you can bring up the other plugged cpu by executing 3744 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3745 only takes effect during system bootup. 3746 While n=0 is a special case, it is equivalent to "nosmp", 3747 which also disables the IO APIC. 3748 3749 max_loop= [LOOP] The number of loop block devices that get 3750 (loop.max_loop) unconditionally pre-created at init time. The default 3751 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3752 of statically allocating a predefined number, loop 3753 devices can be requested on-demand with the 3754 /dev/loop-control interface. 3755 3756 mce= [X86-{32,64}] 3757 3758 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3759 3760 off 3761 disable machine check 3762 3763 no_cmci 3764 disable CMCI(Corrected Machine Check Interrupt) that 3765 Intel processor supports. Usually this disablement is 3766 not recommended, but it might be handy if your 3767 hardware is misbehaving. 3768 3769 Note that you'll get more problems without CMCI than 3770 with due to the shared banks, i.e. you might get 3771 duplicated error logs. 3772 3773 dont_log_ce 3774 don't make logs for corrected errors. All events 3775 reported as corrected are silently cleared by OS. This 3776 option will be useful if you have no interest in any 3777 of corrected errors. 3778 3779 ignore_ce 3780 disable features for corrected errors, e.g. 3781 polling timer and CMCI. All events reported as 3782 corrected are not cleared by OS and remained in its 3783 error banks. 3784 3785 Usually this disablement is not recommended, however 3786 if there is an agent checking/clearing corrected 3787 errors (e.g. BIOS or hardware monitoring 3788 applications), conflicting with OS's error handling, 3789 and you cannot deactivate the agent, then this option 3790 will be a help. 3791 3792 no_lmce 3793 do not opt-in to Local MCE delivery. Use legacy method 3794 to broadcast MCEs. 3795 3796 bootlog 3797 enable logging of machine checks left over from 3798 booting. Disabled by default on AMD Fam10h and older 3799 because some BIOS leave bogus ones. 3800 3801 If your BIOS doesn't do that it's a good idea to 3802 enable though to make sure you log even machine check 3803 events that result in a reboot. On Intel systems it is 3804 enabled by default. 3805 3806 nobootlog 3807 disable boot machine check logging. 3808 3809 print_all 3810 print all machine check logs to the console. 3811 3812 monarchtimeout (number) 3813 sets the time in us to wait for other CPUs on machine 3814 checks. 0 to disable. 3815 3816 bios_cmci_threshold 3817 don't overwrite the bios-set CMCI threshold. This boot 3818 option prevents Linux from overwriting the CMCI 3819 threshold set by the bios. Without this option, Linux 3820 always sets the CMCI threshold to 1. Enabling this may 3821 make memory predictive failure analysis less effective 3822 if the bios sets thresholds for memory errors since we 3823 will not see details for all errors. 3824 3825 recovery 3826 force-enable recoverable machine check code paths 3827 3828 Everything else is in sysfs now. 3829 3830 3831 md= [HW] RAID subsystems devices and level 3832 See Documentation/admin-guide/md.rst. 3833 3834 mds= [X86,INTEL,EARLY] 3835 Control mitigation for the Micro-architectural Data 3836 Sampling (MDS) vulnerability. 3837 3838 Certain CPUs are vulnerable to an exploit against CPU 3839 internal buffers which can forward information to a 3840 disclosure gadget under certain conditions. 3841 3842 In vulnerable processors, the speculatively 3843 forwarded data can be used in a cache side channel 3844 attack, to access data to which the attacker does 3845 not have direct access. 3846 3847 This parameter controls the MDS mitigation. The 3848 options are: 3849 3850 full - Enable MDS mitigation on vulnerable CPUs 3851 full,nosmt - Enable MDS mitigation and disable 3852 SMT on vulnerable CPUs 3853 off - Unconditionally disable MDS mitigation 3854 3855 On TAA-affected machines, mds=off can be prevented by 3856 an active TAA mitigation as both vulnerabilities are 3857 mitigated with the same mechanism so in order to disable 3858 this mitigation, you need to specify tsx_async_abort=off 3859 too. 3860 3861 Not specifying this option is equivalent to 3862 mds=full. 3863 3864 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3865 3866 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3867 Must be specified, otherwise memory size will be 0. 3868 3869 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3870 of memory Amount of memory to be used in cases 3871 as follows: 3872 3873 1 for test; 3874 2 when the kernel is not able to see the whole system memory; 3875 3 memory that lies after 'mem=' boundary is excluded from 3876 the hypervisor, then assigned to KVM guests. 3877 4 to limit the memory available for kdump kernel. 3878 3879 [ARC,MICROBLAZE] - the limit applies only to low memory, 3880 high memory is not affected. 3881 3882 [ARM64] - only limits memory covered by the linear 3883 mapping. The NOMAP regions are not affected. 3884 3885 [X86] Work as limiting max address. Use together 3886 with memmap= to avoid physical address space collisions. 3887 Without memmap= PCI devices could be placed at addresses 3888 belonging to unused RAM. 3889 3890 Note that this only takes effects during boot time since 3891 in above case 3, memory may need be hot added after boot 3892 if system memory of hypervisor is not sufficient. 3893 3894 mem=nn[KMG]@ss[KMG] 3895 [ARM,MIPS,EARLY] - override the memory layout 3896 reported by firmware. 3897 Define a memory region of size nn[KMG] starting at 3898 ss[KMG]. 3899 Multiple different regions can be specified with 3900 multiple mem= parameters on the command line. 3901 3902 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3903 memory. 3904 3905 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3906 3907 memchunk=nn[KMG] 3908 [KNL,SH] Allow user to override the default size for 3909 per-device physically contiguous DMA buffers. 3910 3911 memhp_default_state=online/offline/online_kernel/online_movable 3912 [KNL] Set the initial state for the memory hotplug 3913 onlining policy. If not specified, the default value is 3914 set according to the 3915 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3916 options. 3917 See Documentation/admin-guide/mm/memory-hotplug.rst. 3918 3919 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3920 E820 memory map, as specified by the user. 3921 Such memmap=exactmap lines can be constructed based on 3922 BIOS output or other requirements. See the memmap=nn@ss 3923 option description. 3924 3925 memmap=nn[KMG]@ss[KMG] 3926 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3927 Region of memory to be used is from ss to ss+nn. 3928 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3929 which limits max address to nn[KMG]. 3930 Multiple different regions can be specified, 3931 comma delimited. 3932 Example: 3933 memmap=100M@2G,100M#3G,1G!1024G 3934 3935 memmap=nn[KMG]#ss[KMG] 3936 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3937 Region of memory to be marked is from ss to ss+nn. 3938 3939 memmap=nn[KMG]$ss[KMG] 3940 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3941 Region of memory to be reserved is from ss to ss+nn. 3942 Example: Exclude memory from 0x18690000-0x1869ffff 3943 memmap=64K$0x18690000 3944 or 3945 memmap=0x10000$0x18690000 3946 Some bootloaders may need an escape character before '$', 3947 like Grub2, otherwise '$' and the following number 3948 will be eaten. 3949 3950 memmap=nn[KMG]!ss[KMG] 3951 [KNL,X86,EARLY] Mark specific memory as protected. 3952 Region of memory to be used, from ss to ss+nn. 3953 The memory region may be marked as e820 type 12 (0xc) 3954 and is NVDIMM or ADR memory. 3955 3956 memmap=<size>%<offset>-<oldtype>+<newtype> 3957 [KNL,ACPI,EARLY] Convert memory within the specified region 3958 from <oldtype> to <newtype>. If "-<oldtype>" is left 3959 out, the whole region will be marked as <newtype>, 3960 even if previously unavailable. If "+<newtype>" is left 3961 out, matching memory will be removed. Types are 3962 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3963 3 = ACPI, 12 = PRAM. 3964 3965 memory_corruption_check=0/1 [X86,EARLY] 3966 Some BIOSes seem to corrupt the first 64k of 3967 memory when doing things like suspend/resume. 3968 Setting this option will scan the memory 3969 looking for corruption. Enabling this will 3970 both detect corruption and prevent the kernel 3971 from using the memory being corrupted. 3972 However, it's intended as a diagnostic tool; if 3973 repeatable BIOS-originated corruption always 3974 affects the same memory, you can use memmap= 3975 to prevent the kernel from using that memory. 3976 3977 memory_corruption_check_size=size [X86,EARLY] 3978 By default it checks for corruption in the low 3979 64k, making this memory unavailable for normal 3980 use. Use this parameter to scan for 3981 corruption in more or less memory. 3982 3983 memory_corruption_check_period=seconds [X86,EARLY] 3984 By default it checks for corruption every 60 3985 seconds. Use this parameter to check at some 3986 other rate. 0 disables periodic checking. 3987 3988 memory_hotplug.memmap_on_memory 3989 [KNL,X86,ARM] Boolean flag to enable this feature. 3990 Format: {on | off (default)} 3991 When enabled, runtime hotplugged memory will 3992 allocate its internal metadata (struct pages, 3993 those vmemmap pages cannot be optimized even 3994 if hugetlb_free_vmemmap is enabled) from the 3995 hotadded memory which will allow to hotadd a 3996 lot of memory without requiring additional 3997 memory to do so. 3998 This feature is disabled by default because it 3999 has some implication on large (e.g. GB) 4000 allocations in some configurations (e.g. small 4001 memory blocks). 4002 The state of the flag can be read in 4003 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4004 Note that even when enabled, there are a few cases where 4005 the feature is not effective. 4006 4007 mempool_debug [MM] 4008 Enable mempool debugging. This enables element 4009 poison checking when freeing elements back to the 4010 pool. Useful for debugging mempool corruption. 4011 4012 memtest= [KNL,ALPHA,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4013 Format: <integer> 4014 default : 0 <disable> 4015 Specifies the number of memtest passes to be 4016 performed. Each pass selects another test 4017 pattern from a given set of patterns. Memtest 4018 fills the memory with this pattern, validates 4019 memory contents and reserves bad memory 4020 regions that are detected. 4021 4022 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4023 Valid arguments: on, off 4024 Default: off 4025 mem_encrypt=on: Activate SME 4026 mem_encrypt=off: Do not activate SME 4027 4028 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4029 for details on when memory encryption can be activated. 4030 4031 mem_sleep_default= [SUSPEND] Default system suspend mode: 4032 s2idle - Suspend-To-Idle 4033 shallow - Power-On Suspend or equivalent (if supported) 4034 deep - Suspend-To-RAM or equivalent (if supported) 4035 See Documentation/admin-guide/pm/sleep-states.rst. 4036 4037 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4038 the BIOS has incorrectly applied a workaround. TinyBIOS 4039 version 0.98 is known to be affected, 0.99 fixes the 4040 problem by letting the user disable the workaround. 4041 4042 mga= [HW,DRM] 4043 4044 microcode= [X86] Control the behavior of the microcode loader. 4045 Available options, comma separated: 4046 4047 base_rev=X - with <X> with format: <u32> 4048 Set the base microcode revision of each thread when in 4049 debug mode. 4050 4051 dis_ucode_ldr: disable the microcode loader 4052 4053 force_minrev: 4054 Enable or disable the microcode minimal revision 4055 enforcement for the runtime microcode loader. 4056 4057 mitigations= 4058 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4059 CPU vulnerabilities. This is a set of curated, 4060 arch-independent options, each of which is an 4061 aggregation of existing arch-specific options. 4062 4063 Note, "mitigations" is supported if and only if the 4064 kernel was built with CPU_MITIGATIONS=y. 4065 4066 off 4067 Disable all optional CPU mitigations. This 4068 improves system performance, but it may also 4069 expose users to several CPU vulnerabilities. 4070 Equivalent to: if nokaslr then kpti=0 [ARM64] 4071 gather_data_sampling=off [X86] 4072 indirect_target_selection=off [X86] 4073 kvm.nx_huge_pages=off [X86] 4074 l1tf=off [X86] 4075 mds=off [X86] 4076 mmio_stale_data=off [X86] 4077 no_entry_flush [PPC] 4078 no_uaccess_flush [PPC] 4079 nobp=0 [S390] 4080 nopti [X86,PPC] 4081 nospectre_bhb [ARM64] 4082 nospectre_v1 [X86,PPC] 4083 nospectre_v2 [X86,PPC,S390,ARM64] 4084 reg_file_data_sampling=off [X86] 4085 retbleed=off [X86] 4086 spec_rstack_overflow=off [X86] 4087 spec_store_bypass_disable=off [X86,PPC] 4088 spectre_bhi=off [X86] 4089 spectre_v2_user=off [X86] 4090 srbds=off [X86,INTEL] 4091 ssbd=force-off [ARM64] 4092 tsa=off [X86,AMD] 4093 tsx_async_abort=off [X86] 4094 vmscape=off [X86] 4095 4096 Exceptions: 4097 This does not have any effect on 4098 kvm.nx_huge_pages when 4099 kvm.nx_huge_pages=force. 4100 4101 auto (default) 4102 Mitigate all CPU vulnerabilities, but leave SMT 4103 enabled, even if it's vulnerable. This is for 4104 users who don't want to be surprised by SMT 4105 getting disabled across kernel upgrades, or who 4106 have other ways of avoiding SMT-based attacks. 4107 Equivalent to: (default behavior) 4108 4109 auto,nosmt 4110 Mitigate all CPU vulnerabilities, disabling SMT 4111 if needed. This is for users who always want to 4112 be fully mitigated, even if it means losing SMT. 4113 Equivalent to: l1tf=flush,nosmt [X86] 4114 mds=full,nosmt [X86] 4115 tsx_async_abort=full,nosmt [X86] 4116 mmio_stale_data=full,nosmt [X86] 4117 retbleed=auto,nosmt [X86] 4118 4119 [X86] After one of the above options, additionally 4120 supports attack-vector based controls as documented in 4121 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4122 4123 mminit_loglevel= 4124 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4125 parameter allows control of the logging verbosity for 4126 the additional memory initialisation checks. A value 4127 of 0 disables mminit logging and a level of 4 will 4128 log everything. Information is printed at KERN_DEBUG 4129 so loglevel=8 may also need to be specified. 4130 4131 mmio_stale_data= 4132 [X86,INTEL,EARLY] Control mitigation for the Processor 4133 MMIO Stale Data vulnerabilities. 4134 4135 Processor MMIO Stale Data is a class of 4136 vulnerabilities that may expose data after an MMIO 4137 operation. Exposed data could originate or end in 4138 the same CPU buffers as affected by MDS and TAA. 4139 Therefore, similar to MDS and TAA, the mitigation 4140 is to clear the affected CPU buffers. 4141 4142 This parameter controls the mitigation. The 4143 options are: 4144 4145 full - Enable mitigation on vulnerable CPUs 4146 4147 full,nosmt - Enable mitigation and disable SMT on 4148 vulnerable CPUs. 4149 4150 off - Unconditionally disable mitigation 4151 4152 On MDS or TAA affected machines, 4153 mmio_stale_data=off can be prevented by an active 4154 MDS or TAA mitigation as these vulnerabilities are 4155 mitigated with the same mechanism so in order to 4156 disable this mitigation, you need to specify 4157 mds=off and tsx_async_abort=off too. 4158 4159 Not specifying this option is equivalent to 4160 mmio_stale_data=full. 4161 4162 For details see: 4163 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4164 4165 <module>.async_probe[=<bool>] [KNL] 4166 If no <bool> value is specified or if the value 4167 specified is not a valid <bool>, enable asynchronous 4168 probe on this module. Otherwise, enable/disable 4169 asynchronous probe on this module as indicated by the 4170 <bool> value. See also: module.async_probe 4171 4172 module.async_probe=<bool> 4173 [KNL] When set to true, modules will use async probing 4174 by default. To enable/disable async probing for a 4175 specific module, use the module specific control that 4176 is documented under <module>.async_probe. When both 4177 module.async_probe and <module>.async_probe are 4178 specified, <module>.async_probe takes precedence for 4179 the specific module. 4180 4181 module.enable_dups_trace 4182 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4183 this means that duplicate request_module() calls will 4184 trigger a WARN_ON() instead of a pr_warn(). Note that 4185 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4186 will always be issued and this option does nothing. 4187 module.sig_enforce 4188 [KNL] When CONFIG_MODULE_SIG is set, this means that 4189 modules without (valid) signatures will fail to load. 4190 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4191 is always true, so this option does nothing. 4192 4193 module_blacklist= [KNL] Do not load a comma-separated list of 4194 modules. Useful for debugging problem modules. 4195 4196 mousedev.tap_time= 4197 [MOUSE] Maximum time between finger touching and 4198 leaving touchpad surface for touch to be considered 4199 a tap and be reported as a left button click (for 4200 touchpads working in absolute mode only). 4201 Format: <msecs> 4202 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4203 reporting absolute coordinates, such as tablets 4204 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4205 reporting absolute coordinates, such as tablets 4206 4207 movablecore= [KNL,X86,PPC,EARLY] 4208 Format: nn[KMGTPE] | nn% 4209 This parameter is the complement to kernelcore=, it 4210 specifies the amount of memory used for migratable 4211 allocations. If both kernelcore and movablecore is 4212 specified, then kernelcore will be at *least* the 4213 specified value but may be more. If movablecore on its 4214 own is specified, the administrator must be careful 4215 that the amount of memory usable for all allocations 4216 is not too small. 4217 4218 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4219 NUMA nodes to be movable. This means that the memory 4220 of such nodes will be usable only for movable 4221 allocations which rules out almost all kernel 4222 allocations. Use with caution! 4223 4224 MTD_Partition= [MTD] 4225 Format: <name>,<region-number>,<size>,<offset> 4226 4227 MTD_Region= [MTD] Format: 4228 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4229 4230 mtdparts= [MTD] 4231 See drivers/mtd/parsers/cmdlinepart.c 4232 4233 mtouchusb.raw_coordinates= 4234 [HW] Make the MicroTouch USB driver use raw coordinates 4235 ('y', default) or cooked coordinates ('n') 4236 4237 mtrr=debug [X86,EARLY] 4238 Enable printing debug information related to MTRR 4239 registers at boot time. 4240 4241 mtrr_chunk_size=nn[KMG] [X86,EARLY] 4242 used for mtrr cleanup. It is largest continuous chunk 4243 that could hold holes aka. UC entries. 4244 4245 mtrr_gran_size=nn[KMG] [X86,EARLY] 4246 Used for mtrr cleanup. It is granularity of mtrr block. 4247 Default is 1. 4248 Large value could prevent small alignment from 4249 using up MTRRs. 4250 4251 mtrr_spare_reg_nr=n [X86,EARLY] 4252 Format: <integer> 4253 Range: 0,7 : spare reg number 4254 Default : 1 4255 Used for mtrr cleanup. It is spare mtrr entries number. 4256 Set to 2 or more if your graphical card needs more. 4257 4258 multitce=off [PPC] This parameter disables the use of the pSeries 4259 firmware feature for updating multiple TCE entries 4260 at a time. 4261 4262 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4263 4264 netdev= [NET] NE2000 ISA network devices parameters 4265 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4266 4267 netpoll.carrier_timeout= 4268 [NET] Specifies amount of time (in seconds) that 4269 netpoll should wait for a carrier. By default netpoll 4270 waits 4 seconds. 4271 4272 nf_conntrack.acct= 4273 [NETFILTER] Enable connection tracking flow accounting 4274 0 to disable accounting 4275 1 to enable accounting 4276 Default value is 0. 4277 4278 nfs.cache_getent= 4279 [NFS] sets the pathname to the program which is used 4280 to update the NFS client cache entries. 4281 4282 nfs.cache_getent_timeout= 4283 [NFS] sets the timeout after which an attempt to 4284 update a cache entry is deemed to have failed. 4285 4286 nfs.callback_nr_threads= 4287 [NFSv4] set the total number of threads that the 4288 NFS client will assign to service NFSv4 callback 4289 requests. 4290 4291 nfs.callback_tcpport= 4292 [NFS] set the TCP port on which the NFSv4 callback 4293 channel should listen. 4294 4295 nfs.delay_retrans= 4296 [NFS] specifies the number of times the NFSv4 client 4297 retries the request before returning an EAGAIN error, 4298 after a reply of NFS4ERR_DELAY from the server. 4299 Only applies if the softerr mount option is enabled, 4300 and the specified value is >= 0. 4301 4302 nfs.idmap_cache_timeout= 4303 [NFS] set the maximum lifetime for idmapper cache 4304 entries. 4305 4306 nfs.max_session_cb_slots= 4307 [NFSv4.1] Sets the maximum number of session 4308 slots the client will assign to the callback 4309 channel. This determines the maximum number of 4310 callbacks the client will process in parallel for 4311 a particular server. 4312 4313 nfs.max_session_slots= 4314 [NFSv4.1] Sets the maximum number of session slots 4315 the client will attempt to negotiate with the server. 4316 This limits the number of simultaneous RPC requests 4317 that the client can send to the NFSv4.1 server. 4318 Note that there is little point in setting this 4319 value higher than the max_tcp_slot_table_limit. 4320 4321 nfs.nfs4_disable_idmapping= 4322 [NFSv4] When set to the default of '1', this option 4323 ensures that both the RPC level authentication 4324 scheme and the NFS level operations agree to use 4325 numeric uids/gids if the mount is using the 4326 'sec=sys' security flavour. In effect it is 4327 disabling idmapping, which can make migration from 4328 legacy NFSv2/v3 systems to NFSv4 easier. 4329 Servers that do not support this mode of operation 4330 will be autodetected by the client, and it will fall 4331 back to using the idmapper. 4332 To turn off this behaviour, set the value to '0'. 4333 4334 nfs.nfs4_unique_id= 4335 [NFS4] Specify an additional fixed unique ident- 4336 ification string that NFSv4 clients can insert into 4337 their nfs_client_id4 string. This is typically a 4338 UUID that is generated at system install time. 4339 4340 nfs.recover_lost_locks= 4341 [NFSv4] Attempt to recover locks that were lost due 4342 to a lease timeout on the server. Please note that 4343 doing this risks data corruption, since there are 4344 no guarantees that the file will remain unchanged 4345 after the locks are lost. 4346 If you want to enable the kernel legacy behaviour of 4347 attempting to recover these locks, then set this 4348 parameter to '1'. 4349 The default parameter value of '0' causes the kernel 4350 not to attempt recovery of lost locks. 4351 4352 nfs.send_implementation_id= 4353 [NFSv4.1] Send client implementation identification 4354 information in exchange_id requests. 4355 If zero, no implementation identification information 4356 will be sent. 4357 The default is to send the implementation identification 4358 information. 4359 4360 nfs4.layoutstats_timer= 4361 [NFSv4.2] Change the rate at which the kernel sends 4362 layoutstats to the pNFS metadata server. 4363 4364 Setting this to value to 0 causes the kernel to use 4365 whatever value is the default set by the layout 4366 driver. A non-zero value sets the minimum interval 4367 in seconds between layoutstats transmissions. 