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 DRM Direct Rendering Management support is enabled. 12 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 13 EARLY Parameter processed too early to be embedded in initrd. 14 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 15 EFI EFI Partitioning (GPT) is enabled 16 EVM Extended Verification Module 17 FB The frame buffer device is enabled. 18 FTRACE Function tracing enabled. 19 GCOV GCOV profiling is enabled. 20 HIBERNATION HIBERNATION is enabled. 21 HW Appropriate hardware is enabled. 22 HYPER_V HYPERV support is enabled. 23 IMA Integrity measurement architecture is enabled. 24 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 25 IPV6 IPv6 support is enabled. 26 ISAPNP ISA PnP code is enabled. 27 ISDN Appropriate ISDN support is enabled. 28 ISOL CPU Isolation is enabled. 29 JOY Appropriate joystick support is enabled. 30 KGDB Kernel debugger support is enabled. 31 KVM Kernel Virtual Machine support is enabled. 32 LIBATA Libata driver is enabled 33 LOONGARCH LoongArch architecture is enabled. 34 LOOP Loopback device support is enabled. 35 LP Printer support is enabled. 36 M68k M68k architecture is enabled. 37 These options have more detailed description inside of 38 Documentation/arch/m68k/kernel-options.rst. 39 MDA MDA console support is enabled. 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 PNP Plug & Play support is enabled. 53 PPC PowerPC architecture is enabled. 54 PPT Parallel port support is enabled. 55 PS2 Appropriate PS/2 support is enabled. 56 PV_OPS A paravirtualized kernel is enabled. 57 RAM RAM disk support is enabled. 58 RDT Intel Resource Director Technology. 59 RISCV RISCV architecture is enabled. 60 S390 S390 architecture is enabled. 61 SCSI Appropriate SCSI support is enabled. 62 A lot of drivers have their options described inside 63 the Documentation/scsi/ sub-directory. 64 SDW SoundWire support is enabled. 65 SECURITY Different security models are enabled. 66 SELINUX SELinux support is enabled. 67 SERIAL Serial support is enabled. 68 SH SuperH architecture is enabled. 69 SMP The kernel is an SMP kernel. 70 SPARC Sparc architecture is enabled. 71 SUSPEND System suspend states are enabled. 72 SWSUSP Software suspend (hibernation) is enabled. 73 TPM TPM drivers are enabled. 74 UMS USB Mass Storage support is enabled. 75 USB USB support is enabled. 76 NVME NVMe support is enabled 77 USBHID USB Human Interface Device support is enabled. 78 V4L Video For Linux support is enabled. 79 VGA The VGA console has been enabled. 80 VMMIO Driver for memory mapped virtio devices is enabled. 81 VT Virtual terminal support is enabled. 82 WDT Watchdog support is enabled. 83 X86-32 X86-32, aka i386 architecture is enabled. 84 X86-64 X86-64 architecture is enabled. 85 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 86 X86_UV SGI UV support is enabled. 87 XEN Xen support is enabled 88 XTENSA xtensa architecture is enabled. 89 90In addition, the following text indicates that the option 91 92 BOOT Is a boot loader parameter. 93 BUGS= Relates to possible processor bugs on the said processor. 94 KNL Is a kernel start-up parameter. 95 96 97Kernel parameters 98 99 accept_memory= [MM] 100 Format: { eager | lazy } 101 default: lazy 102 By default, unaccepted memory is accepted lazily to 103 avoid prolonged boot times. The lazy option will add 104 some runtime overhead until all memory is eventually 105 accepted. In most cases the overhead is negligible. 106 For some workloads or for debugging purposes 107 accept_memory=eager can be used to accept all memory 108 at once during boot. 109 110 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 111 Advanced Configuration and Power Interface 112 Format: { force | on | off | strict | noirq | rsdt | 113 copy_dsdt | nospcr } 114 force -- enable ACPI if default was off 115 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 116 off -- disable ACPI if default was on 117 noirq -- do not use ACPI for IRQ routing 118 strict -- Be less tolerant of platforms that are not 119 strictly ACPI specification compliant. 120 rsdt -- prefer RSDT over (default) XSDT 121 copy_dsdt -- copy DSDT to memory 122 nocmcff -- Disable firmware first mode for corrected 123 errors. This disables parsing the HEST CMC error 124 source to check if firmware has set the FF flag. This 125 may result in duplicate corrected error reports. 126 nospcr -- disable console in ACPI SPCR table as 127 default _serial_ console on ARM64 128 spcr -- enable console in ACPI SPCR table as 129 default _serial_ console on x86 130 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 131 "acpi=nospcr" are available 132 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 133 are available 134 135 See also Documentation/power/runtime_pm.rst, pci=noacpi 136 137 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 138 Format: <int> 139 2: use 2nd APIC table, if available 140 1,0: use 1st APIC table 141 default: 0 142 143 acpi_backlight= [HW,ACPI] 144 { vendor | video | native | none } 145 If set to vendor, prefer vendor-specific driver 146 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 147 of the ACPI video.ko driver. 148 If set to video, use the ACPI video.ko driver. 149 If set to native, use the device's native backlight mode. 150 If set to none, disable the ACPI backlight interface. 151 152 acpi_force_32bit_fadt_addr [ACPI,EARLY] 153 force FADT to use 32 bit addresses rather than the 154 64 bit X_* addresses. Some firmware have broken 64 155 bit addresses for force ACPI ignore these and use 156 the older legacy 32 bit addresses. 157 158 acpica_no_return_repair [HW, ACPI] 159 Disable AML predefined validation mechanism 160 This mechanism can repair the evaluation result to make 161 the return objects more ACPI specification compliant. 162 This option is useful for developers to identify the 163 root cause of an AML interpreter issue when the issue 164 has something to do with the repair mechanism. 165 166 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 167 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 168 Format: <int> 169 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 170 debug output. Bits in debug_layer correspond to a 171 _COMPONENT in an ACPI source file, e.g., 172 #define _COMPONENT ACPI_EVENTS 173 Bits in debug_level correspond to a level in 174 ACPI_DEBUG_PRINT statements, e.g., 175 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 176 The debug_level mask defaults to "info". See 177 Documentation/firmware-guide/acpi/debug.rst for more information about 178 debug layers and levels. 179 180 Enable processor driver info messages: 181 acpi.debug_layer=0x20000000 182 Enable AML "Debug" output, i.e., stores to the Debug 183 object while interpreting AML: 184 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 185 Enable all messages related to ACPI hardware: 186 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 187 188 Some values produce so much output that the system is 189 unusable. The "log_buf_len" parameter may be useful 190 if you need to capture more output. 191 192 acpi.poweroff_on_fatal= [ACPI] 193 {0 | 1} 194 Causes the system to poweroff when the ACPI bytecode signals 195 a fatal error. The default value of this setting is 1. 196 Overriding this value should only be done for diagnosing 197 ACPI firmware problems, as the system might behave erratically 198 after having encountered a fatal ACPI error. 199 200 acpi_enforce_resources= [ACPI] 201 { strict | lax | no } 202 Check for resource conflicts between native drivers 203 and ACPI OperationRegions (SystemIO and SystemMemory 204 only). IO ports and memory declared in ACPI might be 205 used by the ACPI subsystem in arbitrary AML code and 206 can interfere with legacy drivers. 207 strict (default): access to resources claimed by ACPI 208 is denied; legacy drivers trying to access reserved 209 resources will fail to bind to device using them. 210 lax: access to resources claimed by ACPI is allowed; 211 legacy drivers trying to access reserved resources 212 will bind successfully but a warning message is logged. 213 no: ACPI OperationRegions are not marked as reserved, 214 no further checks are performed. 215 216 acpi_force_table_verification [HW,ACPI,EARLY] 217 Enable table checksum verification during early stage. 218 By default, this is disabled due to x86 early mapping 219 size limitation. 220 221 acpi_irq_balance [HW,ACPI] 222 ACPI will balance active IRQs 223 default in APIC mode 224 225 acpi_irq_nobalance [HW,ACPI] 226 ACPI will not move active IRQs (default) 227 default in PIC mode 228 229 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 230 Format: <irq>,<irq>... 231 232 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 233 use by PCI 234 Format: <irq>,<irq>... 235 236 acpi_mask_gpe= [HW,ACPI] 237 Due to the existence of _Lxx/_Exx, some GPEs triggered 238 by unsupported hardware/firmware features can result in 239 GPE floodings that cannot be automatically disabled by 240 the GPE dispatcher. 241 This facility can be used to prevent such uncontrolled 242 GPE floodings. 243 Format: <byte> or <bitmap-list> 244 245 acpi_no_auto_serialize [HW,ACPI] 246 Disable auto-serialization of AML methods 247 AML control methods that contain the opcodes to create 248 named objects will be marked as "Serialized" by the 249 auto-serialization feature. 250 This feature is enabled by default. 251 This option allows to turn off the feature. 252 253 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 254 kernels. 255 256 acpi_no_static_ssdt [HW,ACPI,EARLY] 257 Disable installation of static SSDTs at early boot time 258 By default, SSDTs contained in the RSDT/XSDT will be 259 installed automatically and they will appear under 260 /sys/firmware/acpi/tables. 261 This option turns off this feature. 262 Note that specifying this option does not affect 263 dynamic table installation which will install SSDT 264 tables to /sys/firmware/acpi/tables/dynamic. 265 266 acpi_no_watchdog [HW,ACPI,WDT] 267 Ignore the ACPI-based watchdog interface (WDAT) and let 268 a native driver control the watchdog device instead. 269 270 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 271 Pass the RSDP address to the kernel, mostly used 272 on machines running EFI runtime service to boot the 273 second kernel for kdump. 274 275 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 276 Format: To spoof as Windows 98: ="Microsoft Windows" 277 278 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 279 of 2 which is mandated by ACPI 6) as the supported ACPI 280 specification revision (when using this switch, it may 281 be necessary to carry out a cold reboot _twice_ in a 282 row to make it take effect on the platform firmware). 283 284 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 285 acpi_osi="string1" # add string1 286 acpi_osi="!string2" # remove string2 287 acpi_osi=!* # remove all strings 288 acpi_osi=! # disable all built-in OS vendor 289 strings 290 acpi_osi=!! # enable all built-in OS vendor 291 strings 292 acpi_osi= # disable all strings 293 294 'acpi_osi=!' can be used in combination with single or 295 multiple 'acpi_osi="string1"' to support specific OS 296 vendor string(s). Note that such command can only 297 affect the default state of the OS vendor strings, thus 298 it cannot affect the default state of the feature group 299 strings and the current state of the OS vendor strings, 300 specifying it multiple times through kernel command line 301 is meaningless. This command is useful when one do not 302 care about the state of the feature group strings which 303 should be controlled by the OSPM. 304 Examples: 305 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 306 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 307 can make '_OSI("Windows 2000")' TRUE. 308 309 'acpi_osi=' cannot be used in combination with other 310 'acpi_osi=' command lines, the _OSI method will not 311 exist in the ACPI namespace. NOTE that such command can 312 only affect the _OSI support state, thus specifying it 313 multiple times through kernel command line is also 314 meaningless. 315 Examples: 316 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 317 FALSE. 318 319 'acpi_osi=!*' can be used in combination with single or 320 multiple 'acpi_osi="string1"' to support specific 321 string(s). Note that such command can affect the 322 current state of both the OS vendor strings and the 323 feature group strings, thus specifying it multiple times 324 through kernel command line is meaningful. But it may 325 still not able to affect the final state of a string if 326 there are quirks related to this string. This command 327 is useful when one want to control the state of the 328 feature group strings to debug BIOS issues related to 329 the OSPM features. 330 Examples: 331 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 332 '_OSI("Module Device")' FALSE. 333 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 334 '_OSI("Module Device")' TRUE. 335 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 336 equivalent to 337 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 338 and 339 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 340 they all will make '_OSI("Windows 2000")' TRUE. 341 342 acpi_pm_good [X86] 343 Override the pmtimer bug detection: force the kernel 344 to assume that this machine's pmtimer latches its value 345 and always returns good values. 346 347 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 348 Format: { level | edge | high | low } 349 350 acpi_skip_timer_override [HW,ACPI,EARLY] 351 Recognize and ignore IRQ0/pin2 Interrupt Override. 352 For broken nForce2 BIOS resulting in XT-PIC timer. 353 354 acpi_sleep= [HW,ACPI] Sleep options 355 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 356 s4_nohwsig, old_ordering, nonvs, 357 sci_force_enable, nobl } 358 See Documentation/power/video.rst for information on 359 s3_bios and s3_mode. 360 s3_beep is for debugging; it makes the PC's speaker beep 361 as soon as the kernel's real-mode entry point is called. 362 s4_hwsig causes the kernel to check the ACPI hardware 363 signature during resume from hibernation, and gracefully 364 refuse to resume if it has changed. This complies with 365 the ACPI specification but not with reality, since 366 Windows does not do this and many laptops do change it 367 on docking. So the default behaviour is to allow resume 368 and simply warn when the signature changes, unless the 369 s4_hwsig option is enabled. 370 s4_nohwsig prevents ACPI hardware signature from being 371 used (or even warned about) during resume. 372 old_ordering causes the ACPI 1.0 ordering of the _PTS 373 control method, with respect to putting devices into 374 low power states, to be enforced (the ACPI 2.0 ordering 375 of _PTS is used by default). 376 nonvs prevents the kernel from saving/restoring the 377 ACPI NVS memory during suspend/hibernation and resume. 378 sci_force_enable causes the kernel to set SCI_EN directly 379 on resume from S1/S3 (which is against the ACPI spec, 380 but some broken systems don't work without it). 381 nobl causes the internal blacklist of systems known to 382 behave incorrectly in some ways with respect to system 383 suspend and resume to be ignored (use wisely). 384 385 acpi_use_timer_override [HW,ACPI,EARLY] 386 Use timer override. For some broken Nvidia NF5 boards 387 that require a timer override, but don't have HPET 388 389 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 390 kernel's map of available physical RAM. 391 392 agp= [AGP] 393 { off | try_unsupported } 394 off: disable AGP support 395 try_unsupported: try to drive unsupported chipsets 396 (may crash computer or cause data corruption) 397 398 ALSA [HW,ALSA] 399 See Documentation/sound/alsa-configuration.rst 400 401 alignment= [KNL,ARM] 402 Allow the default userspace alignment fault handler 403 behaviour to be specified. Bit 0 enables warnings, 404 bit 1 enables fixups, and bit 2 sends a segfault. 405 406 align_va_addr= [X86-64] 407 Align virtual addresses by clearing slice [14:12] when 408 allocating a VMA at process creation time. This option 409 gives you up to 3% performance improvement on AMD F15h 410 machines (where it is enabled by default) for a 411 CPU-intensive style benchmark, and it can vary highly in 412 a microbenchmark depending on workload and compiler. 413 414 32: only for 32-bit processes 415 64: only for 64-bit processes 416 on: enable for both 32- and 64-bit processes 417 off: disable for both 32- and 64-bit processes 418 419 alloc_snapshot [FTRACE] 420 Allocate the ftrace snapshot buffer on boot up when the 421 main buffer is allocated. This is handy if debugging 422 and you need to use tracing_snapshot() on boot up, and 423 do not want to use tracing_snapshot_alloc() as it needs 424 to be done where GFP_KERNEL allocations are allowed. 425 426 allow_mismatched_32bit_el0 [ARM64,EARLY] 427 Allow execve() of 32-bit applications and setting of the 428 PER_LINUX32 personality on systems where only a strict 429 subset of the CPUs support 32-bit EL0. When this 430 parameter is present, the set of CPUs supporting 32-bit 431 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 432 and hot-unplug operations may be restricted. 433 434 See Documentation/arch/arm64/asymmetric-32bit.rst for more 435 information. 436 437 amd_iommu= [HW,X86-64] 438 Pass parameters to the AMD IOMMU driver in the system. 439 Possible values are: 440 fullflush - Deprecated, equivalent to iommu.strict=1 441 off - do not initialize any AMD IOMMU found in 442 the system 443 force_isolation - Force device isolation for all 444 devices. The IOMMU driver is not 445 allowed anymore to lift isolation 446 requirements as needed. This option 447 does not override iommu=pt 448 force_enable - Force enable the IOMMU on platforms known 449 to be buggy with IOMMU enabled. Use this 450 option with care. 451 pgtbl_v1 - Use v1 page table for DMA-API (Default). 452 pgtbl_v2 - Use v2 page table for DMA-API. 453 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 454 nohugepages - Limit page-sizes used for v1 page-tables 455 to 4 KiB. 456 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 457 to 4KiB/2Mib/1GiB. 458 459 460 amd_iommu_dump= [HW,X86-64] 461 Enable AMD IOMMU driver option to dump the ACPI table 462 for AMD IOMMU. With this option enabled, AMD IOMMU 463 driver will print ACPI tables for AMD IOMMU during 464 IOMMU initialization. 465 466 amd_iommu_intr= [HW,X86-64] 467 Specifies one of the following AMD IOMMU interrupt 468 remapping modes: 469 legacy - Use legacy interrupt remapping mode. 470 vapic - Use virtual APIC mode, which allows IOMMU 471 to inject interrupts directly into guest. 472 This mode requires kvm-amd.avic=1. 473 (Default when IOMMU HW support is present.) 474 475 amd_pstate= [X86,EARLY] 476 disable 477 Do not enable amd_pstate as the default 478 scaling driver for the supported processors 479 passive 480 Use amd_pstate with passive mode as a scaling driver. 481 In this mode autonomous selection is disabled. 482 Driver requests a desired performance level and platform 483 tries to match the same performance level if it is 484 satisfied by guaranteed performance level. 485 active 486 Use amd_pstate_epp driver instance as the scaling driver, 487 driver provides a hint to the hardware if software wants 488 to bias toward performance (0x0) or energy efficiency (0xff) 489 to the CPPC firmware. then CPPC power algorithm will 490 calculate the runtime workload and adjust the realtime cores 491 frequency. 492 guided 493 Activate guided autonomous mode. Driver requests minimum and 494 maximum performance level and the platform autonomously 495 selects a performance level in this range and appropriate 496 to the current workload. 497 498 amd_prefcore= 499 [X86] 500 disable 501 Disable amd-pstate preferred core. 502 503 amd_dynamic_epp= 504 [X86] 505 disable 506 Disable amd-pstate dynamic EPP. 507 enable 508 Enable amd-pstate dynamic EPP. 509 510 amijoy.map= [HW,JOY] Amiga joystick support 511 Map of devices attached to JOY0DAT and JOY1DAT 512 Format: <a>,<b> 513 See also Documentation/input/joydev/joystick.rst 514 515 analog.map= [HW,JOY] Analog joystick and gamepad support 516 Specifies type or capabilities of an analog joystick 517 connected to one of 16 gameports 518 Format: <type1>,<type2>,..<type16> 519 520 apc= [HW,SPARC] 521 Power management functions (SPARCstation-4/5 + deriv.) 522 Format: noidle 523 Disable APC CPU standby support. SPARCstation-Fox does 524 not play well with APC CPU idle - disable it if you have 525 APC and your system crashes randomly. 526 527 apic [APIC,X86-64] Use IO-APIC. Default. 528 529 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 530 Change the output verbosity while booting 531 Format: { quiet (default) | verbose | debug } 532 Change the amount of debugging information output 533 when initialising the APIC and IO-APIC components. 534 535 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 536 Format: { bsp (default) | all | none } 537 bsp: External NMI is delivered only to CPU 0 538 all: External NMIs are broadcast to all CPUs as a 539 backup of CPU 0 540 none: External NMI is masked for all CPUs. This is 541 useful so that a dump capture kernel won't be 542 shot down by NMI 543 544 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 545 apicmaintimer. Useful when your PIT timer is totally 546 broken. 547 548 autoconf= [IPV6] 549 See Documentation/networking/ipv6.rst. 550 551 apm= [APM] Advanced Power Management 552 See header of arch/x86/kernel/apm_32.c. 553 554 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 555 Format: { "0" | "1" } 556 See security/apparmor/Kconfig help text 557 0 -- disable. 558 1 -- enable. 559 Default value is set via kernel config option. 560 561 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 562 Format: <io>,<irq>,<nodeID> 563 564 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 565 32 bit applications. 566 567 arm64.nobti [ARM64] Unconditionally disable Branch Target 568 Identification support 569 570 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 571 support 572 573 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 574 Set instructions support 575 576 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 577 Monitoring support 578 579 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 580 support 581 582 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 583 support 584 585 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 586 Extension support 587 588 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 589 Extension support 590 591 ataflop= [HW,M68k] 592 593 atarimouse= [HW,MOUSE] Atari Mouse 594 595 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 596 EzKey and similar keyboards 597 598 atkbd.reset= [HW] Reset keyboard during initialization 599 600 atkbd.set= [HW] Select keyboard code set 601 Format: <int> (2 = AT (default), 3 = PS/2) 602 603 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 604 keyboards 605 606 atkbd.softraw= [HW] Choose between synthetic and real raw mode 607 Format: <bool> (0 = real, 1 = synthetic (default)) 608 609 atkbd.softrepeat= [HW] 610 Use software keyboard repeat 611 612 audit= [KNL] Enable the audit sub-system 613 Format: { "0" | "1" | "off" | "on" } 614 0 | off - kernel audit is disabled and can not be 615 enabled until the next reboot 616 unset - kernel audit is initialized but disabled and 617 will be fully enabled by the userspace auditd. 618 1 | on - kernel audit is initialized and partially 619 enabled, storing at most audit_backlog_limit 620 messages in RAM until it is fully enabled by the 621 userspace auditd. 622 Default: unset 623 624 audit_backlog_limit= [KNL] Set the audit queue size limit. 625 Format: <int> (must be >=0) 626 Default: 64 627 628 bau= [X86_UV] Enable the BAU on SGI UV. The default 629 behavior is to disable the BAU (i.e. bau=0). 630 Format: { "0" | "1" } 631 0 - Disable the BAU. 632 1 - Enable the BAU. 633 unset - Disable the BAU. 634 635 bdev_allow_write_mounted= 636 Format: <bool> 637 Control the ability to open a mounted block device 638 for writing, i.e., allow / disallow writes that bypass 639 the FS. This was implemented as a means to prevent 640 fuzzers from crashing the kernel by overwriting the 641 metadata underneath a mounted FS without its awareness. 642 This also prevents destructive formatting of mounted 643 filesystems by naive storage tooling that don't use 644 O_EXCL. Default is Y and can be changed through the 645 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 646 647 bert_disable [ACPI] 648 Disable BERT OS support on buggy BIOSes. 649 650 bgrt_disable [ACPI,X86,EARLY] 651 Disable BGRT to avoid flickering OEM logo. 652 653 blkdevparts= Manual partition parsing of block device(s) for 654 embedded devices based on command line input. 655 See Documentation/block/cmdline-partition.rst 656 657 boot_delay= [KNL,EARLY] 658 Milliseconds to delay each printk during boot. 659 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 660 and you may also have to specify "lpj=". Boot_delay 661 values larger than 10 seconds (10000) are assumed 662 erroneous and ignored. 663 Format: integer 664 665 bootconfig [KNL,EARLY] 666 Extended command line options can be added to an initrd 667 and this will cause the kernel to look for it. 668 669 See Documentation/admin-guide/bootconfig.rst 670 671 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 672 bttv.radio= Most important insmod options are available as 673 kernel args too. 674 bttv.pll= See Documentation/admin-guide/media/bttv.rst 675 bttv.tuner= 676 677 bulk_remove=off [PPC] This parameter disables the use of the pSeries 678 firmware feature for flushing multiple hpte entries 679 at a time. 680 681 c101= [NET] Moxa C101 synchronous serial card 682 683 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 684 Sometimes CPU hardware bugs make them report the cache 685 size incorrectly. The kernel will attempt work arounds 686 to fix known problems, but for some CPUs it is not 687 possible to determine what the correct size should be. 688 This option provides an override for these situations. 689 690 carrier_timeout= 691 [NET] Specifies amount of time (in seconds) that 692 the kernel should wait for a network carrier. By default 693 it waits 120 seconds. 694 695 ca_keys= [KEYS] This parameter identifies a specific key(s) on 696 the system trusted keyring to be used for certificate 697 trust validation. 698 format: { id:<keyid> | builtin } 699 700 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 701 algorithm. Accepted values range from 0 to 7 702 inclusive. See arch/mips/include/asm/pgtable-bits.h 703 for platform specific values (SB1, Loongson3 and 704 others). 705 706 ccw_timeout_log [S390] 707 See Documentation/arch/s390/common_io.rst for details. 708 709 cfi= [X86-64] Set Control Flow Integrity checking features 710 when CONFIG_FINEIBT is enabled. 711 Format: feature[,feature...] 712 Default: auto 713 714 auto: Use FineIBT if IBT available, otherwise kCFI. 715 Under FineIBT, enable "paranoid" mode when 716 FRED is not available. 717 off: Turn off CFI checking. 718 kcfi: Use kCFI (disable FineIBT). 719 fineibt: Use FineIBT (even if IBT not available). 720 norand: Do not re-randomize CFI hashes. 721 paranoid: Add caller hash checking under FineIBT. 722 bhi: Enable register poisoning to stop speculation 723 across FineIBT. (Disabled by default.) 724 warn: Do not enforce CFI checking: warn only. 725 debug: Report CFI initialization details. 726 727 cgroup_disable= [KNL] Disable a particular controller or optional feature 728 Format: {name of the controller(s) or feature(s) to disable} 729 The effects of cgroup_disable=foo are: 730 - foo isn't auto-mounted if you mount all cgroups in 731 a single hierarchy 732 - foo isn't visible as an individually mountable 733 subsystem 734 - if foo is an optional feature then the feature is 735 disabled and corresponding cgroup files are not 736 created 737 {Currently only "memory" controller deal with this and 738 cut the overhead, others just disable the usage. So 739 only cgroup_disable=memory is actually worthy} 740 Specifying "pressure" disables per-cgroup pressure 741 stall information accounting feature 742 743 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 744 Format: { { controller | "all" | "named" } 745 [,{ controller | "all" | "named" }...] } 746 Like cgroup_disable, but only applies to cgroup v1; 747 the blacklisted controllers remain available in cgroup2. 748 "all" blacklists all controllers and "named" disables 749 named mounts. Specifying both "all" and "named" disables 750 all v1 hierarchies. 751 752 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 753 Format: { "true" | "false" } 754 /proc/cgroups lists only v1 controllers by default. 755 This compatibility option enables listing also v2 756 controllers (whose v1 code is not compiled!), so that 757 semi-legacy software can check this file to decide 758 about usage of v2 (sic) controllers. 759 760 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 761 Format: { "true" | "false" } 762 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 763 764 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 765 Format: <string> 766 nosocket -- Disable socket memory accounting. 767 nokmem -- Disable kernel memory accounting. 768 nobpf -- Disable BPF memory accounting. 769 770 check_pages= [MM,EARLY] Enable sanity checking of pages after 771 allocations / before freeing. This adds checks to catch 772 double-frees, use-after-frees, and other sources of 773 page corruption by inspecting page internals (flags, 774 mapcount/refcount, memcg_data, etc.). 775 Format: { "0" | "1" } 776 Default: 0 (1 if CONFIG_DEBUG_VM is set) 777 778 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 779 Format: { "0" | "1" } 780 See security/selinux/Kconfig help text. 781 0 -- check protection applied by kernel (includes 782 any implied execute protection). 783 1 -- check protection requested by application. 784 Default value is set via a kernel config option. 785 Value can be changed at runtime via 786 /sys/fs/selinux/checkreqprot. 787 Setting checkreqprot to 1 is deprecated. 788 789 cio_ignore= [S390] 790 See Documentation/arch/s390/common_io.rst for details. 791 792 clearcpuid=X[,X...] [X86] 793 Disable CPUID feature X for the kernel. See 794 arch/x86/include/asm/cpufeatures.h for the valid bit 795 numbers X. Note the Linux-specific bits are not necessarily 796 stable over kernel options, but the vendor-specific 797 ones should be. 798 X can also be a string as appearing in the flags: line 799 in /proc/cpuinfo which does not have the above 800 instability issue. However, not all features have names 801 in /proc/cpuinfo. 802 Note that using this option will taint your kernel. 803 Also note that user programs calling CPUID directly 804 or using the feature without checking anything 805 will still see it. This just prevents it from 806 being used by the kernel or shown in /proc/cpuinfo. 807 Also note the kernel might malfunction if you disable 808 some critical bits. 809 810 clk_ignore_unused 811 [CLK] 812 Prevents the clock framework from automatically gating 813 clocks that have not been explicitly enabled by a Linux 814 device driver but are enabled in hardware at reset or 815 by the bootloader/firmware. Note that this does not 816 force such clocks to be always-on nor does it reserve 817 those clocks in any way. This parameter is useful for 818 debug and development, but should not be needed on a 819 platform with proper driver support. For more 820 information, see Documentation/driver-api/clk.rst. 821 822 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 823 [Deprecated] 824 Forces specified clocksource (if available) to be used 825 when calculating gettimeofday(). If specified 826 clocksource is not available, it defaults to PIT. 827 Format: { pit | tsc | cyclone | pmtmr } 828 829 clocksource= Override the default clocksource 830 Format: <string> 831 Override the default clocksource and use the clocksource 832 with the name specified. 833 Some clocksource names to choose from, depending on 834 the platform: 835 [all] jiffies (this is the base, fallback clocksource) 836 [ACPI] acpi_pm 837 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 838 pxa_timer,timer3,32k_counter,timer0_1 839 [X86-32] pit,hpet,tsc; 840 scx200_hrt on Geode; cyclone on IBM x440 841 [MIPS] MIPS 842 [PARISC] cr16 843 [S390] tod 844 [SH] SuperH 845 [SPARC64] tick 846 [X86-64] hpet,tsc 847 848 clocksource.arm_arch_timer.evtstrm= 849 [ARM,ARM64,EARLY] 850 Format: <bool> 851 Enable/disable the eventstream feature of the ARM 852 architected timer so that code using WFE-based polling 853 loops can be debugged more effectively on production 854 systems. 855 856 clocksource.verify_n_cpus= [KNL] 857 Limit the number of CPUs checked for clocksources 858 marked with CLOCK_SOURCE_VERIFY_PERCPU that 859 are marked unstable due to excessive skew. 860 A negative value says to check all CPUs, while 861 zero says not to check any. Values larger than 862 nr_cpu_ids are silently truncated to nr_cpu_ids. 863 The actual CPUs are chosen randomly, with 864 no replacement if the same CPU is chosen twice. 865 866 clocksource-wdtest.holdoff= [KNL] 867 Set the time in seconds that the clocksource 868 watchdog test waits before commencing its tests. 869 Defaults to zero when built as a module and to 870 10 seconds when built into the kernel. 871 872 cma=nn[MG]@[start[MG][-end[MG]]] 873 [KNL,CMA,EARLY] 874 Sets the size of kernel global memory area for 875 contiguous memory allocations and optionally the 876 placement constraint by the physical address range of 877 memory allocations. A value of 0 disables CMA 878 altogether. For more information, see 879 kernel/dma/contiguous.c 880 881 cma_pernuma=nn[MG] 882 [KNL,CMA,EARLY] 883 Sets the size of kernel per-numa memory area for 884 contiguous memory allocations. A value of 0 disables 885 per-numa CMA altogether. And If this option is not 886 specified, the default value is 0. 887 With per-numa CMA enabled, DMA users on node nid will 888 first try to allocate buffer from the pernuma area 889 which is located in node nid, if the allocation fails, 890 they will fallback to the global default memory area. 891 892 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 893 [KNL,CMA,EARLY] 894 Sets the size of kernel numa memory area for 895 contiguous memory allocations. It will reserve CMA 896 area for the specified node. 897 898 With numa CMA enabled, DMA users on node nid will 899 first try to allocate buffer from the numa area 900 which is located in node nid, if the allocation fails, 901 they will fallback to the global default memory area. 902 903 cmo_free_hint= [PPC] Format: { yes | no } 904 Specify whether pages are marked as being inactive 905 when they are freed. This is used in CMO environments 906 to determine OS memory pressure for page stealing by 907 a hypervisor. 908 Default: yes 909 910 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 911 Sets the size of memory pool for coherent, atomic dma 912 allocations, by default set to 256K. 913 914 com20020= [HW,NET] ARCnet - COM20020 chipset 915 Format: 916 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 917 918 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 919 Format: <io>[,<irq>] 920 921 com90xx= [HW,NET] 922 ARCnet - COM90xx chipset (memory-mapped buffers) 923 Format: <io>[,<irq>[,<memstart>]] 924 925 condev= [HW,S390] console device 926 conmode= 927 928 con3215_drop= [S390,EARLY] 3215 console drop mode. 929 Format: y|n|Y|N|1|0 930 When set to true, drop data on the 3215 console when 931 the console buffer is full. In this case the 932 operator using a 3270 terminal emulator (for example 933 x3270) does not have to enter the clear key for the 934 console output to advance and the kernel to continue. 935 This leads to a much faster boot time when a 3270 936 terminal emulator is active. If no 3270 terminal 937 emulator is used, this parameter has no effect. 938 939 console= [KNL] Output console device and options. 940 941 tty<n> Use the virtual console device <n>. 942 943 ttyS<n>[,options] 944 ttyUSB0[,options] 945 Use the specified serial port. The options are of 946 the form "bbbbpnf", where "bbbb" is the baud rate, 947 "p" is parity ("n", "o", or "e"), "n" is number of 948 bits, and "f" is flow control ("r" for RTS or 949 omit it). Default is "9600n8". 950 951 See Documentation/admin-guide/serial-console.rst for more 952 information. See 953 Documentation/networking/netconsole.rst for an 954 alternative. 955 956 <DEVNAME>:<n>.<n>[,options] 957 Use the specified serial port on the serial core bus. 958 The addressing uses DEVNAME of the physical serial port 959 device, followed by the serial core controller instance, 960 and the serial port instance. The options are the same 961 as documented for the ttyS addressing above. 962 963 The mapping of the serial ports to the tty instances 964 can be viewed with: 965 966 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 967 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 968 969 In the above example, the console can be addressed with 970 console=00:04:0.0. Note that a console addressed this 971 way will only get added when the related device driver 972 is ready. The use of an earlycon parameter in addition to 973 the console may be desired for console output early on. 974 975 uart[8250],io,<addr>[,options] 976 uart[8250],mmio,<addr>[,options] 977 uart[8250],mmio16,<addr>[,options] 978 uart[8250],mmio32,<addr>[,options] 979 uart[8250],0x<addr>[,options] 980 Start an early, polled-mode console on the 8250/16550 981 UART at the specified I/O port or MMIO address, 982 switching to the matching ttyS device later. 983 MMIO inter-register address stride is either 8-bit 984 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 985 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 986 to be equivalent to 'mmio'. 'options' are specified in 987 the same format described for ttyS above; if unspecified, 988 the h/w is not re-initialized. 989 990 hvc<n> Use the hypervisor console device <n>. This is for 991 both Xen and PowerPC hypervisors. 992 993 { null | "" } 994 Use to disable console output, i.e., to have kernel 995 console messages discarded. 996 This must be the only console= parameter used on the 997 kernel command line. 998 999 If the device connected to the port is not a TTY but a braille 1000 device, prepend "brl," before the device type, for instance 1001 console=brl,ttyS0 1002 For now, only VisioBraille is supported. 1003 1004 console_msg_format= 1005 [KNL] Change console messages format 1006 default 1007 By default we print messages on consoles in 1008 "[time stamp] text\n" format (time stamp may not be 1009 printed, depending on CONFIG_PRINTK_TIME or 1010 `printk_time' param). 1011 syslog 1012 Switch to syslog format: "<%u>[time stamp] text\n" 1013 IOW, each message will have a facility and loglevel 1014 prefix. The format is similar to one used by syslog() 1015 syscall, or to executing "dmesg -S --raw" or to reading 1016 from /proc/kmsg. 1017 1018 consoleblank= [KNL] The console blank (screen saver) timeout in 1019 seconds. A value of 0 disables the blank timer. 1020 Defaults to 0. 1021 1022 coredump_filter= 1023 [KNL] Change the default value for 1024 /proc/<pid>/coredump_filter. 1025 See also Documentation/filesystems/proc.rst. 1026 1027 coresight_cpu_debug.enable 1028 [ARM,ARM64] 1029 Format: <bool> 1030 Enable/disable the CPU sampling based debugging. 1031 0: default value, disable debugging 1032 1: enable debugging at boot time 1033 1034 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1035 Format: 1036 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1037 1038 cpuidle.off=1 [CPU_IDLE] 1039 disable the cpuidle sub-system 1040 1041 cpuidle.governor= 1042 [CPU_IDLE] Name of the cpuidle governor to use. 1043 1044 cpufreq.off=1 [CPU_FREQ] 1045 disable the cpufreq sub-system 1046 1047 cpufreq.default_governor= 1048 [CPU_FREQ] Name of the default cpufreq governor or 1049 policy to use. This governor must be registered in the 1050 kernel before the cpufreq driver probes. 1051 1052 cpu_init_udelay=N 1053 [X86,EARLY] Delay for N microsec between assert and de-assert 1054 of APIC INIT to start processors. This delay occurs 1055 on every CPU online, such as boot, and resume from suspend. 1056 Default: 10000 1057 1058 cpuhp.parallel= 1059 [SMP] Enable/disable parallel bringup of secondary CPUs 1060 Format: <bool> 1061 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1062 the parameter has no effect. 1063 1064 crash_kexec_post_notifiers 1065 Only jump to kdump kernel after running the panic 1066 notifiers and dumping kmsg. This option increases 1067 the risks of a kdump failure, since some panic 1068 notifiers can make the crashed kernel more unstable. 1069 In configurations where kdump may not be reliable, 1070 running the panic notifiers could allow collecting 1071 more data on dmesg, like stack traces from other CPUS 1072 or extra data dumped by panic_print. Note that some 1073 configurations enable this option unconditionally, 1074 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1075 1076 crashkernel=size[KMG][@offset[KMG]] 1077 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1078 upon panic. This parameter reserves the physical 1079 memory region [offset, offset + size] for that kernel 1080 image. If '@offset' is omitted, then a suitable offset 1081 is selected automatically. 1082 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1083 under 4G first, and fall back to reserve region above 1084 4G when '@offset' hasn't been specified. 1085 See Documentation/admin-guide/kdump/kdump.rst for further details. 1086 1087 crashkernel=range1:size1[,range2:size2,...][@offset] 1088 [KNL] Same as above, but depends on the memory 1089 in the running system. The syntax of range is 1090 start-[end] where start and end are both 1091 a memory unit (amount[KMG]). See also 1092 Documentation/admin-guide/kdump/kdump.rst for an example. 1093 1094 crashkernel=size[KMG],high 1095 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1096 above 4G. 1097 Allow kernel to allocate physical memory region from top, 1098 so could be above 4G if system have more than 4G ram 1099 installed. Otherwise memory region will be allocated 1100 below 4G, if available. 1101 It will be ignored if crashkernel=X is specified. 1102 crashkernel=size[KMG],low 1103 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1104 When crashkernel=X,high is passed, kernel could allocate 1105 physical memory region above 4G, that cause second kernel 1106 crash on system that require some amount of low memory, 1107 e.g. swiotlb requires at least 64M+32K low memory, also 1108 enough extra low memory is needed to make sure DMA buffers 1109 for 32-bit devices won't run out. Kernel would try to allocate 1110 default size of memory below 4G automatically. The default 1111 size is platform dependent. 1112 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1113 --> arm64: 128MiB 1114 --> riscv: 128MiB 1115 --> loongarch: 128MiB 1116 This one lets the user specify own low range under 4G 1117 for second kernel instead. 1118 0: to disable low allocation. 1119 It will be ignored when crashkernel=X,high is not used 1120 or memory reserved is below 4G. 1121 crashkernel=size[KMG],cma 1122 [KNL, X86, ppc] Reserve additional crash kernel memory from 1123 CMA. This reservation is usable by the first system's 1124 userspace memory and kernel movable allocations (memory 1125 balloon, zswap). Pages allocated from this memory range 1126 will not be included in the vmcore so this should not 1127 be used if dumping of userspace memory is intended and 1128 it has to be expected that some movable kernel pages 1129 may be missing from the dump. 1130 1131 A standard crashkernel reservation, as described above, 1132 is still needed to hold the crash kernel and initrd. 1133 1134 This option increases the risk of a kdump failure: DMA 1135 transfers configured by the first kernel may end up 1136 corrupting the second kernel's memory. 1137 1138 This reservation method is intended for systems that 1139 can't afford to sacrifice enough memory for standard 1140 crashkernel reservation and where less reliable and 1141 possibly incomplete kdump is preferable to no kdump at 1142 all. 1143 1144 cryptomgr.notests 1145 [KNL] Disable crypto self-tests 1146 1147 cs89x0_dma= [HW,NET] 1148 Format: <dma> 1149 1150 cs89x0_media= [HW,NET] 1151 Format: { rj45 | aui | bnc } 1152 1153 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1154 function call handling. When switched on, 1155 additional debug data is printed to the console 1156 in case a hanging CPU is detected, and that 1157 CPU is pinged again in order to try to resolve 1158 the hang situation. The default value of this 1159 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1160 Kconfig option. 1161 1162 dasd= [HW,NET] 1163 See header of drivers/s390/block/dasd_devmap.c. 1164 1165 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1166 (one device per port) 1167 Format: <port#>,<type> 1168 See also Documentation/input/devices/joystick-parport.rst 1169 1170 debug [KNL,EARLY] Enable kernel debugging (events log level). 1171 1172 debug_boot_weak_hash 1173 [KNL,EARLY] Enable printing [hashed] pointers early in the 1174 boot sequence. If enabled, we use a weak hash instead 1175 of siphash to hash pointers. Use this option if you are 1176 seeing instances of '(___ptrval___)') and need to see a 1177 value (hashed pointer) instead. Cryptographically 1178 insecure, please do not use on production kernels. 1179 1180 debug_locks_verbose= 1181 [KNL] verbose locking self-tests 1182 Format: <int> 1183 Print debugging info while doing the locking API 1184 self-tests. 1185 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1186 (no extra messages), setting it to -1 (all bits set) 1187 will print _a_lot_ more information - normally only 1188 useful to lockdep developers. 1189 1190 debug_objects [KNL,EARLY] Enable object debugging 1191 1192 debug_guardpage_minorder= 1193 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1194 parameter allows control of the order of pages that will 1195 be intentionally kept free (and hence protected) by the 1196 buddy allocator. Bigger value increase the probability 1197 of catching random memory corruption, but reduce the 1198 amount of memory for normal system use. The maximum 1199 possible value is MAX_PAGE_ORDER/2. Setting this 1200 parameter to 1 or 2 should be enough to identify most 1201 random memory corruption problems caused by bugs in 1202 kernel or driver code when a CPU writes to (or reads 1203 from) a random memory location. Note that there exists 1204 a class of memory corruptions problems caused by buggy 1205 H/W or F/W or by drivers badly programming DMA 1206 (basically when memory is written at bus level and the 1207 CPU MMU is bypassed) which are not detectable by 1208 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1209 help tracking down these problems. 1210 1211 debug_pagealloc= 1212 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1213 enables the feature at boot time. By default, it is 1214 disabled and the system will work mostly the same as a 1215 kernel built without CONFIG_DEBUG_PAGEALLOC. 1216 Note: to get most of debug_pagealloc error reports, it's 1217 useful to also enable the page_owner functionality. 1218 on: enable the feature 1219 1220 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1221 userspace and debugfs internal clients. 1222 Format: { on, off } 1223 on: All functions are enabled. 1224 off: Filesystem is not registered and clients 1225 get a -EPERM as result when trying to register files 1226 or directories within debugfs. 1227 This is equivalent of the runtime functionality if 1228 debugfs was not enabled in the kernel at all. 1229 Default value is set in build-time with a kernel configuration. 1230 1231 debugpat [X86] Enable PAT debugging 1232 1233 default_hugepagesz= 1234 [HW] The size of the default HugeTLB page. This is 1235 the size represented by the legacy /proc/ hugepages 1236 APIs. In addition, this is the default hugetlb size 1237 used for shmget(), mmap() and mounting hugetlbfs 1238 filesystems. If not specified, defaults to the 1239 architecture's default huge page size. Huge page 1240 sizes are architecture dependent. See also 1241 Documentation/admin-guide/mm/hugetlbpage.rst. 1242 Format: size[KMG] 1243 1244 deferred_probe_timeout= 1245 [KNL] Debugging option to set a timeout in seconds for 1246 deferred probe to give up waiting on dependencies to 1247 probe. Only specific dependencies (subsystems or 1248 drivers) that have opted in will be ignored. A timeout 1249 of 0 will timeout at the end of initcalls. If the time 1250 out hasn't expired, it'll be restarted by each 1251 successful driver registration. This option will also 1252 dump out devices still on the deferred probe list after 1253 retrying. 1254 1255 delayacct [KNL] Enable per-task delay accounting 1256 1257 dell_smm_hwmon.ignore_dmi= 1258 [HW] Continue probing hardware even if DMI data 1259 indicates that the driver is running on unsupported 1260 hardware. 1261 1262 dell_smm_hwmon.force= 1263 [HW] Activate driver even if SMM BIOS signature does 1264 not match list of supported models and enable otherwise 1265 blacklisted features. 1266 1267 dell_smm_hwmon.power_status= 1268 [HW] Report power status in /proc/i8k 1269 (disabled by default). 1270 1271 dell_smm_hwmon.restricted= 1272 [HW] Allow controlling fans only if SYS_ADMIN 1273 capability is set. 1274 1275 dell_smm_hwmon.fan_mult= 1276 [HW] Factor to multiply fan speed with. 1277 1278 dell_smm_hwmon.fan_max= 1279 [HW] Maximum configurable fan speed. 1280 1281 dfltcc= [HW,S390] 1282 Format: { on | off | def_only | inf_only | always } 1283 on: s390 zlib hardware support for compression on 1284 level 1 and decompression (default) 1285 off: No s390 zlib hardware support 1286 def_only: s390 zlib hardware support for deflate 1287 only (compression on level 1) 1288 inf_only: s390 zlib hardware support for inflate 1289 only (decompression) 1290 always: Same as 'on' but ignores the selected compression 1291 level always using hardware support (used for debugging) 1292 1293 dhash_entries= [KNL] 1294 Set number of hash buckets for dentry cache. 1295 1296 disable_1tb_segments [PPC,EARLY] 1297 Disables the use of 1TB hash page table segments. This 1298 causes the kernel to fall back to 256MB segments which 1299 can be useful when debugging issues that require an SLB 1300 miss to occur. 1301 1302 disable= [IPV6] 1303 See Documentation/networking/ipv6.rst. 1304 1305 disable_radix [PPC,EARLY] 1306 Disable RADIX MMU mode on POWER9 1307 1308 disable_tlbie [PPC] 1309 Disable TLBIE instruction. Currently does not work 1310 with KVM, with HASH MMU, or with coherent accelerators. 1311 1312 disable_ddw [PPC/PSERIES,EARLY] 1313 Disable Dynamic DMA Window support. Use this 1314 to workaround buggy firmware. 1315 1316 disable_ipv6= [IPV6] 1317 See Documentation/networking/ipv6.rst. 1318 1319 disable_mtrr_cleanup [X86,EARLY] 1320 The kernel tries to adjust MTRR layout from continuous 1321 to discrete, to make X server driver able to add WB 1322 entry later. This parameter disables that. 1323 1324 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1325 By default the kernel will trim any uncacheable 1326 memory out of your available memory pool based on 1327 MTRR settings. This parameter disables that behavior, 1328 possibly causing your machine to run very slowly. 1329 1330 disable_timer_pin_1 [X86,EARLY] 1331 Disable PIN 1 of APIC timer 1332 Can be useful to work around chipset bugs. 1333 1334 dis_ucode_ldr [X86] Disable the microcode loader. 1335 1336 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1337 this option disables the debugging code at boot. 1338 1339 dma_debug_entries=<number> 1340 This option allows to tune the number of preallocated 1341 entries for DMA-API debugging code. One entry is 1342 required per DMA-API allocation. Use this if the 1343 DMA-API debugging code disables itself because the 1344 architectural default is too low. 1345 1346 dma_debug_driver=<driver_name> 1347 With this option the DMA-API debugging driver 1348 filter feature can be enabled at boot time. Just 1349 pass the driver to filter for as the parameter. 1350 The filter can be disabled or changed to another 1351 driver later using sysfs. 1352 1353 reg_file_data_sampling= 1354 [X86] Controls mitigation for Register File Data 1355 Sampling (RFDS) vulnerability. RFDS is a CPU 1356 vulnerability which may allow userspace to infer 1357 kernel data values previously stored in floating point 1358 registers, vector registers, or integer registers. 1359 RFDS only affects Intel Atom processors. 1360 1361 on: Turns ON the mitigation. 1362 off: Turns OFF the mitigation. 1363 1364 This parameter overrides the compile time default set 1365 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1366 disabled when other VERW based mitigations (like MDS) 1367 are enabled. In order to disable RFDS mitigation all 1368 VERW based mitigations need to be disabled. 1369 1370 For details see: 1371 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1372 1373 dm_verity.keyring_unsealed= 1374 [KNL] When set to 1, leave the dm-verity keyring 1375 unsealed after initialization so userspace can 1376 provision keys. Once the keyring is restricted 1377 it becomes active and is searched during signature 1378 verification. 1379 1380 driver_async_probe= [KNL] 1381 List of driver names to be probed asynchronously. * 1382 matches with all driver names. If * is specified, the 1383 rest of the listed driver names are those that will NOT 1384 match the *. 1385 Format: <driver_name1>,<driver_name2>... 1386 1387 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1388 Broken monitors, graphic adapters, KVMs and EDIDless 1389 panels may send no or incorrect EDID data sets. 1390 This parameter allows to specify an EDID data sets 1391 in the /lib/firmware directory that are used instead. 1392 An EDID data set will only be used for a particular 1393 connector, if its name and a colon are prepended to 1394 the EDID name. Each connector may use a unique EDID 1395 data set by separating the files with a comma. An EDID 1396 data set with no connector name will be used for 1397 any connectors not explicitly specified. 1398 1399 dscc4.setup= [NET] 1400 1401 dt_cpu_ftrs= [PPC,EARLY] 1402 Format: {"off" | "known"} 1403 Control how the dt_cpu_ftrs device-tree binding is 1404 used for CPU feature discovery and setup (if it 1405 exists). 1406 off: Do not use it, fall back to legacy cpu table. 1407 known: Do not pass through unknown features to guests 1408 or userspace, only those that the kernel is aware of. 1409 1410 dump_apple_properties [X86] 1411 Dump name and content of EFI device properties on 1412 x86 Macs. Useful for driver authors to determine 1413 what data is available or for reverse-engineering. 1414 1415 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1416 <module>.dyndbg[="val"] 1417 Enable debug messages at boot time. See 1418 Documentation/admin-guide/dynamic-debug-howto.rst 1419 for details. 1420 1421 early_ioremap_debug [KNL,EARLY] 1422 Enable debug messages in early_ioremap support. This 1423 is useful for tracking down temporary early mappings 1424 which are not unmapped. 1425 1426 earlycon= [KNL,EARLY] Output early console device and options. 1427 1428 When used with no options, the early console is 1429 determined by stdout-path property in device tree's 1430 chosen node or the ACPI SPCR table if supported by 1431 the platform. 1432 1433 cdns,<addr>[,options] 1434 Start an early, polled-mode console on a Cadence 1435 (xuartps) serial port at the specified address. Only 1436 supported option is baud rate. If baud rate is not 1437 specified, the serial port must already be setup and 1438 configured. 1439 1440 uart[8250],io,<addr>[,options[,uartclk]] 1441 uart[8250],mmio,<addr>[,options[,uartclk]] 1442 uart[8250],mmio32,<addr>[,options[,uartclk]] 1443 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1444 uart[8250],0x<addr>[,options] 1445 Start an early, polled-mode console on the 8250/16550 1446 UART at the specified I/O port or MMIO address. 1447 MMIO inter-register address stride is either 8-bit 1448 (mmio) or 32-bit (mmio32 or mmio32be). 1449 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1450 to be equivalent to 'mmio'. 