4368 4369 nfsd.inter_copy_offload_enable= 4370 [NFSv4.2] When set to 1, the server will support 4371 server-to-server copies for which this server is 4372 the destination of the copy. 4373 4374 nfsd.nfs4_disable_idmapping= 4375 [NFSv4] When set to the default of '1', the NFSv4 4376 server will return only numeric uids and gids to 4377 clients using auth_sys, and will accept numeric uids 4378 and gids from such clients. This is intended to ease 4379 migration from NFSv2/v3. 4380 4381 nfsd.nfsd4_ssc_umount_timeout= 4382 [NFSv4.2] When used as the destination of a 4383 server-to-server copy, knfsd temporarily mounts 4384 the source server. It caches the mount in case 4385 it will be needed again, and discards it if not 4386 used for the number of milliseconds specified by 4387 this parameter. 4388 4389 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4390 See Documentation/admin-guide/nfs/nfsroot.rst. 4391 4392 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4393 See Documentation/admin-guide/nfs/nfsroot.rst. 4394 4395 nfsrootdebug [NFS] enable nfsroot debugging messages. 4396 See Documentation/admin-guide/nfs/nfsroot.rst. 4397 4398 nmi_backtrace.backtrace_idle [KNL] 4399 Dump stacks even of idle CPUs in response to an 4400 NMI stack-backtrace request. 4401 4402 nmi_debug= [KNL,SH] Specify one or more actions to take 4403 when a NMI is triggered. 4404 Format: [state][,regs][,debounce][,die] 4405 4406 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4407 Format: [panic,][nopanic,][rNNN,][num] 4408 Valid num: 0 or 1 4409 0 - turn hardlockup detector in nmi_watchdog off 4410 1 - turn hardlockup detector in nmi_watchdog on 4411 rNNN - configure the watchdog with raw perf event 0xNNN 4412 4413 When panic is specified, panic when an NMI watchdog 4414 timeout occurs (or 'nopanic' to not panic on an NMI 4415 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4416 To disable both hard and soft lockup detectors, 4417 please see 'nowatchdog'. 4418 This is useful when you use a panic=... timeout and 4419 need the box quickly up again. 4420 4421 These settings can be accessed at runtime via 4422 the nmi_watchdog and hardlockup_panic sysctls. 4423 4424 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4425 Forces kernel to use 3-level paging instead. 4426 4427 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4428 kernel to use 4-level paging instead. 4429 4430 noalign [KNL,ARM] 4431 4432 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4433 IOAPICs that may be present in the system. 4434 4435 noapictimer [APIC,X86] Don't set up the APIC timer 4436 4437 noautogroup Disable scheduler automatic task group creation. 4438 4439 nocache [ARM,EARLY] 4440 4441 no_console_suspend 4442 [HW] Never suspend the console 4443 Disable suspending of consoles during suspend and 4444 hibernate operations. Once disabled, debugging 4445 messages can reach various consoles while the rest 4446 of the system is being put to sleep (ie, while 4447 debugging driver suspend/resume hooks). This may 4448 not work reliably with all consoles, but is known 4449 to work with serial and VGA consoles. 4450 To facilitate more flexible debugging, we also add 4451 console_suspend, a printk module parameter to control 4452 it. Users could use console_suspend (usually 4453 /sys/module/printk/parameters/console_suspend) to 4454 turn on/off it dynamically. 4455 4456 no_debug_objects 4457 [KNL,EARLY] Disable object debugging 4458 4459 nodsp [SH] Disable hardware DSP at boot time. 4460 4461 noefi [EFI,EARLY] Disable EFI runtime services support. 4462 4463 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4464 4465 noexec32 [X86-64] 4466 This affects only 32-bit executables. 4467 noexec32=on: enable non-executable mappings (default) 4468 read doesn't imply executable mappings 4469 noexec32=off: disable non-executable mappings 4470 read implies executable mappings 4471 4472 no_file_caps Tells the kernel not to honor file capabilities. The 4473 only way then for a file to be executed with privilege 4474 is to be setuid root or executed by root. 4475 4476 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4477 4478 nofsgsbase [X86] Disables FSGSBASE instructions. 4479 4480 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4481 register save and restore. The kernel will only save 4482 legacy floating-point registers on task switch. 4483 4484 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4485 4486 no_hash_pointers 4487 [KNL,EARLY] 4488 Alias for "hash_pointers=never". 4489 4490 nohibernate [HIBERNATION] Disable hibernation and resume. 4491 4492 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4493 busy wait in do_idle() and not use the arch_cpu_idle() 4494 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4495 to be effective. This is useful on platforms where the 4496 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4497 correctly or when doing power measurements to evaluate 4498 the impact of the sleep instructions. This is also 4499 useful when using JTAG debugger. 4500 4501 nohpet [X86] Don't use the HPET timer. 4502 4503 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4504 4505 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4506 4507 nohz= [KNL] Boottime enable/disable dynamic ticks 4508 Valid arguments: on, off 4509 Default: on 4510 4511 nohz_full= [KNL,BOOT,SMP,ISOL] 4512 The argument is a cpu list, as described above. 4513 In kernels built with CONFIG_NO_HZ_FULL=y, set 4514 the specified list of CPUs whose tick will be stopped 4515 whenever possible. The boot CPU will be forced outside 4516 the range to maintain the timekeeping. Any CPUs 4517 in this list will have their RCU callbacks offloaded, 4518 just as if they had also been called out in the 4519 rcu_nocbs= boot parameter. 4520 4521 Note that this argument takes precedence over 4522 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4523 4524 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4525 initial RAM disk. Currently this parameter applies to 4526 initrd only, not to initramfs. But it applies to both 4527 in EFI mode. 4528 4529 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4530 remapping. 4531 [Deprecated - use intremap=off] 4532 4533 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4534 4535 noiotrap [SH] Disables trapped I/O port accesses. 4536 4537 noirqdebug [X86-32] Disables the code which attempts to detect and 4538 disable unhandled interrupt sources. 4539 4540 noisapnp [ISAPNP] Disables ISA PnP code. 4541 4542 nokaslr [KNL,EARLY] 4543 When CONFIG_RANDOMIZE_BASE is set, this disables 4544 kernel and module base offset ASLR (Address Space 4545 Layout Randomization). 4546 4547 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4548 fault handling. 4549 4550 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4551 4552 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4553 4554 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4555 4556 nomce [X86-32] Disable Machine Check Exception 4557 4558 nomodeset Disable kernel modesetting. Most systems' firmware 4559 sets up a display mode and provides framebuffer memory 4560 for output. With nomodeset, DRM and fbdev drivers will 4561 not load if they could possibly displace the pre- 4562 initialized output. Only the system framebuffer will 4563 be available for use. The respective drivers will not 4564 perform display-mode changes or accelerated rendering. 4565 4566 Useful as error fallback, or for testing and debugging. 4567 4568 nomodule Disable module load 4569 4570 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4571 shutdown the other cpus. Instead use the REBOOT_VECTOR 4572 irq. 4573 4574 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4575 pagetables) support. 4576 4577 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4578 4579 nopku [X86] Disable Memory Protection Keys CPU feature found 4580 in some Intel CPUs. 4581 4582 nopti [X86-64,EARLY] 4583 Equivalent to pti=off 4584 4585 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4586 Disables the PV optimizations forcing the guest to run 4587 as generic guest with no PV drivers. Currently support 4588 XEN HVM, KVM, HYPER_V and VMWARE guest. 4589 4590 nopvspin [X86,XEN,KVM,EARLY] 4591 Disables the qspinlock slow path using PV optimizations 4592 which allow the hypervisor to 'idle' the guest on lock 4593 contention. 4594 4595 norandmaps Don't use address space randomization. Equivalent to 4596 echo 0 > /proc/sys/kernel/randomize_va_space 4597 4598 noresume [SWSUSP] Disables resume and restores original swap 4599 space. 4600 4601 no-scroll [VGA] Disables scrollback. 4602 This is required for the Braillex ib80-piezo Braille 4603 reader made by F.H. Papenmeier (Germany). 4604 4605 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4606 4607 nosmap [PPC,EARLY] 4608 Disable SMAP (Supervisor Mode Access Prevention) 4609 even if it is supported by processor. 4610 4611 nosmep [PPC64s,EARLY] 4612 Disable SMEP (Supervisor Mode Execution Prevention) 4613 even if it is supported by processor. 4614 4615 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4616 and disable the IO APIC. legacy for "maxcpus=0". 4617 4618 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4619 Equivalent to smt=1. 4620 4621 [KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). 4622 nosmt=force: Force disable SMT, cannot be undone 4623 via the sysfs control file. 4624 4625 nosoftlockup [KNL] Disable the soft-lockup detector. 4626 4627 nospec_store_bypass_disable 4628 [HW,EARLY] Disable all mitigations for the Speculative 4629 Store Bypass vulnerability 4630 4631 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4632 history injection) vulnerability. System may allow data leaks 4633 with this option. 4634 4635 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4636 (bounds check bypass). With this option data leaks are 4637 possible in the system. 4638 4639 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4640 for the Spectre variant 2 (indirect branch 4641 prediction) vulnerability. System may allow data 4642 leaks with this option. 4643 4644 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4645 Disable paravirtualized steal time accounting. steal time 4646 is computed, but won't influence scheduler behaviour 4647 4648 nosync [HW,M68K] Disables sync negotiation for all devices. 4649 4650 no_timer_check [X86,APIC] Disables the code which tests for broken 4651 timer IRQ sources, i.e., the IO-APIC timer. This can 4652 work around problems with incorrect timer 4653 initialization on some boards. 4654 4655 no_uaccess_flush 4656 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4657 4658 novmcoredd [KNL,KDUMP] 4659 Disable device dump. Device dump allows drivers to 4660 append dump data to vmcore so you can collect driver 4661 specified debug info. Drivers can append the data 4662 without any limit and this data is stored in memory, 4663 so this may cause significant memory stress. Disabling 4664 device dump can help save memory but the driver debug 4665 data will be no longer available. This parameter 4666 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4667 is set. 4668 4669 no-vmw-sched-clock 4670 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4671 scheduler clock and use the default one. 4672 4673 nowatchdog [KNL] Disable both lockup detectors, i.e. 4674 soft-lockup and NMI watchdog (hard-lockup). 4675 4676 nowb [ARM,EARLY] 4677 4678 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4679 4680 NOTE: this parameter will be ignored on systems with the 4681 LEGACY_XAPIC_DISABLED bit set in the 4682 IA32_XAPIC_DISABLE_STATUS MSR. 4683 4684 noxsave [BUGS=X86] Disables x86 extended register state save 4685 and restore using xsave. The kernel will fallback to 4686 enabling legacy floating-point and sse state. 4687 4688 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4689 register states. The kernel will fall back to use 4690 xsave to save the states. By using this parameter, 4691 performance of saving the states is degraded because 4692 xsave doesn't support modified optimization while 4693 xsaveopt supports it on xsaveopt enabled systems. 4694 4695 noxsaves [X86] Disables xsaves and xrstors used in saving and 4696 restoring x86 extended register state in compacted 4697 form of xsave area. The kernel will fall back to use 4698 xsaveopt and xrstor to save and restore the states 4699 in standard form of xsave area. By using this 4700 parameter, xsave area per process might occupy more 4701 memory on xsaves enabled systems. 4702 4703 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4704 could support. nr_cpus=n : n >= 1 limits the kernel to 4705 support 'n' processors. It could be larger than the 4706 number of already plugged CPU during bootup, later in 4707 runtime you can physically add extra cpu until it reaches 4708 n. So during boot up some boot time memory for per-cpu 4709 variables need be pre-allocated for later physical cpu 4710 hot plugging. 4711 4712 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4713 4714 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4715 Disable NUMA, Only set up a single NUMA node 4716 spanning all memory. 4717 4718 numa=fake=<size>[MG] 4719 [KNL, ARM64, RISCV, X86, EARLY] 4720 If given as a memory unit, fills all system RAM with 4721 nodes of size interleaved over physical nodes. 4722 4723 numa=fake=<N> 4724 [KNL, ARM64, RISCV, X86, EARLY] 4725 If given as an integer, fills all system RAM with N 4726 fake nodes interleaved over physical nodes. 4727 4728 numa=fake=<N>U 4729 [KNL, ARM64, RISCV, X86, EARLY] 4730 If given as an integer followed by 'U', it will 4731 divide each physical node into N emulated nodes. 4732 4733 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4734 4735 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4736 soft-reserved memory partitioning. 4737 4738 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4739 NUMA balancing. 4740 Allowed values are enable and disable 4741 4742 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4743 'node', 'default' can be specified 4744 This can be set from sysctl after boot. 4745 See Documentation/admin-guide/sysctl/vm.rst for details. 4746 4747 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4748 nvme quirk list. List entries are separated by a 4749 '-' character. 4750 Each entry has the form VendorID:ProductID:quirk_names. 4751 The IDs are 4-digits hex numbers and quirk_names is a 4752 list of quirk names separated by commas. A quirk name 4753 can be prefixed by '^', meaning that the specified 4754 quirk must be disabled. 4755 4756 Example: 4757 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4758 4759 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4760 See Documentation/core-api/debugging-via-ohci1394.rst for more 4761 info. 4762 4763 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4764 Rather than timing out after 20 ms if an EC 4765 command is not properly ACKed, override the length 4766 of the timeout. We have interrupts disabled while 4767 waiting for the ACK, so if this is set too high 4768 interrupts *may* be lost! 4769 4770 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4771 4772 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4773 4774 boundary - index of last SLC block on Flex-OneNAND. 4775 The remaining blocks are configured as MLC blocks. 4776 lock - Configure if Flex-OneNAND boundary should be locked. 4777 Once locked, the boundary cannot be changed. 4778 1 indicates lock status, 0 indicates unlock status. 4779 4780 oops=panic [KNL,EARLY] 4781 Always panic on oopses. Default is to just kill the 4782 process, but there is a small probability of 4783 deadlocking the machine. 4784 This will also cause panics on machine check exceptions. 4785 Useful together with panic=30 to trigger a reboot. 4786 4787 page_alloc.shuffle= 4788 [KNL] Boolean flag to control whether the page allocator 4789 should randomize its free lists. This parameter can be 4790 used to enable/disable page randomization. The state of 4791 the flag can be read from sysfs at: 4792 /sys/module/page_alloc/parameters/shuffle. 4793 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4794 4795 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4796 Storage of the information about who allocated 4797 each page is disabled in default. With this switch, 4798 we can turn it on. 4799 on: enable the feature 4800 4801 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4802 poisoning on the buddy allocator, available with 4803 CONFIG_PAGE_POISONING=y. 4804 off: turn off poisoning (default) 4805 on: turn on poisoning 4806 4807 page_reporting.page_reporting_order= 4808 [KNL] Minimal page reporting order 4809 Format: <integer> 4810 Adjust the minimal page reporting order. The page 4811 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4812 4813 page_reporting.page_reporting_delay_ms= 4814 [KNL] Free page reporting delay in milliseconds 4815 Format: <unsigned integer> 4816 Adjust the delay in milliseconds between free page 4817 reporting intervals. Default is 2000 (2 seconds). 4818 4819 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4820 timeout > 0: seconds before rebooting 4821 timeout = 0: wait forever 4822 timeout < 0: reboot immediately 4823 Format: <timeout> 4824 4825 panic_on_taint= [KNL,EARLY] 4826 Bitmask for conditionally calling panic() in add_taint() 4827 Format: <hex>[,nousertaint] 4828 Hexadecimal bitmask representing the set of TAINT flags 4829 that will cause the kernel to panic when add_taint() is 4830 called with any of the flags in this set. 4831 The optional switch "nousertaint" can be utilized to 4832 prevent userspace forced crashes by writing to sysctl 4833 /proc/sys/kernel/tainted any flagset matching with the 4834 bitmask set on panic_on_taint. 4835 See Documentation/admin-guide/tainted-kernels.rst for 4836 extra details on the taint flags that users can pick 4837 to compose the bitmask to assign to panic_on_taint. 4838 4839 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4840 on a WARN(). 4841 4842 panic_force_cpu= 4843 [KNL,SMP] Force panic handling to execute on a specific CPU. 4844 Format: <cpu number> 4845 Some platforms require panic handling to occur on a 4846 specific CPU for the crash kernel to function correctly. 4847 This can be due to firmware limitations, interrupt routing 4848 constraints, or platform-specific requirements where only 4849 a particular CPU can safely enter the crash kernel. 4850 When set, panic() will redirect execution to the specified 4851 CPU before proceeding with the normal panic and kexec flow. 4852 If the target CPU is offline or unavailable, panic proceeds 4853 on the current CPU. 4854 This option should only be used for systems with the above 4855 constraints as it might cause the panic operation to be less reliable. 4856 4857 panic_print= Bitmask for printing system info when panic happens. 4858 User can chose combination of the following bits: 4859 4860 bit 0: print all tasks info 4861 bit 1: print system memory info 4862 bit 2: print timer info 4863 bit 3: print locks info if CONFIG_LOCKDEP is on 4864 bit 4: print ftrace buffer 4865 bit 5: replay all kernel messages on consoles at the end of panic 4866 bit 6: print all CPUs backtrace (if available in the arch) 4867 bit 7: print only tasks in uninterruptible (blocked) state 4868 4869 *Be aware* that this option may print a _lot_ of lines. 4870 4871 There is an increased risk of losing older messages in 4872 the log. Maybe worth to setup a bigger log buffer with 4873 "log_buf_len" along with this. 4874 4875 Also consider using "printk.console_no_auto_verbose=Y" 4876 if using this along with pstore, to avoid extra delays 4877 due to increased console verbosity during panic. 4878 4879 panic_sys_info= A comma separated list of extra information to be dumped 4880 on panic. 4881 Format: val[,val...] 4882 Where @val can be any of the following: 4883 4884 tasks: print all tasks info 4885 mem: print system memory info 4886 timers: print timers info 4887 locks: print locks info if CONFIG_LOCKDEP is on 4888 ftrace: print ftrace buffer 4889 all_bt: print all CPUs backtrace (if available in the arch) 4890 blocked_tasks: print only tasks in uninterruptible (blocked) state 4891 4892 This is a human readable alternative to the 'panic_print' 4893 option above. Please be aware of the caveats using this, 4894 check the 'panic_print' parameter for more details. 4895 4896 panic_console_replay 4897 When panic happens, replay all kernel messages on 4898 consoles at the end of panic. 4899 4900 parkbd.port= [HW] Parallel port number the keyboard adapter is 4901 connected to, default is 0. 4902 Format: <parport#> 4903 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4904 0 for XT, 1 for AT (default is AT). 4905 Format: <mode> 4906 4907 parport= [HW,PPT] Specify parallel ports. 0 disables. 4908 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4909 Use 'auto' to force the driver to use any 4910 IRQ/DMA settings detected (the default is to 4911 ignore detected IRQ/DMA settings because of 4912 possible conflicts). You can specify the base 4913 address, IRQ, and DMA settings; IRQ and DMA 4914 should be numbers, or 'auto' (for using detected 4915 settings on that particular port), or 'nofifo' 4916 (to avoid using a FIFO even if it is detected). 4917 Parallel ports are assigned in the order they 4918 are specified on the command line, starting 4919 with parport0. 4920 4921 parport_init_mode= [HW,PPT] 4922 Configure VIA parallel port to operate in 4923 a specific mode. This is necessary on Pegasos 4924 computer where firmware has no options for setting 4925 up parallel port mode and sets it to spp. 4926 Currently this function knows 686a and 8231 chips. 4927 Format: [spp|ps2|epp|ecp|ecpepp] 4928 4929 pata_legacy.all= [HW,LIBATA] 4930 Format: <int> 4931 Set to non-zero to probe primary and secondary ISA 4932 port ranges on PCI systems where no PCI PATA device 4933 has been found at either range. Disabled by default. 4934 4935 pata_legacy.autospeed= [HW,LIBATA] 4936 Format: <int> 4937 Set to non-zero if a chip is present that snoops speed 4938 changes. Disabled by default. 4939 4940 pata_legacy.iordy_mask= [HW,LIBATA] 4941 Format: <int> 4942 IORDY enable mask. Set individual bits to allow IORDY 4943 for the respective channel. Bit 0 is for the first 4944 legacy channel handled by this driver, bit 1 is for 4945 the second channel, and so on. The sequence will often 4946 correspond to the primary legacy channel, the secondary 4947 legacy channel, and so on, but the handling of a PCI 4948 bus and the use of other driver options may interfere 4949 with the sequence. By default IORDY is allowed across 4950 all channels. 4951 4952 pata_legacy.pio_mask= [HW,LIBATA] 4953 Format: <int> 4954 PIO mode mask for autospeed devices. Set individual 4955 bits to allow the use of the respective PIO modes. 4956 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4957 All modes allowed by default. 4958 4959 pata_legacy.probe_all= [HW,LIBATA] 4960 Format: <int> 4961 Set to non-zero to probe tertiary and further ISA 4962 port ranges on PCI systems. Disabled by default. 4963 4964 pata_legacy.probe_mask= [HW,LIBATA] 4965 Format: <int> 4966 Probe mask for legacy ISA PATA ports. Depending on 4967 platform configuration and the use of other driver 4968 options up to 6 legacy ports are supported: 0x1f0, 4969 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4970 of individual ports can be disabled by setting the 4971 corresponding bits in the mask to 1. Bit 0 is for 4972 the first port in the list above (0x1f0), and so on. 4973 By default all supported ports are probed. 4974 4975 pata_platform.pio_mask= [HW,LIBATA] 4976 Format: <int> 4977 Supported PIO mode mask. Set individual bits to allow 4978 the use of the respective PIO modes. Bit 0 is for 4979 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4980 allowed by default. 