'options' are specified 1451 in the same format described for "console=ttyS<n>"; if 1452 unspecified, the h/w is not initialized. 'uartclk' is 1453 the uart clock frequency; if unspecified, it is set 1454 to 'BASE_BAUD' * 16. 1455 1456 pl011,<addr> 1457 pl011,mmio32,<addr> 1458 Start an early, polled-mode console on a pl011 serial 1459 port at the specified address. The pl011 serial port 1460 must already be setup and configured. Options are not 1461 yet supported. If 'mmio32' is specified, then only 1462 the driver will use only 32-bit accessors to read/write 1463 the device registers. 1464 1465 liteuart,<addr> 1466 Start an early console on a litex serial port at the 1467 specified address. The serial port must already be 1468 setup and configured. Options are not yet supported. 1469 1470 meson,<addr> 1471 Start an early, polled-mode console on a meson serial 1472 port at the specified address. The serial port must 1473 already be setup and configured. Options are not yet 1474 supported. 1475 1476 msm_serial,<addr> 1477 Start an early, polled-mode console on an msm serial 1478 port at the specified address. The serial port 1479 must already be setup and configured. Options are not 1480 yet supported. 1481 1482 msm_serial_dm,<addr> 1483 Start an early, polled-mode console on an msm serial 1484 dm port at the specified address. The serial port 1485 must already be setup and configured. Options are not 1486 yet supported. 1487 1488 owl,<addr> 1489 Start an early, polled-mode console on a serial port 1490 of an Actions Semi SoC, such as S500 or S900, at the 1491 specified address. The serial port must already be 1492 setup and configured. Options are not yet supported. 1493 1494 rda,<addr> 1495 Start an early, polled-mode console on a serial port 1496 of an RDA Micro SoC, such as RDA8810PL, at the 1497 specified address. The serial port must already be 1498 setup and configured. Options are not yet supported. 1499 1500 sbi 1501 Use RISC-V SBI (Supervisor Binary Interface) for early 1502 console. 1503 1504 smh Use ARM semihosting calls for early console. 1505 1506 s3c2410,<addr> 1507 s3c2412,<addr> 1508 s3c2440,<addr> 1509 s3c6400,<addr> 1510 s5pv210,<addr> 1511 exynos4210,<addr> 1512 Use early console provided by serial driver available 1513 on Samsung SoCs, requires selecting proper type and 1514 a correct base address of the selected UART port. The 1515 serial port must already be setup and configured. 1516 Options are not yet supported. 1517 1518 lantiq,<addr> 1519 Start an early, polled-mode console on a lantiq serial 1520 (lqasc) port at the specified address. The serial port 1521 must already be setup and configured. Options are not 1522 yet supported. 1523 1524 lpuart,<addr> 1525 lpuart32,<addr> 1526 Use early console provided by Freescale LP UART driver 1527 found on Freescale Vybrid and QorIQ LS1021A processors. 1528 A valid base address must be provided, and the serial 1529 port must already be setup and configured. 1530 1531 ec_imx21,<addr> 1532 ec_imx6q,<addr> 1533 Start an early, polled-mode, output-only console on the 1534 Freescale i.MX UART at the specified address. The UART 1535 must already be setup and configured. 1536 1537 ar3700_uart,<addr> 1538 Start an early, polled-mode console on the 1539 Armada 3700 serial port at the specified 1540 address. The serial port must already be setup 1541 and configured. Options are not yet supported. 1542 1543 qcom_geni,<addr> 1544 Start an early, polled-mode console on a Qualcomm 1545 Generic Interface (GENI) based serial port at the 1546 specified address. The serial port must already be 1547 setup and configured. Options are not yet supported. 1548 1549 efifb,[options] 1550 Start an early, unaccelerated console on the EFI 1551 memory mapped framebuffer (if available). On cache 1552 coherent non-x86 systems that use system memory for 1553 the framebuffer, pass the 'ram' option so that it is 1554 mapped with the correct attributes. 1555 1556 linflex,<addr> 1557 Use early console provided by Freescale LINFlexD UART 1558 serial driver for NXP S32V234 SoCs. A valid base 1559 address must be provided, and the serial port must 1560 already be setup and configured. 1561 1562 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1563 earlyprintk=vga 1564 earlyprintk=sclp 1565 earlyprintk=xen 1566 earlyprintk=serial[,ttySn[,baudrate]] 1567 earlyprintk=serial[,0x...[,baudrate]] 1568 earlyprintk=ttySn[,baudrate] 1569 earlyprintk=dbgp[debugController#] 1570 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1571 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1572 earlyprintk=xdbc[xhciController#] 1573 earlyprintk=bios 1574 1575 earlyprintk is useful when the kernel crashes before 1576 the normal console is initialized. It is not enabled by 1577 default because it has some cosmetic problems. 1578 1579 Use "nocfg" to skip UART configuration, assume 1580 BIOS/firmware has configured UART correctly. 1581 1582 Append ",keep" to not disable it when the real console 1583 takes over. 1584 1585 Only one of vga, serial, or usb debug port can 1586 be used at a time. 1587 1588 Currently only ttyS0 and ttyS1 may be specified by 1589 name. Other I/O ports may be explicitly specified 1590 on some architectures (x86 and arm at least) by 1591 replacing ttySn with an I/O port address, like this: 1592 earlyprintk=serial,0x1008,115200 1593 You can find the port for a given device in 1594 /proc/tty/driver/serial: 1595 2: uart:ST16650V2 port:00001008 irq:18 ... 1596 1597 Interaction with the standard serial driver is not 1598 very good. 1599 1600 The VGA output is eventually overwritten by 1601 the real console. 1602 1603 The xen option can only be used in Xen domains. 1604 1605 The sclp output can only be used on s390. 1606 1607 The bios output can only be used on SuperH. 1608 1609 The optional "force" to "pciserial" enables use of a 1610 PCI device even when its classcode is not of the 1611 UART class. 1612 1613 edac_report= [HW,EDAC] Control how to report EDAC event 1614 Format: {"on" | "off" | "force"} 1615 on: enable EDAC to report H/W event. May be overridden 1616 by other higher priority error reporting module. 1617 off: disable H/W event reporting through EDAC. 1618 force: enforce the use of EDAC to report H/W event. 1619 default: on. 1620 1621 edd= [EDD] 1622 Format: {"off" | "on" | "skip[mbr]"} 1623 1624 efi= [EFI,EARLY] 1625 Format: { "debug", "disable_early_pci_dma", 1626 "nochunk", "noruntime", "nosoftreserve", 1627 "novamap", "no_disable_early_pci_dma" } 1628 debug: enable misc debug output. 1629 disable_early_pci_dma: disable the busmaster bit on all 1630 PCI bridges while in the EFI boot stub. 1631 nochunk: disable reading files in "chunks" in the EFI 1632 boot stub, as chunking can cause problems with some 1633 firmware implementations. 1634 noruntime : disable EFI runtime services support 1635 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1636 attribute may cause the kernel to reserve the 1637 memory range for a memory mapping driver to 1638 claim. Specify efi=nosoftreserve to disable this 1639 reservation and treat the memory by its base type 1640 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1641 novamap: do not call SetVirtualAddressMap(). 1642 no_disable_early_pci_dma: Leave the busmaster bit set 1643 on all PCI bridges while in the EFI boot stub 1644 1645 efi_no_storage_paranoia [EFI,X86,EARLY] 1646 Using this parameter you can use more than 50% of 1647 your efi variable storage. Use this parameter only if 1648 you are really sure that your UEFI does sane gc and 1649 fulfills the spec otherwise your board may brick. 1650 1651 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1652 that is to be dynamically loaded by Linux. If there are 1653 multiple variables with the same name but with different 1654 vendor GUIDs, all of them will be loaded. See 1655 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1656 1657 1658 eisa_irq_edge= [PARISC,HW] 1659 See header of drivers/parisc/eisa.c. 1660 1661 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1662 Format: ekgdboc=kbd 1663 1664 This is designed to be used in conjunction with 1665 the boot argument: earlyprintk=vga 1666 1667 This parameter works in place of the kgdboc parameter 1668 but can only be used if the backing tty is available 1669 very early in the boot process. For early debugging 1670 via a serial port see kgdboc_earlycon instead. 1671 1672 elanfreq= [X86-32] 1673 See comment before function elanfreq_setup() in 1674 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1675 1676 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1677 Specifies physical address of start of kernel core 1678 image elf header and optionally the size. Generally 1679 kexec loader will pass this option to capture kernel. 1680 See Documentation/admin-guide/kdump/kdump.rst for details. 1681 1682 enable_mtrr_cleanup [X86,EARLY] 1683 The kernel tries to adjust MTRR layout from continuous 1684 to discrete, to make X server driver able to add WB 1685 entry later. This parameter enables that. 1686 1687 enable_timer_pin_1 [X86] 1688 Enable PIN 1 of APIC timer 1689 Can be useful to work around chipset bugs 1690 (in particular on some ATI chipsets). 1691 The kernel tries to set a reasonable default. 1692 1693 enforcing= [SELINUX] Set initial enforcing status. 1694 Format: {"0" | "1"} 1695 See security/selinux/Kconfig help text. 1696 0 -- permissive (log only, no denials). 1697 1 -- enforcing (deny and log). 1698 Default value is 0. 1699 Value can be changed at runtime via 1700 /sys/fs/selinux/enforce. 1701 1702 erst_disable [ACPI] 1703 Disable Error Record Serialization Table (ERST) 1704 support. 1705 1706 ether= [HW,NET] Ethernet cards parameters 1707 This option is obsoleted by the "netdev=" option, which 1708 has equivalent usage. See its documentation for details. 1709 1710 evm= [EVM] 1711 Format: { "fix" } 1712 Permit 'security.evm' to be updated regardless of 1713 current integrity status. 1714 1715 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1716 stages so cover more early boot allocations. 1717 Please note that as side effect some optimizations 1718 might be disabled to achieve that (e.g. parallelized 1719 memory initialization is disabled) so the boot process 1720 might take longer, especially on systems with a lot of 1721 memory. Available with CONFIG_PAGE_EXTENSION=y. 1722 1723 failslab= 1724 fail_usercopy= 1725 fail_page_alloc= 1726 fail_skb_realloc= 1727 fail_make_request=[KNL] 1728 General fault injection mechanism. 1729 Format: <interval>,<probability>,<space>,<times> 1730 See also Documentation/fault-injection/. 1731 1732 fb_tunnels= [NET] 1733 Format: { initns | none } 1734 See Documentation/admin-guide/sysctl/net.rst for 1735 fb_tunnels_only_for_init_ns 1736 1737 floppy= [HW] 1738 See Documentation/admin-guide/blockdev/floppy.rst. 1739 1740 forcepae [X86-32] 1741 Forcefully enable Physical Address Extension (PAE). 1742 Many Pentium M systems disable PAE but may have a 1743 functionally usable PAE implementation. 1744 Warning: use of this parameter will taint the kernel 1745 and may cause unknown problems. 1746 1747 fred= [X86-64] 1748 Enable/disable Flexible Return and Event Delivery. 1749 Format: { on | off } 1750 on: enable FRED when it's present, the default setting. 1751 off: disable FRED. 1752 1753 ftrace=[tracer] 1754 [FTRACE] will set and start the specified tracer 1755 as early as possible in order to facilitate early 1756 boot debugging. 1757 1758 ftrace_boot_snapshot 1759 [FTRACE] On boot up, a snapshot will be taken of the 1760 ftrace ring buffer that can be read at: 1761 /sys/kernel/tracing/snapshot. 1762 This is useful if you need tracing information from kernel 1763 boot up that is likely to be overridden by user space 1764 start up functionality. 1765 1766 Optionally, the snapshot can also be defined for a tracing 1767 instance that was created by the trace_instance= command 1768 line parameter. 1769 1770 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1771 1772 The above will cause the "foo" tracing instance to trigger 1773 a snapshot at the end of boot up. 1774 1775 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1776 ,<instance>=2(orig_cpu)] 1777 [FTRACE] will dump the trace buffers on oops. 1778 If no parameter is passed, ftrace will dump global 1779 buffers of all CPUs, if you pass 2 or orig_cpu, it 1780 will dump only the buffer of the CPU that triggered 1781 the oops, or the specific instance will be dumped if 1782 its name is passed. Multiple instance dump is also 1783 supported, and instances are separated by commas. Each 1784 instance supports only dump on CPU that triggered the 1785 oops by passing 2 or orig_cpu to it. 1786 1787 ftrace_dump_on_oops=foo=orig_cpu 1788 1789 The above will dump only the buffer of "foo" instance 1790 on CPU that triggered the oops. 1791 1792 ftrace_dump_on_oops,foo,bar=orig_cpu 1793 1794 The above will dump global buffer on all CPUs, the 1795 buffer of "foo" instance on all CPUs and the buffer 1796 of "bar" instance on CPU that triggered the oops. 1797 1798 ftrace_filter=[function-list] 1799 [FTRACE] Limit the functions traced by the function 1800 tracer at boot up. function-list is a comma-separated 1801 list of functions. This list can be changed at run 1802 time by the set_ftrace_filter file in the debugfs 1803 tracing directory. 1804 1805 ftrace_notrace=[function-list] 1806 [FTRACE] Do not trace the functions specified in 1807 function-list. This list can be changed at run time 1808 by the set_ftrace_notrace file in the debugfs 1809 tracing directory. 1810 1811 ftrace_graph_filter=[function-list] 1812 [FTRACE] Limit the top level callers functions traced 1813 by the function graph tracer at boot up. 1814 function-list is a comma-separated list of functions 1815 that can be changed at run time by the 1816 set_graph_function file in the debugfs tracing directory. 1817 1818 ftrace_graph_notrace=[function-list] 1819 [FTRACE] Do not trace from the functions specified in 1820 function-list. This list is a comma-separated list of 1821 functions that can be changed at run time by the 1822 set_graph_notrace file in the debugfs tracing directory. 1823 1824 ftrace_graph_max_depth=<uint> 1825 [FTRACE] Used with the function graph tracer. This is 1826 the max depth it will trace into a function. This value 1827 can be changed at run time by the max_graph_depth file 1828 in the tracefs tracing directory. default: 0 (no limit) 1829 1830 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1831 devices by scanning the firmware to infer the 1832 consumer/supplier relationships. This feature is 1833 especially useful when drivers are loaded as modules as 1834 it ensures proper ordering of tasks like device probing 1835 (suppliers first, then consumers), supplier boot state 1836 clean up (only after all consumers have probed), 1837 suspend/resume & runtime PM (consumers first, then 1838 suppliers). 1839 Format: { off | permissive | on | rpm } 1840 off -- Don't create device links from firmware info. 1841 permissive -- Create device links from firmware info 1842 but use it only for ordering boot state clean 1843 up (sync_state() calls). 1844 on -- Create device links from firmware info and use it 1845 to enforce probe and suspend/resume ordering. 1846 rpm -- Like "on", but also use to order runtime PM. 1847 1848 fw_devlink.strict=<bool> 1849 [KNL,EARLY] Treat all inferred dependencies as mandatory 1850 dependencies. This only applies for fw_devlink=on|rpm. 1851 Format: <bool> 1852 1853 fw_devlink.sync_state = 1854 [KNL,EARLY] When all devices that could probe have finished 1855 probing, this parameter controls what to do with 1856 devices that haven't yet received their sync_state() 1857 calls. 1858 Format: { strict | timeout } 1859 strict -- Default. Continue waiting on consumers to 1860 probe successfully. 1861 timeout -- Give up waiting on consumers and call 1862 sync_state() on any devices that haven't yet 1863 received their sync_state() calls after 1864 deferred_probe_timeout has expired or by 1865 late_initcall() if !CONFIG_MODULES. 1866 1867 gamecon.map[2|3]= 1868 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1869 support via parallel port (up to 5 devices per port) 1870 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1871 See also Documentation/input/devices/joystick-parport.rst 1872 1873 gamma= [HW,DRM] 1874 1875 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1876 Format: off | on 1877 default: on 1878 1879 gather_data_sampling= 1880 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1881 mitigation. 1882 1883 Gather Data Sampling is a hardware vulnerability which 1884 allows unprivileged speculative access to data which was 1885 previously stored in vector registers. 1886 1887 This issue is mitigated by default in updated microcode. 1888 The mitigation may have a performance impact but can be 1889 disabled. On systems without the microcode mitigation 1890 disabling AVX serves as a mitigation. 1891 1892 force: Disable AVX to mitigate systems without 1893 microcode mitigation. No effect if the microcode 1894 mitigation is present. Known to cause crashes in 1895 userspace with buggy AVX enumeration. 1896 1897 off: Disable GDS mitigation. 1898 1899 gbpages [X86] Use GB pages for kernel direct mappings. 1900 1901 gcov_persist= [GCOV] When non-zero (default), profiling data for 1902 kernel modules is saved and remains accessible via 1903 debugfs, even when the module is unloaded/reloaded. 1904 When zero, profiling data is discarded and associated 1905 debugfs files are removed at module unload time. 1906 1907 goldfish [X86] Enable the goldfish android emulator platform. 1908 Don't use this when you are not running on the 1909 android emulator 1910 1911 gpio-mockup.gpio_mockup_ranges 1912 [HW] Sets the ranges of gpiochip of for this device. 1913 Format: <start1>,<end1>,<start2>,<end2>... 1914 gpio-mockup.gpio_mockup_named_lines 1915 [HW] Let the driver know GPIO lines should be named. 1916 1917 gpt [EFI] Forces disk with valid GPT signature but 1918 invalid Protective MBR to be treated as GPT. If the 1919 primary GPT is corrupted, it enables the backup/alternate 1920 GPT to be used instead. 1921 1922 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1923 the "Enable 0" bit of the configuration register. 1924 Format: 0 | 1 1925 Default: 0 1926 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1927 the "Enable 0" bit of the configuration register. 1928 Format: 0 | 1 1929 Default: 0 1930 grcan.select= [HW] Select which physical interface to use. 1931 Format: 0 | 1 1932 Default: 0 1933 grcan.txsize= [HW] Sets the size of the tx buffer. 1934 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1935 Default: 1024 1936 grcan.rxsize= [HW] Sets the size of the rx buffer. 1937 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1938 Default: 1024 1939 1940 hardened_usercopy= 1941 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1942 hardening is enabled for this boot. Hardened 1943 usercopy checking is used to protect the kernel 1944 from reading or writing beyond known memory 1945 allocation boundaries as a proactive defense 1946 against bounds-checking flaws in the kernel's 1947 copy_to_user()/copy_from_user() interface. 1948 The default is determined by 1949 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1950 on Perform hardened usercopy checks. 1951 off Disable hardened usercopy checks. 1952 1953 hardlockup_all_cpu_backtrace= 1954 [KNL] Should the hard-lockup detector generate 1955 backtraces on all cpus. 1956 Format: 0 | 1 1957 1958 hash_pointers= 1959 [KNL,EARLY] 1960 By default, when pointers are printed to the console 1961 or buffers via the %p format string, that pointer is 1962 "hashed", i.e. obscured by hashing the pointer value. 1963 This is a security feature that hides actual kernel 1964 addresses from unprivileged users, but it also makes 1965 debugging the kernel more difficult since unequal 1966 pointers can no longer be compared. The choices are: 1967 Format: { auto | always | never } 1968 Default: auto 1969 1970 auto - Hash pointers unless slab_debug is enabled. 1971 always - Always hash pointers (even if slab_debug is 1972 enabled). 1973 never - Never hash pointers. This option should only 1974 be specified when debugging the kernel. Do 1975 not use on production kernels. The boot 1976 param "no_hash_pointers" is an alias for 1977 this mode. 1978 1979 For controlling hashing dynamically at runtime, 1980 use the "kernel.kptr_restrict" sysctl instead. 1981 1982 hashdist= [KNL,NUMA] Large hashes allocated during boot 1983 are distributed across NUMA nodes. Defaults on 1984 for 64-bit NUMA, off otherwise. 1985 Format: 0 | 1 (for off | on) 1986 1987 hd= [EIDE] (E)IDE hard drive subsystem geometry 1988 Format: <cyl>,<head>,<sect> 1989 1990 hest_disable [ACPI] 1991 Disable Hardware Error Source Table (HEST) support; 1992 corresponding firmware-first mode error processing 1993 logic will be disabled. 1994 1995 hibernate= [HIBERNATION] 1996 noresume Don't check if there's a hibernation image 1997 present during boot. 1998 nocompress Don't compress/decompress hibernation images. 1999 no Disable hibernation and resume. 2000 protect_image Turn on image protection during restoration 2001 (that will set all pages holding image data 2002 during restoration read-only). 2003 2004 hibernate.compressor= [HIBERNATION] Compression algorithm to be 2005 used with hibernation. 2006 Format: { lzo | lz4 } 2007 Default: lzo 2008 2009 lzo: Select LZO compression algorithm to 2010 compress/decompress hibernation image. 2011 2012 lz4: Select LZ4 compression algorithm to 2013 compress/decompress hibernation image. 2014 2015 hibernate.pm_test_delay= 2016 [HIBERNATION] 2017 Sets the number of seconds to remain in a hibernation test 2018 mode before resuming the system (see 2019 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2020 is set. Default value is 5. 2021 2022 hibernate_compression_threads= 2023 [HIBERNATION] 2024 Set the number of threads used for compressing or decompressing 2025 hibernation images. 2026 2027 Format: <integer> 2028 Default: 3 2029 Minimum: 1 2030 Example: hibernate_compression_threads=4 2031 2032 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2033 size of <nn>. This works even on boxes that have no 2034 highmem otherwise. This also works to reduce highmem 2035 size on bigger boxes. 2036 2037 highres= [KNL] Enable/disable high resolution timer mode. 2038 Valid parameters: "on", "off" 2039 Default: "on" 2040 2041 hlt [BUGS=ARM,SH] 2042 2043 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2044 Format: <string> 2045 This allows setting the system's hostname during early 2046 startup. This sets the name returned by gethostname. 2047 Using this parameter to set the hostname makes it 2048 possible to ensure the hostname is correctly set before 2049 any userspace processes run, avoiding the possibility 2050 that a process may call gethostname before the hostname 2051 has been explicitly set, resulting in the calling 2052 process getting an incorrect result. The string must 2053 not exceed the maximum allowed hostname length (usually 2054 64 characters) and will be truncated otherwise. 2055 2056 hpet= [X86-32,HPET] option to control HPET usage 2057 Format: { enable (default) | disable | force | 2058 verbose } 2059 disable: disable HPET and use PIT instead 2060 force: allow force enabled of undocumented chips (ICH4, 2061 VIA, nVidia) 2062 verbose: show contents of HPET registers during setup 2063 2064 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2065 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2066 2067 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2068 If this follows hugepagesz (below), it specifies 2069 the number of pages of hugepagesz to be allocated. 2070 If this is the first HugeTLB parameter on the command 2071 line, it specifies the number of pages to allocate for 2072 the default huge page size. If using node format, the 2073 number of pages to allocate per-node can be specified. 2074 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2075 Format: <integer> or (node format) 2076 <node>:<integer>[,<node>:<integer>] 2077 2078 hugepagesz= 2079 [HW,EARLY] The size of the HugeTLB pages. This is 2080 used in conjunction with hugepages (above) to 2081 allocate huge pages of a specific size at boot. The 2082 pair hugepagesz=X hugepages=Y can be specified once 2083 for each supported huge page size. Huge page sizes 2084 are architecture dependent. See also 2085 Documentation/admin-guide/mm/hugetlbpage.rst. 2086 Format: size[KMG] 2087 2088 hugepage_alloc_threads= 2089 [HW] The number of threads that should be used to 2090 allocate hugepages during boot. This option can be 2091 used to improve system bootup time when allocating 2092 a large amount of huge pages. 2093 The default value is 25% of the available hardware threads. 2094 2095 Note that this parameter only applies to non-gigantic huge pages. 2096 2097 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2098 of gigantic hugepages. Or using node format, the size 2099 of a CMA area per node can be specified. 2100 Format: nn[KMGTPE] or (node format) 2101 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2102 2103 Reserve a CMA area of given size and allocate gigantic 2104 hugepages using the CMA allocator. If enabled, the 2105 boot-time allocation of gigantic hugepages is skipped. 2106 2107 hugetlb_cma_only= 2108 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2109 try to allocate from the CMA areas. 2110 2111 This option does nothing if hugetlb_cma= is not also 2112 specified. 2113 2114 hugetlb_free_vmemmap= 2115 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2116 enabled. 2117 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2118 Allows heavy hugetlb users to free up some more 2119 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2120 Format: { on | off (default) } 2121 2122 on: enable HVO 2123 off: disable HVO 2124 2125 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2126 the default is on. 2127 2128 Note that the vmemmap pages may be allocated from the added 2129 memory block itself when memory_hotplug.memmap_on_memory is 2130 enabled, those vmemmap pages cannot be optimized even if this 2131 feature is enabled. Other vmemmap pages not allocated from 2132 the added memory block itself do not be affected. 2133 2134 hung_task_panic= 2135 [KNL] Number of hung tasks to trigger kernel panic. 2136 Format: <int> 2137 2138 When set to a non-zero value, a kernel panic will be triggered if 2139 the number of detected hung tasks reaches this value. 2140 2141 0: don't panic 2142 1: panic immediately on first hung task 2143 N: panic after N hung tasks are detected in a single scan 2144 2145 The default value is controlled by the 2146 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2147 selected by this boot parameter can be changed later by the 2148 kernel.hung_task_panic sysctl. 2149 2150 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2151 terminal devices. Valid values: 0..8 2152 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2153 If specified, z/VM IUCV HVC accepts connections 2154 from listed z/VM user IDs only. 2155 2156 hv_nopvspin [X86,HYPER_V,EARLY] 2157 Disables the paravirt spinlock optimizations 2158 which allow the hypervisor to 'idle' the guest 2159 on lock contention. 2160 2161 hw_protection= [HW] 2162 Format: reboot | shutdown 2163 2164 Hardware protection action taken on critical events like 2165 overtemperature or imminent voltage loss. 2166 2167 i2c_bus= [HW] Override the default board specific I2C bus speed 2168 or register an additional I2C bus that is not 2169 registered from board initialization code. 2170 Format: 2171 <bus_id>,<clkrate> 2172 2173 i2c_touchscreen_props= [HW,ACPI,X86] 2174 Set device-properties for ACPI-enumerated I2C-attached 2175 touchscreen, to e.g. fix coordinates of upside-down 2176 mounted touchscreens. If you need this option please 2177 submit a drivers/platform/x86/touchscreen_dmi.c patch 2178 adding a DMI quirk for this. 2179 2180 Format: 2181 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2182 Where <val> is one of: 2183 Omit "=<val>" entirely Set a boolean device-property 2184 Unsigned number Set a u32 device-property 2185 Anything else Set a string device-property 2186 2187 Examples (split over multiple lines): 2188 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2189 touchscreen-inverted-y 2190 2191 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2192 touchscreen-size-y=1080:touchscreen-inverted-y: 2193 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2194 2195 i8042.debug [HW] Toggle i8042 debug mode 2196 i8042.unmask_kbd_data 2197 [HW] Enable printing of interrupt data from the KBD port 2198 (disabled by default, and as a pre-condition 2199 requires that i8042.debug=1 be enabled) 2200 i8042.direct [HW] Put keyboard port into non-translated mode 2201 i8042.dumbkbd [HW] Pretend that controller can only read data from 2202 keyboard and cannot control its state 2203 (Don't attempt to blink the leds) 2204 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2205 i8042.nokbd [HW] Don't check/create keyboard port 2206 i8042.noloop [HW] Disable the AUX Loopback command while probing 2207 for the AUX port 2208 i8042.nomux [HW] Don't check presence of an active multiplexing 2209 controller 2210 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2211 controllers 2212 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2213 i8042.reset [HW] Reset the controller during init, cleanup and 2214 suspend-to-ram transitions, only during s2r 2215 transitions, or never reset 2216 Format: { 1 | Y | y | 0 | N | n } 2217 1, Y, y: always reset controller 2218 0, N, n: don't ever reset controller 2219 Default: only on s2r transitions on x86; most other 2220 architectures force reset to be always executed 2221 i8042.unlock [HW] Unlock (ignore) the keylock 2222 i8042.kbdreset [HW] Reset device connected to KBD port 2223 i8042.probe_defer 2224 [HW] Allow deferred probing upon i8042 probe errors 2225 2226 i810= [HW,DRM] 2227 2228 i915.invert_brightness= 2229 [DRM] Invert the sense of the variable that is used to 2230 set the brightness of the panel backlight. Normally a 2231 brightness value of 0 indicates backlight switched off, 2232 and the maximum of the brightness value sets the backlight 2233 to maximum brightness. If this parameter is set to 0 2234 (default) and the machine requires it, or this parameter 2235 is set to 1, a brightness value of 0 sets the backlight 2236 to maximum brightness, and the maximum of the brightness 2237 value switches the backlight off. 2238 -1 -- never invert brightness 2239 0 -- machine default 2240 1 -- force brightness inversion 2241 2242 ia32_emulation= [X86-64] 2243 Format: <bool> 2244 When true, allows loading 32-bit programs and executing 32-bit 2245 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2246 boot time. When false, unconditionally disables IA32 emulation. 2247 2248 icn= [HW,ISDN] 2249 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2250 2251 2252 idle= [X86,EARLY] 2253 Format: idle=poll, idle=halt, idle=nomwait 2254 2255 idle=poll: Don't do power saving in the idle loop 2256 using HLT, but poll for rescheduling event. This will 2257 make the CPUs eat a lot more power, but may be useful 2258 to get slightly better performance in multiprocessor 2259 benchmarks. It also makes some profiling using 2260 performance counters more accurate. Please note that 2261 on systems with MONITOR/MWAIT support (like Intel 2262 EM64T CPUs) this option has no performance advantage 2263 over the normal idle loop. It may also interact badly 2264 with hyperthreading. 2265 2266 idle=halt: Halt is forced to be used for CPU idle. 2267 In such case C2/C3 won't be used again. 2268 2269 idle=nomwait: Disable mwait for CPU C-states 2270 2271 idxd.sva= [HW] 2272 Format: <bool> 2273 Allow force disabling of Shared Virtual Memory (SVA) 2274 support for the idxd driver. By default it is set to 2275 true (1). 2276 2277 idxd.tc_override= [HW] 2278 Format: <bool> 2279 Allow override of default traffic class configuration 2280 for the device. By default it is set to false (0). 2281 2282 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2283 Format: { strict | legacy | 2008 | relaxed | emulated } 2284 Default: strict 2285 2286 Choose which programs will be accepted for execution 2287 based on the IEEE 754 NaN encoding(s) supported by 2288 the FPU and the NaN encoding requested with the value 2289 of an ELF file header flag individually set by each 2290 binary. Hardware implementations are permitted to 2291 support either or both of the legacy and the 2008 NaN 2292 encoding mode. 2293 2294 Available settings are as follows: 2295 strict accept binaries that request a NaN encoding 2296 supported by the FPU 2297 legacy only accept legacy-NaN binaries, if supported 2298 by the FPU 2299 2008 only accept 2008-NaN binaries, if supported 2300 by the FPU 2301 relaxed accept any binaries regardless of whether 2302 supported by the FPU 2303 emulated accept any binaries but enable FPU emulator 2304 if binary mode is unsupported by the FPU. 2305 2306 The FPU emulator is always able to support both NaN 2307 encodings, so if no FPU hardware is present or it has 2308 been disabled with 'nofpu', then the settings of 2309 'legacy' and '2008' strap the emulator accordingly, 2310 'relaxed' straps the emulator for both legacy-NaN and 2311 2008-NaN, whereas 'strict' enables legacy-NaN only on 2312 legacy processors and both NaN encodings on MIPS32 or 2313 MIPS64 CPUs. 2314 2315 The setting for ABS.fmt/NEG.fmt instruction execution 2316 mode generally follows that for the NaN encoding, 2317 except where unsupported by hardware. 2318 2319 ignore_loglevel [KNL,EARLY] 2320 Ignore loglevel setting - this will print /all/ 2321 kernel messages to the console. Useful for debugging. 2322 We also add it as printk module parameter, so users 2323 could change it dynamically, usually by 2324 /sys/module/printk/parameters/ignore_loglevel. 2325 2326 ignore_rlimit_data 2327 Ignore RLIMIT_DATA setting for data mappings, 2328 print warning at first misuse. Can be changed via 2329 /sys/module/kernel/parameters/ignore_rlimit_data. 2330 2331 ihash_entries= [KNL] 2332 Set number of hash buckets for inode cache. 2333 2334 ima_appraise= [IMA] appraise integrity measurements 2335 Format: { "off" | "enforce" | "fix" | "log" } 2336 default: "enforce" 2337 2338 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2339 The builtin appraise policy appraises all files 2340 owned by uid=0. 2341 2342 ima_canonical_fmt [IMA] 2343 Use the canonical format for the binary runtime 2344 measurements, instead of host native format. 2345 2346 ima_hash= [IMA] 2347 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2348 | sha512 | ... } 2349 default: "sha1" 2350 2351 The list of supported hash algorithms is defined 2352 in crypto/hash_info.h. 2353 2354 ima_policy= [IMA] 2355 The builtin policies to load during IMA setup. 2356 Format: "tcb | appraise_tcb | secure_boot | 2357 fail_securely | critical_data" 2358 2359 The "tcb" policy measures all programs exec'd, files 2360 mmap'd for exec, and all files opened with the read 2361 mode bit set by either the effective uid (euid=0) or 2362 uid=0. 2363 2364 The "appraise_tcb" policy appraises the integrity of 2365 all files owned by root. 2366 2367 The "secure_boot" policy appraises the integrity 2368 of files (eg. kexec kernel image, kernel modules, 2369 firmware, policy, etc) based on file signatures. 2370 2371 The "fail_securely" policy forces file signature 2372 verification failure also on privileged mounted 2373 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2374 flag. 2375 2376 The "critical_data" policy measures kernel integrity 2377 critical data. 2378 2379 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2380 Load a policy which meets the needs of the Trusted 2381 Computing Base. This means IMA will measure all 2382 programs exec'd, files mmap'd for exec, and all files 2383 opened for read by uid=0. 2384 2385 ima_template= [IMA] 2386 Select one of defined IMA measurements template formats. 2387 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2388 "ima-sigv2" } 2389 Default: "ima-ng" 2390 2391 ima_template_fmt= 2392 [IMA] Define a custom template format. 2393 Format: { "field1|...|fieldN" } 2394 2395 ima= [IMA] Enable or disable IMA 2396 Format: { "off" | "on" } 2397 Default: "on" 2398 Note that disabling IMA is limited to kdump kernel. 2399 2400 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2401 Target Selection(ITS) bug in Intel CPUs. Updated 2402 microcode is also required for a fix in IBPB. 2403 2404 on: Enable mitigation (default). 2405 off: Disable mitigation. 2406 force: Force the ITS bug and deploy default 2407 mitigation. 2408 vmexit: Only deploy mitigation if CPU is affected by 2409 guest/host isolation part of ITS. 2410 stuff: Deploy RSB-fill mitigation when retpoline is 2411 also deployed. Otherwise, deploy the default 2412 mitigation. 2413 2414 For details see: 2415 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2416 2417 init= [KNL] 2418 Format: <full_path> 2419 Run specified binary instead of /sbin/init as init 2420 process. 2421 2422 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2423 for working out where the kernel is dying during 2424 startup. 2425 2426 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2427 initcall functions. Useful for debugging built-in 2428 modules and initcalls. 2429 2430 initramfs_async= [KNL] 2431 Format: <bool> 2432 Default: 1 2433 This parameter controls whether the initramfs 2434 image is unpacked asynchronously, concurrently 2435 with devices being probed and 2436 initialized. This should normally just work, 2437 but as a debugging aid, one can get the 2438 historical behaviour of the initramfs 2439 unpacking being completed before device_ and 2440 late_ initcalls. 2441 2442 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2443 2444 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2445 load the initrd. If an initrd is compiled in or 2446 specified in the bootparams, it takes priority over this 2447 setting. 2448 Format: ss[KMG],nn[KMG] 2449 Default is 0, 0 2450 2451 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2452 zeroes. 2453 Format: 0 | 1 2454 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2455 2456 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2457 Format: 0 | 1 2458 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2459 2460 init_pkru= [X86] Specify the default memory protection keys rights 2461 register contents for all processes. 0x55555554 by 2462 default (disallow access to all but pkey 0). Can 2463 override in debugfs after boot. 2464 2465 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2466 Format: <irq> 2467 2468 int_pln_enable [X86] Enable power limit notification interrupt 2469 2470 integrity_audit=[IMA] 2471 Format: { "0" | "1" } 2472 0 -- basic integrity auditing messages. (Default) 2473 1 -- additional integrity auditing messages. 2474 2475 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2476 on 2477 Enable intel iommu driver. 2478 off 2479 Disable intel iommu driver. 2480 igfx_off [Default Off] 2481 By default, gfx is mapped as normal device. If a gfx 2482 device has a dedicated DMAR unit, the DMAR unit is 2483 bypassed by not enabling DMAR with this option. In 2484 this case, gfx device will use physical address for 2485 DMA. 2486 strict [Default Off] 2487 Deprecated, equivalent to iommu.strict=1. 2488 sp_off [Default Off] 2489 By default, super page will be supported if Intel IOMMU 2490 has the capability. With this option, super page will 2491 not be supported. 2492 sm_on 2493 Enable the Intel IOMMU scalable mode if the hardware 2494 advertises that it has support for the scalable mode 2495 translation. 2496 sm_off 2497 Disallow use of the Intel IOMMU scalable mode. 2498 tboot_noforce [Default Off] 2499 Do not force the Intel IOMMU enabled under tboot. 2500 By default, tboot will force Intel IOMMU on, which 2501 could harm performance of some high-throughput 2502 devices like 40GBit network cards, even if identity 2503 mapping is enabled. 2504 Note that using this option lowers the security 2505 provided by tboot because it makes the system 2506 vulnerable to DMA attacks. 2507 2508 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2509 0 disables intel_idle and fall back on acpi_idle. 2510 1 to 9 specify maximum depth of C-state. 2511 2512 intel_pstate= [X86,EARLY] 2513 disable 2514 Do not enable intel_pstate as the default 2515 scaling driver for the supported processors 2516 active 2517 Use intel_pstate driver to bypass the scaling 2518 governors layer of cpufreq and provides it own 2519 algorithms for p-state selection. There are two 2520 P-state selection algorithms provided by 2521 intel_pstate in the active mode: powersave and 2522 performance. The way they both operate depends 2523 on whether or not the hardware managed P-states 2524 (HWP) feature has been enabled in the processor 2525 and possibly on the processor model. 2526 passive 2527 Use intel_pstate as a scaling driver, but configure it 2528 to work with generic cpufreq governors (instead of 2529 enabling its internal governor). This mode cannot be 2530 used along with the hardware-managed P-states (HWP) 2531 feature. 2532 force 2533 Enable intel_pstate on systems that prohibit it by default 2534 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2535 instead of acpi-cpufreq may disable platform features, such 2536 as thermal controls and power capping, that rely on ACPI 2537 P-States information being indicated to OSPM and therefore 2538 should be used with caution. This option does not work with 2539 processors that aren't supported by the intel_pstate driver 2540 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2541 no_hwp 2542 Do not enable hardware P state control (HWP) 2543 if available. 2544 hwp_only 2545 Only load intel_pstate on systems which support 2546 hardware P state control (HWP) if available. 2547 support_acpi_ppc 2548 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2549 Description Table, specifies preferred power management 2550 profile as "Enterprise Server" or "Performance Server", 2551 then this feature is turned on by default. 2552 per_cpu_perf_limits 2553 Allow per-logical-CPU P-State performance control limits using 2554 cpufreq sysfs interface 2555 no_cas 2556 Do not enable capacity-aware scheduling (CAS) on 2557 hybrid systems 2558 2559 intremap= [X86-64,Intel-IOMMU,EARLY] 2560 on enable Interrupt Remapping (default) 2561 off disable Interrupt Remapping 2562 nosid disable Source ID checking 2563 no_x2apic_optout 2564 BIOS x2APIC opt-out request will be ignored 2565 nopost disable Interrupt Posting 2566 posted_msi 2567 enable MSIs delivered as posted interrupts 2568 2569 iomem= Disable strict checking of access to MMIO memory 2570 strict regions from userspace. 2571 relaxed 2572 2573 iommu= [X86,EARLY] 2574 2575 off 2576 Don't initialize and use any kind of IOMMU. 2577 2578 force 2579 Force the use of the hardware IOMMU even when 2580 it is not actually needed (e.g. because < 3 GB 2581 memory). 2582 2583 noforce 2584 Don't force hardware IOMMU usage when it is not 2585 needed. (default). 2586 2587 biomerge 2588 panic 2589 nopanic 2590 merge 2591 nomerge 2592 2593 soft 2594 Use software bounce buffering (SWIOTLB) (default for 2595 Intel machines). This can be used to prevent the usage 2596 of an available hardware IOMMU. 2597 2598 pt 2599 nopt 2600 nobypass [PPC/POWERNV] 2601 Disable IOMMU bypass, using IOMMU for PCI devices. 2602 2603 AMD Gart HW IOMMU-specific options: 2604 2605 <size> 2606 Set the size of the remapping area in bytes. 2607 2608 allowed 2609 Overwrite iommu off workarounds for specific chipsets 2610 2611 fullflush 2612 Flush IOMMU on each allocation (default). 2613 2614 nofullflush 2615 Don't use IOMMU fullflush. 2616 2617 memaper[=<order>] 2618 Allocate an own aperture over RAM with size 2619 32MB<<order. (default: order=1, i.e. 64MB) 2620 2621 merge 2622 Do scatter-gather (SG) merging. Implies "force" 2623 (experimental). 2624 2625 nomerge 2626 Don't do scatter-gather (SG) merging. 2627 2628 noaperture 2629 Ask the IOMMU not to touch the aperture for AGP. 2630 2631 noagp 2632 Don't initialize the AGP driver and use full aperture. 2633 2634 panic 2635 Always panic when IOMMU overflows. 2636 2637 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2638 Format: { "0" | "1" } 2639 0 - Try to allocate a 32-bit DMA address first, before 2640 falling back to the full range if needed. 2641 1 - Allocate directly from the full usable range, 2642 forcing Dual Address Cycle for PCI cards supporting 2643 greater than 32-bit addressing. 2644 2645 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2646 Format: { "0" | "1" } 2647 0 - Lazy mode. 2648 Request that DMA unmap operations use deferred 2649 invalidation of hardware TLBs, for increased 2650 throughput at the cost of reduced device isolation. 2651 Will fall back to strict mode if not supported by 2652 the relevant IOMMU driver. 2653 1 - Strict mode. 2654 DMA unmap operations invalidate IOMMU hardware TLBs 2655 synchronously. 2656 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2657 Note: on x86, strict mode specified via one of the 2658 legacy driver-specific options takes precedence. 2659 2660 iommu.passthrough= 2661 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2662 Format: { "0" | "1" } 2663 0 - Use IOMMU translation for DMA. 2664 1 - Bypass the IOMMU for DMA. 2665 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2666 2667 iommu.debug_pagealloc= 2668 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2669 parameter enables the feature at boot time. By default, it 2670 is disabled and the system behaves the same way as a kernel 2671 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2672 Format: { "0" | "1" } 2673 0 - Sanitizer disabled. 2674 1 - Sanitizer enabled, expect runtime overhead. 2675 2676 io7= [HW] IO7 for Marvel-based Alpha systems 2677 See comment before marvel_specify_io7 in 2678 arch/alpha/kernel/core_marvel.c. 2679 2680 io_delay= [X86,EARLY] I/O delay method 2681 0x80 2682 Standard port 0x80 based delay 2683 0xed 2684 Alternate port 0xed based delay (needed on some systems) 2685 udelay 2686 Simple two microseconds delay 2687 none 2688 No delay 2689 2690 ip= [IP_PNP] 2691 See Documentation/admin-guide/nfs/nfsroot.rst. 2692 2693 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2694 IPC identifiers from 32,768 to 16,777,216. 2695 2696 ipe.enforce= [IPE] 2697 Format: <bool> 2698 Determine whether IPE starts in permissive (0) or 2699 enforce (1) mode. The default is enforce. 2700 2701 ipe.success_audit= 2702 [IPE] 2703 Format: <bool> 2704 Start IPE with success auditing enabled, emitting 2705 an audit event when a binary is allowed. The default 2706 is 0. 2707 2708 irqaffinity= [SMP] Set the default irq affinity mask 2709 The argument is a cpu list, as described above. 2710 2711 irqchip.gicv2_force_probe= 2712 [ARM,ARM64,EARLY] 2713 Format: <bool> 2714 Force the kernel to look for the second 4kB page 2715 of a GICv2 controller even if the memory range 2716 exposed by the device tree is too small. 2717 2718 irqchip.gicv3_nolpi= 2719 [ARM,ARM64,EARLY] 2720 Force the kernel to ignore the availability of 2721 LPIs (and by consequence ITSs). Intended for system 2722 that use the kernel as a bootloader, and thus want 2723 to let secondary kernels in charge of setting up 2724 LPIs. 2725 2726 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2727 Enables support for pseudo-NMIs in the kernel. This 2728 requires the kernel to be built with 2729 CONFIG_ARM64_PSEUDO_NMI. 2730 2731 irqchip.riscv_imsic_noipi 2732 [RISC-V,EARLY] 2733 Force the kernel to not use IMSIC software injected MSIs 2734 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2735 and thus want to reduce MMIO traps when triggering IPIs 2736 to multiple harts. 2737 2738 irqfixup [HW] 2739 When an interrupt is not handled search all handlers 2740 for it. Intended to get systems with badly broken 2741 firmware running. 2742 2743 irqhandler.duration_warn_us= [KNL] 2744 Warn if an IRQ handler exceeds the specified duration 2745 threshold in microseconds. Useful for identifying 2746 long-running IRQs in the system. 2747 2748 irqpoll [HW] 2749 When an interrupt is not handled search all handlers 2750 for it. Also check all handlers each timer 2751 interrupt. Intended to get systems with badly broken 2752 firmware running. 2753 2754 isapnp= [ISAPNP] 2755 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2756 2757 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2758 [Deprecated - use cpusets instead] 2759 Format: [flag-list,]<cpu-list> 2760 2761 Specify one or more CPUs to isolate from disturbances 2762 specified in the flag list (default: domain): 2763 2764 nohz 2765 Disable the tick when a single task runs as well as 2766 disabling other kernel noises like having RCU callbacks 2767 offloaded. This is equivalent to the nohz_full parameter. 2768 2769 A residual 1Hz tick is offloaded to workqueues, which you 2770 need to affine to housekeeping through the global 2771 workqueue's affinity configured via the 2772 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2773 by using the 'domain' flag described below. 2774 2775 NOTE: by default the global workqueue runs on all CPUs, 2776 so to protect individual CPUs the 'cpumask' file has to 2777 be configured manually after bootup. 2778 2779 domain 2780 Isolate from the general SMP balancing and scheduling 2781 algorithms. Note that performing domain isolation this way 2782 is irreversible: it's not possible to bring back a CPU to 2783 the domains once isolated through isolcpus. It's strongly 2784 advised to use cpusets instead to disable scheduler load 2785 balancing through the "cpuset.sched_load_balance" file. 2786 It offers a much more flexible interface where CPUs can 2787 move in and out of an isolated set anytime. 2788 2789 You can move a process onto or off an "isolated" CPU via 2790 the CPU affinity syscalls or cpuset. 2791 <cpu number> begins at 0 and the maximum value is 2792 "number of CPUs in system - 1". 2793 2794 managed_irq 2795 2796 Isolate from being targeted by managed interrupts 2797 which have an interrupt mask containing isolated 2798 CPUs. The affinity of managed interrupts is 2799 handled by the kernel and cannot be changed via 2800 the /proc/irq/* interfaces. 2801 2802 This isolation is best effort and only effective 2803 if the automatically assigned interrupt mask of a 2804 device queue contains isolated and housekeeping 2805 CPUs. If housekeeping CPUs are online then such 2806 interrupts are directed to the housekeeping CPU 2807 so that IO submitted on the housekeeping CPU 2808 cannot disturb the isolated CPU. 2809 2810 If a queue's affinity mask contains only isolated 2811 CPUs then this parameter has no effect on the 2812 interrupt routing decision, though interrupts are 2813 only delivered when tasks running on those 2814 isolated CPUs submit IO. IO submitted on 2815 housekeeping CPUs has no influence on those 2816 queues. 2817 2818 The format of <cpu-list> is described above. 2819 2820 iucv= [HW,NET] 2821 2822 ivrs_ioapic [HW,X86-64] 2823 Provide an override to the IOAPIC-ID<->DEVICE-ID 2824 mapping provided in the IVRS ACPI table. 2825 By default, PCI segment is 0, and can be omitted. 2826 2827 For example, to map IOAPIC-ID decimal 10 to 2828 PCI segment 0x1 and PCI device 00:14.0, 2829 write the parameter as: 2830 ivrs_ioapic=10@0001:00:14.0 2831 2832 Deprecated formats: 2833 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2834 write the parameter as: 2835 ivrs_ioapic[10]=00:14.0 2836 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2837 PCI device 00:14.0 write the parameter as: 2838 ivrs_ioapic[10]=0001:00:14.0 2839 2840 ivrs_hpet [HW,X86-64] 2841 Provide an override to the HPET-ID<->DEVICE-ID 2842 mapping provided in the IVRS ACPI table. 2843 By default, PCI segment is 0, and can be omitted. 2844 2845 For example, to map HPET-ID decimal 10 to 2846 PCI segment 0x1 and PCI device 00:14.0, 2847 write the parameter as: 2848 ivrs_hpet=10@0001:00:14.0 2849 2850 Deprecated formats: 2851 * To map HPET-ID decimal 0 to PCI device 00:14.0 2852 write the parameter as: 2853 ivrs_hpet[0]=00:14.0 2854 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2855 PCI device 00:14.0 write the parameter as: 2856 ivrs_ioapic[10]=0001:00:14.0 2857 2858 ivrs_acpihid [HW,X86-64] 2859 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2860 mapping provided in the IVRS ACPI table. 2861 By default, PCI segment is 0, and can be omitted. 2862 2863 For example, to map UART-HID:UID AMD0020:0 to 2864 PCI segment 0x1 and PCI device ID 00:14.5, 2865 write the parameter as: 2866 ivrs_acpihid=AMD0020:0@0001:00:14.5 2867 2868 Deprecated formats: 2869 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2870 PCI device ID 00:14.5, write the parameter as: 2871 ivrs_acpihid[00:14.5]=AMD0020:0 2872 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2873 PCI device ID 00:14.5, write the parameter as: 2874 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2875 2876 js= [HW,JOY] Analog joystick 2877 See Documentation/input/joydev/joystick.rst. 2878 2879 kasan_multi_shot 2880 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2881 report on every invalid memory access. Without this 2882 parameter KASAN will print report only for the first 2883 invalid access. 2884 2885 keep_bootcon [KNL,EARLY] 2886 Do not unregister boot console at start. This is only 2887 useful for debugging when something happens in the window 2888 between unregistering the boot console and initializing 2889 the real console. 2890 2891 keepinitrd [HW,ARM] See retain_initrd. 2892 2893 kernelcore= [KNL,X86,PPC,EARLY] 2894 Format: nn[KMGTPE] | nn% | "mirror" 2895 This parameter specifies the amount of memory usable by 2896 the kernel for non-movable allocations. The requested 2897 amount is spread evenly throughout all nodes in the 2898 system as ZONE_NORMAL. The remaining memory is used for 2899 movable memory in its own zone, ZONE_MOVABLE. In the 2900 event, a node is too small to have both ZONE_NORMAL and 2901 ZONE_MOVABLE, kernelcore memory will take priority and 2902 other nodes will have a larger ZONE_MOVABLE. 2903 2904 ZONE_MOVABLE is used for the allocation of pages that 2905 may be reclaimed or moved by the page migration 2906 subsystem. Note that allocations like PTEs-from-HighMem 2907 still use the HighMem zone if it exists, and the Normal 2908 zone if it does not. 2909 2910 It is possible to specify the exact amount of memory in 2911 the form of "nn[KMGTPE]", a percentage of total system 2912 memory in the form of "nn%", or "mirror". If "mirror" 2913 option is specified, mirrored (reliable) memory is used 2914 for non-movable allocations and remaining memory is used 2915 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2916 are exclusive, so you cannot specify multiple forms. 2917 2918 kfence.burst= [MM,KFENCE] The number of additional successive 2919 allocations to be attempted through KFENCE for each 2920 sample interval. 2921 Format: <unsigned integer> 2922 Default: 0 2923 2924 kfence.check_on_panic= 2925 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2926 canaries on panic. 2927 Format: <bool> 2928 Default: false 2929 2930 kfence.deferrable= 2931 [MM,KFENCE] Whether to use a deferrable timer to trigger 2932 allocations. This avoids forcing CPU wake-ups if the 2933 system is idle, at the risk of a less predictable 2934 sample interval. 2935 Format: <bool> 2936 Default: CONFIG_KFENCE_DEFERRABLE 2937 2938 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2939 error is detected. 2940 report - print the error report and continue (default). 2941 oops - print the error report and oops. 2942 panic - print the error report and panic. 2943 2944 kfence.sample_interval= 2945 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2946 Format: <unsigned integer> 2947 0 - Disable KFENCE. 2948 >0 - Enabled KFENCE with given sample interval. 2949 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2950 2951 kfence.skip_covered_thresh= 2952 [MM,KFENCE] If pool utilization reaches this threshold 2953 (pool usage%), KFENCE limits currently covered 2954 allocations of the same source from further filling 2955 up the pool. 2956 Format: <unsigned integer> 2957 Default: 75 2958 2959 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2960 Format: <Controller#>[,poll interval] 2961 The controller # is the number of the ehci usb debug 2962 port as it is probed via PCI. The poll interval is 2963 optional and is the number seconds in between 2964 each poll cycle to the debug port in case you need 2965 the functionality for interrupting the kernel with 2966 gdb or control-c on the dbgp connection. When 2967 not using this parameter you use sysrq-g to break into 2968 the kernel debugger. 