4981 4982 pause_on_oops=<int> 4983 Halt all CPUs after the first oops has been printed for 4984 the specified number of seconds. This is to be used if 4985 your oopses keep scrolling off the screen. 4986 4987 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4988 4989 Some options herein operate on a specific device 4990 or a set of devices (<pci_dev>). These are 4991 specified in one of the following formats: 4992 4993 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4994 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4995 4996 Note: the first format specifies a PCI 4997 bus/device/function address which may change 4998 if new hardware is inserted, if motherboard 4999 firmware changes, or due to changes caused 5000 by other kernel parameters. If the 5001 domain is left unspecified, it is 5002 taken to be zero. Optionally, a path 5003 to a device through multiple device/function 5004 addresses can be specified after the base 5005 address (this is more robust against 5006 renumbering issues). The second format 5007 selects devices using IDs from the 5008 configuration space which may match multiple 5009 devices in the system. 5010 5011 earlydump dump PCI config space before the kernel 5012 changes anything 5013 off [X86] don't probe for the PCI bus 5014 bios [X86-32] force use of PCI BIOS, don't access 5015 the hardware directly. Use this if your machine 5016 has a non-standard PCI host bridge. 5017 nobios [X86-32] disallow use of PCI BIOS, only direct 5018 hardware access methods are allowed. Use this 5019 if you experience crashes upon bootup and you 5020 suspect they are caused by the BIOS. 5021 conf1 [X86] Force use of PCI Configuration Access 5022 Mechanism 1 (config address in IO port 0xCF8, 5023 data in IO port 0xCFC, both 32-bit). 5024 conf2 [X86] Force use of PCI Configuration Access 5025 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5026 the function, IO port 0xCFA, also 8-bit, sets 5027 bus number. The config space is then accessed 5028 through ports 0xC000-0xCFFF). 5029 See http://wiki.osdev.org/PCI for more info 5030 on the configuration access mechanisms. 5031 noaer [PCIE] If the PCIEAER kernel config parameter is 5032 enabled, this kernel boot option can be used to 5033 disable the use of PCIE advanced error reporting. 5034 nodomains [PCI] Disable support for multiple PCI 5035 root domains (aka PCI segments, in ACPI-speak). 5036 nommconf [X86] Disable use of MMCONFIG for PCI 5037 Configuration 5038 check_enable_amd_mmconf [X86] check for and enable 5039 properly configured MMIO access to PCI 5040 config space on AMD family 10h CPU 5041 nomsi [MSI] If the PCI_MSI kernel config parameter is 5042 enabled, this kernel boot option can be used to 5043 disable the use of MSI interrupts system-wide. 5044 noioapicquirk [APIC] Disable all boot interrupt quirks. 5045 Safety option to keep boot IRQs enabled. This 5046 should never be necessary. 5047 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5048 primary IO-APIC for bridges that cannot disable 5049 boot IRQs. This fixes a source of spurious IRQs 5050 when the system masks IRQs. 5051 noioapicreroute [APIC] Disable workaround that uses the 5052 boot IRQ equivalent of an IRQ that connects to 5053 a chipset where boot IRQs cannot be disabled. 5054 The opposite of ioapicreroute. 5055 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5056 routing table. These calls are known to be buggy 5057 on several machines and they hang the machine 5058 when used, but on other computers it's the only 5059 way to get the interrupt routing table. Try 5060 this option if the kernel is unable to allocate 5061 IRQs or discover secondary PCI buses on your 5062 motherboard. 5063 rom [X86] Assign address space to expansion ROMs. 5064 Use with caution as certain devices share 5065 address decoders between ROMs and other 5066 resources. 5067 norom [X86] Do not assign address space to 5068 expansion ROMs that do not already have 5069 BIOS assigned address ranges. 5070 nobar [X86] Do not assign address space to the 5071 BARs that weren't assigned by the BIOS. 5072 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5073 assigned automatically to PCI devices. You can 5074 make the kernel exclude IRQs of your ISA cards 5075 this way. 5076 pirqaddr=0xAAAAA [X86] Specify the physical address 5077 of the PIRQ table (normally generated 5078 by the BIOS) if it is outside the 5079 F0000h-100000h range. 5080 lastbus=N [X86] Scan all buses thru bus #N. Can be 5081 useful if the kernel is unable to find your 5082 secondary buses and you want to tell it 5083 explicitly which ones they are. 5084 assign-busses [X86] Always assign all PCI bus 5085 numbers ourselves, overriding 5086 whatever the firmware may have done. 5087 usepirqmask [X86] Honor the possible IRQ mask stored 5088 in the BIOS $PIR table. This is needed on 5089 some systems with broken BIOSes, notably 5090 some HP Pavilion N5400 and Omnibook XE3 5091 notebooks. This will have no effect if ACPI 5092 IRQ routing is enabled. 5093 noacpi [X86] Do not use ACPI for IRQ routing 5094 or for PCI scanning. 5095 use_crs [X86] Use PCI host bridge window information 5096 from ACPI. On BIOSes from 2008 or later, this 5097 is enabled by default. If you need to use this, 5098 please report a bug. 5099 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5100 If you need to use this, please report a bug. 5101 use_e820 [X86] Use E820 reservations to exclude parts of 5102 PCI host bridge windows. This is a workaround 5103 for BIOS defects in host bridge _CRS methods. 5104 If you need to use this, please report a bug to 5105 <linux-pci@vger.kernel.org>. 5106 no_e820 [X86] Ignore E820 reservations for PCI host 5107 bridge windows. This is the default on modern 5108 hardware. If you need to use this, please report 5109 a bug to <linux-pci@vger.kernel.org>. 5110 routeirq Do IRQ routing for all PCI devices. 5111 This is normally done in pci_enable_device(), 5112 so this option is a temporary workaround 5113 for broken drivers that don't call it. 5114 skip_isa_align [X86] do not align io start addr, so can 5115 handle more pci cards 5116 noearly [X86] Don't do any early type 1 scanning. 5117 This might help on some broken boards which 5118 machine check when some devices' config space 5119 is read. But various workarounds are disabled 5120 and some IOMMU drivers will not work. 5121 bfsort Sort PCI devices into breadth-first order. 5122 This sorting is done to get a device 5123 order compatible with older (<= 2.4) kernels. 5124 nobfsort Don't sort PCI devices into breadth-first order. 5125 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5126 tuning and use the BIOS-configured MPS defaults. 5127 pcie_bus_safe Set every device's MPS to the largest value 5128 supported by all devices below the root complex. 5129 pcie_bus_perf Set device MPS to the largest allowable MPS 5130 based on its parent bus. Also set MRRS (Max 5131 Read Request Size) to the largest supported 5132 value (no larger than the MPS that the device 5133 or bus can support) for best performance. 5134 pcie_bus_peer2peer Set every device's MPS to 128B, which 5135 every device is guaranteed to support. This 5136 configuration allows peer-to-peer DMA between 5137 any pair of devices, possibly at the cost of 5138 reduced performance. This also guarantees 5139 that hot-added devices will work. 5140 cbiosize=nn[KMG] The fixed amount of bus space which is 5141 reserved for the CardBus bridge's IO window. 5142 The default value is 256 bytes. 5143 cbmemsize=nn[KMG] The fixed amount of bus space which is 5144 reserved for the CardBus bridge's memory 5145 window. The default value is 64 megabytes. 5146 resource_alignment= 5147 Format: 5148 [<order of align>@]<pci_dev>[; ...] 5149 Specifies alignment and device to reassign 5150 aligned memory resources. How to 5151 specify the device is described above. 5152 If <order of align> is not specified, 5153 PAGE_SIZE is used as alignment. 5154 A PCI-PCI bridge can be specified if resource 5155 windows need to be expanded. 5156 To specify the alignment for several 5157 instances of a device, the PCI vendor, 5158 device, subvendor, and subdevice may be 5159 specified, e.g., 12@pci:8086:9c22:103c:198f 5160 for 4096-byte alignment. 5161 ecrc= Enable/disable PCIe ECRC (transaction layer 5162 end-to-end CRC checking). Only effective if 5163 OS has native AER control (either granted by 5164 ACPI _OSC or forced via "pcie_ports=native") 5165 bios: Use BIOS/firmware settings. This is the 5166 the default. 5167 off: Turn ECRC off 5168 on: Turn ECRC on. 5169 hpiosize=nn[KMG] The fixed amount of bus space which is 5170 reserved for hotplug bridge's IO window. 5171 Default size is 256 bytes. 5172 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5173 reserved for hotplug bridge's MMIO window. 5174 Default size is 2 megabytes. 5175 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5176 reserved for hotplug bridge's MMIO_PREF window. 5177 Default size is 2 megabytes. 5178 hpmemsize=nn[KMG] The fixed amount of bus space which is 5179 reserved for hotplug bridge's MMIO and 5180 MMIO_PREF window. 5181 Default size is 2 megabytes. 5182 hpbussize=nn The minimum amount of additional bus numbers 5183 reserved for buses below a hotplug bridge. 5184 Default is 1. 5185 realloc= Enable/disable reallocating PCI bridge resources 5186 if allocations done by BIOS are too small to 5187 accommodate resources required by all child 5188 devices. 5189 off: Turn realloc off 5190 on: Turn realloc on 5191 realloc same as realloc=on 5192 noari do not use PCIe ARI. 5193 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5194 do not use PCIe ATS (and IOMMU device IOTLB). 5195 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5196 only look for one device below a PCIe downstream 5197 port. 5198 big_root_window Try to add a big 64bit memory window to the PCIe 5199 root complex on AMD CPUs. Some GFX hardware 5200 can resize a BAR to allow access to all VRAM. 5201 Adding the window is slightly risky (it may 5202 conflict with unreported devices), so this 5203 taints the kernel. 5204 disable_acs_redir=<pci_dev>[; ...] 5205 Specify one or more PCI devices (in the format 5206 specified above) separated by semicolons. 5207 Each device specified will have the PCI ACS 5208 redirect capabilities forced off which will 5209 allow P2P traffic between devices through 5210 bridges without forcing it upstream. Note: 5211 this removes isolation between devices and 5212 may put more devices in an IOMMU group. 5213 config_acs= 5214 Format: 5215 <ACS flags>@<pci_dev>[; ...] 5216 Specify one or more PCI devices (in the format 5217 specified above) optionally prepended with flags 5218 and separated by semicolons. The respective 5219 capabilities will be enabled, disabled or 5220 unchanged based on what is specified in 5221 flags. 5222 5223 ACS Flags is defined as follows: 5224 bit-0 : ACS Source Validation 5225 bit-1 : ACS Translation Blocking 5226 bit-2 : ACS P2P Request Redirect 5227 bit-3 : ACS P2P Completion Redirect 5228 bit-4 : ACS Upstream Forwarding 5229 bit-5 : ACS P2P Egress Control 5230 bit-6 : ACS Direct Translated P2P 5231 Each bit can be marked as: 5232 '0' – force disabled 5233 '1' – force enabled 5234 'x' – unchanged 5235 For example, 5236 pci=config_acs=10x@pci:0:0 5237 would configure all devices that support 5238 ACS to enable P2P Request Redirect, disable 5239 Translation Blocking, and leave Source 5240 Validation unchanged from whatever power-up 5241 or firmware set it to. 5242 5243 Note: this may remove isolation between devices 5244 and may put more devices in an IOMMU group. 5245 force_floating [S390] Force usage of floating interrupts. 5246 nomio [S390] Do not use MIO instructions. 5247 norid [S390] ignore the RID field and force use of 5248 one PCI domain per PCI function 5249 notph [PCIE] If the PCIE_TPH kernel config parameter 5250 is enabled, this kernel boot option can be used 5251 to disable PCIe TLP Processing Hints support 5252 system-wide. 5253 5254 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5255 Management. 5256 off Don't touch ASPM configuration at all. Leave any 5257 configuration done by firmware unchanged. 5258 force Enable ASPM even on devices that claim not to support it. 5259 WARNING: Forcing ASPM on may cause system lockups. 5260 5261 pcie_ports= [PCIE] PCIe port services handling: 5262 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5263 even if the platform doesn't give the OS permission to 5264 use them. This may cause conflicts if the platform 5265 also tries to use these services. 5266 dpc-native Use native PCIe service for DPC only. May 5267 cause conflicts if firmware uses AER or DPC. 5268 compat Disable native PCIe services (PME, AER, DPC, PCIe 5269 hotplug). 5270 5271 pcie_port_pm= [PCIE] PCIe port power management handling: 5272 off Disable power management of all PCIe ports 5273 force Forcibly enable power management of all PCIe ports 5274 5275 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5276 nomsi Do not use MSI for native PCIe PME signaling (this makes 5277 all PCIe root ports use INTx for all services). 5278 5279 pd_ignore_unused 5280 [PM] 5281 Keep all power-domains already enabled by bootloader on, 5282 even if no driver has claimed them. This is useful 5283 for debug and development, but should not be 5284 needed on a platform with proper driver support. 5285 5286 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5287 boot time. 5288 Format: { 0 | 1 } 5289 See arch/parisc/kernel/pdc_chassis.c 5290 5291 percpu_alloc= [MM,EARLY] 5292 Select which percpu first chunk allocator to use. 5293 Currently supported values are "embed" and "page". 5294 Archs may support subset or none of the selections. 5295 See comments in mm/percpu.c for details on each 5296 allocator. This parameter is primarily for debugging 5297 and performance comparison. 5298 5299 pirq= [SMP,APIC] Manual mp-table setup 5300 See Documentation/arch/x86/i386/IO-APIC.rst. 5301 5302 plip= [PPT,NET] Parallel port network link 5303 Format: { parport<nr> | timid | 0 } 5304 See also Documentation/admin-guide/parport.rst. 5305 5306 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5307 Override pmtimer IOPort with a hex value. 5308 e.g. pmtmr=0x508 5309 5310 pmu_override= [PPC] Override the PMU. 5311 This option takes over the PMU facility, so it is no 5312 longer usable by perf. Setting this option starts the 5313 PMU counters by setting MMCR0 to 0 (the FC bit is 5314 cleared). If a number is given, then MMCR1 is set to 5315 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5316 remains 0. 5317 5318 pm_async= [PM] 5319 Format: off 5320 This parameter sets the initial value of the 5321 /sys/power/pm_async sysfs knob at boot time. 5322 If set to "off", disables asynchronous suspend and 5323 resume of devices during system-wide power transitions. 5324 This can be useful on platforms where device 5325 dependencies are not well-defined, or for debugging 5326 power management issues. Asynchronous operations are 5327 enabled by default. 5328 5329 5330 pm_debug_messages [SUSPEND,KNL] 5331 Enable suspend/resume debug messages during boot up. 5332 5333 pm.dpm_watchdog_enabled= 5334 [PM] Enable or disable the DPM watchdog. Requires 5335 CONFIG_PM_SLEEP and CONFIG_DPM_WATCHDOG enabled. 5336 Format: <bool> 5337 Default value is set by CONFIG_DPM_WATCHDOG_ENABLED. 5338 5339 pnp.debug=1 [PNP] 5340 Enable PNP debug messages (depends on the 5341 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5342 via /sys/module/pnp/parameters/debug. We always show 5343 current resource usage; turning this on also shows 5344 possible settings and some assignment information. 5345 5346 pnpacpi= [ACPI] 5347 { off } 5348 5349 pnpbios= [ISAPNP] 5350 { on | off | curr | res | no-curr | no-res } 5351 5352 pnp_reserve_irq= 5353 [ISAPNP] Exclude IRQs for the autoconfiguration 5354 5355 pnp_reserve_dma= 5356 [ISAPNP] Exclude DMAs for the autoconfiguration 5357 5358 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5359 Ranges are in pairs (I/O port base and size). 5360 5361 pnp_reserve_mem= 5362 [ISAPNP] Exclude memory regions for the 5363 autoconfiguration. 5364 Ranges are in pairs (memory base and size). 5365 5366 ports= [IP_VS_FTP] IPVS ftp helper module 5367 Default is 21. 5368 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5369 may be specified. 5370 Format: <port>,<port>.... 5371 5372 possible_cpus= [SMP,S390,X86] 5373 Format: <unsigned int> 5374 Set the number of possible CPUs, overriding the 5375 regular discovery mechanisms (such as ACPI/FW, etc). 5376 5377 powersave=off [PPC] This option disables power saving features. 5378 It specifically disables cpuidle and sets the 5379 platform machine description specific power_save 5380 function to NULL. On Idle the CPU just reduces 5381 execution priority. 5382 5383 ppc_strict_facility_enable 5384 [PPC,ENABLE] This option catches any kernel floating point, 5385 Altivec, VSX and SPE outside of regions specifically 5386 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5387 There is some performance impact when enabling this. 5388 5389 ppc_tm= [PPC,EARLY] 5390 Format: {"off"} 5391 Disable Hardware Transactional Memory 5392 5393 preempt= [KNL] 5394 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5395 none - Limited to cond_resched() calls 5396 voluntary - Limited to cond_resched() and might_sleep() calls 5397 full - Any section that isn't explicitly preempt disabled 5398 can be preempted anytime. Tasks will also yield 5399 contended spinlocks (if the critical section isn't 5400 explicitly preempt disabled beyond the lock itself). 5401 lazy - Scheduler controlled. Similar to full but instead 5402 of preempting the task immediately, the task gets 5403 one HZ tick time to yield itself before the 5404 preemption will be forced. One such preemption 5405 point is when the task returns to user space. 5406 5407 print-fatal-signals= 5408 [KNL] debug: print fatal signals 5409 5410 If enabled, warn about various signal handling 5411 related application anomalies: too many signals, 5412 too many POSIX.1 timers, fatal signals causing a 5413 coredump - etc. 5414 5415 If you hit the warning due to signal overflow, 5416 you might want to try "ulimit -i unlimited". 5417 5418 default: off. 5419 5420 printk.always_kmsg_dump= 5421 Trigger kmsg_dump for cases other than kernel oops or 5422 panics 5423 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5424 default: disabled 5425 5426 printk.console_no_auto_verbose= 5427 Disable console loglevel raise on oops, panic 5428 or lockdep-detected issues (only if lock debug is on). 5429 With an exception to setups with low baudrate on 5430 serial console, keeping this 0 is a good choice 5431 in order to provide more debug information. 5432 Format: <bool> 5433 default: 0 (auto_verbose is enabled) 5434 5435 printk.debug_non_panic_cpus= 5436 Allows storing messages from non-panic CPUs into 5437 the printk log buffer during panic(). They are 5438 flushed to consoles by the panic-CPU on 5439 a best-effort basis. 5440 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5441 Default: disabled 5442 5443 printk.devkmsg={on,off,ratelimit} 5444 Control writing to /dev/kmsg. 5445 on - unlimited logging to /dev/kmsg from userspace 5446 off - logging to /dev/kmsg disabled 5447 ratelimit - ratelimit the logging 5448 Default: ratelimit 5449 5450 printk.time= Show timing data prefixed to each printk message line 5451 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5452 5453 proc_mem.force_override= [KNL] 5454 Format: {always | ptrace | never} 5455 Traditionally /proc/pid/mem allows memory permissions to be 5456 overridden without restrictions. This option may be set to 5457 restrict that. Can be one of: 5458 - 'always': traditional behavior always allows mem overrides. 5459 - 'ptrace': only allow mem overrides for active ptracers. 5460 - 'never': never allow mem overrides. 5461 If not specified, default is the CONFIG_PROC_MEM_* choice. 5462 5463 processor.max_cstate= [HW,ACPI] 5464 Limit processor to maximum C-state 5465 max_cstate=9 overrides any DMI blacklist limit. 5466 5467 processor.nocst [HW,ACPI] 5468 Ignore the _CST method to determine C-states, 5469 instead using the legacy FADT method 5470 5471 profile= [KNL] Enable kernel profiling via /proc/profile 5472 Format: [<profiletype>,]<number> 5473 Param: <profiletype>: "schedule" or "kvm" 5474 [defaults to kernel profiling] 5475 Param: "schedule" - profile schedule points. 5476 Param: "kvm" - profile VM exits. 5477 Param: <number> - step/bucket size as a power of 2 for 5478 statistical time based profiling. 5479 5480 prot_virt= [S390] enable hosting protected virtual machines 5481 isolated from the hypervisor (if hardware supports 5482 that). If enabled, the default kernel base address 5483 might be overridden even when Kernel Address Space 5484 Layout Randomization is disabled. 5485 Format: <bool> 5486 5487 psi= [KNL] Enable or disable pressure stall information 5488 tracking. 5489 Format: <bool> 5490 5491 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5492 probe for; one of (bare|imps|exps|lifebook|any). 5493 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5494 per second. 5495 psmouse.resetafter= [HW,MOUSE] 5496 Try to reset the device after so many bad packets 5497 (0 = never). 5498 psmouse.resolution= 5499 [HW,MOUSE] Set desired mouse resolution, in dpi. 5500 psmouse.smartscroll= 5501 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5502 0 = disabled, 1 = enabled (default). 5503 5504 pstore.backend= Specify the name of the pstore backend to use 5505 5506 pti= [X86-64] Control Page Table Isolation of user and 5507 kernel address spaces. Disabling this feature 5508 removes hardening, but improves performance of 5509 system calls and interrupts. 5510 5511 on - unconditionally enable 5512 off - unconditionally disable 5513 auto - kernel detects whether your CPU model is 5514 vulnerable to issues that PTI mitigates 5515 5516 Not specifying this option is equivalent to pti=auto. 5517 5518 pty.legacy_count= 5519 [KNL] Number of legacy pty's. Overwrites compiled-in 5520 default number. 5521 5522 quiet [KNL,EARLY] Disable most log messages 5523 5524 r128= [HW,DRM] 5525 5526 radix_hcall_invalidate=on [PPC/PSERIES] 5527 Disable RADIX GTSE feature and use hcall for TLB 5528 invalidate. 5529 5530 raid= [HW,RAID] 5531 See Documentation/admin-guide/md.rst. 5532 5533 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5534 See Documentation/admin-guide/blockdev/ramdisk.rst. 5535 5536 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5537 5538 random.trust_cpu=off 5539 [KNL,EARLY] Disable trusting the use of the CPU's 5540 random number generator (if available) to 5541 initialize the kernel's RNG. 5542 5543 random.trust_bootloader=off 5544 [KNL,EARLY] Disable trusting the use of the a seed 5545 passed by the bootloader (if available) to 5546 initialize the kernel's RNG. 5547 5548 randomize_kstack_offset= 5549 [KNL,EARLY] Enable or disable kernel stack offset 5550 randomization, which provides roughly 5 bits of 5551 entropy, frustrating memory corruption attacks 5552 that depend on stack address determinism or 5553 cross-syscall address exposures. This is only 5554 available on architectures that have defined 5555 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5556 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5557 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5558 5559 ras=option[,option,...] [KNL] RAS-specific options 5560 5561 cec_disable [X86] 5562 Disable the Correctable Errors Collector, 5563 see CONFIG_RAS_CEC help text. 5564 5565 rcu_nocbs[=cpu-list] 5566 [KNL] The optional argument is a cpu list, 5567 as described above. 5568 5569 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5570 enable the no-callback CPU mode, which prevents 5571 such CPUs' callbacks from being invoked in 5572 softirq context. Invocation of such CPUs' RCU 5573 callbacks will instead be offloaded to "rcuox/N" 5574 kthreads created for that purpose, where "x" is 5575 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5576 for the kthreads that mediate grace periods; and 5577 "N" is the CPU number. This reduces OS jitter on 5578 the offloaded CPUs, which can be useful for HPC 5579 and real-time workloads. It can also improve 5580 energy efficiency for asymmetric multiprocessors. 5581 5582 If a cpulist is passed as an argument, the specified 5583 list of CPUs is set to no-callback mode from boot. 5584 5585 Otherwise, if the '=' sign and the cpulist 5586 arguments are omitted, no CPU will be set to 5587 no-callback mode from boot but the mode may be 5588 toggled at runtime via cpusets. 5589 5590 Note that this argument takes precedence over 5591 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5592 5593 rcu_nocb_poll [KNL] 5594 Rather than requiring that offloaded CPUs 5595 (specified by rcu_nocbs= above) explicitly 5596 awaken the corresponding "rcuoN" kthreads, 5597 make these kthreads poll for callbacks. 5598 This improves the real-time response for the 5599 offloaded CPUs by relieving them of the need to 5600 wake up the corresponding kthread, but degrades 5601 energy efficiency by requiring that the kthreads 5602 periodically wake up to do the polling. 5603 5604 rcutree.blimit= [KNL] 5605 Set maximum number of finished RCU callbacks to 5606 process in one batch. 5607 5608 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5609 Do only a one-line RCU CPU stall warning when 5610 there is an ongoing too-long CSD-lock wait. 5611 5612 rcutree.do_rcu_barrier= [KNL] 5613 Wait for deferred kfree_rcu() frees and ordinary 5614 call_rcu() callbacks queued before this request to 5615 complete. This does not prevent new work from being 5616 queued concurrently. Requests are throttled so that 5617 userspace tests can safely hammer on the sysfs 5618 variable if they so choose. 5619 If triggered before the RCU grace-period machinery 5620 is fully active, this will error out with EAGAIN. 5621 5622 rcutree.dump_tree= [KNL] 5623 Dump the structure of the rcu_node combining tree 5624 out at early boot. This is used for diagnostic 5625 purposes, to verify correct tree setup. 5626 5627 rcutree.gp_cleanup_delay= [KNL] 5628 Set the number of jiffies to delay each step of 5629 RCU grace-period cleanup. 5630 5631 rcutree.gp_init_delay= [KNL] 5632 Set the number of jiffies to delay each step of 5633 RCU grace-period initialization. 5634 5635 rcutree.gp_preinit_delay= [KNL] 5636 Set the number of jiffies to delay each step of 5637 RCU grace-period pre-initialization, that is, 5638 the propagation of recent CPU-hotplug changes up 5639 the rcu_node combining tree. 5640 5641 rcutree.jiffies_till_first_fqs= [KNL] 5642 Set delay from grace-period initialization to 5643 first attempt to force quiescent states. 5644 Units are jiffies, minimum value is zero, 5645 and maximum value is HZ. 5646 5647 rcutree.jiffies_till_next_fqs= [KNL] 5648 Set delay between subsequent attempts to force 5649 quiescent states. Units are jiffies, minimum 5650 value is one, and maximum value is HZ. 5651 5652 rcutree.jiffies_till_sched_qs= [KNL] 5653 Set required age in jiffies for a 5654 given grace period before RCU starts 5655 soliciting quiescent-state help from 5656 rcu_note_context_switch() and cond_resched(). 5657 If not specified, the kernel will calculate 5658 a value based on the most recent settings 5659 of rcutree.jiffies_till_first_fqs 5660 and rcutree.jiffies_till_next_fqs. 5661 This calculated value may be viewed in 5662 rcutree.jiffies_to_sched_qs. Any attempt to set 5663 rcutree.jiffies_to_sched_qs will be cheerfully 5664 overwritten. 5665 5666 rcutree.kthread_prio= [KNL,BOOT] 5667 Set the SCHED_FIFO priority of the RCU per-CPU 5668 kthreads (rcuc/N). This value is also used for 5669 the priority of the RCU boost threads (rcub/N) 5670 and for the RCU grace-period kthreads (rcu_bh, 5671 rcu_preempt, and rcu_sched). If RCU_BOOST is 5672 set, valid values are 1-99 and the default is 1 5673 (the least-favored priority). Otherwise, when 5674 RCU_BOOST is not set, valid values are 0-99 and 5675 the default is zero (non-realtime operation). 5676 When RCU_NOCB_CPU is set, also adjust the 5677 priority of NOCB callback kthreads. 5678 5679 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5680 On callback-offloaded (rcu_nocbs) CPUs, 5681 RCU reduces the lock contention that would 5682 otherwise be caused by callback floods through 5683 use of the ->nocb_bypass list. However, in the 5684 common non-flooded case, RCU queues directly to 5685 the main ->cblist in order to avoid the extra 5686 overhead of the ->nocb_bypass list and its lock. 5687 But if there are too many callbacks queued during 5688 a single jiffy, RCU pre-queues the callbacks into 5689 the ->nocb_bypass queue. The definition of "too 5690 many" is supplied by this kernel boot parameter. 5691 5692 rcutree.nohz_full_patience_delay= [KNL] 5693 On callback-offloaded (rcu_nocbs) CPUs, avoid 5694 disturbing RCU unless the grace period has 5695 reached the specified age in milliseconds. 5696 Defaults to zero. Large values will be capped 5697 at five seconds. All values will be rounded down 5698 to the nearest value representable by jiffies. 5699 5700 rcutree.qhimark= [KNL] 5701 Set threshold of queued RCU callbacks beyond which 5702 batch limiting is disabled. 5703 5704 rcutree.qlowmark= [KNL] 5705 Set threshold of queued RCU callbacks below which 5706 batch limiting is re-enabled. 5707 5708 rcutree.qovld= [KNL] 5709 Set threshold of queued RCU callbacks beyond which 5710 RCU's force-quiescent-state scan will aggressively 5711 enlist help from cond_resched() and sched IPIs to 5712 help CPUs more quickly reach quiescent states. 5713 Set to less than zero to make this be set based 5714 on rcutree.qhimark at boot time and to zero to 5715 disable more aggressive help enlistment. 5716 5717 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5718 Set the page-cache refill delay (in milliseconds) 5719 in response to low-memory conditions. The range 5720 of permitted values is in the range 0:100000. 5721 5722 rcutree.rcu_divisor= [KNL] 5723 Set the shift-right count to use to compute 5724 the callback-invocation batch limit bl from 5725 the number of callbacks queued on this CPU. 5726 The result will be bounded below by the value of 5727 the rcutree.blimit kernel parameter. Every bl 5728 callbacks, the softirq handler will exit in 5729 order to allow the CPU to do other work. 5730 5731 Please note that this callback-invocation batch 5732 limit applies only to non-offloaded callback 5733 invocation. Offloaded callbacks are instead 5734 invoked in the context of an rcuoc kthread, which 5735 scheduler will preempt as it does any other task. 5736 5737 rcutree.rcu_fanout_exact= [KNL] 5738 Disable autobalancing of the rcu_node combining 5739 tree. This is used by rcutorture, and might 5740 possibly be useful for architectures having high 5741 cache-to-cache transfer latencies. 5742 5743 rcutree.rcu_fanout_leaf= [KNL] 5744 Change the number of CPUs assigned to each 5745 leaf rcu_node structure. Useful for very 5746 large systems, which will choose the value 64, 5747 and for NUMA systems with large remote-access 5748 latencies, which will choose a value aligned 5749 with the appropriate hardware boundaries. 5750 5751 rcutree.rcu_min_cached_objs= [KNL] 5752 Minimum number of objects which are cached and 5753 maintained per one CPU. Object size is equal 5754 to PAGE_SIZE. The cache allows to reduce the 5755 pressure to page allocator, also it makes the 5756 whole algorithm to behave better in low memory 5757 condition. 5758 5759 rcutree.rcu_nocb_gp_stride= [KNL] 5760 Set the number of NOCB callback kthreads in 5761 each group, which defaults to the square root 5762 of the number of CPUs. Larger numbers reduce 5763 the wakeup overhead on the global grace-period 5764 kthread, but increases that same overhead on 5765 each group's NOCB grace-period kthread. 5766 5767 rcutree.rcu_kick_kthreads= [KNL] 5768 Cause the grace-period kthread to get an extra 5769 wake_up() if it sleeps three times longer than 5770 it should at force-quiescent-state time. 5771 This wake_up() will be accompanied by a 5772 WARN_ONCE() splat and an ftrace_dump(). 5773 5774 rcutree.rcu_resched_ns= [KNL] 5775 Limit the time spend invoking a batch of RCU 5776 callbacks to the specified number of nanoseconds. 5777 By default, this limit is checked only once 5778 every 32 callbacks in order to limit the pain 5779 inflicted by local_clock() overhead. 5780 5781 rcutree.rcu_unlock_delay= [KNL] 5782 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5783 this specifies an rcu_read_unlock()-time delay 5784 in microseconds. This defaults to zero. 5785 Larger delays increase the probability of 5786 catching RCU pointer leaks, that is, buggy use 5787 of RCU-protected pointers after the relevant 5788 rcu_read_unlock() has completed. 5789 5790 rcutree.sysrq_rcu= [KNL] 5791 Commandeer a sysrq key to dump out Tree RCU's 5792 rcu_node tree with an eye towards determining 5793 why a new grace period has not yet started. 5794 5795 rcutree.use_softirq= [KNL] 5796 If set to zero, move all RCU_SOFTIRQ processing to 5797 per-CPU rcuc kthreads. Defaults to a non-zero 5798 value, meaning that RCU_SOFTIRQ is used by default. 5799 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5800 5801 But note that CONFIG_PREEMPT_RT=y kernels disable 5802 this kernel boot parameter, forcibly setting it 5803 to zero. 5804 5805 rcutree.enable_rcu_lazy= [KNL] 5806 To save power, batch RCU callbacks and flush after 5807 delay, memory pressure or callback list growing too 5808 big. 5809 5810 rcutree.rcu_normal_wake_from_gp= [KNL] 5811 Reduces a latency of synchronize_rcu() call. This approach 5812 maintains its own track of synchronize_rcu() callers, so it 5813 does not interact with regular callbacks because it does not 5814 use a call_rcu[_hurry]() path. Please note, this is for a 5815 normal grace period. 5816 5817 How to disable it: 5818 5819 echo 0 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5820 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=0" 5821 5822 Default is 1 if it is not explicitly disabled by the boot parameter 5823 passing 0. 5824 5825 rcuscale.gp_async= [KNL] 5826 Measure performance of asynchronous 5827 grace-period primitives such as call_rcu(). 5828 5829 rcuscale.gp_async_max= [KNL] 5830 Specify the maximum number of outstanding 5831 callbacks per writer thread. When a writer 5832 thread exceeds this limit, it invokes the 5833 corresponding flavor of rcu_barrier() to allow 5834 previously posted callbacks to drain. 5835 5836 rcuscale.gp_exp= [KNL] 5837 Measure performance of expedited synchronous 5838 grace-period primitives. 5839 5840 rcuscale.holdoff= [KNL] 5841 Set test-start holdoff period. The purpose of 5842 this parameter is to delay the start of the 5843 test until boot completes in order to avoid 5844 interference. 5845 5846 rcuscale.kfree_by_call_rcu= [KNL] 5847 In kernels built with CONFIG_RCU_LAZY=y, test 5848 call_rcu() instead of kfree_rcu(). 5849 5850 rcuscale.kfree_mult= [KNL] 5851 Instead of allocating an object of size kfree_obj, 5852 allocate one of kfree_mult * sizeof(kfree_obj). 5853 Defaults to 1. 5854 5855 rcuscale.kfree_rcu_test= [KNL] 5856 Set to measure performance of kfree_rcu() flooding. 5857 5858 rcuscale.kfree_rcu_test_double= [KNL] 5859 Test the double-argument variant of kfree_rcu(). 5860 If this parameter has the same value as 5861 rcuscale.kfree_rcu_test_single, both the single- 5862 and double-argument variants are tested. 5863 5864 rcuscale.kfree_rcu_test_single= [KNL] 5865 Test the single-argument variant of kfree_rcu(). 5866 If this parameter has the same value as 5867 rcuscale.kfree_rcu_test_double, both the single- 5868 and double-argument variants are tested. 5869 5870 rcuscale.kfree_nthreads= [KNL] 5871 The number of threads running loops of kfree_rcu(). 5872 5873 rcuscale.kfree_alloc_num= [KNL] 5874 Number of allocations and frees done in an iteration. 5875 5876 rcuscale.kfree_loops= [KNL] 5877 Number of loops doing rcuscale.kfree_alloc_num number 5878 of allocations and frees. 5879 5880 rcuscale.minruntime= [KNL] 5881 Set the minimum test run time in seconds. This 5882 does not affect the data-collection interval, 5883 but instead allows better measurement of things 5884 like CPU consumption. 5885 5886 rcuscale.nreaders= [KNL] 5887 Set number of RCU readers. The value -1 selects 5888 N, where N is the number of CPUs. A value 5889 "n" less than -1 selects N-n+1, where N is again 5890 the number of CPUs. For example, -2 selects N 5891 (the number of CPUs), -3 selects N+1, and so on. 5892 A value of "n" less than or equal to -N selects 5893 a single reader. 5894 5895 rcuscale.nwriters= [KNL] 5896 Set number of RCU writers. The values operate 5897 the same as for rcuscale.nreaders. 5898 N, where N is the number of CPUs 5899 5900 rcuscale.scale_type= [KNL] 5901 Specify the RCU implementation to test. 5902 5903 rcuscale.shutdown= [KNL] 5904 Shut the system down after performance tests 5905 complete. This is useful for hands-off automated 5906 testing. 5907 5908 rcuscale.verbose= [KNL] 5909 Enable additional printk() statements. 5910 5911 rcuscale.writer_holdoff= [KNL] 5912 Write-side holdoff between grace periods, 5913 in microseconds. The default of zero says 5914 no holdoff. 5915 5916 rcuscale.writer_holdoff_jiffies= [KNL] 5917 Additional write-side holdoff between grace 5918 periods, but in jiffies. The default of zero 5919 says no holdoff. 5920 5921 rcutorture.fqs_duration= [KNL] 5922 Set duration of force_quiescent_state bursts 5923 in microseconds. 5924 5925 rcutorture.fqs_holdoff= [KNL] 5926 Set holdoff time within force_quiescent_state bursts 5927 in microseconds. 5928 5929 rcutorture.fqs_stutter= [KNL] 5930 Set wait time between force_quiescent_state bursts 5931 in seconds. 5932 5933 rcutorture.fwd_progress= [KNL] 5934 Specifies the number of kthreads to be used 5935 for RCU grace-period forward-progress testing 5936 for the types of RCU supporting this notion. 5937 Defaults to 1 kthread, values less than zero or 5938 greater than the number of CPUs cause the number 5939 of CPUs to be used. 5940 5941 rcutorture.fwd_progress_div= [KNL] 5942 Specify the fraction of a CPU-stall-warning 5943 period to do tight-loop forward-progress testing. 5944 5945 rcutorture.fwd_progress_holdoff= [KNL] 5946 Number of seconds to wait between successive 5947 forward-progress tests. 5948 5949 rcutorture.fwd_progress_need_resched= [KNL] 5950 Enclose cond_resched() calls within checks for 5951 need_resched() during tight-loop forward-progress 5952 testing. 5953 5954 rcutorture.gp_cond= [KNL] 5955 Use conditional/asynchronous update-side 5956 normal-grace-period primitives, if available. 5957 5958 rcutorture.gp_cond_exp= [KNL] 5959 Use conditional/asynchronous update-side 5960 expedited-grace-period primitives, if available. 5961 5962 rcutorture.gp_cond_full= [KNL] 5963 Use conditional/asynchronous update-side 5964 normal-grace-period primitives that also take 5965 concurrent expedited grace periods into account, 5966 if available. 5967 5968 rcutorture.gp_cond_exp_full= [KNL] 5969 Use conditional/asynchronous update-side 5970 expedited-grace-period primitives that also take 5971 concurrent normal grace periods into account, 5972 if available. 5973 5974 rcutorture.gp_cond_wi= [KNL] 5975 Nominal wait interval for normal conditional 5976 grace periods (specified by rcutorture's 5977 gp_cond and gp_cond_full module parameters), 5978 in microseconds. The actual wait interval will 5979 be randomly selected to nanosecond granularity up 5980 to this wait interval. Defaults to 16 jiffies, 5981 for example, 16,000 microseconds on a system 5982 with HZ=1000. 5983 5984 rcutorture.gp_cond_wi_exp= [KNL] 5985 Nominal wait interval for expedited conditional 5986 grace periods (specified by rcutorture's 5987 gp_cond_exp and gp_cond_exp_full module 5988 parameters), in microseconds. The actual wait 5989 interval will be randomly selected to nanosecond 5990 granularity up to this wait interval. Defaults to 5991 128 microseconds. 5992 5993 rcutorture.gp_exp= [KNL] 5994 Use expedited update-side primitives, if available. 5995 5996 rcutorture.gp_normal= [KNL] 5997 Use normal (non-expedited) asynchronous 5998 update-side primitives, if available. 5999 6000 rcutorture.gp_poll= [KNL] 6001 Use polled update-side normal-grace-period 6002 primitives, if available. 6003 6004 rcutorture.gp_poll_exp= [KNL] 6005 Use polled update-side expedited-grace-period 6006 primitives, if available. 6007 6008 rcutorture.gp_poll_full= [KNL] 6009 Use polled update-side normal-grace-period 6010 primitives that also take concurrent expedited 6011 grace periods into account, if available. 6012 6013 rcutorture.gp_poll_exp_full= [KNL] 6014 Use polled update-side expedited-grace-period 6015 primitives that also take concurrent normal 6016 grace periods into account, if available. 6017 6018 rcutorture.gp_poll_wi= [KNL] 6019 Nominal wait interval for normal conditional 6020 grace periods (specified by rcutorture's 6021 gp_poll and gp_poll_full module parameters), 6022 in microseconds. The actual wait interval will 6023 be randomly selected to nanosecond granularity up 6024 to this wait interval. Defaults to 16 jiffies, 6025 for example, 16,000 microseconds on a system 6026 with HZ=1000. 6027 6028 rcutorture.gp_poll_wi_exp= [KNL] 6029 Nominal wait interval for expedited conditional 6030 grace periods (specified by rcutorture's 6031 gp_poll_exp and gp_poll_exp_full module 6032 parameters), in microseconds. The actual wait 6033 interval will be randomly selected to nanosecond 6034 granularity up to this wait interval. Defaults to 6035 128 microseconds. 6036 6037 rcutorture.gp_sync= [KNL] 6038 Use normal (non-expedited) synchronous 6039 update-side primitives, if available. If all 6040 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6041 rcutorture.gp_normal=, and rcutorture.gp_sync= 6042 are zero, rcutorture acts as if is interpreted 6043 they are all non-zero. 6044 6045 rcutorture.gpwrap_lag= [KNL] 6046 Enable grace-period wrap lag testing. Setting 6047 to false prevents the gpwrap lag test from 6048 running. Default is true. 6049 6050 rcutorture.gpwrap_lag_gps= [KNL] 6051 Set the value for grace-period wrap lag during 6052 active lag testing periods. This controls how many 6053 grace periods differences we tolerate between 6054 rdp and rnp's gp_seq before setting overflow flag. 6055 The default is always set to 8. 6056 6057 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6058 Set the total cycle duration for gpwrap lag 6059 testing in minutes. This is the total time for 6060 one complete cycle of active and inactive 6061 testing periods. Default is 30 minutes. 6062 6063 rcutorture.gpwrap_lag_active_mins= [KNL] 6064 Set the duration for which gpwrap lag is active 6065 within each cycle, in minutes. During this time, 6066 the grace-period wrap lag will be set to the 6067 value specified by gpwrap_lag_gps. Default is 6068 5 minutes. 6069 6070 rcutorture.irqreader= [KNL] 6071 Run RCU readers from irq handlers, or, more 6072 accurately, from a timer handler. Not all RCU 6073 flavors take kindly to this sort of thing. 6074 6075 rcutorture.leakpointer= [KNL] 6076 Leak an RCU-protected pointer out of the reader. 6077 This can of course result in splats, and is 6078 intended to test the ability of things like 6079 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6080 such leaks. 6081 6082 rcutorture.n_barrier_cbs= [KNL] 6083 Set callbacks/threads for rcu_barrier() testing. 6084 6085 rcutorture.nfakewriters= [KNL] 6086 Set number of concurrent RCU writers. These just 6087 stress RCU, they don't participate in the actual 6088 test, hence the "fake". 6089 6090 rcutorture.nmi_calls= [KNL] 6091 Enable issuing RCU callbacks from an NMI, on the 6092 RCU flavors that support it, to exercise the 6093 any-context callback path. Requires 6094 CONFIG_PERF_EVENTS and a hardware PMU; without 6095 both, nothing is issued. Defaults to enabled. 6096 6097 rcutorture.nocbs_nthreads= [KNL] 6098 Set number of RCU callback-offload togglers. 6099 Zero (the default) disables toggling. 6100 6101 rcutorture.nocbs_toggle= [KNL] 6102 Set the delay in milliseconds between successive 6103 callback-offload toggling attempts. 6104 6105 rcutorture.nreaders= [KNL] 6106 Set number of RCU readers. The value -1 selects 6107 N-1, where N is the number of CPUs. A value 6108 "n" less than -1 selects N-n-2, where N is again 6109 the number of CPUs. For example, -2 selects N 6110 (the number of CPUs), -3 selects N+1, and so on. 6111 6112 rcutorture.nwriters= [KNL] 6113 Set number of RCU writers, which must be either 6114 zero or one. For additional writers, use instead 6115 the rcutorture.nfakewriters parameter. 6116 6117 rcutorture.object_debug= [KNL] 6118 Enable debug-object double-call_rcu() testing. 6119 6120 rcutorture.onoff_holdoff= [KNL] 6121 Set time (s) after boot for CPU-hotplug testing. 6122 6123 rcutorture.onoff_interval= [KNL] 6124 Set time (jiffies) between CPU-hotplug operations, 6125 or zero to disable CPU-hotplug testing. 6126 6127 rcutorture.preempt_duration= [KNL] 6128 Set duration (in milliseconds) of preemptions 6129 by a high-priority FIFO real-time task. Set to 6130 zero (the default) to disable. The CPUs to 6131 preempt are selected randomly from the set that 6132 are online at a given point in time. Races with 6133 CPUs going offline are ignored, with that attempt 6134 at preemption skipped. 6135 6136 rcutorture.preempt_interval= [KNL] 6137 Set interval (in milliseconds, defaulting to one 6138 second) between preemptions by a high-priority 6139 FIFO real-time task. This delay is mediated 6140 by an hrtimer and is further fuzzed to avoid 6141 inadvertent synchronizations. 6142 6143 rcutorture.read_exit_burst= [KNL] 6144 The number of times in a given read-then-exit 6145 episode that a set of read-then-exit kthreads 6146 is spawned. 6147 6148 rcutorture.read_exit_delay= [KNL] 6149 The delay, in seconds, between successive 6150 read-then-exit testing episodes. 6151 6152 rcutorture.reader_flavor= [KNL] 6153 A bit mask indicating which readers to use. 6154 If there is more than one bit set, the readers 6155 are entered from low-order bit up, and are 6156 exited in the opposite order. For SRCU, the 6157 0x1 bit is normal readers, 0x2 NMI-safe readers, 6158 and 0x4 light-weight readers. 6159 6160 rcutorture.shuffle_interval= [KNL] 6161 Set task-shuffle interval (s). Shuffling tasks 6162 allows some CPUs to go into dyntick-idle mode 6163 during the rcutorture test. 6164 6165 rcutorture.shutdown_secs= [KNL] 6166 Set time (s) after boot system shutdown. This 6167 is useful for hands-off automated testing. 6168 6169 rcutorture.stall_cpu= [KNL] 6170 Duration of CPU stall (s) to test RCU CPU stall 6171 warnings, zero to disable. 6172 6173 rcutorture.stall_cpu_block= [KNL] 6174 Sleep while stalling if set. This will result 6175 in warnings from preemptible RCU in addition to 6176 any other stall-related activity. Note that 6177 in kernels built with CONFIG_PREEMPTION=n and 6178 CONFIG_PREEMPT_COUNT=y, this parameter will 6179 cause the CPU to pass through a quiescent state. 6180 Given CONFIG_PREEMPTION=n, this will suppress 6181 RCU CPU stall warnings, but will instead result 6182 in scheduling-while-atomic splats. 6183 6184 Use of this module parameter results in splats. 6185 6186 6187 rcutorture.stall_cpu_holdoff= [KNL] 6188 Time to wait (s) after boot before inducing stall. 