2969 2970 kgdboc= [KGDB,HW] kgdb over consoles. 2971 Requires a tty driver that supports console polling, 2972 or a supported polling keyboard driver (non-usb). 2973 Serial only format: <serial_device>[,baud] 2974 keyboard only format: kbd 2975 keyboard and serial format: kbd,<serial_device>[,baud] 2976 Optional Kernel mode setting: 2977 kms, kbd format: kms,kbd 2978 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2979 2980 kgdboc_earlycon= [KGDB,HW,EARLY] 2981 If the boot console provides the ability to read 2982 characters and can work in polling mode, you can use 2983 this parameter to tell kgdb to use it as a backend 2984 until the normal console is registered. Intended to 2985 be used together with the kgdboc parameter which 2986 specifies the normal console to transition to. 2987 2988 The name of the early console should be specified 2989 as the value of this parameter. Note that the name of 2990 the early console might be different than the tty 2991 name passed to kgdboc. It's OK to leave the value 2992 blank and the first boot console that implements 2993 read() will be picked. 2994 2995 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2996 kernel debugger at the earliest opportunity. 2997 2998 kho= [KEXEC,EARLY] 2999 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3000 Enables or disables Kexec HandOver. 3001 "0" | "off" | "n" - kexec handover is disabled 3002 "1" | "on" | "y" - kexec handover is enabled 3003 3004 kho_scratch= [KEXEC,EARLY] 3005 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3006 Defines the size of the KHO scratch region. The KHO 3007 scratch regions are physically contiguous memory 3008 ranges that can only be used for non-kernel 3009 allocations. That way, even when memory is heavily 3010 fragmented with handed over memory, the kexeced 3011 kernel will always have enough contiguous ranges to 3012 bootstrap itself. 3013 3014 It is possible to specify the exact amount of 3015 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3016 where the first parameter defines the size of a low 3017 memory scratch area, the second parameter defines 3018 the size of a global scratch area and the third 3019 parameter defines the size of additional per-node 3020 scratch areas. The form "nn%" defines scale factor 3021 (in percents) of memory that was used during boot. 3022 3023 kmac= [MIPS] Korina ethernet MAC address. 3024 Configure the RouterBoard 532 series on-chip 3025 Ethernet adapter MAC address. 3026 3027 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3028 Valid arguments: on, off 3029 Default: on 3030 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3031 the default is off. 3032 3033 kprobe_event=[probe-list] 3034 [FTRACE] Add kprobe events and enable at boot time. 3035 The probe-list is a semicolon delimited list of probe 3036 definitions. Each definition is same as kprobe_events 3037 interface, but the parameters are comma delimited. 3038 For example, to add a kprobe event on vfs_read with 3039 arg1 and arg2, add to the command line; 3040 3041 kprobe_event=p,vfs_read,$arg1,$arg2 3042 3043 See also Documentation/trace/kprobetrace.rst "Kernel 3044 Boot Parameter" section. 3045 3046 kpti= [ARM64,EARLY] Control page table isolation of 3047 user and kernel address spaces. 3048 Default: enabled on cores which need mitigation. 3049 0: force disabled 3050 1: force enabled 3051 3052 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3053 CONFIG_KUNIT to be set to be fully enabled. The 3054 default value can be overridden via 3055 KUNIT_DEFAULT_ENABLED. 3056 Default is 1 (enabled) 3057 3058 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3059 Default is 0 (don't ignore, but inject #GP) 3060 3061 kvm.eager_page_split= 3062 [KVM,X86] Controls whether or not KVM will try to 3063 proactively split all huge pages during dirty logging. 3064 Eager page splitting reduces interruptions to vCPU 3065 execution by eliminating the write-protection faults 3066 and MMU lock contention that would otherwise be 3067 required to split huge pages lazily. 3068 3069 VM workloads that rarely perform writes or that write 3070 only to a small region of VM memory may benefit from 3071 disabling eager page splitting to allow huge pages to 3072 still be used for reads. 3073 3074 The behavior of eager page splitting depends on whether 3075 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3076 disabled, all huge pages in a memslot will be eagerly 3077 split when dirty logging is enabled on that memslot. If 3078 enabled, eager page splitting will be performed during 3079 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3080 cleared. 3081 3082 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3083 3084 Default is Y (on). 3085 3086 kvm.enable_pmu=[KVM,X86] 3087 If enabled, KVM will virtualize PMU functionality based 3088 on the virtual CPU model defined by userspace. This 3089 can be overridden on a per-VM basis via 3090 KVM_CAP_PMU_CAPABILITY. 3091 3092 If disabled, KVM will not virtualize PMU functionality, 3093 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3094 a virtual CPU model that contains PMU assets. 3095 3096 Note, KVM's vPMU support implicitly requires running 3097 with an in-kernel local APIC, e.g. to deliver PMIs to 3098 the guest. Running without an in-kernel local APIC is 3099 not supported, though KVM will allow such a combination 3100 (with severely degraded functionality). 3101 3102 See also enable_mediated_pmu. 3103 3104 Default is Y (on). 3105 3106 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3107 If enabled, KVM will enable virtualization in hardware 3108 when KVM is loaded, and disable virtualization when KVM 3109 is unloaded (if KVM is built as a module). 3110 3111 If disabled, KVM will dynamically enable and disable 3112 virtualization on-demand when creating and destroying 3113 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3114 number of VMs. 3115 3116 Enabling virtualization at module load avoids potential 3117 latency for creation of the 0=>1 VM, as KVM serializes 3118 virtualization enabling across all online CPUs. The 3119 "cost" of enabling virtualization when KVM is loaded, 3120 is that doing so may interfere with using out-of-tree 3121 hypervisors that want to "own" virtualization hardware. 3122 3123 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3124 Default is false (don't support). 3125 3126 kvm.nx_huge_pages= 3127 [KVM] Controls the software workaround for the 3128 X86_BUG_ITLB_MULTIHIT bug. 3129 force : Always deploy workaround. 3130 off : Never deploy workaround. 3131 auto : Deploy workaround based on the presence of 3132 X86_BUG_ITLB_MULTIHIT. 3133 3134 Default is 'auto'. 3135 3136 If the software workaround is enabled for the host, 3137 guests do need not to enable it for nested guests. 3138 3139 kvm.nx_huge_pages_recovery_ratio= 3140 [KVM] Controls how many 4KiB pages are periodically zapped 3141 back to huge pages. 0 disables the recovery, otherwise if 3142 the value is N KVM will zap 1/Nth of the 4KiB pages every 3143 period (see below). The default is 60. 3144 3145 kvm.nx_huge_pages_recovery_period_ms= 3146 [KVM] Controls the time period at which KVM zaps 4KiB pages 3147 back to huge pages. If the value is a non-zero N, KVM will 3148 zap a portion (see ratio above) of the pages every N msecs. 3149 If the value is 0 (the default), KVM will pick a period based 3150 on the ratio, such that a page is zapped after 1 hour on average. 3151 3152 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3153 If enabled, KVM will provide a mediated virtual PMU, 3154 instead of the default perf-based virtual PMU (if 3155 kvm.enable_pmu is true and PMU is enumerated via the 3156 virtual CPU model). 3157 3158 With a perf-based vPMU, KVM operates as a user of perf, 3159 i.e. emulates guest PMU counters using perf events. 3160 KVM-created perf events are managed by perf as regular 3161 (guest-only) events, e.g. are scheduled in/out, contend 3162 for hardware resources, etc. Using a perf-based vPMU 3163 allows guest and host usage of the PMU to co-exist, but 3164 incurs non-trivial overhead and can result in silently 3165 dropped guest events (due to resource contention). 3166 3167 With a mediated vPMU, hardware PMU state is context 3168 switched around the world switch to/from the guest. 3169 KVM mediates which events the guest can utilize, but 3170 gives the guest direct access to all other PMU assets 3171 when possible (KVM may intercept some accesses if the 3172 virtual CPU model provides a subset of hardware PMU 3173 functionality). Using a mediated vPMU significantly 3174 reduces PMU virtualization overhead and eliminates lost 3175 guest events, but is mutually exclusive with using perf 3176 to profile KVM guests and adds latency to most VM-Exits 3177 (to context switch PMU state). 3178 3179 Default is N (off). 3180 3181 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3182 KVM/SVM. Default is 1 (enabled). 3183 3184 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3185 a.k.a. Two-Dimensional Page Tables. Default is 1 3186 (enabled). Disable by KVM if hardware lacks support 3187 for NPT. 3188 3189 kvm-amd.ciphertext_hiding_asids= 3190 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3191 to SNP private memory from reading ciphertext. Instead, 3192 reads will see constant default values (0xff). 3193 3194 If ciphertext hiding is enabled, the joint SEV-ES and 3195 SEV-SNP ASID space is partitioned into separate SEV-ES 3196 and SEV-SNP ASID ranges, with the SEV-SNP range being 3197 [1..max_snp_asid] and the SEV-ES range being 3198 (max_snp_asid..min_sev_asid), where min_sev_asid is 3199 enumerated by CPUID.0x.8000_001F[EDX]. 3200 3201 A non-zero value enables SEV-SNP ciphertext hiding and 3202 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3203 KVM caps the number of SEV-SNP ASIDs at the maximum 3204 possible value, e.g. specifying -1u will assign all 3205 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3206 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3207 max_snp_asid == min_sev_asid-1, will effectively make 3208 SEV-ES unusable. 3209 3210 kvm-arm.mode= 3211 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3212 operation. 3213 3214 none: Forcefully disable KVM. 3215 3216 nvhe: Standard nVHE-based mode, without support for 3217 protected guests. 3218 3219 protected: Mode with support for guests whose state is 3220 kept private from the host, using VHE or 3221 nVHE depending on HW support. 3222 3223 nested: VHE-based mode with support for nested 3224 virtualization. Requires at least ARMv8.4 3225 hardware (with FEAT_NV2). 3226 3227 Defaults to VHE/nVHE based on hardware support. Setting 3228 mode to "protected" will disable kexec and hibernation 3229 for the host. To force nVHE on VHE hardware, add 3230 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3231 command-line. 3232 "nested" and "protected" are experimental and should be 3233 used with extreme caution. 3234 3235 kvm-arm.vgic_v3_group0_trap= 3236 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3237 system registers 3238 3239 kvm-arm.vgic_v3_group1_trap= 3240 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3241 system registers 3242 3243 kvm-arm.vgic_v3_common_trap= 3244 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3245 system registers 3246 3247 kvm-arm.vgic_v4_enable= 3248 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3249 injection of LPIs. 3250 3251 kvm-arm.wfe_trap_policy= 3252 [KVM,ARM] Control when to set WFE instruction trap for 3253 KVM VMs. Traps are allowed but not guaranteed by the 3254 CPU architecture. 3255 3256 trap: set WFE instruction trap 3257 3258 notrap: clear WFE instruction trap 3259 3260 kvm-arm.wfi_trap_policy= 3261 [KVM,ARM] Control when to set WFI instruction trap for 3262 KVM VMs. Traps are allowed but not guaranteed by the 3263 CPU architecture. 3264 3265 trap: set WFI instruction trap 3266 3267 notrap: clear WFI instruction trap 3268 3269 kvm_cma_resv_ratio=n [PPC,EARLY] 3270 Reserves given percentage from system memory area for 3271 contiguous memory allocation for KVM hash pagetable 3272 allocation. 3273 By default it reserves 5% of total system memory. 3274 Format: <integer> 3275 Default: 5 3276 3277 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3278 a.k.a. Two-Dimensional Page Tables. Default is 1 3279 (enabled). Disable by KVM if hardware lacks support 3280 for EPT. 3281 3282 kvm-intel.emulate_invalid_guest_state= 3283 [KVM,Intel] Control whether to emulate invalid guest 3284 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3285 as guest state is never invalid for unrestricted 3286 guests. This param doesn't apply to nested guests (L2), 3287 as KVM never emulates invalid L2 guest state. 3288 Default is 1 (enabled). 3289 3290 kvm-intel.flexpriority= 3291 [KVM,Intel] Control KVM's use of FlexPriority feature 3292 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3293 hardware lacks support for it. 3294 3295 kvm-intel.nested= 3296 [KVM,Intel] Control nested virtualization feature in 3297 KVM/VMX. Default is 1 (enabled). 3298 3299 kvm-intel.unrestricted_guest= 3300 [KVM,Intel] Control KVM's use of unrestricted guest 3301 feature (virtualized real and unpaged mode). Default 3302 is 1 (enabled). Disable by KVM if EPT is disabled or 3303 hardware lacks support for it. 3304 3305 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3306 CVE-2018-3620. 3307 3308 Valid arguments: never, cond, always 3309 3310 always: L1D cache flush on every VMENTER. 3311 cond: Flush L1D on VMENTER only when the code between 3312 VMEXIT and VMENTER can leak host memory. 3313 never: Disables the mitigation 3314 3315 Default is cond (do L1 cache flush in specific instances) 3316 3317 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3318 Identification feature (tagged TLBs). Default is 1 3319 (enabled). Disable by KVM if hardware lacks support 3320 for it. 3321 3322 l1d_flush= [X86,INTEL,EARLY] 3323 Control mitigation for L1D based snooping vulnerability. 3324 3325 Certain CPUs are vulnerable to an exploit against CPU 3326 internal buffers which can forward information to a 3327 disclosure gadget under certain conditions. 3328 3329 In vulnerable processors, the speculatively 3330 forwarded data can be used in a cache side channel 3331 attack, to access data to which the attacker does 3332 not have direct access. 3333 3334 This parameter controls the mitigation. The 3335 options are: 3336 3337 on - enable the interface for the mitigation 3338 3339 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3340 affected CPUs 3341 3342 The kernel PTE inversion protection is unconditionally 3343 enabled and cannot be disabled. 3344 3345 full 3346 Provides all available mitigations for the 3347 L1TF vulnerability. Disables SMT and 3348 enables all mitigations in the 3349 hypervisors, i.e. unconditional L1D flush. 3350 3351 SMT control and L1D flush control via the 3352 sysfs interface is still possible after 3353 boot. Hypervisors will issue a warning 3354 when the first VM is started in a 3355 potentially insecure configuration, 3356 i.e. SMT enabled or L1D flush disabled. 3357 3358 full,force 3359 Same as 'full', but disables SMT and L1D 3360 flush runtime control. Implies the 3361 'nosmt=force' command line option. 3362 (i.e. sysfs control of SMT is disabled.) 3363 3364 flush 3365 Leaves SMT enabled and enables the default 3366 hypervisor mitigation, i.e. conditional 3367 L1D flush. 3368 3369 SMT control and L1D flush control via the 3370 sysfs interface is still possible after 3371 boot. Hypervisors will issue a warning 3372 when the first VM is started in a 3373 potentially insecure configuration, 3374 i.e. SMT enabled or L1D flush disabled. 3375 3376 flush,nosmt 3377 3378 Disables SMT and enables the default 3379 hypervisor mitigation. 3380 3381 SMT control and L1D flush control via the 3382 sysfs interface is still possible after 3383 boot. Hypervisors will issue a warning 3384 when the first VM is started in a 3385 potentially insecure configuration, 3386 i.e. SMT enabled or L1D flush disabled. 3387 3388 flush,nowarn 3389 Same as 'flush', but hypervisors will not 3390 warn when a VM is started in a potentially 3391 insecure configuration. 3392 3393 off 3394 Disables hypervisor mitigations and doesn't 3395 emit any warnings. 3396 It also drops the swap size and available 3397 RAM limit restriction on both hypervisor and 3398 bare metal. 3399 3400 Default is 'flush'. 3401 3402 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3403 3404 l2cr= [PPC] 3405 3406 l3cr= [PPC] 3407 3408 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3409 disabled it. 3410 3411 lapic= [X86,APIC] Do not use TSC deadline 3412 value for LAPIC timer one-shot implementation. Default 3413 back to the programmable timer unit in the LAPIC. 3414 Format: notscdeadline 3415 3416 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3417 in C2 power state. 3418 3419 libata.dma= [LIBATA] DMA control 3420 libata.dma=0 Disable all PATA and SATA DMA 3421 libata.dma=1 PATA and SATA Disk DMA only 3422 libata.dma=2 ATAPI (CDROM) DMA only 3423 libata.dma=4 Compact Flash DMA only 3424 Combinations also work, so libata.dma=3 enables DMA 3425 for disks and CDROMs, but not CFs. 3426 3427 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3428 libata.ignore_hpa=0 keep BIOS limits (default) 3429 libata.ignore_hpa=1 ignore limits, using full disk 3430 3431 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3432 when set. 3433 Format: <int> 3434 3435 libata.force= [LIBATA] Force configurations. The format is a comma- 3436 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3437 PORT and DEVICE are decimal numbers matching port, link 3438 or device. Basically, it matches the ATA ID string 3439 printed on console by libata. If the whole ID part is 3440 omitted, the last PORT and DEVICE values are used. If 3441 ID hasn't been specified yet, the configuration applies 3442 to all ports, links and devices. 3443 3444 If only DEVICE is omitted, the parameter applies to 3445 the port and all links and devices behind it. DEVICE 3446 number of 0 either selects the first device or the 3447 first fan-out link behind PMP device. It does not 3448 select the host link. DEVICE number of 15 selects the 3449 host link and device attached to it. 3450 3451 The VAL specifies the configuration to force. As long 3452 as there is no ambiguity, shortcut notation is allowed. 3453 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3454 The following configurations can be forced. 3455 3456 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3457 Any ID with matching PORT is used. 3458 3459 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3460 3461 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3462 udma[/][16,25,33,44,66,100,133] notation is also 3463 allowed. 3464 3465 * nohrst, nosrst, norst: suppress hard, soft and both 3466 resets. 3467 3468 * rstonce: only attempt one reset during hot-unplug 3469 link recovery. 3470 3471 * [no]dbdelay: Enable or disable the extra 200ms delay 3472 before debouncing a link PHY and device presence 3473 detection. 3474 3475 * [no]ncq: Turn on or off NCQ. 3476 3477 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3478 3479 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3480 3481 * [no]trim: Enable or disable (unqueued) TRIM. 3482 3483 * trim_zero: Indicate that TRIM command zeroes data. 3484 3485 * max_trim_128m: Set 128M maximum trim size limit. 3486 3487 * [no]dma: Turn on or off DMA transfers. 3488 3489 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3490 3491 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3492 commands that are not a multiple of 16 bytes. 3493 3494 * [no]dmalog: Enable or disable the use of the 3495 READ LOG DMA EXT command to access logs. 3496 3497 * [no]iddevlog: Enable or disable access to the 3498 identify device data log. 3499 3500 * [no]logdir: Enable or disable access to the general 3501 purpose log directory. 3502 3503 * max_sec=<sectors>: Set the transfer size limit, in 3504 number of 512-byte sectors, to the value specified in 3505 <sectors>. The value specified in <sectors> has to be 3506 a non-zero positive integer. 3507 3508 * max_sec_128: Set transfer size limit to 128 sectors. 3509 3510 * max_sec_1024: Set or clear transfer size limit to 3511 1024 sectors. 3512 3513 * max_sec_lba48: Set or clear transfer size limit to 3514 65535 sectors. 3515 3516 * external: Mark port as external (hotplug-capable). 3517 3518 * [no]lpm: Enable or disable link power management. 3519 3520 * [no]setxfer: Indicate if transfer speed mode setting 3521 should be skipped. 3522 3523 * [no]fua: Disable or enable FUA (Force Unit Access) 3524 support for devices supporting this feature. 3525 3526 * dump_id: Dump IDENTIFY data. 3527 3528 * disable: Disable this device. 3529 3530 If there are multiple matching configurations changing 3531 the same attribute, the last one is used. 3532 3533 liveupdate= [KNL,EARLY] 3534 Format: <bool> 3535 Enable Live Update Orchestrator (LUO). 3536 Default: off. 3537 3538 lockd.nlm_grace_period=P [NFS] Assign grace period. 3539 Format: <integer> 3540 3541 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3542 Format: <integer> 3543 3544 lockd.nlm_timeout=T [NFS] Assign timeout value. 3545 Format: <integer> 3546 3547 lockd.nlm_udpport=M [NFS] Assign UDP port. 3548 Format: <integer> 3549 3550 lockdown= [SECURITY,EARLY] 3551 { integrity | confidentiality } 3552 Enable the kernel lockdown feature. If set to 3553 integrity, kernel features that allow userland to 3554 modify the running kernel are disabled. If set to 3555 confidentiality, kernel features that allow userland 3556 to extract confidential information from the kernel 3557 are also disabled. 3558 3559 locktorture.acq_writer_lim= [KNL] 3560 Set the time limit in jiffies for a lock 3561 acquisition. Acquisitions exceeding this limit 3562 will result in a splat once they do complete. 3563 3564 locktorture.bind_readers= [KNL] 3565 Specify the list of CPUs to which the readers are 3566 to be bound. 3567 3568 locktorture.bind_writers= [KNL] 3569 Specify the list of CPUs to which the writers are 3570 to be bound. 3571 3572 locktorture.call_rcu_chains= [KNL] 3573 Specify the number of self-propagating call_rcu() 3574 chains to set up. These are used to ensure that 3575 there is a high probability of an RCU grace period 3576 in progress at any given time. Defaults to 0, 3577 which disables these call_rcu() chains. 3578 3579 locktorture.long_hold= [KNL] 3580 Specify the duration in milliseconds for the 3581 occasional long-duration lock hold time. Defaults 3582 to 100 milliseconds. Select 0 to disable. 3583 3584 locktorture.nested_locks= [KNL] 3585 Specify the maximum lock nesting depth that 3586 locktorture is to exercise, up to a limit of 8 3587 (MAX_NESTED_LOCKS). Specify zero to disable. 3588 Note that this parameter is ineffective on types 3589 of locks that do not support nested acquisition. 3590 3591 locktorture.nreaders_stress= [KNL] 3592 Set the number of locking read-acquisition kthreads. 3593 Defaults to being automatically set based on the 3594 number of online CPUs. 3595 3596 locktorture.nwriters_stress= [KNL] 3597 Set the number of locking write-acquisition kthreads. 3598 3599 locktorture.onoff_holdoff= [KNL] 3600 Set time (s) after boot for CPU-hotplug testing. 3601 3602 locktorture.onoff_interval= [KNL] 3603 Set time (s) between CPU-hotplug operations, or 3604 zero to disable CPU-hotplug testing. 3605 3606 locktorture.rt_boost= [KNL] 3607 Do periodic testing of real-time lock priority 3608 boosting. Select 0 to disable, 1 to boost 3609 only rt_mutex, and 2 to boost unconditionally. 3610 Defaults to 2, which might seem to be an 3611 odd choice, but which should be harmless for 3612 non-real-time spinlocks, due to their disabling 3613 of preemption. Note that non-realtime mutexes 3614 disable boosting. 3615 3616 locktorture.rt_boost_factor= [KNL] 3617 Number that determines how often and for how 3618 long priority boosting is exercised. This is 3619 scaled down by the number of writers, so that the 3620 number of boosts per unit time remains roughly 3621 constant as the number of writers increases. 3622 On the other hand, the duration of each boost 3623 increases with the number of writers. 3624 3625 locktorture.shuffle_interval= [KNL] 3626 Set task-shuffle interval (jiffies). Shuffling 3627 tasks allows some CPUs to go into dyntick-idle 3628 mode during the locktorture test. 3629 3630 locktorture.shutdown_secs= [KNL] 3631 Set time (s) after boot system shutdown. This 3632 is useful for hands-off automated testing. 3633 3634 locktorture.stat_interval= [KNL] 3635 Time (s) between statistics printk()s. 3636 3637 locktorture.stutter= [KNL] 3638 Time (s) to stutter testing, for example, 3639 specifying five seconds causes the test to run for 3640 five seconds, wait for five seconds, and so on. 3641 This tests the locking primitive's ability to 3642 transition abruptly to and from idle. 3643 3644 locktorture.torture_type= [KNL] 3645 Specify the locking implementation to test. 3646 3647 locktorture.verbose= [KNL] 3648 Enable additional printk() statements. 3649 3650 locktorture.writer_fifo= [KNL] 3651 Run the write-side locktorture kthreads at 3652 sched_set_fifo() real-time priority. 3653 3654 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3655 Format: <irq> 3656 3657 loglevel= [KNL,EARLY] 3658 All Kernel Messages with a loglevel smaller than the 3659 console loglevel will be printed to the console. It can 3660 also be changed with klogd or other programs. The 3661 loglevels are defined as follows: 3662 3663 0 (KERN_EMERG) system is unusable 3664 1 (KERN_ALERT) action must be taken immediately 3665 2 (KERN_CRIT) critical conditions 3666 3 (KERN_ERR) error conditions 3667 4 (KERN_WARNING) warning conditions 3668 5 (KERN_NOTICE) normal but significant condition 3669 6 (KERN_INFO) informational 3670 7 (KERN_DEBUG) debug-level messages 3671 3672 log_buf_len=n[KMG] [KNL,EARLY] 3673 Sets the size of the printk ring buffer, in bytes. 3674 n must be a power of two and greater than the 3675 minimal size. The minimal size is defined by 3676 LOG_BUF_SHIFT kernel config parameter. There 3677 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3678 parameter that allows to increase the default size 3679 depending on the number of CPUs. See init/Kconfig 3680 for more details. 3681 3682 logo.nologo [FB] Disables display of the built-in Linux logo. 3683 This may be used to provide more screen space for 3684 kernel log messages and is useful when debugging 3685 kernel boot problems. 3686 3687 lp=0 [LP] Specify parallel ports to use, e.g, 3688 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3689 lp=reset first parallel port). 'lp=0' disables the 3690 lp=auto printer driver. 'lp=reset' (which can be 3691 specified in addition to the ports) causes 3692 attached printers to be reset. Using 3693 lp=port1,port2,... specifies the parallel ports 3694 to associate lp devices with, starting with 3695 lp0. A port specification may be 'none' to skip 3696 that lp device, or a parport name such as 3697 'parport0'. Specifying 'lp=auto' instead of a 3698 port specification list means that device IDs 3699 from each port should be examined, to see if 3700 an IEEE 1284-compliant printer is attached; if 3701 so, the driver will manage that printer. 3702 See also header of drivers/char/lp.c. 3703 3704 lpj=n [KNL] 3705 Sets loops_per_jiffy to given constant, thus avoiding 3706 time-consuming boot-time autodetection (up to 250 ms per 3707 CPU). 0 enables autodetection (default). To determine 3708 the correct value for your kernel, boot with normal 3709 autodetection and see what value is printed. Note that 3710 on SMP systems the preset will be applied to all CPUs, 3711 which is likely to cause problems if your CPUs need 3712 significantly divergent settings. An incorrect value 3713 will cause delays in the kernel to be wrong, leading to 3714 unpredictable I/O errors and other breakage. Although 3715 unlikely, in the extreme case this might damage your 3716 hardware. 