6189 6190 rcutorture.stall_cpu_irqsoff= [KNL] 6191 Disable interrupts while stalling if set, but only 6192 on the first stall in the set. 6193 6194 rcutorture.stall_cpu_repeat= [KNL] 6195 Number of times to repeat the stall sequence, 6196 so that rcutorture.stall_cpu_repeat=3 will result 6197 in four stall sequences. 6198 6199 rcutorture.stall_gp_kthread= [KNL] 6200 Duration (s) of forced sleep within RCU 6201 grace-period kthread to test RCU CPU stall 6202 warnings, zero to disable. If both stall_cpu 6203 and stall_gp_kthread are specified, the 6204 kthread is starved first, then the CPU. 6205 6206 rcutorture.stall_only= [KNL] 6207 Shut off all rcutorture kthreads other than the 6208 RCU CPU stall-warning test kthreads. The purpose 6209 of this is to test production applictions' 6210 reactions to CPU stalls, and with minimal 6211 additional overhead. Or you can omit the 6212 stall-warning tests as well and get a heavy 6213 no-op, your choice! 6214 6215 rcutorture.stat_interval= [KNL] 6216 Time (s) between statistics printk()s. 6217 6218 rcutorture.stutter= [KNL] 6219 Time (s) to stutter testing, for example, specifying 6220 five seconds causes the test to run for five seconds, 6221 wait for five seconds, and so on. This tests RCU's 6222 ability to transition abruptly to and from idle. 6223 6224 rcutorture.test_boost= [KNL] 6225 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6226 "Maybe" means test if the RCU implementation 6227 under test support RCU priority boosting. 6228 6229 rcutorture.test_boost_duration= [KNL] 6230 Duration (s) of each individual boost test. 6231 6232 rcutorture.test_boost_holdoff= [KNL] 6233 Holdoff time (s) from start of test to the start 6234 of RCU priority-boost testing. Defaults to zero, 6235 that is, no holdoff. 6236 6237 rcutorture.test_boost_interval= [KNL] 6238 Interval (s) between each boost test. 6239 6240 rcutorture.test_no_idle_hz= [KNL] 6241 Test RCU's dyntick-idle handling. See also the 6242 rcutorture.shuffle_interval parameter. 6243 6244 rcutorture.torture_type= [KNL] 6245 Specify the RCU implementation to test. 6246 6247 rcutorture.verbose= [KNL] 6248 Enable additional printk() statements. 6249 6250 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6251 Dump ftrace buffer after reporting RCU CPU 6252 stall warning. 6253 6254 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6255 Provide RCU CPU stall notifiers, but see the 6256 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6257 option's help text. TL;DR: You almost certainly 6258 do not want rcupdate.rcu_cpu_stall_notifiers. 6259 6260 rcupdate.rcu_cpu_stall_suppress= [KNL] 6261 Suppress RCU CPU stall warning messages. 6262 6263 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6264 Suppress RCU CPU stall warning messages and 6265 rcutorture writer stall warnings that occur 6266 during early boot, that is, during the time 6267 before the init task is spawned. 6268 6269 rcupdate.rcu_cpu_stall_timeout= [KNL] 6270 Set timeout for RCU CPU stall warning messages. 6271 The value is in seconds and the maximum allowed 6272 value is 300 seconds. 6273 6274 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6275 Set timeout for expedited RCU CPU stall warning 6276 messages. The value is in milliseconds 6277 and the maximum allowed value is 21000 6278 milliseconds. Please note that this value is 6279 adjusted to an arch timer tick resolution. 6280 Setting this to zero causes the value from 6281 rcupdate.rcu_cpu_stall_timeout to be used (after 6282 conversion from seconds to milliseconds). 6283 6284 rcupdate.rcu_cpu_stall_cputime= [KNL] 6285 Provide statistics on the cputime and count of 6286 interrupts and tasks during the sampling period. For 6287 multiple continuous RCU stalls, all sampling periods 6288 begin at half of the first RCU stall timeout. 6289 6290 rcupdate.rcu_exp_stall_task_details= [KNL] 6291 Print stack dumps of any tasks blocking the 6292 current expedited RCU grace period during an 6293 expedited RCU CPU stall warning. 6294 6295 rcupdate.rcu_expedited= [KNL] 6296 Use expedited grace-period primitives, for 6297 example, synchronize_rcu_expedited() instead 6298 of synchronize_rcu(). This reduces latency, 6299 but can increase CPU utilization, degrade 6300 real-time latency, and degrade energy efficiency. 6301 No effect on CONFIG_TINY_RCU kernels. 6302 6303 rcupdate.rcu_normal= [KNL] 6304 Use only normal grace-period primitives, 6305 for example, synchronize_rcu() instead of 6306 synchronize_rcu_expedited(). This improves 6307 real-time latency, CPU utilization, and 6308 energy efficiency, but can expose users to 6309 increased grace-period latency. This parameter 6310 overrides rcupdate.rcu_expedited. No effect on 6311 CONFIG_TINY_RCU kernels. 6312 6313 rcupdate.rcu_normal_after_boot= [KNL] 6314 Once boot has completed (that is, after 6315 rcu_end_inkernel_boot() has been invoked), use 6316 only normal grace-period primitives. No effect 6317 on CONFIG_TINY_RCU kernels. 6318 6319 But note that CONFIG_PREEMPT_RT=y kernels enables 6320 this kernel boot parameter, forcibly setting 6321 it to the value one, that is, converting any 6322 post-boot attempt at an expedited RCU grace 6323 period to instead use normal non-expedited 6324 grace-period processing. 6325 6326 rcupdate.rcu_task_collapse_debug= [KNL] 6327 Enable debugging prints that record when RCU Tasks 6328 and RCU Tasks Trace expand to per-CPU callback 6329 queuing and collapse back to CPU-0 queuing. 6330 This is default-disabled due to the fact that 6331 some workloads can make it quite noisy. 6332 6333 rcupdate.rcu_task_collapse_lim= [KNL] 6334 Set the maximum number of callbacks present 6335 at the beginning of a grace period that allows 6336 the RCU Tasks flavors to collapse back to using 6337 a single callback queue. This switching only 6338 occurs when rcupdate.rcu_task_enqueue_lim is 6339 set to the default value of -1. 6340 6341 rcupdate.rcu_task_contend_lim= [KNL] 6342 Set the minimum number of callback-queuing-time 6343 lock-contention events per jiffy required to 6344 cause the RCU Tasks flavors to switch to per-CPU 6345 callback queuing. This switching only occurs 6346 when rcupdate.rcu_task_enqueue_lim is set to 6347 the default value of -1. 6348 6349 rcupdate.rcu_task_enqueue_lim= [KNL] 6350 Set the number of callback queues to use for the 6351 RCU Tasks family of RCU flavors. The default 6352 of -1 allows this to be automatically (and 6353 dynamically) adjusted. This parameter is intended 6354 for use in testing. 6355 6356 rcupdate.rcu_task_lazy_lim= [KNL] 6357 Number of callbacks on a given CPU that will 6358 cancel laziness on that CPU. Use -1 to disable 6359 cancellation of laziness, but be advised that 6360 doing so increases the danger of OOM due to 6361 callback flooding. 6362 6363 rcupdate.rcu_task_stall_info= [KNL] 6364 Set initial timeout in jiffies for RCU task stall 6365 informational messages, which give some indication 6366 of the problem for those not patient enough to 6367 wait for ten minutes. Informational messages are 6368 only printed prior to the stall-warning message 6369 for a given grace period. Disable with a value 6370 less than or equal to zero. Defaults to ten 6371 seconds. A change in value does not take effect 6372 until the beginning of the next grace period. 6373 6374 rcupdate.rcu_task_stall_info_mult= [KNL] 6375 Multiplier for time interval between successive 6376 RCU task stall informational messages for a given 6377 RCU tasks grace period. This value is clamped 6378 to one through ten, inclusive. It defaults to 6379 the value three, so that the first informational 6380 message is printed 10 seconds into the grace 6381 period, the second at 40 seconds, the third at 6382 160 seconds, and then the stall warning at 600 6383 seconds would prevent a fourth at 640 seconds. 6384 6385 rcupdate.rcu_task_stall_timeout= [KNL] 6386 Set timeout in jiffies for RCU task stall 6387 warning messages. Disable with a value less 6388 than or equal to zero. Defaults to ten minutes. 6389 A change in value does not take effect until 6390 the beginning of the next grace period. 6391 6392 rcupdate.rcu_tasks_lazy_ms= [KNL] 6393 Set timeout in milliseconds RCU Tasks asynchronous 6394 callback batching for call_rcu_tasks(). 6395 A negative value will take the default. A value 6396 of zero will disable batching. Batching is 6397 always disabled for synchronize_rcu_tasks(). 6398 6399 rcupdate.rcu_self_test= [KNL] 6400 Run the RCU early boot self tests 6401 6402 rdinit= [KNL] 6403 Format: <full_path> 6404 Run specified binary instead of /init from the ramdisk, 6405 used for early userspace startup. See initrd. 6406 6407 rdrand= [X86,EARLY] 6408 force - Override the decision by the kernel to hide the 6409 advertisement of RDRAND support (this affects 6410 certain AMD processors because of buggy BIOS 6411 support, specifically around the suspend/resume 6412 path). 6413 6414 rdt= [HW,X86,RDT] 6415 Turn on/off individual RDT features. List is: 6416 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6417 mba, smba, bmec, abmc, sdciae, energy[:guid], 6418 perf[:guid]. 6419 E.g. to turn on cmt and turn off mba use: 6420 rdt=cmt,!mba 6421 To turn off all energy telemetry monitoring and ensure that 6422 perf telemetry monitoring associated with guid 0x12345 6423 is enabled use: 6424 rdt=!energy,perf:0x12345 6425 6426 reboot= [KNL] 6427 Format (x86 or x86_64): 6428 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6429 [[,]s[mp]####] \ 6430 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6431 [[,]f[orce]] 6432 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6433 (prefix with 'panic_' to set mode for panic 6434 reboot only), 6435 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6436 reboot_force is either force or not specified, 6437 reboot_cpu is s[mp]#### with #### being the processor 6438 to be used for rebooting. 6439 6440 acpi 6441 Use the ACPI RESET_REG in the FADT. If ACPI is not 6442 configured or the ACPI reset does not work, the reboot 6443 path attempts the reset using the keyboard controller. 6444 6445 bios 6446 Use the CPU reboot vector for warm reset 6447 6448 cold 6449 Set the cold reboot flag 6450 6451 default 6452 There are some built-in platform specific "quirks" 6453 - you may see: "reboot: <name> series board detected. 6454 Selecting <type> for reboots." In the case where you 6455 think the quirk is in error (e.g. you have newer BIOS, 6456 or newer board) using this option will ignore the 6457 built-in quirk table, and use the generic default 6458 reboot actions. 6459 6460 efi 6461 Use efi reset_system runtime service. If EFI is not 6462 configured or the EFI reset does not work, the reboot 6463 path attempts the reset using the keyboard controller. 6464 6465 force 6466 Don't stop other CPUs on reboot. This can make reboot 6467 more reliable in some cases. 6468 6469 kbd 6470 Use the keyboard controller. cold reset (default) 6471 6472 pci 6473 Use a write to the PCI config space register 0xcf9 to 6474 trigger reboot. 6475 6476 triple 6477 Force a triple fault (init) 6478 6479 warm 6480 Don't set the cold reboot flag 6481 6482 Using warm reset will be much faster especially on big 6483 memory systems because the BIOS will not go through 6484 the memory check. Disadvantage is that not all 6485 hardware will be completely reinitialized on reboot so 6486 there may be boot problems on some systems. 6487 6488 6489 refscale.holdoff= [KNL] 6490 Set test-start holdoff period. The purpose of 6491 this parameter is to delay the start of the 6492 test until boot completes in order to avoid 6493 interference. 6494 6495 refscale.lookup_instances= [KNL] 6496 Number of data elements to use for the forms of 6497 SLAB_TYPESAFE_BY_RCU testing. A negative number 6498 is negated and multiplied by nr_cpu_ids, while 6499 zero specifies nr_cpu_ids. 6500 6501 refscale.loops= [KNL] 6502 Set the number of loops over the synchronization 6503 primitive under test. Increasing this number 6504 reduces noise due to loop start/end overhead, 6505 but the default has already reduced the per-pass 6506 noise to a handful of picoseconds on ca. 2020 6507 x86 laptops. 6508 6509 refscale.nreaders= [KNL] 6510 Set number of readers. The default value of -1 6511 selects N, where N is roughly 75% of the number 6512 of CPUs. A value of zero is an interesting choice. 6513 6514 refscale.nruns= [KNL] 6515 Set number of runs, each of which is dumped onto 6516 the console log. 6517 6518 refscale.readdelay= [KNL] 6519 Set the read-side critical-section duration, 6520 measured in microseconds. 6521 6522 refscale.scale_type= [KNL] 6523 Specify the read-protection implementation to test. 6524 6525 refscale.shutdown= [KNL] 6526 Shut down the system at the end of the performance 6527 test. This defaults to 1 (shut it down) when 6528 refscale is built into the kernel and to 0 (leave 6529 it running) when refscale is built as a module. 6530 6531 refscale.verbose= [KNL] 6532 Enable additional printk() statements. 6533 6534 refscale.verbose_batched= [KNL] 6535 Batch the additional printk() statements. If zero 6536 (the default) or negative, print everything. Otherwise, 6537 print every Nth verbose statement, where N is the value 6538 specified. 6539 6540 regulator_ignore_unused 6541 [REGULATOR] 6542 Prevents regulator framework from disabling regulators 6543 that are unused, due no driver claiming them. This may 6544 be useful for debug and development, but should not be 6545 needed on a platform with proper driver support. 6546 6547 relax_domain_level= 6548 [KNL, SMP] Set scheduler's default relax_domain_level. 6549 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6550 6551 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6552 Format: <base1>,<size1>[,<base2>,<size2>,...] 6553 Reserve I/O ports or memory so the kernel won't use 6554 them. If <base> is less than 0x10000, the region 6555 is assumed to be I/O ports; otherwise it is memory. 6556 6557 reserve_mem= [MM] 6558 Format: nn[KMG]:<align>:<label> 6559 Reserve physical memory and label it with a name that 6560 other subsystems can use to access it. This is typically 6561 used for systems that do not wipe the RAM, and this command 6562 line will try to reserve the same physical memory on 6563 soft reboots. Note, it is not guaranteed to be the same 6564 location. For example, if anything about the system changes 6565 or if booting a different kernel. It can also fail if KASLR 6566 places the kernel at the location of where the RAM reservation 6567 was from a previous boot, the new reservation will be at a 6568 different location. 6569 Any subsystem using this feature must add a way to verify 6570 that the contents of the physical memory is from a previous 6571 boot, as there may be cases where the memory will not be 6572 located at the same location. 6573 6574 The format is size:align:label for example, to request 6575 12 megabytes of 4096 alignment for ramoops: 6576 6577 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6578 6579 reservetop= [X86-32,EARLY] 6580 Format: nn[KMG] 6581 Reserves a hole at the top of the kernel virtual 6582 address space. 6583 6584 reset_devices [KNL] Force drivers to reset the underlying device 6585 during initialization. 6586 6587 resume= [SWSUSP] 6588 Specify the partition device for software suspend 6589 Format: 6590 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6591 6592 resume_offset= [SWSUSP] 6593 Specify the offset from the beginning of the partition 6594 given by "resume=" at which the swap header is located, 6595 in <PAGE_SIZE> units (needed only for swap files). 6596 See Documentation/power/swsusp-and-swap-files.rst 6597 6598 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6599 read the resume files 6600 6601 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6602 Useful for devices that are detected asynchronously 6603 (e.g. USB and MMC devices). 6604 6605 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6606 be accessible via /sys/firmware/initrd. 6607 6608 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6609 Speculative Code Execution with Return Instructions) 6610 vulnerability. 6611 6612 AMD-based UNRET and IBPB mitigations alone do not stop 6613 sibling threads from influencing the predictions of other 6614 sibling threads. For that reason, STIBP is used on pro- 6615 cessors that support it, and mitigate SMT on processors 6616 that don't. 6617 6618 off - no mitigation 6619 auto - automatically select a mitigation 6620 auto,nosmt - automatically select a mitigation, 6621 disabling SMT if necessary for 6622 the full mitigation (only on Zen1 6623 and older without STIBP). 6624 ibpb - On AMD, mitigate short speculation 6625 windows on basic block boundaries too. 6626 Safe, highest perf impact. It also 6627 enables STIBP if present. Not suitable 6628 on Intel. 6629 ibpb,nosmt - Like "ibpb" above but will disable SMT 6630 when STIBP is not available. This is 6631 the alternative for systems which do not 6632 have STIBP. 6633 unret - Force enable untrained return thunks, 6634 only effective on AMD f15h-f17h based 6635 systems. 6636 unret,nosmt - Like unret, but will disable SMT when STIBP 6637 is not available. This is the alternative for 6638 systems which do not have STIBP. 6639 6640 Selecting 'auto' will choose a mitigation method at run 6641 time according to the CPU. 6642 6643 Not specifying this option is equivalent to retbleed=auto. 6644 6645 rfkill.default_state= 6646 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6647 etc. communication is blocked by default. 6648 1 Unblocked. 6649 6650 rfkill.master_switch_mode= 6651 0 The "airplane mode" button does nothing. 6652 1 The "airplane mode" button toggles between everything 6653 blocked and the previous configuration. 6654 2 The "airplane mode" button toggles between everything 6655 blocked and everything unblocked. 6656 6657 ring3mwait=disable 6658 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6659 CPUs. 6660 6661 riscv_isa_fallback [RISCV,EARLY] 6662 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6663 falling back to detecting extension support by parsing 6664 "riscv,isa" property on devicetree systems when the 6665 replacement properties are not found. See the Kconfig 6666 entry for RISCV_ISA_FALLBACK. 6667 6668 riscv_nousercfi= 6669 all Disable user CFI ABI to userspace even if cpu extension 6670 are available. 6671 bcfi Disable user backward CFI ABI to userspace even if 6672 the shadow stack extension is available. 6673 fcfi Disable user forward CFI ABI to userspace even if the 6674 landing pad extension is available. 6675 6676 ro [KNL] Mount root device read-only on boot 6677 6678 rodata= [KNL,EARLY] 6679 on Mark read-only kernel memory as read-only (default). 6680 off Leave read-only kernel memory writable for debugging. 6681 noalias Mark read-only kernel memory as read-only but retain 6682 writable aliases in the direct map for regions outside 6683 of the kernel image. [arm64] 6684 6685 rockchip.usb_uart 6686 [EARLY] 6687 Enable the uart passthrough on the designated usb port 6688 on Rockchip SoCs. When active, the signals of the 6689 debug-uart get routed to the D+ and D- pins of the usb 6690 port and the regular usb controller gets disabled. 6691 6692 root= [KNL] Root filesystem 6693 Usually this is a block device specifier of some kind, 6694 see the early_lookup_bdev comment in 6695 block/early-lookup.c for details. 6696 Alternatively this can be "ram" for the legacy initial 6697 ramdisk, "nfs" and "cifs" for root on a network file 6698 system, or "mtd" and "ubi" for mounting from raw flash. 6699 6700 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6701 mount the root filesystem 6702 6703 rootflags= [KNL] Set root filesystem mount option string 6704 6705 rseq_slice_ext= [KNL] RSEQ based time slice extension 6706 Format: boolean 6707 Control enablement of RSEQ based time slice extension. 6708 Default is 'on'. 6709 6710 initramfs_options= [KNL] 6711 Specify mount options for the initramfs mount. 6712 6713 rootfstype= [KNL] Set root filesystem type 6714 6715 rootwait [KNL] Wait (indefinitely) for root device to show up. 6716 Useful for devices that are detected asynchronously 6717 (e.g. USB and MMC devices). 6718 6719 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6720 to show up before attempting to mount the root 6721 filesystem. 6722 6723 rproc_mem=nn[KMG][@address] 6724 [KNL,ARM,CMA] Remoteproc physical memory block. 6725 Memory area to be used by remote processor image, 6726 managed by CMA. 6727 6728 rseq_debug= [KNL] Enable or disable restartable sequence 6729 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6730 Format: <bool> 6731 6732 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6733 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6734 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6735 Format: <bool> 6736 6737 rw [KNL] Mount root device read-write on boot 6738 6739 S [KNL] Run init in single mode 6740 6741 s390_iommu= [HW,S390] 6742 Set s390 IOTLB flushing mode 6743 strict 6744 With strict flushing every unmap operation will result 6745 in an IOTLB flush. Default is lazy flushing before 6746 reuse, which is faster. Deprecated, equivalent to 6747 iommu.strict=1. 6748 6749 s390_iommu_aperture= [KNL,S390] 6750 Specifies the size of the per device DMA address space 6751 accessible through the DMA and IOMMU APIs as a decimal 6752 factor of the size of main memory. 6753 The default is 1 meaning that one can concurrently use 6754 as many DMA addresses as physical memory is installed, 6755 if supported by hardware, and thus map all of memory 6756 once. With a value of 2 one can map all of memory twice 6757 and so on. As a special case a factor of 0 imposes no 6758 restrictions other than those given by hardware at the 6759 cost of significant additional memory use for tables. 6760 6761 6762 sched_proxy_exec= [KNL] 6763 Enables or disables "proxy execution" style 6764 solution to mutex-based priority inversion. 6765 Format: <bool> 6766 6767 sched_smt_asym_packing= [KNL,SMP] 6768 Format: on 6769 Force asymmetric packing at the SMT scheduling domain. 6770 Idle CPU selection prefers siblings with a higher 6771 arch_asym_cpu_priority(). The default implementation 6772 prefers lower-numbered logical CPUs, but architecture 6773 overrides remain authoritative. Equal priorities do 6774 not establish a sibling preference. For example, x86 6775 with CONFIG_SCHED_MC_PRIO normally assigns the same 6776 core priority to both SMT siblings, so this option 6777 does not favor either sibling. 6778 6779 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6780 6781 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6782 Allowed values are enable and disable. This feature 6783 incurs a small amount of overhead in the scheduler 6784 but is useful for debugging and performance tuning. 6785 6786 sched_thermal_decay_shift= 6787 [Deprecated] 6788 [KNL, SMP] Set a decay shift for scheduler thermal 6789 pressure signal. Thermal pressure signal follows the 6790 default decay period of other scheduler pelt 6791 signals(usually 32 ms but configurable). Setting 6792 sched_thermal_decay_shift will left shift the decay 6793 period for the thermal pressure signal by the shift 6794 value. 6795 i.e. with the default pelt decay period of 32 ms 6796 sched_thermal_decay_shift thermal pressure decay pr 6797 1 64 ms 6798 2 128 ms 6799 and so on. 6800 Format: integer between 0 and 10 6801 Default is 0. 6802 6803 scftorture.holdoff= [KNL] 6804 Number of seconds to hold off before starting 6805 test. Defaults to zero for module insertion and 6806 to 10 seconds for built-in smp_call_function() 6807 tests. 6808 6809 scftorture.longwait= [KNL] 6810 Request ridiculously long waits randomly selected 6811 up to the chosen limit in seconds. Zero (the 6812 default) disables this feature. Please note 6813 that requesting even small non-zero numbers of 6814 seconds can result in RCU CPU stall warnings, 6815 softlockup complaints, and so on. 6816 6817 scftorture.nthreads= [KNL] 6818 Number of kthreads to spawn to invoke the 6819 smp_call_function() family of functions. 6820 The default of -1 specifies a number of kthreads 6821 equal to the number of CPUs. 6822 6823 scftorture.onoff_holdoff= [KNL] 6824 Number seconds to wait after the start of the 6825 test before initiating CPU-hotplug operations. 6826 6827 scftorture.onoff_interval= [KNL] 6828 Number seconds to wait between successive 6829 CPU-hotplug operations. Specifying zero (which 6830 is the default) disables CPU-hotplug operations. 6831 6832 scftorture.shutdown_secs= [KNL] 6833 The number of seconds following the start of the 6834 test after which to shut down the system. The 6835 default of zero avoids shutting down the system. 6836 Non-zero values are useful for automated tests. 6837 6838 scftorture.stat_interval= [KNL] 6839 The number of seconds between outputting the 6840 current test statistics to the console. A value 6841 of zero disables statistics output. 6842 6843 scftorture.stutter_cpus= [KNL] 6844 The number of jiffies to wait between each change 6845 to the set of CPUs under test. 6846 6847 scftorture.use_cpus_read_lock= [KNL] 6848 Use use_cpus_read_lock() instead of the default 6849 preempt_disable() to disable CPU hotplug 6850 while invoking one of the smp_call_function*() 6851 functions. 6852 6853 scftorture.verbose= [KNL] 6854 Enable additional printk() statements. 6855 6856 scftorture.weight_single= [KNL] 6857 The probability weighting to use for the 6858 smp_call_function_single() function with a zero 6859 "wait" parameter. A value of -1 selects the 6860 default if all other weights are -1. However, 6861 if at least one weight has some other value, a 6862 value of -1 will instead select a weight of zero. 6863 6864 scftorture.weight_single_wait= [KNL] 6865 The probability weighting to use for the 6866 smp_call_function_single() function with a 6867 non-zero "wait" parameter. See weight_single. 6868 6869 scftorture.weight_many= [KNL] 6870 The probability weighting to use for the 6871 smp_call_function_many() function with a zero 6872 "wait" parameter. See weight_single. 6873 Note well that setting a high probability for 6874 this weighting can place serious IPI load 6875 on the system. 6876 6877 scftorture.weight_many_wait= [KNL] 6878 The probability weighting to use for the 6879 smp_call_function_many() function with a 6880 non-zero "wait" parameter. See weight_single 6881 and weight_many. 6882 6883 scftorture.weight_all= [KNL] 6884 The probability weighting to use for the 6885 smp_call_function_all() function with a zero 6886 "wait" parameter. See weight_single and 6887 weight_many. 6888 6889 scftorture.weight_all_wait= [KNL] 6890 The probability weighting to use for the 6891 smp_call_function_all() function with a 6892 non-zero "wait" parameter. See weight_single 6893 and weight_many. 6894 6895 sdw_mclk_divider=[SDW] 6896 Specify the MCLK divider for Intel SoundWire buses in 6897 case the BIOS does not provide the clock rate properly. 6898 6899 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6900 xtime_lock contention on larger systems, and/or RCU lock 6901 contention on all systems with CONFIG_MAXSMP set. 6902 Format: { "0" | "1" } 6903 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1") 6904 1 -- enable. 6905 Note: increases power consumption, thus should only be 6906 enabled if running jitter sensitive (HPC/RT) workloads. 6907 6908 security= [SECURITY] Choose a legacy "major" security module to 6909 enable at boot. This has been deprecated by the 6910 "lsm=" parameter. 6911 6912 selinux= [SELINUX] Disable or enable SELinux at boot time. 6913 Format: { "0" | "1" } 6914 See security/selinux/Kconfig help text. 6915 0 -- disable. 6916 1 -- enable. 6917 Default value is 1. 6918 6919 serialnumber [BUGS=X86-32] 6920 6921 sev=option[,option...] [X86-64] 6922 6923 debug 6924 Enable debug messages. 6925 6926 nosnp 6927 Do not enable SEV-SNP (applies to host/hypervisor 6928 only). Setting 'nosnp' avoids the RMP check overhead 6929 in memory accesses when users do not want to run 6930 SEV-SNP guests. 6931 6932 shapers= [NET] 6933 Maximal number of shapers. 6934 6935 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6936 Limit apic dumping. The parameter defines the maximal 6937 number of local apics being dumped. Also it is possible 6938 to set it to "all" by meaning -- no limit here. 6939 Format: { 1 (default) | 2 | ... | all }. 6940 The parameter valid if only apic=debug or 6941 apic=verbose is specified. 6942 Example: apic=debug show_lapic=all 6943 6944 slab_debug[=options[,slabs][;[options[,slabs]]...]] [MM] 6945 Enabling slab_debug allows one to determine the 6946 culprit if slab objects become corrupted. Enabling 6947 slab_debug can create guard zones around objects and 6948 may poison objects when not in use. Also tracks the 6949 last alloc / free. For more information see 6950 Documentation/admin-guide/mm/slab.rst. 6951 (slub_debug legacy name also accepted for now) 6952 6953 Using this option implies the "no_hash_pointers" 6954 option which can be undone by adding the 6955 "hash_pointers=always" option. 6956 6957 slab_max_order= [MM] 6958 Determines the maximum allowed order for slabs. 6959 A high setting may cause OOMs due to memory 6960 fragmentation. For more information see 6961 Documentation/admin-guide/mm/slab.rst. 6962 (slub_max_order legacy name also accepted for now) 6963 6964 slab_merge [MM] 6965 Enable merging of slabs with similar size when the 6966 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6967 (slub_merge legacy name also accepted for now) 6968 6969 slab_min_objects= [MM] 6970 The minimum number of objects per slab. SLUB will 6971 increase the slab order up to slab_max_order to 6972 generate a sufficiently large slab able to contain 6973 the number of objects indicated. The higher the number 6974 of objects the smaller the overhead of tracking slabs 6975 and the less frequently locks need to be acquired. 6976 For more information see 6977 Documentation/admin-guide/mm/slab.rst. 6978 (slub_min_objects legacy name also accepted for now) 6979 6980 slab_min_order= [MM] 6981 Determines the minimum page order for slabs. Must be 6982 lower or equal to slab_max_order. For more information see 6983 Documentation/admin-guide/mm/slab.rst. 6984 (slub_min_order legacy name also accepted for now) 6985 6986 slab_nomerge [MM] 6987 Disable merging of slabs with similar size. May be 6988 necessary if there is some reason to distinguish 6989 allocs to different slabs, especially in hardened 6990 environments where the risk of heap overflows and 6991 layout control by attackers can usually be 6992 frustrated by disabling merging. This will reduce 6993 most of the exposure of a heap attack to a single 6994 cache (risks via metadata attacks are mostly 6995 unchanged). Debug options disable merging on their 6996 own. 6997 For more information see 6998 Documentation/admin-guide/mm/slab.rst. 6999 (slub_nomerge legacy name also accepted for now) 7000 7001 slab_strict_numa [MM] 7002 Support memory policies on a per object level 7003 in the slab allocator. The default is for memory 7004 policies to be applied at the folio level when 7005 a new folio is needed or a partial folio is 7006 retrieved from the lists. Increases overhead 7007 in the slab fastpaths but gains more accurate 7008 NUMA kernel object placement which helps with slow 7009 interconnects in NUMA systems. 7010 7011 slram= [HW,MTD] 7012 7013 smart2= [HW] 7014 Format: <io1>[,<io2>[,...,<io8>]] 7015 7016 smp.csd_lock_timeout= [KNL] 7017 Specify the period of time in milliseconds 7018 that smp_call_function() and friends will wait 7019 for a CPU to release the CSD lock. This is 7020 useful when diagnosing bugs involving CPUs 7021 disabling interrupts for extended periods 7022 of time. Defaults to 5,000 milliseconds, and 7023 setting a value of zero disables this feature. 7024 This feature may be more efficiently disabled 7025 using the csdlock_debug- kernel parameter. 7026 7027 smp.panic_on_ipistall= [KNL] 7028 If a csd_lock_timeout extends for more than 7029 the specified number of milliseconds, panic the 7030 system. By default, let CSD-lock acquisition 7031 take as long as they take. Specifying 300,000 7032 for this value provides a 5-minute timeout. 7033 7034 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7035 (logical CPUs) to use per physical CPU on systems 7036 capable of symmetric multithreading (SMT). Will 7037 be capped to the actual hardware limit. 7038 Format: <integer> 7039 Default: -1 (no limit) 7040 7041 softlockup_panic= 7042 [KNL] Should the soft-lockup detector generate panics. 7043 Format: <int> 7044 7045 A value of non-zero instructs the soft-lockup detector 7046 to panic the machine when a soft-lockup duration exceeds 7047 N thresholds. It is also controlled by the kernel.softlockup_panic 7048 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7049 respective build-time switch to that functionality. 7050 7051 softlockup_all_cpu_backtrace= 7052 [KNL] Should the soft-lockup detector generate 7053 backtraces on all cpus. 7054 Format: 0 | 1 7055 7056 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7057 See Documentation/admin-guide/laptops/sonypi.rst 7058 7059 spectre_bhi= [X86] Control mitigation of Branch History Injection 7060 (BHI) vulnerability. This setting affects the 7061 deployment of the HW BHI control and the SW BHB 7062 clearing sequence. 7063 7064 on - (default) Enable the HW or SW mitigation as 7065 needed. This protects the kernel from 7066 both syscalls and VMs. 7067 vmexit - On systems which don't have the HW mitigation 7068 available, enable the SW mitigation on vmexit 7069 ONLY. On such systems, the host kernel is 7070 protected from VM-originated BHI attacks, but 7071 may still be vulnerable to syscall attacks. 7072 off - Disable the mitigation. 7073 7074 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7075 (indirect branch speculation) vulnerability. 7076 The default operation protects the kernel from 7077 user space attacks. 7078 7079 on - unconditionally enable, implies 7080 spectre_v2_user=on 7081 off - unconditionally disable, implies 7082 spectre_v2_user=off 7083 auto - kernel detects whether your CPU model is 7084 vulnerable 7085 7086 Selecting 'on' will, and 'auto' may, choose a 7087 mitigation method at run time according to the 7088 CPU, the available microcode, the setting of the 7089 CONFIG_MITIGATION_RETPOLINE configuration option, 7090 and the compiler with which the kernel was built. 7091 7092 Selecting 'on' will also enable the mitigation 7093 against user space to user space task attacks. 7094 Selecting specific mitigation does not force enable 7095 user mitigations. 7096 7097 Selecting 'off' will disable both the kernel and 7098 the user space protections. 7099 7100 Specific mitigations can also be selected manually: 7101 7102 retpoline - replace indirect branches 7103 retpoline,generic - Retpolines 7104 retpoline,lfence - LFENCE; indirect branch 7105 retpoline,amd - alias for retpoline,lfence 7106 eibrs - Enhanced/Auto IBRS 7107 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7108 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7109 ibrs - use IBRS to protect kernel 7110 7111 Not specifying this option is equivalent to 7112 spectre_v2=auto. 7113 7114 spectre_v2_user= 7115 [X86] Control mitigation of Spectre variant 2 7116 (indirect branch speculation) vulnerability between 7117 user space tasks 7118 7119 on - Unconditionally enable mitigations. Is 7120 enforced by spectre_v2=on 7121 7122 off - Unconditionally disable mitigations. Is 7123 enforced by spectre_v2=off 7124 7125 prctl - Indirect branch speculation is enabled, 7126 but mitigation can be enabled via prctl 7127 per thread. The mitigation control state 7128 is inherited on fork. 7129 7130 prctl,ibpb 7131 - Like "prctl" above, but only STIBP is 7132 controlled per thread. IBPB is issued 7133 always when switching between different user 7134 space processes. 7135 7136 seccomp 7137 - Same as "prctl" above, but all seccomp 7138 threads will enable the mitigation unless 7139 they explicitly opt out. 7140 7141 seccomp,ibpb 7142 - Like "seccomp" above, but only STIBP is 7143 controlled per thread. IBPB is issued 7144 always when switching between different 7145 user space processes. 7146 7147 auto - Kernel selects the mitigation depending on 7148 the available CPU features and vulnerability. 7149 7150 Default mitigation: "prctl" 7151 7152 Not specifying this option is equivalent to 7153 spectre_v2_user=auto. 7154 7155 spec_rstack_overflow= 7156 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7157 7158 off - Disable mitigation 7159 microcode - Enable microcode mitigation only 7160 safe-ret - Enable sw-only safe RET mitigation (default) 7161 ibpb - Enable mitigation by issuing IBPB on 7162 kernel entry 7163 ibpb-vmexit - Issue IBPB only on VMEXIT 7164 (cloud-specific mitigation) 7165 7166 spec_store_bypass_disable= 7167 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7168 (Speculative Store Bypass vulnerability) 7169 7170 Certain CPUs are vulnerable to an exploit against a 7171 a common industry wide performance optimization known 7172 as "Speculative Store Bypass" in which recent stores 7173 to the same memory location may not be observed by 7174 later loads during speculative execution. The idea 7175 is that such stores are unlikely and that they can 7176 be detected prior to instruction retirement at the 7177 end of a particular speculation execution window. 7178 7179 In vulnerable processors, the speculatively forwarded 7180 store can be used in a cache side channel attack, for 7181 example to read memory to which the attacker does not 7182 directly have access (e.g. inside sandboxed code). 7183 7184 This parameter controls whether the Speculative Store 7185 Bypass optimization is used. 7186 7187 On x86 the options are: 7188 7189 on - Unconditionally disable Speculative Store Bypass 7190 off - Unconditionally enable Speculative Store Bypass 7191 auto - Kernel detects whether the CPU model contains an 7192 implementation of Speculative Store Bypass and 7193 picks the most appropriate mitigation. If the 7194 CPU is not vulnerable, "off" is selected. If the 7195 CPU is vulnerable the default mitigation is 7196 architecture and Kconfig dependent. See below. 7197 prctl - Control Speculative Store Bypass per thread 7198 via prctl. Speculative Store Bypass is enabled 7199 for a process by default. The state of the control 7200 is inherited on fork. 7201 seccomp - Same as "prctl" above, but all seccomp threads 7202 will disable SSB unless they explicitly opt out. 7203 7204 Default mitigations: 7205 X86: "prctl" 7206 7207 On powerpc the options are: 7208 7209 on,auto - On Power8 and Power9 insert a store-forwarding 7210 barrier on kernel entry and exit. On Power7 7211 perform a software flush on kernel entry and 7212 exit. 7213 off - No action. 7214 7215 Not specifying this option is equivalent to 7216 spec_store_bypass_disable=auto. 7217 7218 split_llc= 7219 [X86,EARLY] Split the LLC N-ways 7220 7221 When set, the LLC is split this many ways by matching 7222 'core_id % n'. This is setup before SMP bringup and 7223 used during SMP bringup before it knows the full 7224 topology. If your core count doesn't nicely divide by 7225 the number given, you get to keep the pieces. 7226 7227 This is mostly a debug feature to emulate multiple LLCs 7228 on hardware that only have a single LLC. 7229 7230 split_lock_detect= 7231 [X86] Enable split lock detection or bus lock detection 7232 7233 When enabled (and if hardware support is present), atomic 7234 instructions that access data across cache line 7235 boundaries will result in an alignment check exception 7236 for split lock detection or a debug exception for 7237 bus lock detection. 7238 7239 off - not enabled 7240 7241 warn - the kernel will emit rate-limited warnings 7242 about applications triggering the #AC 7243 exception or the #DB exception. This mode is 7244 the default on CPUs that support split lock 7245 detection or bus lock detection. Default 7246 behavior is by #AC if both features are 7247 enabled in hardware. 7248 7249 fatal - the kernel will send SIGBUS to applications 7250 that trigger the #AC exception or the #DB 7251 exception. Default behavior is by #AC if 7252 both features are enabled in hardware. 7253 7254 ratelimit:N - 7255 Set system wide rate limit to N bus locks 7256 per second for bus lock detection. 7257 0 < N <= 1000. 7258 7259 N/A for split lock detection. 7260 7261 7262 If an #AC exception is hit in the kernel or in 7263 firmware (i.e. not while executing in user mode) 7264 the kernel will oops in either "warn" or "fatal" 7265 mode. 7266 7267 #DB exception for bus lock is triggered only when 7268 CPL > 0. 7269 7270 srbds= [X86,INTEL,EARLY] 7271 Control the Special Register Buffer Data Sampling 7272 (SRBDS) mitigation. 7273 7274 Certain CPUs are vulnerable to an MDS-like 7275 exploit which can leak bits from the random 7276 number generator. 7277 7278 By default, this issue is mitigated by 7279 microcode. However, the microcode fix can cause 7280 the RDRAND and RDSEED instructions to become 7281 much slower. Among other effects, this will 7282 result in reduced throughput from /dev/urandom. 7283 7284 The microcode mitigation can be disabled with 7285 the following option: 7286 7287 off: Disable mitigation and remove 7288 performance impact to RDRAND and RDSEED 7289 7290 srcutree.big_cpu_lim [KNL] 7291 Specifies the number of CPUs constituting a 7292 large system, such that srcu_struct structures 7293 should immediately allocate an srcu_node array. 7294 This kernel-boot parameter defaults to 128, 7295 but takes effect only when the low-order four 7296 bits of srcutree.convert_to_big is equal to 3 7297 (decide at boot). 7298 7299 srcutree.convert_to_big [KNL] 7300 Specifies under what conditions an SRCU tree 7301 srcu_struct structure will be converted to big 7302 form, that is, with an rcu_node tree: 7303 7304 0: Never. 7305 1: At init_srcu_struct() time. 7306 2: When rcutorture decides to. 7307 3: Decide at boot time (default). 7308 0x1X: Above plus if high contention. 7309 7310 Either way, the srcu_node tree will be sized based 7311 on the actual runtime number of CPUs (nr_cpu_ids) 7312 instead of the compile-time CONFIG_NR_CPUS. 7313 7314 srcutree.counter_wrap_check [KNL] 7315 Specifies how frequently to check for 7316 grace-period sequence counter wrap for the 7317 srcu_data structure's ->srcu_gp_seq_needed field. 7318 The greater the number of bits set in this kernel 7319 parameter, the less frequently counter wrap will 7320 be checked for. Note that the bottom two bits 7321 are ignored. 7322 7323 srcutree.exp_holdoff [KNL] 7324 Specifies how many nanoseconds must elapse 7325 since the end of the last SRCU grace period for 7326 a given srcu_struct until the next normal SRCU 7327 grace period will be considered for automatic 7328 expediting. Set to zero to disable automatic 7329 expediting. 7330 7331 srcutree.srcu_max_nodelay [KNL] 7332 Specifies the number of no-delay instances 7333 per jiffy for which the SRCU grace period 7334 worker thread will be rescheduled with zero 7335 delay. Beyond this limit, worker thread will 7336 be rescheduled with a sleep delay of one jiffy. 7337 7338 srcutree.srcu_max_nodelay_phase [KNL] 7339 Specifies the per-grace-period phase, number of 7340 non-sleeping polls of readers. Beyond this limit, 7341 grace period worker thread will be rescheduled 7342 with a sleep delay of one jiffy, between each 7343 rescan of the readers, for a grace period phase. 7344 7345 srcutree.srcu_retry_check_delay [KNL] 7346 Specifies number of microseconds of non-sleeping 7347 delay between each non-sleeping poll of readers. 7348 7349 srcutree.small_contention_lim [KNL] 7350 Specifies the number of update-side contention 7351 events per jiffy will be tolerated before 7352 initiating a conversion of an srcu_struct 7353 structure to big form. Note that the value of 7354 srcutree.convert_to_big must have the 0x10 bit 7355 set for contention-based conversions to occur. 7356 7357 ssbd= [ARM64,HW,EARLY] 7358 Speculative Store Bypass Disable control 7359 7360 On CPUs that are vulnerable to the Speculative 7361 Store Bypass vulnerability and offer a 7362 firmware based mitigation, this parameter 7363 indicates how the mitigation should be used: 7364 7365 force-on: Unconditionally enable mitigation for 7366 for both kernel and userspace 7367 force-off: Unconditionally disable mitigation for 7368 for both kernel and userspace 7369 kernel: Always enable mitigation in the 7370 kernel, and offer a prctl interface 7371 to allow userspace to register its 7372 interest in being mitigated too. 7373 7374 stack_guard_gap= [MM] 7375 override the default stack gap protection. The value 7376 is in page units and it defines how many pages prior 7377 to (for stacks growing down) resp. after (for stacks 7378 growing up) the main stack are reserved for no other 7379 mapping. Default value is 256 pages. 7380 7381 stack_depot_disable= [KNL,EARLY] 7382 Setting this to true through kernel command line will 7383 disable the stack depot thereby saving the static memory 7384 consumed by the stack hash table. By default this is set 7385 to false. 7386 7387 stack_depot_max_pools= [KNL,EARLY] 7388 Specify the maximum number of pools to use for storing 7389 stack traces. Pools are allocated on-demand up to this 7390 limit. Default value is 8191 pools. 7391 7392 stacktrace [FTRACE] 7393 Enable the stack tracer on boot up. 7394 7395 stacktrace_filter=[function-list] 7396 [FTRACE] Limit the functions that the stack tracer 7397 will trace at boot up. function-list is a comma-separated 7398 list of functions. This list can be changed at run 7399 time by the stack_trace_filter file in the debugfs 7400 tracing directory. Note, this enables stack tracing 7401 and the stacktrace above is not needed. 7402 7403 sti= [PARISC,HW] 7404 Format: <num> 7405 Set the STI (builtin display/keyboard on the HP-PARISC 7406 machines) console (graphic card) which should be used 7407 as the initial boot-console. 7408 See also comment in drivers/video/sticore.c. 7409 7410 sti_font= [HW] 7411 See comment in drivers/video/sticore.c. 7412 7413 stifb= [HW] 7414 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7415 7416 strict_sas_size= 7417 [X86] 7418 Format: <bool> 7419 Enable or disable strict sigaltstack size checks 7420 against the required signal frame size which 7421 depends on the supported FPU features. This can 7422 be used to filter out binaries which have 7423 not yet been made aware of AT_MINSIGSTKSZ. 7424 7425 stress_hpt [PPC,EARLY] 7426 Limits the number of kernel HPT entries in the hash 7427 page table to increase the rate of hash page table 7428 faults on kernel addresses. 7429 7430 stress_slb [PPC,EARLY] 7431 Limits the number of kernel SLB entries, and flushes 7432 them frequently to increase the rate of SLB faults 7433 on kernel addresses. 7434 7435 no_slb_preload [PPC,EARLY] 7436 Disables slb preloading for userspace. 7437 7438 sunrpc.min_resvport= 7439 sunrpc.max_resvport= 7440 [NFS,SUNRPC] 7441 SunRPC servers often require that client requests 7442 originate from a privileged port (i.e. a port in the 7443 range 0 < portnr < 1024). 7444 An administrator who wishes to reserve some of these 7445 ports for other uses may adjust the range that the 7446 kernel's sunrpc client considers to be privileged 7447 using these two parameters to set the minimum and 7448 maximum port values. 7449 7450 sunrpc.svc_rpc_per_connection_limit= 7451 [NFS,SUNRPC] 7452 Limit the number of requests that the server will 7453 process in parallel from a single connection. 