3717 3718 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3719 3720 lsm=lsm1,...,lsmN 3721 [SECURITY] Choose order of LSM initialization. This 3722 overrides CONFIG_LSM, and the "security=" parameter. 3723 3724 machtype= [Loongson] Share the same kernel image file between 3725 different yeeloong laptops. 3726 Example: machtype=lemote-yeeloong-2f-7inch 3727 3728 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3729 will bring up during bootup. maxcpus=n : n >= 0 limits 3730 the kernel to bring up 'n' processors. Surely after 3731 bootup you can bring up the other plugged cpu by executing 3732 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3733 only takes effect during system bootup. 3734 While n=0 is a special case, it is equivalent to "nosmp", 3735 which also disables the IO APIC. 3736 3737 max_loop= [LOOP] The number of loop block devices that get 3738 (loop.max_loop) unconditionally pre-created at init time. The default 3739 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3740 of statically allocating a predefined number, loop 3741 devices can be requested on-demand with the 3742 /dev/loop-control interface. 3743 3744 mce= [X86-{32,64}] 3745 3746 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3747 3748 off 3749 disable machine check 3750 3751 no_cmci 3752 disable CMCI(Corrected Machine Check Interrupt) that 3753 Intel processor supports. Usually this disablement is 3754 not recommended, but it might be handy if your 3755 hardware is misbehaving. 3756 3757 Note that you'll get more problems without CMCI than 3758 with due to the shared banks, i.e. you might get 3759 duplicated error logs. 3760 3761 dont_log_ce 3762 don't make logs for corrected errors. All events 3763 reported as corrected are silently cleared by OS. This 3764 option will be useful if you have no interest in any 3765 of corrected errors. 3766 3767 ignore_ce 3768 disable features for corrected errors, e.g. 3769 polling timer and CMCI. All events reported as 3770 corrected are not cleared by OS and remained in its 3771 error banks. 3772 3773 Usually this disablement is not recommended, however 3774 if there is an agent checking/clearing corrected 3775 errors (e.g. BIOS or hardware monitoring 3776 applications), conflicting with OS's error handling, 3777 and you cannot deactivate the agent, then this option 3778 will be a help. 3779 3780 no_lmce 3781 do not opt-in to Local MCE delivery. Use legacy method 3782 to broadcast MCEs. 3783 3784 bootlog 3785 enable logging of machine checks left over from 3786 booting. Disabled by default on AMD Fam10h and older 3787 because some BIOS leave bogus ones. 3788 3789 If your BIOS doesn't do that it's a good idea to 3790 enable though to make sure you log even machine check 3791 events that result in a reboot. On Intel systems it is 3792 enabled by default. 3793 3794 nobootlog 3795 disable boot machine check logging. 3796 3797 monarchtimeout (number) 3798 sets the time in us to wait for other CPUs on machine 3799 checks. 0 to disable. 3800 3801 bios_cmci_threshold 3802 don't overwrite the bios-set CMCI threshold. This boot 3803 option prevents Linux from overwriting the CMCI 3804 threshold set by the bios. Without this option, Linux 3805 always sets the CMCI threshold to 1. Enabling this may 3806 make memory predictive failure analysis less effective 3807 if the bios sets thresholds for memory errors since we 3808 will not see details for all errors. 3809 3810 recovery 3811 force-enable recoverable machine check code paths 3812 3813 Everything else is in sysfs now. 3814 3815 3816 md= [HW] RAID subsystems devices and level 3817 See Documentation/admin-guide/md.rst. 3818 3819 mdacon= [MDA] 3820 Format: <first>,<last> 3821 Specifies range of consoles to be captured by the MDA. 3822 3823 mds= [X86,INTEL,EARLY] 3824 Control mitigation for the Micro-architectural Data 3825 Sampling (MDS) vulnerability. 3826 3827 Certain CPUs are vulnerable to an exploit against CPU 3828 internal buffers which can forward information to a 3829 disclosure gadget under certain conditions. 3830 3831 In vulnerable processors, the speculatively 3832 forwarded data can be used in a cache side channel 3833 attack, to access data to which the attacker does 3834 not have direct access. 3835 3836 This parameter controls the MDS mitigation. The 3837 options are: 3838 3839 full - Enable MDS mitigation on vulnerable CPUs 3840 full,nosmt - Enable MDS mitigation and disable 3841 SMT on vulnerable CPUs 3842 off - Unconditionally disable MDS mitigation 3843 3844 On TAA-affected machines, mds=off can be prevented by 3845 an active TAA mitigation as both vulnerabilities are 3846 mitigated with the same mechanism so in order to disable 3847 this mitigation, you need to specify tsx_async_abort=off 3848 too. 3849 3850 Not specifying this option is equivalent to 3851 mds=full. 3852 3853 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3854 3855 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3856 Must be specified, otherwise memory size will be 0. 3857 3858 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3859 of memory Amount of memory to be used in cases 3860 as follows: 3861 3862 1 for test; 3863 2 when the kernel is not able to see the whole system memory; 3864 3 memory that lies after 'mem=' boundary is excluded from 3865 the hypervisor, then assigned to KVM guests. 3866 4 to limit the memory available for kdump kernel. 3867 3868 [ARC,MICROBLAZE] - the limit applies only to low memory, 3869 high memory is not affected. 3870 3871 [ARM64] - only limits memory covered by the linear 3872 mapping. The NOMAP regions are not affected. 3873 3874 [X86] Work as limiting max address. Use together 3875 with memmap= to avoid physical address space collisions. 3876 Without memmap= PCI devices could be placed at addresses 3877 belonging to unused RAM. 3878 3879 Note that this only takes effects during boot time since 3880 in above case 3, memory may need be hot added after boot 3881 if system memory of hypervisor is not sufficient. 3882 3883 mem=nn[KMG]@ss[KMG] 3884 [ARM,MIPS,EARLY] - override the memory layout 3885 reported by firmware. 3886 Define a memory region of size nn[KMG] starting at 3887 ss[KMG]. 3888 Multiple different regions can be specified with 3889 multiple mem= parameters on the command line. 3890 3891 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3892 memory. 3893 3894 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3895 3896 memchunk=nn[KMG] 3897 [KNL,SH] Allow user to override the default size for 3898 per-device physically contiguous DMA buffers. 3899 3900 memhp_default_state=online/offline/online_kernel/online_movable 3901 [KNL] Set the initial state for the memory hotplug 3902 onlining policy. If not specified, the default value is 3903 set according to the 3904 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3905 options. 3906 See Documentation/admin-guide/mm/memory-hotplug.rst. 3907 3908 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3909 E820 memory map, as specified by the user. 3910 Such memmap=exactmap lines can be constructed based on 3911 BIOS output or other requirements. See the memmap=nn@ss 3912 option description. 3913 3914 memmap=nn[KMG]@ss[KMG] 3915 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3916 Region of memory to be used is from ss to ss+nn. 3917 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3918 which limits max address to nn[KMG]. 3919 Multiple different regions can be specified, 3920 comma delimited. 3921 Example: 3922 memmap=100M@2G,100M#3G,1G!1024G 3923 3924 memmap=nn[KMG]#ss[KMG] 3925 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3926 Region of memory to be marked is from ss to ss+nn. 3927 3928 memmap=nn[KMG]$ss[KMG] 3929 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3930 Region of memory to be reserved is from ss to ss+nn. 3931 Example: Exclude memory from 0x18690000-0x1869ffff 3932 memmap=64K$0x18690000 3933 or 3934 memmap=0x10000$0x18690000 3935 Some bootloaders may need an escape character before '$', 3936 like Grub2, otherwise '$' and the following number 3937 will be eaten. 3938 3939 memmap=nn[KMG]!ss[KMG,EARLY] 3940 [KNL,X86] Mark specific memory as protected. 3941 Region of memory to be used, from ss to ss+nn. 3942 The memory region may be marked as e820 type 12 (0xc) 3943 and is NVDIMM or ADR memory. 3944 3945 memmap=<size>%<offset>-<oldtype>+<newtype> 3946 [KNL,ACPI,EARLY] Convert memory within the specified region 3947 from <oldtype> to <newtype>. If "-<oldtype>" is left 3948 out, the whole region will be marked as <newtype>, 3949 even if previously unavailable. If "+<newtype>" is left 3950 out, matching memory will be removed. Types are 3951 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3952 3 = ACPI, 12 = PRAM. 3953 3954 memory_corruption_check=0/1 [X86,EARLY] 3955 Some BIOSes seem to corrupt the first 64k of 3956 memory when doing things like suspend/resume. 3957 Setting this option will scan the memory 3958 looking for corruption. Enabling this will 3959 both detect corruption and prevent the kernel 3960 from using the memory being corrupted. 3961 However, it's intended as a diagnostic tool; if 3962 repeatable BIOS-originated corruption always 3963 affects the same memory, you can use memmap= 3964 to prevent the kernel from using that memory. 3965 3966 memory_corruption_check_size=size [X86,EARLY] 3967 By default it checks for corruption in the low 3968 64k, making this memory unavailable for normal 3969 use. Use this parameter to scan for 3970 corruption in more or less memory. 3971 3972 memory_corruption_check_period=seconds [X86,EARLY] 3973 By default it checks for corruption every 60 3974 seconds. Use this parameter to check at some 3975 other rate. 0 disables periodic checking. 3976 3977 memory_hotplug.memmap_on_memory 3978 [KNL,X86,ARM] Boolean flag to enable this feature. 3979 Format: {on | off (default)} 3980 When enabled, runtime hotplugged memory will 3981 allocate its internal metadata (struct pages, 3982 those vmemmap pages cannot be optimized even 3983 if hugetlb_free_vmemmap is enabled) from the 3984 hotadded memory which will allow to hotadd a 3985 lot of memory without requiring additional 3986 memory to do so. 3987 This feature is disabled by default because it 3988 has some implication on large (e.g. GB) 3989 allocations in some configurations (e.g. small 3990 memory blocks). 3991 The state of the flag can be read in 3992 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3993 Note that even when enabled, there are a few cases where 3994 the feature is not effective. 3995 3996 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3997 Format: <integer> 3998 default : 0 <disable> 3999 Specifies the number of memtest passes to be 4000 performed. Each pass selects another test 4001 pattern from a given set of patterns. Memtest 4002 fills the memory with this pattern, validates 4003 memory contents and reserves bad memory 4004 regions that are detected. 4005 4006 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4007 Valid arguments: on, off 4008 Default: off 4009 mem_encrypt=on: Activate SME 4010 mem_encrypt=off: Do not activate SME 4011 4012 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4013 for details on when memory encryption can be activated. 4014 4015 mem_sleep_default= [SUSPEND] Default system suspend mode: 4016 s2idle - Suspend-To-Idle 4017 shallow - Power-On Suspend or equivalent (if supported) 4018 deep - Suspend-To-RAM or equivalent (if supported) 4019 See Documentation/admin-guide/pm/sleep-states.rst. 4020 4021 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4022 the BIOS has incorrectly applied a workaround. TinyBIOS 4023 version 0.98 is known to be affected, 0.99 fixes the 4024 problem by letting the user disable the workaround. 4025 4026 mga= [HW,DRM] 4027 4028 microcode= [X86] Control the behavior of the microcode loader. 4029 Available options, comma separated: 4030 4031 base_rev=X - with <X> with format: <u32> 4032 Set the base microcode revision of each thread when in 4033 debug mode. 4034 4035 dis_ucode_ldr: disable the microcode loader 4036 4037 force_minrev: 4038 Enable or disable the microcode minimal revision 4039 enforcement for the runtime microcode loader. 4040 4041 mini2440= [ARM,HW,KNL] 4042 Format:[0..2][b][c][t] 4043 Default: "0tb" 4044 MINI2440 configuration specification: 4045 0 - The attached screen is the 3.5" TFT 4046 1 - The attached screen is the 7" TFT 4047 2 - The VGA Shield is attached (1024x768) 4048 Leaving out the screen size parameter will not load 4049 the TFT driver, and the framebuffer will be left 4050 unconfigured. 4051 b - Enable backlight. The TFT backlight pin will be 4052 linked to the kernel VESA blanking code and a GPIO 4053 LED. This parameter is not necessary when using the 4054 VGA shield. 4055 c - Enable the s3c camera interface. 4056 t - Reserved for enabling touchscreen support. The 4057 touchscreen support is not enabled in the mainstream 4058 kernel as of 2.6.30, a preliminary port can be found 4059 in the "bleeding edge" mini2440 support kernel at 4060 https://repo.or.cz/w/linux-2.6/mini2440.git 4061 4062 mitigations= 4063 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4064 CPU vulnerabilities. This is a set of curated, 4065 arch-independent options, each of which is an 4066 aggregation of existing arch-specific options. 4067 4068 Note, "mitigations" is supported if and only if the 4069 kernel was built with CPU_MITIGATIONS=y. 4070 4071 off 4072 Disable all optional CPU mitigations. This 4073 improves system performance, but it may also 4074 expose users to several CPU vulnerabilities. 4075 Equivalent to: if nokaslr then kpti=0 [ARM64] 4076 gather_data_sampling=off [X86] 4077 indirect_target_selection=off [X86] 4078 kvm.nx_huge_pages=off [X86] 4079 l1tf=off [X86] 4080 mds=off [X86] 4081 mmio_stale_data=off [X86] 4082 no_entry_flush [PPC] 4083 no_uaccess_flush [PPC] 4084 nobp=0 [S390] 4085 nopti [X86,PPC] 4086 nospectre_bhb [ARM64] 4087 nospectre_v1 [X86,PPC] 4088 nospectre_v2 [X86,PPC,S390,ARM64] 4089 reg_file_data_sampling=off [X86] 4090 retbleed=off [X86] 4091 spec_rstack_overflow=off [X86] 4092 spec_store_bypass_disable=off [X86,PPC] 4093 spectre_bhi=off [X86] 4094 spectre_v2_user=off [X86] 4095 srbds=off [X86,INTEL] 4096 ssbd=force-off [ARM64] 4097 tsa=off [X86,AMD] 4098 tsx_async_abort=off [X86] 4099 vmscape=off [X86] 4100 4101 Exceptions: 4102 This does not have any effect on 4103 kvm.nx_huge_pages when 4104 kvm.nx_huge_pages=force. 4105 4106 auto (default) 4107 Mitigate all CPU vulnerabilities, but leave SMT 4108 enabled, even if it's vulnerable. This is for 4109 users who don't want to be surprised by SMT 4110 getting disabled across kernel upgrades, or who 4111 have other ways of avoiding SMT-based attacks. 4112 Equivalent to: (default behavior) 4113 4114 auto,nosmt 4115 Mitigate all CPU vulnerabilities, disabling SMT 4116 if needed. This is for users who always want to 4117 be fully mitigated, even if it means losing SMT. 4118 Equivalent to: l1tf=flush,nosmt [X86] 4119 mds=full,nosmt [X86] 4120 tsx_async_abort=full,nosmt [X86] 4121 mmio_stale_data=full,nosmt [X86] 4122 retbleed=auto,nosmt [X86] 4123 4124 [X86] After one of the above options, additionally 4125 supports attack-vector based controls as documented in 4126 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4127 4128 mminit_loglevel= 4129 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4130 parameter allows control of the logging verbosity for 4131 the additional memory initialisation checks. A value 4132 of 0 disables mminit logging and a level of 4 will 4133 log everything. Information is printed at KERN_DEBUG 4134 so loglevel=8 may also need to be specified. 4135 4136 mmio_stale_data= 4137 [X86,INTEL,EARLY] Control mitigation for the Processor 4138 MMIO Stale Data vulnerabilities. 4139 4140 Processor MMIO Stale Data is a class of 4141 vulnerabilities that may expose data after an MMIO 4142 operation. Exposed data could originate or end in 4143 the same CPU buffers as affected by MDS and TAA. 4144 Therefore, similar to MDS and TAA, the mitigation 4145 is to clear the affected CPU buffers. 4146 4147 This parameter controls the mitigation. The 4148 options are: 4149 4150 full - Enable mitigation on vulnerable CPUs 4151 4152 full,nosmt - Enable mitigation and disable SMT on 4153 vulnerable CPUs. 4154 4155 off - Unconditionally disable mitigation 4156 4157 On MDS or TAA affected machines, 4158 mmio_stale_data=off can be prevented by an active 4159 MDS or TAA mitigation as these vulnerabilities are 4160 mitigated with the same mechanism so in order to 4161 disable this mitigation, you need to specify 4162 mds=off and tsx_async_abort=off too. 4163 4164 Not specifying this option is equivalent to 4165 mmio_stale_data=full. 4166 4167 For details see: 4168 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4169 4170 <module>.async_probe[=<bool>] [KNL] 4171 If no <bool> value is specified or if the value 4172 specified is not a valid <bool>, enable asynchronous 4173 probe on this module. Otherwise, enable/disable 4174 asynchronous probe on this module as indicated by the 4175 <bool> value. See also: module.async_probe 4176 4177 module.async_probe=<bool> 4178 [KNL] When set to true, modules will use async probing 4179 by default. To enable/disable async probing for a 4180 specific module, use the module specific control that 4181 is documented under <module>.async_probe. When both 4182 module.async_probe and <module>.async_probe are 4183 specified, <module>.async_probe takes precedence for 4184 the specific module. 4185 4186 module.enable_dups_trace 4187 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4188 this means that duplicate request_module() calls will 4189 trigger a WARN_ON() instead of a pr_warn(). Note that 4190 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4191 will always be issued and this option does nothing. 4192 module.sig_enforce 4193 [KNL] When CONFIG_MODULE_SIG is set, this means that 4194 modules without (valid) signatures will fail to load. 4195 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4196 is always true, so this option does nothing. 4197 4198 module_blacklist= [KNL] Do not load a comma-separated list of 4199 modules. Useful for debugging problem modules. 4200 4201 mousedev.tap_time= 4202 [MOUSE] Maximum time between finger touching and 4203 leaving touchpad surface for touch to be considered 4204 a tap and be reported as a left button click (for 4205 touchpads working in absolute mode only). 4206 Format: <msecs> 4207 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4208 reporting absolute coordinates, such as tablets 4209 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4210 reporting absolute coordinates, such as tablets 4211 4212 movablecore= [KNL,X86,PPC,EARLY] 4213 Format: nn[KMGTPE] | nn% 4214 This parameter is the complement to kernelcore=, it 4215 specifies the amount of memory used for migratable 4216 allocations. If both kernelcore and movablecore is 4217 specified, then kernelcore will be at *least* the 4218 specified value but may be more. If movablecore on its 4219 own is specified, the administrator must be careful 4220 that the amount of memory usable for all allocations 4221 is not too small. 4222 4223 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4224 NUMA nodes to be movable. This means that the memory 4225 of such nodes will be usable only for movable 4226 allocations which rules out almost all kernel 4227 allocations. Use with caution! 4228 4229 MTD_Partition= [MTD] 4230 Format: <name>,<region-number>,<size>,<offset> 4231 4232 MTD_Region= [MTD] Format: 4233 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4234 4235 mtdparts= [MTD] 4236 See drivers/mtd/parsers/cmdlinepart.c 4237 4238 mtouchusb.raw_coordinates= 4239 [HW] Make the MicroTouch USB driver use raw coordinates 4240 ('y', default) or cooked coordinates ('n') 4241 4242 mtrr=debug [X86,EARLY] 4243 Enable printing debug information related to MTRR 4244 registers at boot time. 4245 4246 mtrr_chunk_size=nn[KMG,X86,EARLY] 4247 used for mtrr cleanup. It is largest continuous chunk 4248 that could hold holes aka. UC entries. 4249 4250 mtrr_gran_size=nn[KMG,X86,EARLY] 4251 Used for mtrr cleanup. It is granularity of mtrr block. 4252 Default is 1. 4253 Large value could prevent small alignment from 4254 using up MTRRs. 4255 4256 mtrr_spare_reg_nr=n [X86,EARLY] 4257 Format: <integer> 4258 Range: 0,7 : spare reg number 4259 Default : 1 4260 Used for mtrr cleanup. It is spare mtrr entries number. 4261 Set to 2 or more if your graphical card needs more. 4262 4263 multitce=off [PPC] This parameter disables the use of the pSeries 4264 firmware feature for updating multiple TCE entries 4265 at a time. 4266 4267 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4268 4269 netdev= [NET] NE2000 ISA network devices parameters 4270 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4271 4272 netpoll.carrier_timeout= 4273 [NET] Specifies amount of time (in seconds) that 4274 netpoll should wait for a carrier. By default netpoll 4275 waits 4 seconds. 4276 4277 nf_conntrack.acct= 4278 [NETFILTER] Enable connection tracking flow accounting 4279 0 to disable accounting 4280 1 to enable accounting 4281 Default value is 0. 4282 4283 nfs.cache_getent= 4284 [NFS] sets the pathname to the program which is used 4285 to update the NFS client cache entries. 4286 4287 nfs.cache_getent_timeout= 4288 [NFS] sets the timeout after which an attempt to 4289 update a cache entry is deemed to have failed. 4290 4291 nfs.callback_nr_threads= 4292 [NFSv4] set the total number of threads that the 4293 NFS client will assign to service NFSv4 callback 4294 requests. 4295 4296 nfs.callback_tcpport= 4297 [NFS] set the TCP port on which the NFSv4 callback 4298 channel should listen. 4299 4300 nfs.delay_retrans= 4301 [NFS] specifies the number of times the NFSv4 client 4302 retries the request before returning an EAGAIN error, 4303 after a reply of NFS4ERR_DELAY from the server. 4304 Only applies if the softerr mount option is enabled, 4305 and the specified value is >= 0. 4306 4307 nfs.enable_ino64= 4308 [NFS] enable 64-bit inode numbers. 4309 If zero, the NFS client will fake up a 32-bit inode 4310 number for the readdir() and stat() syscalls instead 4311 of returning the full 64-bit number. 4312 The default is to return 64-bit inode numbers. 4313 4314 nfs.idmap_cache_timeout= 4315 [NFS] set the maximum lifetime for idmapper cache 4316 entries. 4317 4318 nfs.max_session_cb_slots= 4319 [NFSv4.1] Sets the maximum number of session 4320 slots the client will assign to the callback 4321 channel. This determines the maximum number of 4322 callbacks the client will process in parallel for 4323 a particular server. 4324 4325 nfs.max_session_slots= 4326 [NFSv4.1] Sets the maximum number of session slots 4327 the client will attempt to negotiate with the server. 4328 This limits the number of simultaneous RPC requests 4329 that the client can send to the NFSv4.1 server. 4330 Note that there is little point in setting this 4331 value higher than the max_tcp_slot_table_limit. 4332 4333 nfs.nfs4_disable_idmapping= 4334 [NFSv4] When set to the default of '1', this option 4335 ensures that both the RPC level authentication 4336 scheme and the NFS level operations agree to use 4337 numeric uids/gids if the mount is using the 4338 'sec=sys' security flavour. In effect it is 4339 disabling idmapping, which can make migration from 4340 legacy NFSv2/v3 systems to NFSv4 easier. 4341 Servers that do not support this mode of operation 4342 will be autodetected by the client, and it will fall 4343 back to using the idmapper. 4344 To turn off this behaviour, set the value to '0'. 4345 4346 nfs.nfs4_unique_id= 4347 [NFS4] Specify an additional fixed unique ident- 4348 ification string that NFSv4 clients can insert into 4349 their nfs_client_id4 string. This is typically a 4350 UUID that is generated at system install time. 4351 4352 nfs.recover_lost_locks= 4353 [NFSv4] Attempt to recover locks that were lost due 4354 to a lease timeout on the server. Please note that 4355 doing this risks data corruption, since there are 4356 no guarantees that the file will remain unchanged 4357 after the locks are lost. 4358 If you want to enable the kernel legacy behaviour of 4359 attempting to recover these locks, then set this 4360 parameter to '1'. 4361 The default parameter value of '0' causes the kernel 4362 not to attempt recovery of lost locks. 4363 4364 nfs.send_implementation_id= 4365 [NFSv4.1] Send client implementation identification 4366 information in exchange_id requests. 4367 If zero, no implementation identification information 4368 will be sent. 4369 The default is to send the implementation identification 4370 information. 4371 4372 nfs4.layoutstats_timer= 4373 [NFSv4.2] Change the rate at which the kernel sends 4374 layoutstats to the pNFS metadata server. 4375 4376 Setting this to value to 0 causes the kernel to use 4377 whatever value is the default set by the layout 4378 driver. A non-zero value sets the minimum interval 4379 in seconds between layoutstats transmissions. 4380 4381 nfsd.inter_copy_offload_enable= 4382 [NFSv4.2] When set to 1, the server will support 4383 server-to-server copies for which this server is 4384 the destination of the copy. 4385 4386 nfsd.nfs4_disable_idmapping= 4387 [NFSv4] When set to the default of '1', the NFSv4 4388 server will return only numeric uids and gids to 4389 clients using auth_sys, and will accept numeric uids 4390 and gids from such clients. This is intended to ease 4391 migration from NFSv2/v3. 4392 4393 nfsd.nfsd4_ssc_umount_timeout= 4394 [NFSv4.2] When used as the destination of a 4395 server-to-server copy, knfsd temporarily mounts 4396 the source server. It caches the mount in case 4397 it will be needed again, and discards it if not 4398 used for the number of milliseconds specified by 4399 this parameter. 4400 4401 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4402 See Documentation/admin-guide/nfs/nfsroot.rst. 4403 4404 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4405 See Documentation/admin-guide/nfs/nfsroot.rst. 4406 4407 nfsrootdebug [NFS] enable nfsroot debugging messages. 4408 See Documentation/admin-guide/nfs/nfsroot.rst. 4409 4410 nmi_backtrace.backtrace_idle [KNL] 4411 Dump stacks even of idle CPUs in response to an 4412 NMI stack-backtrace request. 4413 4414 nmi_debug= [KNL,SH] Specify one or more actions to take 4415 when a NMI is triggered. 4416 Format: [state][,regs][,debounce][,die] 4417 4418 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4419 Format: [panic,][nopanic,][rNNN,][num] 4420 Valid num: 0 or 1 4421 0 - turn hardlockup detector in nmi_watchdog off 4422 1 - turn hardlockup detector in nmi_watchdog on 4423 rNNN - configure the watchdog with raw perf event 0xNNN 4424 4425 When panic is specified, panic when an NMI watchdog 4426 timeout occurs (or 'nopanic' to not panic on an NMI 4427 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4428 To disable both hard and soft lockup detectors, 4429 please see 'nowatchdog'. 4430 This is useful when you use a panic=... timeout and 4431 need the box quickly up again. 4432 4433 These settings can be accessed at runtime via 4434 the nmi_watchdog and hardlockup_panic sysctls. 4435 4436 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4437 emulation library even if a 387 maths coprocessor 4438 is present. 4439 4440 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4441 Forces kernel to use 3-level paging instead. 4442 4443 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4444 kernel to use 4-level paging instead. 4445 4446 noalign [KNL,ARM] 4447 4448 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4449 IOAPICs that may be present in the system. 4450 4451 noapictimer [APIC,X86] Don't set up the APIC timer 4452 4453 noautogroup Disable scheduler automatic task group creation. 