7454 The default value is 0 (no limit). 7455 7456 sunrpc.pool_mode= 7457 [NFS] 7458 Deprecated. The NFS server now always uses one 7459 service thread pool per NUMA node (equivalent to a 7460 single global pool on non-NUMA machines). All of 7461 the previously accepted values (auto, global, 7462 percpu, pernode) are still accepted for backward 7463 compatibility but are ignored: the mode is always 7464 pernode, and reads always return "pernode". 7465 7466 sunrpc.tcp_slot_table_entries= 7467 sunrpc.udp_slot_table_entries= 7468 [NFS,SUNRPC] 7469 Sets the upper limit on the number of simultaneous 7470 RPC calls that can be sent from the client to a 7471 server. Increasing these values may allow you to 7472 improve throughput, but will also increase the 7473 amount of memory reserved for use by the client. 7474 7475 suspend.pm_test_delay= 7476 [SUSPEND] 7477 Sets the number of seconds to remain in a suspend test 7478 mode before resuming the system (see 7479 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7480 is set. Default value is 5. 7481 7482 svm= [PPC] 7483 Format: { on | off | y | n | 1 | 0 } 7484 This parameter controls use of the Protected 7485 Execution Facility on pSeries. 7486 7487 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7488 Format: { <int> [,<int>] | force | noforce | track_hiwater} 7489 <int> -- Number of I/O TLB slabs 7490 <int> -- Second integer after comma. Number of swiotlb 7491 areas with their own lock. Will be rounded up 7492 to a power of 2. 7493 force -- force using of bounce buffers even if they 7494 wouldn't be automatically used by the kernel 7495 noforce -- Never use bounce buffers (for debugging) 7496 track_hiwater -- Track high watermark of swiotlb buffers. 7497 Only available when CONFIG_DEBUG_FS is set. 7498 7499 switches= [HW,M68k,EARLY] 7500 7501 sysctl.*= [KNL] 7502 Set a sysctl parameter, right before loading the init 7503 process, as if the value was written to the respective 7504 /proc/sys/... file. Both '.' and '/' are recognized as 7505 separators. Unrecognized parameters and invalid values 7506 are reported in the kernel log. Sysctls registered 7507 later by a loaded module cannot be set this way. 7508 Example: sysctl.vm.swappiness=40 7509 7510 sysrq_always_enabled 7511 [KNL] 7512 Ignore sysrq setting - this boot parameter will 7513 neutralize any effect of /proc/sys/kernel/sysrq. 7514 Useful for debugging. 7515 7516 tcpmhash_entries= [KNL,NET] 7517 Set the number of tcp_metrics_hash slots. 7518 Default value is 8192 or 16384 depending on total 7519 ram pages. This is used to specify the TCP metrics 7520 cache size. See Documentation/networking/ip-sysctl.rst 7521 "tcp_no_metrics_save" section for more details. 7522 7523 tdfx= [HW,DRM] 7524 7525 test_suspend= [SUSPEND] 7526 Format: { "mem" | "standby" | "freeze" }[,N] 7527 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7528 standby suspend) or "freeze" (for suspend type freeze) 7529 as the system sleep state during system startup with 7530 the optional capability to repeat N number of times. 7531 The system is woken from this state using a 7532 wakeup-capable RTC alarm. 7533 7534 thash_entries= [KNL,NET] 7535 Set number of hash buckets for TCP connection 7536 7537 thermal.act= [HW,ACPI] 7538 -1: disable all active trip points in all thermal zones 7539 <degrees C>: override all lowest active trip points 7540 7541 thermal.crt= [HW,ACPI] 7542 -1: disable all critical trip points in all thermal zones 7543 <degrees C>: override all critical trip points 7544 7545 thermal.off= [HW,ACPI] 7546 1: disable ACPI thermal control 7547 7548 thermal.psv= [HW,ACPI] 7549 -1: disable all passive trip points 7550 <degrees C>: override all passive trip points to this 7551 value 7552 7553 thermal.tzp= [HW,ACPI] 7554 Specify global default ACPI thermal zone polling rate 7555 <deci-seconds>: poll all this frequency 7556 0: no polling (default) 7557 7558 thp_anon= [KNL] 7559 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7560 state is one of "always", "madvise", "never" or "inherit". 7561 Control the default behavior of the system with respect 7562 to anonymous transparent hugepages. 7563 Can be used multiple times for multiple anon THP sizes. 7564 See Documentation/admin-guide/mm/transhuge.rst for more 7565 details. 7566 7567 threadirqs [KNL,EARLY] 7568 Force threading of all interrupt handlers except those 7569 marked explicitly IRQF_NO_THREAD. 7570 7571 thp_shmem= [KNL] 7572 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7573 Control the default policy of each hugepage size for the 7574 internal shmem mount. <policy> is one of policies available 7575 for the shmem mount ("always", "inherit", "never", "within_size", 7576 and "advise"). 7577 It can be used multiple times for multiple shmem THP sizes. 7578 See Documentation/admin-guide/mm/transhuge.rst for more 7579 details. 7580 7581 tlbi= [X86-64] 7582 Format: {ipi} 7583 ipi: switch to IPI-based TLB flushing 7584 7585 topology= [S390,EARLY] 7586 Format: {off | on} 7587 Specify if the kernel should make use of the cpu 7588 topology information if the hardware supports this. 7589 The scheduler will make use of this information and 7590 e.g. base its process migration decisions on it. 7591 Default is on. 7592 7593 torture.disable_onoff_at_boot= [KNL] 7594 Prevent the CPU-hotplug component of torturing 7595 until after init has spawned. 7596 7597 torture.ftrace_dump_at_shutdown= [KNL] 7598 Dump the ftrace buffer at torture-test shutdown, 7599 even if there were no errors. This can be a 7600 very costly operation when many torture tests 7601 are running concurrently, especially on systems 7602 with rotating-rust storage. 7603 7604 torture.verbose_sleep_frequency= [KNL] 7605 Specifies how many verbose printk()s should be 7606 emitted between each sleep. The default of zero 7607 disables verbose-printk() sleeping. 7608 7609 torture.verbose_sleep_duration= [KNL] 7610 Duration of each verbose-printk() sleep in jiffies. 7611 7612 tpm.disable_pcr_integrity= [HW,TPM] 7613 Do not protect PCR registers from unintended physical 7614 access, or interposers in the bus by the means of 7615 having an integrity protected session wrapped around 7616 TPM2_PCR_Extend command. Consider this in a situation 7617 where TPM is heavily utilized by IMA, thus protection 7618 causing a major performance hit, and the space where 7619 machines are deployed is by other means guarded. 7620 7621 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7622 Maximum time in milliseconds to retry sending a message 7623 to the TPM service before giving up. This parameter controls 7624 how long the system will continue retrying when the TPM 7625 service is busy. 7626 Format: <unsigned int> 7627 Default: 2000 (2 seconds) 7628 7629 tpm_suspend_pcr=[HW,TPM] 7630 Format: integer pcr id 7631 Specify that at suspend time, the tpm driver 7632 should extend the specified pcr with zeros, 7633 as a workaround for some chips which fail to 7634 flush the last written pcr on TPM_SaveState. 7635 This will guarantee that all the other pcrs 7636 are saved. 7637 7638 tpm_tis.interrupts= [HW,TPM] 7639 Enable interrupts for the MMIO based physical layer 7640 for the FIFO interface. By default it is set to false 7641 (0). For more information about TPM hardware interfaces 7642 defined by Trusted Computing Group (TCG) see 7643 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7644 7645 tp_printk [FTRACE] 7646 Have the tracepoints sent to printk as well as the 7647 tracing ring buffer. This is useful for early boot up 7648 where the system hangs or reboots and does not give the 7649 option for reading the tracing buffer or performing a 7650 ftrace_dump_on_oops. 7651 7652 To turn off having tracepoints sent to printk, 7653 echo 0 > /proc/sys/kernel/tracepoint_printk 7654 Note, echoing 1 into this file without the 7655 tp_printk kernel cmdline option has no effect. 7656 7657 The tp_printk_stop_on_boot (see below) can also be used 7658 to stop the printing of events to console at 7659 late_initcall_sync. 7660 7661 ** CAUTION ** 7662 7663 Having tracepoints sent to printk() and activating high 7664 frequency tracepoints such as irq or sched, can cause 7665 the system to live lock. 7666 7667 tp_printk_stop_on_boot [FTRACE] 7668 When tp_printk (above) is set, it can cause a lot of noise 7669 on the console. It may be useful to only include the 7670 printing of events during boot up, as user space may 7671 make the system inoperable. 7672 7673 This command line option will stop the printing of events 7674 to console at the late_initcall_sync() time frame. 7675 7676 trace_buf_size=nn[KMG] 7677 [FTRACE] will set tracing buffer size on each cpu. 7678 7679 trace_clock= [FTRACE] Set the clock used for tracing events 7680 at boot up. 7681 local - Use the per CPU time stamp counter 7682 (converted into nanoseconds). Fast, but 7683 depending on the architecture, may not be 7684 in sync between CPUs. 7685 global - Event time stamps are synchronized across 7686 CPUs. May be slower than the local clock, 7687 but better for some race conditions. 7688 counter - Simple counting of events (1, 2, ..) 7689 note, some counts may be skipped due to the 7690 infrastructure grabbing the clock more than 7691 once per event. 7692 uptime - Use jiffies as the time stamp. 7693 perf - Use the same clock that perf uses. 7694 mono - Use ktime_get_mono_fast_ns() for time stamps. 7695 mono_raw - Use ktime_get_raw_fast_ns() for time 7696 stamps. 7697 boot - Use ktime_get_boot_fast_ns() for time stamps. 7698 Architectures may add more clocks. See 7699 Documentation/trace/ftrace.rst for more details. 7700 7701 trace_event=[event-list] 7702 [FTRACE] Set and start specified trace events in order 7703 to facilitate early boot debugging. The event-list is a 7704 comma-separated list of trace events to enable. See 7705 also Documentation/trace/events.rst 7706 7707 To enable modules, use :mod: keyword: 7708 7709 trace_event=:mod:<module> 7710 7711 The value before :mod: will only enable specific events 7712 that are part of the module. See the above mentioned 7713 document for more information. 7714 7715 trace_instance=[instance-info] 7716 [FTRACE] Create a ring buffer instance early in boot up. 7717 This will be listed in: 7718 7719 /sys/kernel/tracing/instances 7720 7721 Events can be enabled at the time the instance is created 7722 via: 7723 7724 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7725 7726 Note, the "<system*>:" portion is optional if the event is 7727 unique. 7728 7729 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7730 7731 will enable the "sched_switch" event (note, the "sched:" is optional, and 7732 the same thing would happen if it was left off). The irq_handler_entry 7733 event, and all events under the "initcall" system. 7734 7735 Flags can be added to the instance to modify its behavior when it is 7736 created. The flags are separated by '^'. 7737 7738 The available flags are: 7739 7740 traceoff - Have the tracing instance tracing disabled after it is created. 7741 traceprintk - Have trace_printk() write into this trace instance 7742 (note, "printk" and "trace_printk" can also be used) 7743 7744 trace_instance=foo^traceoff^traceprintk,sched,irq 7745 7746 The flags must come before the defined events. 7747 7748 If memory has been reserved (see memmap for x86), the instance 7749 can use that memory: 7750 7751 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7752 7753 The above will create a "boot_map" instance that uses the physical 7754 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7755 instance will be split up accordingly. 7756 7757 Alternatively, the memory can be reserved by the reserve_mem option: 7758 7759 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7760 7761 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7762 and place the ring buffer in this memory. Note that due to KASLR, the 7763 memory may not be the same location each time, which will not preserve 7764 the buffer content. 7765 7766 Also note that the layout of the ring buffer data may change between 7767 kernel versions where the validator will fail and reset the ring buffer 7768 if the layout is not the same as the previous kernel. 7769 7770 If the ring buffer is used for persistent bootups and has events enabled, 7771 it is recommend to disable tracing so that events from a previous boot do not 7772 mix with events of the current boot (unless you are debugging a random crash 7773 at boot up). 7774 7775 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7776 7777 Note, saving the trace buffer across reboots does require that the system 7778 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7779 can force a memory reset on boot which will clear any trace that was stored. 7780 This is just one of many ways that can clear memory. Make sure your system 7781 keeps the content of memory across reboots before relying on this option. 7782 7783 NB: Both the mapped address and size must be page aligned for the architecture. 7784 7785 See also Documentation/trace/debugging.rst 7786 7787 7788 trace_options=[option-list] 7789 [FTRACE] Enable or disable tracer options at boot. 7790 The option-list is a comma delimited list of options 7791 that can be enabled or disabled just as if you were 7792 to echo the option name into 7793 7794 /sys/kernel/tracing/trace_options 7795 7796 For example, to enable stacktrace option (to dump the 7797 stack trace of each event), add to the command line: 7798 7799 trace_options=stacktrace 7800 7801 See also Documentation/trace/ftrace.rst "trace options" 7802 section. 7803 7804 trace_trigger=[trigger-list] 7805 [FTRACE] Add an event trigger on specific events. 7806 Set a trigger on top of a specific event, with an optional 7807 filter. 7808 7809 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7810 Where more than one trigger may be specified that are comma delimited. 7811 7812 For example: 7813 7814 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7815 7816 The above will enable the "stacktrace" trigger on the "sched_switch" 7817 event but only trigger it if the "prev_state" of the "sched_switch" 7818 event is "2" (TASK_UNINTERRUPTIBLE). 7819 7820 See also "Event triggers" in Documentation/trace/events.rst 7821 7822 7823 traceoff_after_boot 7824 [FTRACE] Sometimes tracing is used to debug issues 7825 during the boot process. Since the trace buffer has a 7826 limited amount of storage, it may be prudent to 7827 disable tracing after the boot is finished, otherwise 7828 the critical information may be overwritten. With this 7829 option, the main tracing buffer will be turned off at 7830 the end of the boot process. 7831 7832 traceoff_on_warning 7833 [FTRACE] enable this option to disable tracing when a 7834 warning is hit. This turns off "tracing_on". Tracing can 7835 be enabled again by echoing '1' into the "tracing_on" 7836 file located in /sys/kernel/tracing/ 7837 7838 This option is useful, as it disables the trace before 7839 the WARNING dump is called, which prevents the trace to 7840 be filled with content caused by the warning output. 7841 7842 This option can also be set at run time via the sysctl 7843 option: kernel/traceoff_on_warning 7844 7845 transparent_hugepage= 7846 [KNL] 7847 Format: [always|madvise|never] 7848 Can be used to control the default behavior of the system 7849 with respect to transparent hugepages. 7850 See Documentation/admin-guide/mm/transhuge.rst 7851 for more details. 7852 7853 transparent_hugepage_shmem= [KNL] 7854 Format: [always|within_size|advise|never|deny|force] 7855 Can be used to control the hugepage allocation policy for 7856 the internal shmem mount. 7857 See Documentation/admin-guide/mm/transhuge.rst 7858 for more details. 7859 7860 transparent_hugepage_tmpfs= [KNL] 7861 Format: [always|within_size|advise|never] 7862 Can be used to control the default hugepage allocation policy 7863 for the tmpfs mount. 7864 See Documentation/admin-guide/mm/transhuge.rst 7865 for more details. 7866 7867 trusted.source= [KEYS] 7868 Format: <string> 7869 This parameter identifies the trust source as a backend 7870 for trusted keys implementation. Supported trust 7871 sources: 7872 - "tpm" 7873 - "tee" 7874 - "caam" 7875 - "dcp" 7876 - "pkwm" 7877 If not specified then it defaults to iterating through 7878 the trust source list starting with TPM and assigns the 7879 first trust source as a backend which is initialized 7880 successfully during iteration. 7881 7882 trusted.debug= [KEYS] 7883 Format: <bool> 7884 Enable trusted keys debug traces at runtime when 7885 CONFIG_TRUSTED_KEYS_DEBUG=y. 7886 7887 To make the traces visible after enabling the option, 7888 use trusted.dyndbg='+p' as needed. By convention, 7889 the subsystem uses pr_debug() for these traces. 7890 7891 SAFETY: The traces can leak sensitive data, so be 7892 cautious before enabling this. They remain inactive 7893 unless this parameter is set this option to a true 7894 value. 7895 7896 Default: false 7897 7898 trusted.rng= [KEYS] 7899 Format: <string> 7900 The RNG used to generate key material for trusted keys. 7901 Can be one of: 7902 - "kernel" 7903 - the same value as trusted.source: "tpm" or "tee" 7904 - "default" 7905 If not specified, "default" is used. In this case, 7906 the RNG's choice is left to each individual trust source. 7907 7908 trusted.dcp_use_otp_key 7909 This is intended to be used in combination with 7910 trusted.source=dcp and will select the DCP OTP key 7911 instead of the DCP UNIQUE key blob encryption. 7912 7913 trusted.dcp_skip_zk_test 7914 This is intended to be used in combination with 7915 trusted.source=dcp and will disable the check if the 7916 blob key is all zeros. This is helpful for situations where 7917 having this key zero'ed is acceptable. E.g. in testing 7918 scenarios. 7919 7920 tsa= [X86] Control mitigation for Transient Scheduler 7921 Attacks on AMD CPUs. Search the following in your 7922 favourite search engine for more details: 7923 7924 "Technical guidance for mitigating transient scheduler 7925 attacks". 7926 7927 off - disable the mitigation 7928 on - enable the mitigation (default) 7929 user - mitigate only user/kernel transitions 7930 vm - mitigate only guest/host transitions 7931 7932 7933 tsc= Disable clocksource stability checks for TSC. 7934 Format: <string> 7935 [x86] reliable: mark tsc clocksource as reliable, this 7936 disables clocksource verification at runtime, as well 7937 as the stability checks done at bootup. Used to enable 7938 high-resolution timer mode on older hardware, and in 7939 virtualized environment. 7940 [x86] noirqtime: Do not use TSC to do irq accounting. 7941 Used to run time disable IRQ_TIME_ACCOUNTING on any 7942 platforms where RDTSC is slow and this accounting 7943 can add overhead. 7944 [x86] unstable: mark the TSC clocksource as unstable, this 7945 marks the TSC unconditionally unstable at bootup and 7946 avoids any further wobbles once the TSC watchdog notices. 7947 [x86] nowatchdog: disable clocksource watchdog. Used 7948 in situations with strict latency requirements (where 7949 interruptions from clocksource watchdog are not 7950 acceptable). 7951 [x86] recalibrate: force recalibration against a HW timer 7952 (HPET or PM timer) on systems whose TSC frequency was 7953 obtained from HW or FW using either an MSR or CPUID(0x15). 7954 Warn if the difference is more than 500 ppm. 7955 [x86] watchdog: Enforce the clocksource watchdog on TSC 7956 7957 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7958 value instead. Useful when the early TSC frequency discovery 7959 procedure is not reliable, such as on overclocked systems 7960 with CPUID.16h support and partial CPUID.15h support. 7961 Format: <unsigned int> 7962 7963 tsx= [X86] Control Transactional Synchronization 7964 Extensions (TSX) feature in Intel processors that 7965 support TSX control. 7966 7967 This parameter controls the TSX feature. The options are: 7968 7969 on - Enable TSX on the system. Although there are 7970 mitigations for all known security vulnerabilities, 7971 TSX has been known to be an accelerator for 7972 several previous speculation-related CVEs, and 7973 so there may be unknown security risks associated 7974 with leaving it enabled. 7975 7976 off - Disable TSX on the system. (Note that this 7977 option takes effect only on newer CPUs which are 7978 not vulnerable to MDS, i.e., have 7979 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7980 the new IA32_TSX_CTRL MSR through a microcode 7981 update. This new MSR allows for the reliable 7982 deactivation of the TSX functionality.) 7983 7984 auto - Disable TSX if X86_BUG_TAA is present, 7985 otherwise enable TSX on the system. 7986 7987 Not specifying this option is equivalent to tsx=off. 7988 7989 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7990 for more details. 7991 7992 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7993 Abort (TAA) vulnerability. 7994 7995 Similar to Micro-architectural Data Sampling (MDS) 7996 certain CPUs that support Transactional 7997 Synchronization Extensions (TSX) are vulnerable to an 7998 exploit against CPU internal buffers which can forward 7999 information to a disclosure gadget under certain 8000 conditions. 8001 8002 In vulnerable processors, the speculatively forwarded 8003 data can be used in a cache side channel attack, to 8004 access data to which the attacker does not have direct 8005 access. 8006 8007 This parameter controls the TAA mitigation. The 8008 options are: 8009 8010 full - Enable TAA mitigation on vulnerable CPUs 8011 if TSX is enabled. 8012 8013 full,nosmt - Enable TAA mitigation and disable SMT on 8014 vulnerable CPUs. If TSX is disabled, SMT 8015 is not disabled because CPU is not 8016 vulnerable to cross-thread TAA attacks. 8017 off - Unconditionally disable TAA mitigation 8018 8019 On MDS-affected machines, tsx_async_abort=off can be 8020 prevented by an active MDS mitigation as both vulnerabilities 8021 are mitigated with the same mechanism so in order to disable 8022 this mitigation, you need to specify mds=off too. 8023 8024 Not specifying this option is equivalent to 8025 tsx_async_abort=full. On CPUs which are MDS affected 8026 and deploy MDS mitigation, TAA mitigation is not 8027 required and doesn't provide any additional 8028 mitigation. 8029 8030 For details see: 8031 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8032 8033 turbografx.map[2|3]= [HW,JOY] 8034 TurboGraFX parallel port interface 8035 Format: 8036 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8037 See also Documentation/input/devices/joystick-parport.rst 8038 8039 udbg-immortal [PPC] When debugging early kernel crashes that 8040 happen after console_init() and before a proper 8041 console driver takes over, this boot options might 8042 help "seeing" what's going on. 8043 8044 uhash_entries= [KNL,NET] 8045 Set number of hash buckets for UDP/UDP-Lite connections 8046 8047 uhci-hcd.ignore_oc= 8048 [USB] Ignore overcurrent events (default N). 8049 Some badly-designed motherboards generate lots of 8050 bogus events, for ports that aren't wired to 8051 anything. Set this parameter to avoid log spamming. 8052 Note that genuine overcurrent events won't be 8053 reported either. 8054 8055 unaligned_scalar_speed= 8056 [RISCV] 8057 Format: {slow | fast | unsupported} 8058 Allow skipping scalar unaligned access speed tests. This 8059 is useful for testing alternative code paths and to skip 8060 the tests in environments where they run too slowly. All 8061 CPUs must have the same scalar unaligned access speed. 8062 8063 unaligned_vector_speed= 8064 [RISCV] 8065 Format: {slow | fast | unsupported} 8066 Allow skipping vector unaligned access speed tests. This 8067 is useful for testing alternative code paths and to skip 8068 the tests in environments where they run too slowly. All 8069 CPUs must have the same vector unaligned access speed. 8070 8071 unknown_nmi_panic 8072 [X86] Cause panic on unknown NMI. 8073 8074 unwind_debug [X86-64,EARLY] 8075 Enable unwinder debug output. This can be 8076 useful for debugging certain unwinder error 8077 conditions, including corrupt stacks and 8078 bad/missing unwinder metadata. 8079 8080 usbcore.authorized_default= 8081 [USB] Default USB device authorization: 8082 (default -1 = authorized (same as 1), 8083 0 = not authorized, 1 = authorized, 2 = authorized 8084 if device connected to internal port) 8085 8086 usbcore.autosuspend= 8087 [USB] The autosuspend time delay (in seconds) used 8088 for newly-detected USB devices (default 2). This 8089 is the time required before an idle device will be 8090 autosuspended. Devices for which the delay is set 8091 to a negative value won't be autosuspended at all. 8092 8093 usbcore.usbfs_snoop= 8094 [USB] Set to log all usbfs traffic (default 0 = off). 8095 8096 usbcore.usbfs_snoop_max= 8097 [USB] Maximum number of bytes to snoop in each URB 8098 (default = 65536). 8099 8100 usbcore.blinkenlights= 8101 [USB] Set to cycle leds on hubs (default 0 = off). 8102 8103 usbcore.old_scheme_first= 8104 [USB] Start with the old device initialization 8105 scheme (default 0 = off). 8106 8107 usbcore.usbfs_memory_mb= 8108 [USB] Memory limit (in MB) for buffers allocated by 8109 usbfs (default = 16, 0 = max = 2047). 8110 8111 usbcore.use_both_schemes= 8112 [USB] Try the other device initialization scheme 8113 if the first one fails (default 1 = enabled). 8114 8115 usbcore.initial_descriptor_timeout= 8116 [USB] Specifies timeout for the initial 64-byte 8117 USB_REQ_GET_DESCRIPTOR request in milliseconds 8118 (default 5000 = 5.0 seconds). 8119 8120 usbcore.nousb [USB] Disable the USB subsystem 8121 8122 usbcore.quirks= 8123 [USB] A list of quirk entries to augment the built-in 8124 usb core quirk list. List entries are separated by 8125 commas. Each entry has the form 8126 VendorID:ProductID:Flags. The IDs are 4-digit hex 8127 numbers and Flags is a set of letters. Each letter 8128 will change the built-in quirk; setting it if it is 8129 clear and clearing it if it is set. The letters have 8130 the following meanings: 8131 a = USB_QUIRK_STRING_FETCH_255 (string 8132 descriptors must not be fetched using 8133 a 255-byte read); 8134 b = USB_QUIRK_RESET_RESUME (device can't resume 8135 correctly so reset it instead); 8136 c = USB_QUIRK_NO_SET_INTF (device can't handle 8137 Set-Interface requests); 8138 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8139 handle its Configuration or Interface 8140 strings); 8141 e = USB_QUIRK_RESET (device can't be reset 8142 (e.g morph devices), don't use reset); 8143 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8144 more interface descriptions than the 8145 bNumInterfaces count, and can't handle 8146 talking to these interfaces); 8147 g = USB_QUIRK_DELAY_INIT (device needs a pause 8148 during initialization, after we read 8149 the device descriptor); 8150 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8151 high speed and super speed interrupt 8152 endpoints, the USB 2.0 and USB 3.0 spec 8153 require the interval in microframes (1 8154 microframe = 125 microseconds) to be 8155 calculated as interval = 2 ^ 8156 (bInterval-1). 8157 Devices with this quirk report their 8158 bInterval as the result of this 8159 calculation instead of the exponent 8160 variable used in the calculation); 8161 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8162 handle device_qualifier descriptor 8163 requests); 8164 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8165 generates spurious wakeup, ignore 8166 remote wakeup capability); 8167 k = USB_QUIRK_NO_LPM (device can't handle Link 8168 Power Management); 8169 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8170 (Device reports its bInterval as linear 8171 frames instead of the USB 2.0 8172 calculation); 8173 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8174 to be disconnected before suspend to 8175 prevent spurious wakeup); 8176 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8177 pause after every control message); 8178 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8179 delay after resetting its port); 8180 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8181 (Reduce timeout of the SET_ADDRESS 8182 request from 5000 ms to 500 ms); 8183 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8184 claims zero configurations, 8185 forcing to 1); 8186 r = USB_QUIRK_WINDOWS_CONFIG_REQ_SIZE (Device 8187 fails during initialization when asked for 8188 9-bytes configuration descriptor request. 8189 Ask for 255-bytes request instead to mirror 8190 Windows' behavior); 8191 Example: quirks=0781:5580:bk,0a5c:5834:gij 8192 8193 usbhid.mousepoll= 8194 [USBHID] The interval which mice are to be polled at. 8195 8196 usbhid.jspoll= 8197 [USBHID] The interval which joysticks are to be polled at. 8198 8199 usbhid.kbpoll= 8200 [USBHID] The interval which keyboards are to be polled at. 8201 8202 usb-storage.delay_use= 8203 [UMS] The delay in seconds before a new device is 8204 scanned for Logical Units (default 1). 8205 Optionally the delay in milliseconds if the value has 8206 suffix with "ms". 8207 Example: delay_use=2567ms 8208 8209 usb-storage.quirks= 8210 [UMS] A list of quirks entries to supplement or 8211 override the built-in unusual_devs list. List 8212 entries are separated by commas. Each entry has 8213 the form VID:PID:Flags where VID and PID are Vendor 8214 and Product ID values (4-digit hex numbers) and 8215 Flags is a set of characters, each corresponding 8216 to a common usb-storage quirk flag as follows: 8217 a = SANE_SENSE (collect more than 18 bytes 8218 of sense data, not on uas); 8219 b = BAD_SENSE (don't collect more than 18 8220 bytes of sense data, not on uas); 8221 c = FIX_CAPACITY (decrease the reported 8222 device capacity by one sector); 8223 d = NO_READ_DISC_INFO (don't use 8224 READ_DISC_INFO command, not on uas); 8225 e = NO_READ_CAPACITY_16 (don't use 8226 READ_CAPACITY_16 command); 8227 f = NO_REPORT_OPCODES (don't use report opcodes 8228 command, uas only); 8229 g = MAX_SECTORS_240 (don't transfer more than 8230 240 sectors at a time, uas only); 8231 h = CAPACITY_HEURISTICS (decrease the 8232 reported device capacity by one 8233 sector if the number is odd); 8234 i = IGNORE_DEVICE (don't bind to this 8235 device); 8236 j = NO_REPORT_LUNS (don't use report luns 8237 command, uas only); 8238 k = NO_SAME (do not use WRITE_SAME, uas only) 8239 l = NOT_LOCKABLE (don't try to lock and 8240 unlock ejectable media, not on uas); 8241 m = MAX_SECTORS_64 (don't transfer more 8242 than 64 sectors = 32 KB at a time, 8243 not on uas); 8244 n = INITIAL_READ10 (force a retry of the 8245 initial READ(10) command, not on uas); 8246 o = CAPACITY_OK (accept the capacity 8247 reported by the device, not on uas); 8248 p = WRITE_CACHE (the device cache is ON 8249 by default, not on uas); 8250 r = IGNORE_RESIDUE (the device reports 8251 bogus residue values, not on uas); 8252 s = SINGLE_LUN (the device has only one 8253 Logical Unit); 8254 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8255 commands, uas only); 8256 u = IGNORE_UAS (don't bind to the uas driver); 8257 w = NO_WP_DETECT (don't test whether the 8258 medium is write-protected). 8259 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8260 even if the device claims no cache, 8261 not on uas) 8262 Example: quirks=0419:aaf5:rl,0421:0433:rc 8263 8264 user_debug= [KNL,ARM] 8265 Format: <int> 8266 See arch/arm/Kconfig.debug help text. 8267 1 - undefined instruction events 8268 2 - system calls 8269 4 - invalid data aborts 8270 8 - SIGSEGV faults 8271 16 - SIGBUS faults 8272 Example: user_debug=31 8273 8274 vdso= [X86,SH,SPARC] 8275 On X86_32, this is an alias for vdso32=. Otherwise: 8276 8277 vdso=1: enable VDSO (the default) 8278 vdso=0: disable VDSO mapping 8279 8280 vdso32= [X86] Control the 32-bit vDSO 8281 vdso32=1: enable 32-bit VDSO 8282 vdso32=0 or vdso32=2: disable 32-bit VDSO 8283 8284 See the help text for CONFIG_COMPAT_VDSO for more 8285 details. If CONFIG_COMPAT_VDSO is set, the default is 8286 vdso32=0; otherwise, the default is vdso32=1. 8287 8288 For compatibility with older kernels, vdso32=2 is an 8289 alias for vdso32=0. 8290 8291 Try vdso32=0 if you encounter an error that says: 8292 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8293 8294 video= [FB,EARLY] Frame buffer configuration 8295 See Documentation/fb/modedb.rst. 8296 8297 video.brightness_switch_enabled= [ACPI] 8298 Format: [0|1] 8299 If set to 1, on receiving an ACPI notify event 8300 generated by hotkey, video driver will adjust brightness 8301 level and then send out the event to user space through 8302 the allocated input device. If set to 0, video driver 8303 will only send out the event without touching backlight 8304 brightness level. 8305 default: 1 8306 8307 virtio_mmio.device= 8308 [VMMIO] Memory mapped virtio (platform) device. 8309 8310 <size>@<baseaddr>:<irq>[:<id>] 8311 where: 8312 <size> := size (can use standard suffixes 8313 like K, M and G) 8314 <baseaddr> := physical base address 8315 <irq> := interrupt number (as passed to 8316 request_irq()) 8317 <id> := (optional) platform device id 8318 example: 8319 virtio_mmio.device=1K@0x100b0000:48:7 8320 8321 Can be used multiple times for multiple devices. 8322 8323 vga= [BOOT,X86-32] Select a particular video mode 8324 See Documentation/arch/x86/boot.rst and 8325 Documentation/admin-guide/svga.rst. 8326 Use vga=ask for menu. 8327 This is actually a boot loader parameter; the value is 8328 passed to the kernel using a special protocol. 8329 8330 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8331 May slow down system boot speed, especially when 8332 enabled on systems with a large amount of memory. 8333 All options are enabled by default, and this 8334 interface is meant to allow for selectively 8335 enabling or disabling specific virtual memory 8336 debugging features. 8337 8338 Available options are: 8339 P Enable page structure init time poisoning 8340 - Disable all of the above options 8341 8342 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8343 exact size of <nn>. This can be used to increase 8344 the minimum size (128MB on x86, arm32 platforms). 8345 It can also be used to decrease the size and leave more room 8346 for directly mapped kernel RAM. Note that this parameter does 8347 not exist on many other platforms (including arm64, alpha, 8348 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8349 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8350 8351 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8352 Sets the memory size reserved for contiguous memory 8353 allocations for the vmcp device driver. 8354 8355 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8356 Format: <command> 8357 8358 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8359 Format: <command> 8360 8361 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8362 Format: <command> 8363 8364 vmscape= [X86] Controls mitigation for VMscape attacks. 8365 VMscape attacks can leak information from a userspace 8366 hypervisor to a guest via speculative side-channels. 8367 8368 off - disable the mitigation 8369 ibpb - use Indirect Branch Prediction Barrier 8370 (IBPB) mitigation (default) 8371 force - force vulnerability detection even on 8372 unaffected processors 8373 8374 vsyscall= [X86-64,EARLY] 8375 Controls the behavior of vsyscalls (i.e. calls to 8376 fixed addresses of 0xffffffffff600x00 from legacy 8377 code). Most statically-linked binaries and older 8378 versions of glibc use these calls. Because these 8379 functions are at fixed addresses, they make nice 8380 targets for exploits that can control RIP. 8381 8382 emulate Vsyscalls turn into traps and are emulated 8383 reasonably safely. The vsyscall page is 8384 readable. This disables the Linear 8385 Address Space Separation (LASS) security 8386 feature and makes the system less secure. 8387 8388 xonly [default] Vsyscalls turn into traps and are 8389 emulated reasonably safely. The vsyscall 8390 page is not readable. 8391 8392 none Vsyscalls don't work at all. This makes 8393 them quite hard to use for exploits but 8394 might break your system. 8395 8396 vt.color= [VT] Default text color. 8397 Format: 0xYX, X = foreground, Y = background. 8398 Default: 0x07 = light gray on black. 8399 8400 vt.cur_default= [VT] Default cursor shape. 8401 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8402 the parameters of the <Esc>[?A;B;Cc escape sequence; 8403 see vga-softcursor.rst. Default: 2 = underline. 8404 8405 vt.default_blu= [VT] 8406 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8407 Change the default blue palette of the console. 8408 This is a 16-member array composed of values 8409 ranging from 0-255. 8410 8411 vt.default_grn= [VT] 8412 Format: <green0>,<green1>,<green2>,...,<green15> 8413 Change the default green palette of the console. 8414 This is a 16-member array composed of values 8415 ranging from 0-255. 8416 8417 vt.default_red= [VT] 8418 Format: <red0>,<red1>,<red2>,...,<red15> 8419 Change the default red palette of the console. 8420 This is a 16-member array composed of values 8421 ranging from 0-255. 8422 8423 vt.default_utf8= 8424 [VT] 8425 Format=<0|1> 8426 Set system-wide default UTF-8 mode for all tty's. 8427 Default is 1, i.e. UTF-8 mode is enabled for all 8428 newly opened terminals. 8429 8430 vt.global_cursor_default= 8431 [VT] 8432 Format=<-1|0|1> 8433 Set system-wide default for whether a cursor 8434 is shown on new VTs. Default is -1, 8435 i.e. cursors will be created by default unless 8436 overridden by individual drivers. 0 will hide 8437 cursors, 1 will display them. 8438 8439 vt.italic= [VT] Default color for italic text; 0-15. 8440 Default: 2 = green. 8441 8442 vt.underline= [VT] Default color for underlined text; 0-15. 8443 Default: 3 = cyan. 8444 8445 watchdog timers [HW,WDT] For information on watchdog timers, 8446 see Documentation/watchdog/watchdog-parameters.rst 8447 or other driver-specific files in the 8448 Documentation/watchdog/ directory. 8449 8450 watchdog_thresh= 8451 [KNL] 8452 Set the hard lockup detector stall duration 8453 threshold in seconds. The soft lockup detector 8454 threshold is set to twice the value. A value of 0 8455 disables both lockup detectors. Default is 10 8456 seconds. 8457 8458 workqueue.unbound_cpus= 8459 [KNL,SMP] Specify to constrain one or some CPUs 8460 to use in unbound workqueues. 8461 Format: <cpu-list> 8462 By default, all online CPUs are available for 8463 unbound workqueues. 8464 8465 workqueue.watchdog_thresh= 8466 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8467 warn stall conditions and dump internal state to 8468 help debugging. 0 disables workqueue stall 8469 detection; otherwise, it's the stall threshold 8470 duration in seconds. The default value is 30 and 8471 it can be updated at runtime by writing to the 8472 corresponding sysfs file. 8473 8474 workqueue.panic_on_stall=<uint> 8475 Panic when workqueue stall is detected by 8476 CONFIG_WQ_WATCHDOG. It sets the number times of the 8477 stall to trigger panic. 8478 8479 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8480 which is 0 (disabled) if not configured. 8481 8482 workqueue.panic_on_stall_time=<uint> 8483 Panic when a workqueue stall has been continuous for 8484 the specified number of seconds. Unlike panic_on_stall 8485 which counts accumulated stall events, this triggers 8486 based on the duration of a single continuous stall. 8487 8488 The default is 0, which disables the time-based panic. 8489 8490 workqueue.cpu_intensive_thresh_us= 8491 Per-cpu work items which run for longer than this 8492 threshold are automatically considered CPU intensive 8493 and excluded from concurrency management to prevent 8494 them from noticeably delaying other per-cpu work 8495 items. Default is 10000 (10ms). 8496 8497 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8498 will report the work functions which violate this 8499 threshold repeatedly. They are likely good 8500 candidates for using WQ_UNBOUND workqueues instead. 8501 8502 workqueue.cpu_intensive_warning_thresh=<uint> 8503 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8504 will report the work functions which violate the 8505 intensive_threshold_us repeatedly. In order to prevent 8506 spurious warnings, start printing only after a work 8507 function has violated this threshold number of times. 8508 8509 The default is 4 times. 0 disables the warning. 8510 8511 workqueue.power_efficient 8512 Per-cpu workqueues are generally preferred because 8513 they show better performance thanks to cache 8514 locality; unfortunately, per-cpu workqueues tend to 8515 be more power hungry than unbound workqueues. 8516 8517 Enabling this makes the per-cpu workqueues which 8518 were observed to contribute significantly to power 8519 consumption unbound, leading to measurably lower 8520 power usage at the cost of small performance 8521 overhead. 8522 8523 The default value of this parameter is determined by 8524 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8525 8526 workqueue.default_affinity_scope= 8527 Select the default affinity scope to use for unbound 8528 workqueues. Can be one of "cpu", "smt", "cache", 8529 "cache_shard", "numa" and "system". Default is 8530 "cache_shard". For more 8531 information, see the Affinity Scopes section in 8532 Documentation/core-api/workqueue.rst. 8533 8534 This can be changed after boot by writing to the 8535 matching /sys/module/workqueue/parameters file. All 8536 workqueues with the "default" affinity scope will be 8537 updated accordingly. 8538 8539 workqueue.debug_force_rr_cpu 8540 Workqueue used to implicitly guarantee that work 8541 items queued without explicit CPU specified are put 8542 on the local CPU. This guarantee is no longer true 8543 and while local CPU is still preferred work items 8544 may be put on foreign CPUs. This debug option 8545 forces round-robin CPU selection to flush out 8546 usages which depend on the now broken guarantee. 8547 When enabled, memory and cache locality will be 8548 impacted. 8549 8550 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8551 Type) of ioremap_wc(). 8552 8553 on - Enable writecombine, use WUC for ioremap_wc() 8554 off - Disable writecombine, use SUC for ioremap_wc() 8555 8556 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8557 default x2apic cluster mode on platforms 8558 supporting x2apic. 8559 8560 xen_512gb_limit [KNL,X86-64,XEN] 8561 Restricts the kernel running paravirtualized under Xen 8562 to use only up to 512 GB of RAM. The reason to do so is 8563 crash analysis tools and Xen tools for doing domain 8564 save/restore/migration must be enabled to handle larger 8565 domains. 8566 8567 xen_console_io [XEN,EARLY] 8568 Boolean option to enable/disable the usage of the Xen 8569 console_io hypercalls to read and write to the console. 8570 Mostly useful for debugging and development. 8571 8572 xen_emul_unplug= [HW,X86,XEN,EARLY] 8573 Unplug Xen emulated devices 8574 Format: [unplug0,][unplug1] 8575 ide-disks -- unplug primary master IDE devices 8576 aux-ide-disks -- unplug non-primary-master IDE devices 8577 nics -- unplug network devices 8578 all -- unplug all emulated devices (NICs and IDE disks) 8579 unnecessary -- unplugging emulated devices is 8580 unnecessary even if the host did not respond to 8581 the unplug protocol 8582 never -- do not unplug even if version check succeeds 8583 8584 xen_legacy_crash [X86,XEN,EARLY] 8585 Crash from Xen panic notifier, without executing late 8586 panic() code such as dumping handler. 8587 8588 xen_mc_debug [X86,XEN,EARLY] 8589 Enable multicall debugging when running as a Xen PV guest. 8590 Enabling this feature will reduce performance a little 8591 bit, so it should only be enabled for obtaining extended 8592 debug data in case of multicall errors. 8593 8594 xen_msr_safe= [X86,XEN,EARLY] 8595 Format: <bool> 8596 Select whether to always use non-faulting (safe) MSR 8597 access functions when running as Xen PV guest. The 8598 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8599 8600 xen_nopv [X86] 8601 Disables the PV optimizations forcing the HVM guest to 8602 run as generic HVM guest with no PV drivers. 8603 This option is obsoleted by the "nopv" option, which 8604 has equivalent effect for XEN platform. 8605 8606 xen_no_vector_callback 8607 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8608 event channel interrupts. 8609 8610 xen_scrub_pages= [XEN] 8611 Boolean option to control scrubbing pages before giving them back 8612 to Xen, for use by other domains. Can be also changed at runtime 8613 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8614 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8615 8616 xen_timer_slop= [X86-64,XEN,EARLY] 8617 Set the timer slop (in nanoseconds) for the virtual Xen 8618 timers (default is 100000). This adjusts the minimum 8619 delta of virtualized Xen timers, where lower values 8620 improve timer resolution at the expense of processing 8621 more timer interrupts. 8622 8623 xen.balloon_boot_timeout= [XEN] 8624 The time (in seconds) to wait before giving up to boot 8625 in case initial ballooning fails to free enough memory. 8626 Applies only when running as HVM or PVH guest and 8627 started with less memory configured than allowed at 8628 max. Default is 180. 8629 8630 xen.event_eoi_delay= [XEN] 8631 How long to delay EOI handling in case of event 8632 storms (jiffies). Default is 10. 8633 8634 xen.event_loop_timeout= [XEN] 8635 After which time (jiffies) the event handling loop 8636 should start to delay EOI handling. Default is 2. 8637 8638 xen.fifo_events= [XEN] 8639 Boolean parameter to disable using fifo event handling 8640 even if available. Normally fifo event handling is 8641 preferred over the 2-level event handling, as it is 8642 fairer and the number of possible event channels is 8643 much higher. Default is on (use fifo events). 8644 8645 xirc2ps_cs= [NET,PCMCIA] 8646 Format: 8647 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8648 8649 xive= [PPC] 8650 By default on POWER9 and above, the kernel will 8651 natively use the XIVE interrupt controller. This option 8652 allows the fallback firmware mode to be used: 8653 8654 off Fallback to firmware control of XIVE interrupt 8655 controller on both pseries and powernv 8656 platforms. Only useful on POWER9 and above. 8657 8658 xive.store-eoi=off [PPC] 8659 By default on POWER10 and above, the kernel will use 8660 stores for EOI handling when the XIVE interrupt mode 8661 is active. This option allows the XIVE driver to use 8662 loads instead, as on POWER9. 8663 8664 xhci-hcd.quirks [USB,KNL] 8665 A hex value specifying bitmask with supplemental xhci 8666 host controller quirks. Meaning of each bit can be 8667 consulted in header drivers/usb/host/xhci.h. 8668 8669 xmon [PPC,EARLY] 8670 Format: { early | on | rw | ro | off } 8671 Controls if xmon debugger is enabled. Default is off. 8672 Passing only "xmon" is equivalent to "xmon=early". 8673 early Call xmon as early as possible on boot; xmon 8674 debugger is called from setup_arch(). 8675 on xmon debugger hooks will be installed so xmon 8676 is only called on a kernel crash. Default mode, 8677 i.e. either "ro" or "rw" mode, is controlled 8678 with CONFIG_XMON_DEFAULT_RO_MODE. 8679 rw xmon debugger hooks will be installed so xmon 8680 is called only on a kernel crash, mode is write, 8681 meaning SPR registers, memory and, other data 8682 can be written using xmon commands. 8683 ro same as "rw" option above but SPR registers, 8684 memory, and other data can't be written using 8685 xmon commands. 8686 off xmon is disabled. 8687