4454 4455 nocache [ARM,EARLY] 4456 4457 no_console_suspend 4458 [HW] Never suspend the console 4459 Disable suspending of consoles during suspend and 4460 hibernate operations. Once disabled, debugging 4461 messages can reach various consoles while the rest 4462 of the system is being put to sleep (ie, while 4463 debugging driver suspend/resume hooks). This may 4464 not work reliably with all consoles, but is known 4465 to work with serial and VGA consoles. 4466 To facilitate more flexible debugging, we also add 4467 console_suspend, a printk module parameter to control 4468 it. Users could use console_suspend (usually 4469 /sys/module/printk/parameters/console_suspend) to 4470 turn on/off it dynamically. 4471 4472 no_debug_objects 4473 [KNL,EARLY] Disable object debugging 4474 4475 nodsp [SH] Disable hardware DSP at boot time. 4476 4477 noefi [EFI,EARLY] Disable EFI runtime services support. 4478 4479 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4480 4481 noexec32 [X86-64] 4482 This affects only 32-bit executables. 4483 noexec32=on: enable non-executable mappings (default) 4484 read doesn't imply executable mappings 4485 noexec32=off: disable non-executable mappings 4486 read implies executable mappings 4487 4488 no_file_caps Tells the kernel not to honor file capabilities. The 4489 only way then for a file to be executed with privilege 4490 is to be setuid root or executed by root. 4491 4492 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4493 4494 nofsgsbase [X86] Disables FSGSBASE instructions. 4495 4496 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4497 register save and restore. The kernel will only save 4498 legacy floating-point registers on task switch. 4499 4500 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4501 4502 no_hash_pointers 4503 [KNL,EARLY] 4504 Alias for "hash_pointers=never". 4505 4506 nohibernate [HIBERNATION] Disable hibernation and resume. 4507 4508 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4509 busy wait in do_idle() and not use the arch_cpu_idle() 4510 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4511 to be effective. This is useful on platforms where the 4512 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4513 correctly or when doing power measurements to evaluate 4514 the impact of the sleep instructions. This is also 4515 useful when using JTAG debugger. 4516 4517 nohpet [X86] Don't use the HPET timer. 4518 4519 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4520 4521 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4522 4523 nohz= [KNL] Boottime enable/disable dynamic ticks 4524 Valid arguments: on, off 4525 Default: on 4526 4527 nohz_full= [KNL,BOOT,SMP,ISOL] 4528 The argument is a cpu list, as described above. 4529 In kernels built with CONFIG_NO_HZ_FULL=y, set 4530 the specified list of CPUs whose tick will be stopped 4531 whenever possible. The boot CPU will be forced outside 4532 the range to maintain the timekeeping. Any CPUs 4533 in this list will have their RCU callbacks offloaded, 4534 just as if they had also been called out in the 4535 rcu_nocbs= boot parameter. 4536 4537 Note that this argument takes precedence over 4538 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4539 4540 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4541 initial RAM disk. Currently this parameter applies to 4542 initrd only, not to initramfs. But it applies to both 4543 in EFI mode. 4544 4545 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4546 remapping. 4547 [Deprecated - use intremap=off] 4548 4549 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4550 4551 noiotrap [SH] Disables trapped I/O port accesses. 4552 4553 noirqdebug [X86-32] Disables the code which attempts to detect and 4554 disable unhandled interrupt sources. 4555 4556 noisapnp [ISAPNP] Disables ISA PnP code. 4557 4558 nokaslr [KNL,EARLY] 4559 When CONFIG_RANDOMIZE_BASE is set, this disables 4560 kernel and module base offset ASLR (Address Space 4561 Layout Randomization). 4562 4563 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4564 fault handling. 4565 4566 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4567 4568 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4569 4570 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4571 4572 nomce [X86-32] Disable Machine Check Exception 4573 4574 nomfgpt [X86-32] Disable Multi-Function General Purpose 4575 Timer usage (for AMD Geode machines). 4576 4577 nomodeset Disable kernel modesetting. Most systems' firmware 4578 sets up a display mode and provides framebuffer memory 4579 for output. With nomodeset, DRM and fbdev drivers will 4580 not load if they could possibly displace the pre- 4581 initialized output. Only the system framebuffer will 4582 be available for use. The respective drivers will not 4583 perform display-mode changes or accelerated rendering. 4584 4585 Useful as error fallback, or for testing and debugging. 4586 4587 nomodule Disable module load 4588 4589 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4590 shutdown the other cpus. Instead use the REBOOT_VECTOR 4591 irq. 4592 4593 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4594 pagetables) support. 4595 4596 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4597 4598 nopku [X86] Disable Memory Protection Keys CPU feature found 4599 in some Intel CPUs. 4600 4601 nopti [X86-64,EARLY] 4602 Equivalent to pti=off 4603 4604 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4605 Disables the PV optimizations forcing the guest to run 4606 as generic guest with no PV drivers. Currently support 4607 XEN HVM, KVM, HYPER_V and VMWARE guest. 4608 4609 nopvspin [X86,XEN,KVM,EARLY] 4610 Disables the qspinlock slow path using PV optimizations 4611 which allow the hypervisor to 'idle' the guest on lock 4612 contention. 4613 4614 norandmaps Don't use address space randomization. Equivalent to 4615 echo 0 > /proc/sys/kernel/randomize_va_space 4616 4617 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4618 with UP alternatives 4619 4620 noresume [SWSUSP] Disables resume and restores original swap 4621 space. 4622 4623 no-scroll [VGA] Disables scrollback. 4624 This is required for the Braillex ib80-piezo Braille 4625 reader made by F.H. Papenmeier (Germany). 4626 4627 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4628 4629 nosmap [PPC,EARLY] 4630 Disable SMAP (Supervisor Mode Access Prevention) 4631 even if it is supported by processor. 4632 4633 nosmep [PPC64s,EARLY] 4634 Disable SMEP (Supervisor Mode Execution Prevention) 4635 even if it is supported by processor. 4636 4637 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4638 and disable the IO APIC. legacy for "maxcpus=0". 4639 4640 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4641 Equivalent to smt=1. 4642 4643 [KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT). 4644 nosmt=force: Force disable SMT, cannot be undone 4645 via the sysfs control file. 4646 4647 nosoftlockup [KNL] Disable the soft-lockup detector. 4648 4649 nospec_store_bypass_disable 4650 [HW,EARLY] Disable all mitigations for the Speculative 4651 Store Bypass vulnerability 4652 4653 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4654 history injection) vulnerability. System may allow data leaks 4655 with this option. 4656 4657 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4658 (bounds check bypass). With this option data leaks are 4659 possible in the system. 4660 4661 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4662 for the Spectre variant 2 (indirect branch 4663 prediction) vulnerability. System may allow data 4664 leaks with this option. 4665 4666 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4667 Disable paravirtualized steal time accounting. steal time 4668 is computed, but won't influence scheduler behaviour 4669 4670 nosync [HW,M68K] Disables sync negotiation for all devices. 4671 4672 no_timer_check [X86,APIC] Disables the code which tests for broken 4673 timer IRQ sources, i.e., the IO-APIC timer. This can 4674 work around problems with incorrect timer 4675 initialization on some boards. 4676 4677 no_uaccess_flush 4678 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4679 4680 novmcoredd [KNL,KDUMP] 4681 Disable device dump. Device dump allows drivers to 4682 append dump data to vmcore so you can collect driver 4683 specified debug info. Drivers can append the data 4684 without any limit and this data is stored in memory, 4685 so this may cause significant memory stress. Disabling 4686 device dump can help save memory but the driver debug 4687 data will be no longer available. This parameter 4688 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4689 is set. 4690 4691 no-vmw-sched-clock 4692 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4693 scheduler clock and use the default one. 4694 4695 nowatchdog [KNL] Disable both lockup detectors, i.e. 4696 soft-lockup and NMI watchdog (hard-lockup). 4697 4698 nowb [ARM,EARLY] 4699 4700 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4701 4702 NOTE: this parameter will be ignored on systems with the 4703 LEGACY_XAPIC_DISABLED bit set in the 4704 IA32_XAPIC_DISABLE_STATUS MSR. 4705 4706 noxsave [BUGS=X86] Disables x86 extended register state save 4707 and restore using xsave. The kernel will fallback to 4708 enabling legacy floating-point and sse state. 4709 4710 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4711 register states. The kernel will fall back to use 4712 xsave to save the states. By using this parameter, 4713 performance of saving the states is degraded because 4714 xsave doesn't support modified optimization while 4715 xsaveopt supports it on xsaveopt enabled systems. 4716 4717 noxsaves [X86] Disables xsaves and xrstors used in saving and 4718 restoring x86 extended register state in compacted 4719 form of xsave area. The kernel will fall back to use 4720 xsaveopt and xrstor to save and restore the states 4721 in standard form of xsave area. By using this 4722 parameter, xsave area per process might occupy more 4723 memory on xsaves enabled systems. 4724 4725 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4726 could support. nr_cpus=n : n >= 1 limits the kernel to 4727 support 'n' processors. It could be larger than the 4728 number of already plugged CPU during bootup, later in 4729 runtime you can physically add extra cpu until it reaches 4730 n. So during boot up some boot time memory for per-cpu 4731 variables need be pre-allocated for later physical cpu 4732 hot plugging. 4733 4734 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4735 4736 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4737 Disable NUMA, Only set up a single NUMA node 4738 spanning all memory. 4739 4740 numa=fake=<size>[MG] 4741 [KNL, ARM64, RISCV, X86, EARLY] 4742 If given as a memory unit, fills all system RAM with 4743 nodes of size interleaved over physical nodes. 4744 4745 numa=fake=<N> 4746 [KNL, ARM64, RISCV, X86, EARLY] 4747 If given as an integer, fills all system RAM with N 4748 fake nodes interleaved over physical nodes. 4749 4750 numa=fake=<N>U 4751 [KNL, ARM64, RISCV, X86, EARLY] 4752 If given as an integer followed by 'U', it will 4753 divide each physical node into N emulated nodes. 4754 4755 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4756 4757 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4758 soft-reserved memory partitioning. 4759 4760 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4761 NUMA balancing. 4762 Allowed values are enable and disable 4763 4764 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4765 'node', 'default' can be specified 4766 This can be set from sysctl after boot. 4767 See Documentation/admin-guide/sysctl/vm.rst for details. 4768 4769 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4770 nvme quirk list. List entries are separated by a 4771 '-' character. 4772 Each entry has the form VendorID:ProductID:quirk_names. 4773 The IDs are 4-digits hex numbers and quirk_names is a 4774 list of quirk names separated by commas. A quirk name 4775 can be prefixed by '^', meaning that the specified 4776 quirk must be disabled. 4777 4778 Example: 4779 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4780 4781 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4782 See Documentation/core-api/debugging-via-ohci1394.rst for more 4783 info. 4784 4785 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4786 Rather than timing out after 20 ms if an EC 4787 command is not properly ACKed, override the length 4788 of the timeout. We have interrupts disabled while 4789 waiting for the ACK, so if this is set too high 4790 interrupts *may* be lost! 4791 4792 omap_mux= [OMAP] Override bootloader pin multiplexing. 4793 Format: <mux_mode0.mode_name=value>... 4794 For example, to override I2C bus2: 4795 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4796 4797 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4798 4799 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4800 4801 boundary - index of last SLC block on Flex-OneNAND. 4802 The remaining blocks are configured as MLC blocks. 4803 lock - Configure if Flex-OneNAND boundary should be locked. 4804 Once locked, the boundary cannot be changed. 4805 1 indicates lock status, 0 indicates unlock status. 4806 4807 oops=panic [KNL,EARLY] 4808 Always panic on oopses. Default is to just kill the 4809 process, but there is a small probability of 4810 deadlocking the machine. 4811 This will also cause panics on machine check exceptions. 4812 Useful together with panic=30 to trigger a reboot. 4813 4814 page_alloc.shuffle= 4815 [KNL] Boolean flag to control whether the page allocator 4816 should randomize its free lists. This parameter can be 4817 used to enable/disable page randomization. The state of 4818 the flag can be read from sysfs at: 4819 /sys/module/page_alloc/parameters/shuffle. 4820 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4821 4822 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4823 Storage of the information about who allocated 4824 each page is disabled in default. With this switch, 4825 we can turn it on. 4826 on: enable the feature 4827 4828 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4829 poisoning on the buddy allocator, available with 4830 CONFIG_PAGE_POISONING=y. 4831 off: turn off poisoning (default) 4832 on: turn on poisoning 4833 4834 page_reporting.page_reporting_order= 4835 [KNL] Minimal page reporting order 4836 Format: <integer> 4837 Adjust the minimal page reporting order. The page 4838 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4839 4840 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4841 timeout > 0: seconds before rebooting 4842 timeout = 0: wait forever 4843 timeout < 0: reboot immediately 4844 Format: <timeout> 4845 4846 panic_on_taint= [KNL,EARLY] 4847 Bitmask for conditionally calling panic() in add_taint() 4848 Format: <hex>[,nousertaint] 4849 Hexadecimal bitmask representing the set of TAINT flags 4850 that will cause the kernel to panic when add_taint() is 4851 called with any of the flags in this set. 4852 The optional switch "nousertaint" can be utilized to 4853 prevent userspace forced crashes by writing to sysctl 4854 /proc/sys/kernel/tainted any flagset matching with the 4855 bitmask set on panic_on_taint. 4856 See Documentation/admin-guide/tainted-kernels.rst for 4857 extra details on the taint flags that users can pick 4858 to compose the bitmask to assign to panic_on_taint. 4859 4860 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4861 on a WARN(). 4862 4863 panic_force_cpu= 4864 [KNL,SMP] Force panic handling to execute on a specific CPU. 4865 Format: <cpu number> 4866 Some platforms require panic handling to occur on a 4867 specific CPU for the crash kernel to function correctly. 4868 This can be due to firmware limitations, interrupt routing 4869 constraints, or platform-specific requirements where only 4870 a particular CPU can safely enter the crash kernel. 4871 When set, panic() will redirect execution to the specified 4872 CPU before proceeding with the normal panic and kexec flow. 4873 If the target CPU is offline or unavailable, panic proceeds 4874 on the current CPU. 4875 This option should only be used for systems with the above 4876 constraints as it might cause the panic operation to be less reliable. 4877 4878 panic_print= Bitmask for printing system info when panic happens. 4879 User can chose combination of the following bits: 4880 bit 0: print all tasks info 4881 bit 1: print system memory info 4882 bit 2: print timer info 4883 bit 3: print locks info if CONFIG_LOCKDEP is on 4884 bit 4: print ftrace buffer 4885 bit 5: replay all kernel messages on consoles at the end of panic 4886 bit 6: print all CPUs backtrace (if available in the arch) 4887 bit 7: print only tasks in uninterruptible (blocked) state 4888 *Be aware* that this option may print a _lot_ of lines, 4889 so there are risks of losing older messages in the log. 4890 Use this option carefully, maybe worth to setup a 4891 bigger log buffer with "log_buf_len" along with this. 4892 4893 panic_sys_info= A comma separated list of extra information to be dumped 4894 on panic. 4895 Format: val[,val...] 4896 Where @val can be any of the following: 4897 4898 tasks: print all tasks info 4899 mem: print system memory info 4900 timers: print timers info 4901 locks: print locks info if CONFIG_LOCKDEP is on 4902 ftrace: print ftrace buffer 4903 all_bt: print all CPUs backtrace (if available in the arch) 4904 blocked_tasks: print only tasks in uninterruptible (blocked) state 4905 4906 This is a human readable alternative to the 'panic_print' option. 4907 4908 panic_console_replay 4909 When panic happens, replay all kernel messages on 4910 consoles at the end of panic. 4911 4912 parkbd.port= [HW] Parallel port number the keyboard adapter is 4913 connected to, default is 0. 4914 Format: <parport#> 4915 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4916 0 for XT, 1 for AT (default is AT). 4917 Format: <mode> 4918 4919 parport= [HW,PPT] Specify parallel ports. 0 disables. 4920 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4921 Use 'auto' to force the driver to use any 4922 IRQ/DMA settings detected (the default is to 4923 ignore detected IRQ/DMA settings because of 4924 possible conflicts). You can specify the base 4925 address, IRQ, and DMA settings; IRQ and DMA 4926 should be numbers, or 'auto' (for using detected 4927 settings on that particular port), or 'nofifo' 4928 (to avoid using a FIFO even if it is detected). 4929 Parallel ports are assigned in the order they 4930 are specified on the command line, starting 4931 with parport0. 4932 4933 parport_init_mode= [HW,PPT] 4934 Configure VIA parallel port to operate in 4935 a specific mode. This is necessary on Pegasos 4936 computer where firmware has no options for setting 4937 up parallel port mode and sets it to spp. 4938 Currently this function knows 686a and 8231 chips. 4939 Format: [spp|ps2|epp|ecp|ecpepp] 4940 4941 pata_legacy.all= [HW,LIBATA] 4942 Format: <int> 4943 Set to non-zero to probe primary and secondary ISA 4944 port ranges on PCI systems where no PCI PATA device 4945 has been found at either range. Disabled by default. 4946 4947 pata_legacy.autospeed= [HW,LIBATA] 4948 Format: <int> 4949 Set to non-zero if a chip is present that snoops speed 4950 changes. Disabled by default. 4951 4952 pata_legacy.ht6560a= [HW,LIBATA] 4953 Format: <int> 4954 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4955 the secondary channel, or both channels respectively. 4956 Disabled by default. 4957 4958 pata_legacy.ht6560b= [HW,LIBATA] 4959 Format: <int> 4960 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4961 the secondary channel, or both channels respectively. 4962 Disabled by default. 4963 4964 pata_legacy.iordy_mask= [HW,LIBATA] 4965 Format: <int> 4966 IORDY enable mask. Set individual bits to allow IORDY 4967 for the respective channel. Bit 0 is for the first 4968 legacy channel handled by this driver, bit 1 is for 4969 the second channel, and so on. The sequence will often 4970 correspond to the primary legacy channel, the secondary 4971 legacy channel, and so on, but the handling of a PCI 4972 bus and the use of other driver options may interfere 4973 with the sequence. By default IORDY is allowed across 4974 all channels. 4975 4976 pata_legacy.opti82c46x= [HW,LIBATA] 4977 Format: <int> 4978 Set to 1, 2, or 3 for Opti 82c611A on the primary 4979 channel, the secondary channel, or both channels 4980 respectively. Disabled by default. 4981 4982 pata_legacy.opti82c611a= [HW,LIBATA] 4983 Format: <int> 4984 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4985 channel, the secondary channel, or both channels 4986 respectively. Disabled by default. 4987 4988 pata_legacy.pio_mask= [HW,LIBATA] 4989 Format: <int> 4990 PIO mode mask for autospeed devices. Set individual 4991 bits to allow the use of the respective PIO modes. 4992 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4993 All modes allowed by default. 4994 4995 pata_legacy.probe_all= [HW,LIBATA] 4996 Format: <int> 4997 Set to non-zero to probe tertiary and further ISA 4998 port ranges on PCI systems. Disabled by default. 4999 5000 pata_legacy.probe_mask= [HW,LIBATA] 5001 Format: <int> 5002 Probe mask for legacy ISA PATA ports. Depending on 5003 platform configuration and the use of other driver 5004 options up to 6 legacy ports are supported: 0x1f0, 5005 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5006 of individual ports can be disabled by setting the 5007 corresponding bits in the mask to 1. Bit 0 is for 5008 the first port in the list above (0x1f0), and so on. 5009 By default all supported ports are probed. 5010 5011 pata_legacy.qdi= [HW,LIBATA] 5012 Format: <int> 5013 Set to non-zero to probe QDI controllers. By default 5014 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5015 5016 pata_legacy.winbond= [HW,LIBATA] 5017 Format: <int> 5018 Set to non-zero to probe Winbond controllers. Use 5019 the standard I/O port (0x130) if 1, otherwise the 5020 value given is the I/O port to use (typically 0x1b0). 5021 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5022 0 otherwise. 5023 5024 pata_platform.pio_mask= [HW,LIBATA] 5025 Format: <int> 5026 Supported PIO mode mask. Set individual bits to allow 5027 the use of the respective PIO modes. Bit 0 is for 5028 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5029 allowed by default. 5030 5031 pause_on_oops=<int> 5032 Halt all CPUs after the first oops has been printed for 5033 the specified number of seconds. This is to be used if 5034 your oopses keep scrolling off the screen. 5035 5036 pcbit= [HW,ISDN] 5037 5038 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5039 5040 Some options herein operate on a specific device 5041 or a set of devices (<pci_dev>). These are 5042 specified in one of the following formats: 5043 5044 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5045 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5046 5047 Note: the first format specifies a PCI 5048 bus/device/function address which may change 5049 if new hardware is inserted, if motherboard 5050 firmware changes, or due to changes caused 5051 by other kernel parameters. If the 5052 domain is left unspecified, it is 5053 taken to be zero. Optionally, a path 5054 to a device through multiple device/function 5055 addresses can be specified after the base 5056 address (this is more robust against 5057 renumbering issues). The second format 5058 selects devices using IDs from the 5059 configuration space which may match multiple 5060 devices in the system. 5061 5062 earlydump dump PCI config space before the kernel 5063 changes anything 5064 off [X86] don't probe for the PCI bus 5065 bios [X86-32] force use of PCI BIOS, don't access 5066 the hardware directly. Use this if your machine 5067 has a non-standard PCI host bridge. 5068 nobios [X86-32] disallow use of PCI BIOS, only direct 5069 hardware access methods are allowed. Use this 5070 if you experience crashes upon bootup and you 5071 suspect they are caused by the BIOS. 5072 conf1 [X86] Force use of PCI Configuration Access 5073 Mechanism 1 (config address in IO port 0xCF8, 5074 data in IO port 0xCFC, both 32-bit). 5075 conf2 [X86] Force use of PCI Configuration Access 5076 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5077 the function, IO port 0xCFA, also 8-bit, sets 5078 bus number. The config space is then accessed 5079 through ports 0xC000-0xCFFF). 5080 See http://wiki.osdev.org/PCI for more info 5081 on the configuration access mechanisms. 5082 noaer [PCIE] If the PCIEAER kernel config parameter is 5083 enabled, this kernel boot option can be used to 5084 disable the use of PCIE advanced error reporting. 5085 nodomains [PCI] Disable support for multiple PCI 5086 root domains (aka PCI segments, in ACPI-speak). 5087 nommconf [X86] Disable use of MMCONFIG for PCI 5088 Configuration 5089 check_enable_amd_mmconf [X86] check for and enable 5090 properly configured MMIO access to PCI 5091 config space on AMD family 10h CPU 5092 nomsi [MSI] If the PCI_MSI kernel config parameter is 5093 enabled, this kernel boot option can be used to 5094 disable the use of MSI interrupts system-wide. 5095 noioapicquirk [APIC] Disable all boot interrupt quirks. 5096 Safety option to keep boot IRQs enabled. This 5097 should never be necessary. 5098 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5099 primary IO-APIC for bridges that cannot disable 5100 boot IRQs. This fixes a source of spurious IRQs 5101 when the system masks IRQs. 5102 noioapicreroute [APIC] Disable workaround that uses the 5103 boot IRQ equivalent of an IRQ that connects to 5104 a chipset where boot IRQs cannot be disabled. 5105 The opposite of ioapicreroute. 5106 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5107 routing table. These calls are known to be buggy 5108 on several machines and they hang the machine 5109 when used, but on other computers it's the only 5110 way to get the interrupt routing table. Try 5111 this option if the kernel is unable to allocate 5112 IRQs or discover secondary PCI buses on your 5113 motherboard. 5114 rom [X86] Assign address space to expansion ROMs. 5115 Use with caution as certain devices share 5116 address decoders between ROMs and other 5117 resources. 5118 norom [X86] Do not assign address space to 5119 expansion ROMs that do not already have 5120 BIOS assigned address ranges. 5121 nobar [X86] Do not assign address space to the 5122 BARs that weren't assigned by the BIOS. 5123 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5124 assigned automatically to PCI devices. You can 5125 make the kernel exclude IRQs of your ISA cards 5126 this way. 5127 pirqaddr=0xAAAAA [X86] Specify the physical address 5128 of the PIRQ table (normally generated 5129 by the BIOS) if it is outside the 5130 F0000h-100000h range. 5131 lastbus=N [X86] Scan all buses thru bus #N. Can be 5132 useful if the kernel is unable to find your 5133 secondary buses and you want to tell it 5134 explicitly which ones they are. 5135 assign-busses [X86] Always assign all PCI bus 5136 numbers ourselves, overriding 5137 whatever the firmware may have done. 5138 usepirqmask [X86] Honor the possible IRQ mask stored 5139 in the BIOS $PIR table. This is needed on 5140 some systems with broken BIOSes, notably 5141 some HP Pavilion N5400 and Omnibook XE3 5142 notebooks. This will have no effect if ACPI 5143 IRQ routing is enabled. 5144 noacpi [X86] Do not use ACPI for IRQ routing 5145 or for PCI scanning. 5146 use_crs [X86] Use PCI host bridge window information 5147 from ACPI. On BIOSes from 2008 or later, this 5148 is enabled by default. If you need to use this, 5149 please report a bug. 5150 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5151 If you need to use this, please report a bug. 5152 use_e820 [X86] Use E820 reservations to exclude parts of 5153 PCI host bridge windows. This is a workaround 5154 for BIOS defects in host bridge _CRS methods. 5155 If you need to use this, please report a bug to 5156 <linux-pci@vger.kernel.org>. 5157 no_e820 [X86] Ignore E820 reservations for PCI host 5158 bridge windows. This is the default on modern 5159 hardware. If you need to use this, please report 5160 a bug to <linux-pci@vger.kernel.org>. 5161 routeirq Do IRQ routing for all PCI devices. 5162 This is normally done in pci_enable_device(), 5163 so this option is a temporary workaround 5164 for broken drivers that don't call it. 5165 skip_isa_align [X86] do not align io start addr, so can 5166 handle more pci cards 5167 noearly [X86] Don't do any early type 1 scanning. 5168 This might help on some broken boards which 5169 machine check when some devices' config space 5170 is read. But various workarounds are disabled 5171 and some IOMMU drivers will not work. 5172 bfsort Sort PCI devices into breadth-first order. 5173 This sorting is done to get a device 5174 order compatible with older (<= 2.4) kernels. 5175 nobfsort Don't sort PCI devices into breadth-first order. 5176 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5177 tuning and use the BIOS-configured MPS defaults. 5178 pcie_bus_safe Set every device's MPS to the largest value 5179 supported by all devices below the root complex. 5180 pcie_bus_perf Set device MPS to the largest allowable MPS 5181 based on its parent bus. Also set MRRS (Max 5182 Read Request Size) to the largest supported 5183 value (no larger than the MPS that the device 5184 or bus can support) for best performance. 5185 pcie_bus_peer2peer Set every device's MPS to 128B, which 5186 every device is guaranteed to support. This 5187 configuration allows peer-to-peer DMA between 5188 any pair of devices, possibly at the cost of 5189 reduced performance. This also guarantees 5190 that hot-added devices will work. 5191 cbiosize=nn[KMG] The fixed amount of bus space which is 5192 reserved for the CardBus bridge's IO window. 5193 The default value is 256 bytes. 5194 cbmemsize=nn[KMG] The fixed amount of bus space which is 5195 reserved for the CardBus bridge's memory 5196 window. The default value is 64 megabytes. 5197 resource_alignment= 5198 Format: 5199 [<order of align>@]<pci_dev>[; ...] 5200 Specifies alignment and device to reassign 5201 aligned memory resources. How to 5202 specify the device is described above. 5203 If <order of align> is not specified, 5204 PAGE_SIZE is used as alignment. 5205 A PCI-PCI bridge can be specified if resource 5206 windows need to be expanded. 5207 To specify the alignment for several 5208 instances of a device, the PCI vendor, 5209 device, subvendor, and subdevice may be 5210 specified, e.g., 12@pci:8086:9c22:103c:198f 5211 for 4096-byte alignment. 5212 ecrc= Enable/disable PCIe ECRC (transaction layer 5213 end-to-end CRC checking). Only effective if 5214 OS has native AER control (either granted by 5215 ACPI _OSC or forced via "pcie_ports=native") 5216 bios: Use BIOS/firmware settings. This is the 5217 the default. 5218 off: Turn ECRC off 5219 on: Turn ECRC on. 5220 hpiosize=nn[KMG] The fixed amount of bus space which is 5221 reserved for hotplug bridge's IO window. 5222 Default size is 256 bytes. 5223 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5224 reserved for hotplug bridge's MMIO window. 5225 Default size is 2 megabytes. 5226 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5227 reserved for hotplug bridge's MMIO_PREF window. 5228 Default size is 2 megabytes. 5229 hpmemsize=nn[KMG] The fixed amount of bus space which is 5230 reserved for hotplug bridge's MMIO and 5231 MMIO_PREF window. 5232 Default size is 2 megabytes. 5233 hpbussize=nn The minimum amount of additional bus numbers 5234 reserved for buses below a hotplug bridge. 5235 Default is 1. 5236 realloc= Enable/disable reallocating PCI bridge resources 5237 if allocations done by BIOS are too small to 5238 accommodate resources required by all child 5239 devices. 5240 off: Turn realloc off 5241 on: Turn realloc on 5242 realloc same as realloc=on 5243 noari do not use PCIe ARI. 5244 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5245 do not use PCIe ATS (and IOMMU device IOTLB). 5246 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5247 only look for one device below a PCIe downstream 5248 port. 5249 big_root_window Try to add a big 64bit memory window to the PCIe 5250 root complex on AMD CPUs. Some GFX hardware 5251 can resize a BAR to allow access to all VRAM. 5252 Adding the window is slightly risky (it may 5253 conflict with unreported devices), so this 5254 taints the kernel. 5255 disable_acs_redir=<pci_dev>[; ...] 5256 Specify one or more PCI devices (in the format 5257 specified above) separated by semicolons. 5258 Each device specified will have the PCI ACS 5259 redirect capabilities forced off which will 5260 allow P2P traffic between devices through 5261 bridges without forcing it upstream. Note: 5262 this removes isolation between devices and 5263 may put more devices in an IOMMU group. 5264 config_acs= 5265 Format: 5266 <ACS flags>@<pci_dev>[; ...] 5267 Specify one or more PCI devices (in the format 5268 specified above) optionally prepended with flags 5269 and separated by semicolons. The respective 5270 capabilities will be enabled, disabled or 5271 unchanged based on what is specified in 5272 flags. 5273 5274 ACS Flags is defined as follows: 5275 bit-0 : ACS Source Validation 5276 bit-1 : ACS Translation Blocking 5277 bit-2 : ACS P2P Request Redirect 5278 bit-3 : ACS P2P Completion Redirect 5279 bit-4 : ACS Upstream Forwarding 5280 bit-5 : ACS P2P Egress Control 5281 bit-6 : ACS Direct Translated P2P 5282 Each bit can be marked as: 5283 '0' – force disabled 5284 '1' – force enabled 5285 'x' – unchanged 5286 For example, 5287 pci=config_acs=10x@pci:0:0 5288 would configure all devices that support 5289 ACS to enable P2P Request Redirect, disable 5290 Translation Blocking, and leave Source 5291 Validation unchanged from whatever power-up 5292 or firmware set it to. 5293 5294 Note: this may remove isolation between devices 5295 and may put more devices in an IOMMU group. 5296 force_floating [S390] Force usage of floating interrupts. 5297 nomio [S390] Do not use MIO instructions. 5298 norid [S390] ignore the RID field and force use of 5299 one PCI domain per PCI function 5300 notph [PCIE] If the PCIE_TPH kernel config parameter 5301 is enabled, this kernel boot option can be used 5302 to disable PCIe TLP Processing Hints support 5303 system-wide. 5304 5305 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5306 Management. 5307 off Don't touch ASPM configuration at all. Leave any 5308 configuration done by firmware unchanged. 5309 force Enable ASPM even on devices that claim not to support it. 5310 WARNING: Forcing ASPM on may cause system lockups. 5311 5312 pcie_ports= [PCIE] PCIe port services handling: 5313 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5314 even if the platform doesn't give the OS permission to 5315 use them. This may cause conflicts if the platform 5316 also tries to use these services. 5317 dpc-native Use native PCIe service for DPC only. May 5318 cause conflicts if firmware uses AER or DPC. 5319 compat Disable native PCIe services (PME, AER, DPC, PCIe 5320 hotplug). 5321 5322 pcie_port_pm= [PCIE] PCIe port power management handling: 5323 off Disable power management of all PCIe ports 5324 force Forcibly enable power management of all PCIe ports 5325 5326 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5327 nomsi Do not use MSI for native PCIe PME signaling (this makes 5328 all PCIe root ports use INTx for all services). 5329 5330 pcmv= [HW,PCMCIA] BadgePAD 4 5331 5332 pd_ignore_unused 5333 [PM] 5334 Keep all power-domains already enabled by bootloader on, 5335 even if no driver has claimed them. This is useful 5336 for debug and development, but should not be 5337 needed on a platform with proper driver support. 5338 5339 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5340 boot time. 5341 Format: { 0 | 1 } 5342 See arch/parisc/kernel/pdc_chassis.c 5343 5344 percpu_alloc= [MM,EARLY] 5345 Select which percpu first chunk allocator to use. 5346 Currently supported values are "embed" and "page". 5347 Archs may support subset or none of the selections. 5348 See comments in mm/percpu.c for details on each 5349 allocator. This parameter is primarily for debugging 5350 and performance comparison. 5351 5352 pirq= [SMP,APIC] Manual mp-table setup 5353 See Documentation/arch/x86/i386/IO-APIC.rst. 5354 5355 plip= [PPT,NET] Parallel port network link 5356 Format: { parport<nr> | timid | 0 } 5357 See also Documentation/admin-guide/parport.rst. 5358 5359 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5360 Override pmtimer IOPort with a hex value. 5361 e.g. pmtmr=0x508 5362 5363 pmu_override= [PPC] Override the PMU. 5364 This option takes over the PMU facility, so it is no 5365 longer usable by perf. Setting this option starts the 5366 PMU counters by setting MMCR0 to 0 (the FC bit is 5367 cleared). If a number is given, then MMCR1 is set to 5368 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5369 remains 0. 5370 5371 pm_async= [PM] 5372 Format: off 5373 This parameter sets the initial value of the 5374 /sys/power/pm_async sysfs knob at boot time. 5375 If set to "off", disables asynchronous suspend and 5376 resume of devices during system-wide power transitions. 5377 This can be useful on platforms where device 5378 dependencies are not well-defined, or for debugging 5379 power management issues. Asynchronous operations are 5380 enabled by default. 5381 5382 5383 pm_debug_messages [SUSPEND,KNL] 5384 Enable suspend/resume debug messages during boot up. 5385 5386 pnp.debug=1 [PNP] 5387 Enable PNP debug messages (depends on the 5388 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5389 via /sys/module/pnp/parameters/debug. We always show 5390 current resource usage; turning this on also shows 5391 possible settings and some assignment information. 5392 5393 pnpacpi= [ACPI] 5394 { off } 5395 5396 pnpbios= [ISAPNP] 5397 { on | off | curr | res | no-curr | no-res } 5398 5399 pnp_reserve_irq= 5400 [ISAPNP] Exclude IRQs for the autoconfiguration 5401 5402 pnp_reserve_dma= 5403 [ISAPNP] Exclude DMAs for the autoconfiguration 5404 5405 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5406 Ranges are in pairs (I/O port base and size). 5407 5408 pnp_reserve_mem= 5409 [ISAPNP] Exclude memory regions for the 5410 autoconfiguration. 5411 Ranges are in pairs (memory base and size). 5412 5413 ports= [IP_VS_FTP] IPVS ftp helper module 5414 Default is 21. 5415 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5416 may be specified. 5417 Format: <port>,<port>.... 5418 5419 possible_cpus= [SMP,S390,X86] 5420 Format: <unsigned int> 5421 Set the number of possible CPUs, overriding the 5422 regular discovery mechanisms (such as ACPI/FW, etc). 5423 5424 powersave=off [PPC] This option disables power saving features. 5425 It specifically disables cpuidle and sets the 5426 platform machine description specific power_save 5427 function to NULL. On Idle the CPU just reduces 5428 execution priority. 5429 5430 ppc_strict_facility_enable 5431 [PPC,ENABLE] This option catches any kernel floating point, 5432 Altivec, VSX and SPE outside of regions specifically 5433 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5434 There is some performance impact when enabling this. 5435 5436 ppc_tm= [PPC,EARLY] 5437 Format: {"off"} 5438 Disable Hardware Transactional Memory 5439 5440 preempt= [KNL] 5441 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5442 none - Limited to cond_resched() calls 5443 voluntary - Limited to cond_resched() and might_sleep() calls 5444 full - Any section that isn't explicitly preempt disabled 5445 can be preempted anytime. Tasks will also yield 5446 contended spinlocks (if the critical section isn't 5447 explicitly preempt disabled beyond the lock itself). 5448 lazy - Scheduler controlled. Similar to full but instead 5449 of preempting the task immediately, the task gets 5450 one HZ tick time to yield itself before the 5451 preemption will be forced. One preemption is when the 5452 task returns to user space. 5453 5454 print-fatal-signals= 5455 [KNL] debug: print fatal signals 5456 5457 If enabled, warn about various signal handling 5458 related application anomalies: too many signals, 5459 too many POSIX.1 timers, fatal signals causing a 5460 coredump - etc. 5461 5462 If you hit the warning due to signal overflow, 5463 you might want to try "ulimit -i unlimited". 5464 5465 default: off. 5466 5467 printk.always_kmsg_dump= 5468 Trigger kmsg_dump for cases other than kernel oops or 5469 panics 5470 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5471 default: disabled 5472 5473 printk.console_no_auto_verbose= 5474 Disable console loglevel raise on oops, panic 5475 or lockdep-detected issues (only if lock debug is on). 5476 With an exception to setups with low baudrate on 5477 serial console, keeping this 0 is a good choice 5478 in order to provide more debug information. 5479 Format: <bool> 5480 default: 0 (auto_verbose is enabled) 5481 5482 printk.debug_non_panic_cpus= 5483 Allows storing messages from non-panic CPUs into 5484 the printk log buffer during panic(). They are 5485 flushed to consoles by the panic-CPU on 5486 a best-effort basis. 5487 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5488 Default: disabled 5489 5490 printk.devkmsg={on,off,ratelimit} 5491 Control writing to /dev/kmsg. 5492 on - unlimited logging to /dev/kmsg from userspace 5493 off - logging to /dev/kmsg disabled 5494 ratelimit - ratelimit the logging 5495 Default: ratelimit 5496 5497 printk.time= Show timing data prefixed to each printk message line 5498 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5499 5500 proc_mem.force_override= [KNL] 5501 Format: {always | ptrace | never} 5502 Traditionally /proc/pid/mem allows memory permissions to be 5503 overridden without restrictions. This option may be set to 5504 restrict that. Can be one of: 5505 - 'always': traditional behavior always allows mem overrides. 5506 - 'ptrace': only allow mem overrides for active ptracers. 5507 - 'never': never allow mem overrides. 5508 If not specified, default is the CONFIG_PROC_MEM_* choice. 5509 5510 processor.max_cstate= [HW,ACPI] 5511 Limit processor to maximum C-state 5512 max_cstate=9 overrides any DMI blacklist limit. 5513 5514 processor.nocst [HW,ACPI] 5515 Ignore the _CST method to determine C-states, 5516 instead using the legacy FADT method 5517 5518 profile= [KNL] Enable kernel profiling via /proc/profile 5519 Format: [<profiletype>,]<number> 5520 Param: <profiletype>: "schedule" or "kvm" 5521 [defaults to kernel profiling] 5522 Param: "schedule" - profile schedule points. 5523 Param: "kvm" - profile VM exits. 5524 Param: <number> - step/bucket size as a power of 2 for 5525 statistical time based profiling. 5526 5527 prot_virt= [S390] enable hosting protected virtual machines 5528 isolated from the hypervisor (if hardware supports 5529 that). If enabled, the default kernel base address 5530 might be overridden even when Kernel Address Space 5531 Layout Randomization is disabled. 5532 Format: <bool> 5533 5534 psi= [KNL] Enable or disable pressure stall information 5535 tracking. 5536 Format: <bool> 5537 5538 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5539 probe for; one of (bare|imps|exps|lifebook|any). 5540 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5541 per second. 5542 psmouse.resetafter= [HW,MOUSE] 5543 Try to reset the device after so many bad packets 5544 (0 = never). 5545 psmouse.resolution= 5546 [HW,MOUSE] Set desired mouse resolution, in dpi. 5547 psmouse.smartscroll= 5548 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5549 0 = disabled, 1 = enabled (default). 5550 5551 pstore.backend= Specify the name of the pstore backend to use 5552 5553 pti= [X86-64] Control Page Table Isolation of user and 5554 kernel address spaces. Disabling this feature 5555 removes hardening, but improves performance of 5556 system calls and interrupts. 5557 5558 on - unconditionally enable 5559 off - unconditionally disable 5560 auto - kernel detects whether your CPU model is 5561 vulnerable to issues that PTI mitigates 5562 5563 Not specifying this option is equivalent to pti=auto. 5564 5565 pty.legacy_count= 5566 [KNL] Number of legacy pty's. Overwrites compiled-in 5567 default number. 5568 5569 quiet [KNL,EARLY] Disable most log messages 5570 5571 r128= [HW,DRM] 5572 5573 radix_hcall_invalidate=on [PPC/PSERIES] 5574 Disable RADIX GTSE feature and use hcall for TLB 5575 invalidate. 5576 5577 raid= [HW,RAID] 5578 See Documentation/admin-guide/md.rst. 5579 5580 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5581 See Documentation/admin-guide/blockdev/ramdisk.rst. 5582 5583 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5584 5585 random.trust_cpu=off 5586 [KNL,EARLY] Disable trusting the use of the CPU's 5587 random number generator (if available) to 5588 initialize the kernel's RNG. 5589 5590 random.trust_bootloader=off 5591 [KNL,EARLY] Disable trusting the use of the a seed 5592 passed by the bootloader (if available) to 5593 initialize the kernel's RNG. 5594 5595 randomize_kstack_offset= 5596 [KNL,EARLY] Enable or disable kernel stack offset 5597 randomization, which provides roughly 5 bits of 5598 entropy, frustrating memory corruption attacks 5599 that depend on stack address determinism or 5600 cross-syscall address exposures. This is only 5601 available on architectures that have defined 5602 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5603 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5604 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5605 5606 ras=option[,option,...] [KNL] RAS-specific options 5607 5608 cec_disable [X86] 5609 Disable the Correctable Errors Collector, 5610 see CONFIG_RAS_CEC help text. 5611 5612 rcu_nocbs[=cpu-list] 5613 [KNL] The optional argument is a cpu list, 5614 as described above. 5615 5616 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5617 enable the no-callback CPU mode, which prevents 5618 such CPUs' callbacks from being invoked in 5619 softirq context. Invocation of such CPUs' RCU 5620 callbacks will instead be offloaded to "rcuox/N" 5621 kthreads created for that purpose, where "x" is 5622 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5623 for the kthreads that mediate grace periods; and 5624 "N" is the CPU number. This reduces OS jitter on 5625 the offloaded CPUs, which can be useful for HPC 5626 and real-time workloads. It can also improve 5627 energy efficiency for asymmetric multiprocessors. 5628 5629 If a cpulist is passed as an argument, the specified 5630 list of CPUs is set to no-callback mode from boot. 5631 5632 Otherwise, if the '=' sign and the cpulist 5633 arguments are omitted, no CPU will be set to 5634 no-callback mode from boot but the mode may be 5635 toggled at runtime via cpusets. 5636 5637 Note that this argument takes precedence over 5638 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5639 5640 rcu_nocb_poll [KNL] 5641 Rather than requiring that offloaded CPUs 5642 (specified by rcu_nocbs= above) explicitly 5643 awaken the corresponding "rcuoN" kthreads, 5644 make these kthreads poll for callbacks. 5645 This improves the real-time response for the 5646 offloaded CPUs by relieving them of the need to 5647 wake up the corresponding kthread, but degrades 5648 energy efficiency by requiring that the kthreads 5649 periodically wake up to do the polling. 5650 5651 rcutree.blimit= [KNL] 5652 Set maximum number of finished RCU callbacks to 5653 process in one batch. 5654 5655 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5656 Do only a one-line RCU CPU stall warning when 5657 there is an ongoing too-long CSD-lock wait. 5658 5659 rcutree.do_rcu_barrier= [KNL] 5660 Request a call to rcu_barrier(). This is 5661 throttled so that userspace tests can safely 5662 hammer on the sysfs variable if they so choose. 5663 If triggered before the RCU grace-period machinery 5664 is fully active, this will error out with EAGAIN. 5665 5666 rcutree.dump_tree= [KNL] 5667 Dump the structure of the rcu_node combining tree 5668 out at early boot. This is used for diagnostic 5669 purposes, to verify correct tree setup. 5670 5671 rcutree.gp_cleanup_delay= [KNL] 5672 Set the number of jiffies to delay each step of 5673 RCU grace-period cleanup. 5674 5675 rcutree.gp_init_delay= [KNL] 5676 Set the number of jiffies to delay each step of 5677 RCU grace-period initialization. 5678 5679 rcutree.gp_preinit_delay= [KNL] 5680 Set the number of jiffies to delay each step of 5681 RCU grace-period pre-initialization, that is, 5682 the propagation of recent CPU-hotplug changes up 5683 the rcu_node combining tree. 5684 5685 rcutree.jiffies_till_first_fqs= [KNL] 5686 Set delay from grace-period initialization to 5687 first attempt to force quiescent states. 5688 Units are jiffies, minimum value is zero, 5689 and maximum value is HZ. 5690 5691 rcutree.jiffies_till_next_fqs= [KNL] 5692 Set delay between subsequent attempts to force 5693 quiescent states. Units are jiffies, minimum 5694 value is one, and maximum value is HZ. 5695 5696 rcutree.jiffies_till_sched_qs= [KNL] 5697 Set required age in jiffies for a 5698 given grace period before RCU starts 5699 soliciting quiescent-state help from 5700 rcu_note_context_switch() and cond_resched(). 5701 If not specified, the kernel will calculate 5702 a value based on the most recent settings 5703 of rcutree.jiffies_till_first_fqs 5704 and rcutree.jiffies_till_next_fqs. 5705 This calculated value may be viewed in 5706 rcutree.jiffies_to_sched_qs. Any attempt to set 5707 rcutree.jiffies_to_sched_qs will be cheerfully 5708 overwritten. 5709 5710 rcutree.kthread_prio= [KNL,BOOT] 5711 Set the SCHED_FIFO priority of the RCU per-CPU 5712 kthreads (rcuc/N). This value is also used for 5713 the priority of the RCU boost threads (rcub/N) 5714 and for the RCU grace-period kthreads (rcu_bh, 5715 rcu_preempt, and rcu_sched). If RCU_BOOST is 5716 set, valid values are 1-99 and the default is 1 5717 (the least-favored priority). Otherwise, when 5718 RCU_BOOST is not set, valid values are 0-99 and 5719 the default is zero (non-realtime operation). 5720 When RCU_NOCB_CPU is set, also adjust the 5721 priority of NOCB callback kthreads. 5722 5723 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5724 On callback-offloaded (rcu_nocbs) CPUs, 5725 RCU reduces the lock contention that would 5726 otherwise be caused by callback floods through 5727 use of the ->nocb_bypass list. However, in the 5728 common non-flooded case, RCU queues directly to 5729 the main ->cblist in order to avoid the extra 5730 overhead of the ->nocb_bypass list and its lock. 5731 But if there are too many callbacks queued during 5732 a single jiffy, RCU pre-queues the callbacks into 5733 the ->nocb_bypass queue. The definition of "too 5734 many" is supplied by this kernel boot parameter. 5735 5736 rcutree.nohz_full_patience_delay= [KNL] 5737 On callback-offloaded (rcu_nocbs) CPUs, avoid 5738 disturbing RCU unless the grace period has 5739 reached the specified age in milliseconds. 5740 Defaults to zero. Large values will be capped 5741 at five seconds. All values will be rounded down 5742 to the nearest value representable by jiffies. 5743 5744 rcutree.qhimark= [KNL] 5745 Set threshold of queued RCU callbacks beyond which 5746 batch limiting is disabled. 5747 5748 rcutree.qlowmark= [KNL] 5749 Set threshold of queued RCU callbacks below which 5750 batch limiting is re-enabled. 5751 5752 rcutree.qovld= [KNL] 5753 Set threshold of queued RCU callbacks beyond which 5754 RCU's force-quiescent-state scan will aggressively 5755 enlist help from cond_resched() and sched IPIs to 5756 help CPUs more quickly reach quiescent states. 5757 Set to less than zero to make this be set based 5758 on rcutree.qhimark at boot time and to zero to 5759 disable more aggressive help enlistment. 5760 5761 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5762 Set the page-cache refill delay (in milliseconds) 5763 in response to low-memory conditions. The range 5764 of permitted values is in the range 0:100000. 5765 5766 rcutree.rcu_divisor= [KNL] 5767 Set the shift-right count to use to compute 5768 the callback-invocation batch limit bl from 5769 the number of callbacks queued on this CPU. 5770 The result will be bounded below by the value of 5771 the rcutree.blimit kernel parameter. Every bl 5772 callbacks, the softirq handler will exit in 5773 order to allow the CPU to do other work. 5774 5775 Please note that this callback-invocation batch 5776 limit applies only to non-offloaded callback 5777 invocation. Offloaded callbacks are instead 5778 invoked in the context of an rcuoc kthread, which 5779 scheduler will preempt as it does any other task. 5780 5781 rcutree.rcu_fanout_exact= [KNL] 5782 Disable autobalancing of the rcu_node combining 5783 tree. This is used by rcutorture, and might 5784 possibly be useful for architectures having high 5785 cache-to-cache transfer latencies. 5786 5787 rcutree.rcu_fanout_leaf= [KNL] 5788 Change the number of CPUs assigned to each 5789 leaf rcu_node structure. Useful for very 5790 large systems, which will choose the value 64, 5791 and for NUMA systems with large remote-access 5792 latencies, which will choose a value aligned 5793 with the appropriate hardware boundaries. 5794 5795 rcutree.rcu_min_cached_objs= [KNL] 5796 Minimum number of objects which are cached and 5797 maintained per one CPU. Object size is equal 5798 to PAGE_SIZE. The cache allows to reduce the 5799 pressure to page allocator, also it makes the 5800 whole algorithm to behave better in low memory 5801 condition. 5802 5803 rcutree.rcu_nocb_gp_stride= [KNL] 5804 Set the number of NOCB callback kthreads in 5805 each group, which defaults to the square root 5806 of the number of CPUs. Larger numbers reduce 5807 the wakeup overhead on the global grace-period 5808 kthread, but increases that same overhead on 5809 each group's NOCB grace-period kthread. 5810 5811 rcutree.rcu_kick_kthreads= [KNL] 5812 Cause the grace-period kthread to get an extra 5813 wake_up() if it sleeps three times longer than 5814 it should at force-quiescent-state time. 5815 This wake_up() will be accompanied by a 5816 WARN_ONCE() splat and an ftrace_dump(). 5817 5818 rcutree.rcu_resched_ns= [KNL] 5819 Limit the time spend invoking a batch of RCU 5820 callbacks to the specified number of nanoseconds. 5821 By default, this limit is checked only once 5822 every 32 callbacks in order to limit the pain 5823 inflicted by local_clock() overhead. 5824 5825 rcutree.rcu_unlock_delay= [KNL] 5826 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5827 this specifies an rcu_read_unlock()-time delay 5828 in microseconds. This defaults to zero. 5829 Larger delays increase the probability of 5830 catching RCU pointer leaks, that is, buggy use 5831 of RCU-protected pointers after the relevant 5832 rcu_read_unlock() has completed. 5833 5834 rcutree.sysrq_rcu= [KNL] 5835 Commandeer a sysrq key to dump out Tree RCU's 5836 rcu_node tree with an eye towards determining 5837 why a new grace period has not yet started. 5838 5839 rcutree.use_softirq= [KNL] 5840 If set to zero, move all RCU_SOFTIRQ processing to 5841 per-CPU rcuc kthreads. Defaults to a non-zero 5842 value, meaning that RCU_SOFTIRQ is used by default. 5843 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5844 5845 But note that CONFIG_PREEMPT_RT=y kernels disable 5846 this kernel boot parameter, forcibly setting it 5847 to zero. 5848 5849 rcutree.enable_rcu_lazy= [KNL] 5850 To save power, batch RCU callbacks and flush after 5851 delay, memory pressure or callback list growing too 5852 big. 5853 5854 rcutree.rcu_normal_wake_from_gp= [KNL] 5855 Reduces a latency of synchronize_rcu() call. This approach 5856 maintains its own track of synchronize_rcu() callers, so it 5857 does not interact with regular callbacks because it does not 5858 use a call_rcu[_hurry]() path. Please note, this is for a 5859 normal grace period. 5860 5861 How to enable it: 5862 5863 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5864 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5865 5866 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5867 disabled by the boot parameter passing 0. 5868 5869 rcuscale.gp_async= [KNL] 5870 Measure performance of asynchronous 5871 grace-period primitives such as call_rcu(). 5872 5873 rcuscale.gp_async_max= [KNL] 5874 Specify the maximum number of outstanding 5875 callbacks per writer thread. When a writer 5876 thread exceeds this limit, it invokes the 5877 corresponding flavor of rcu_barrier() to allow 5878 previously posted callbacks to drain. 5879 5880 rcuscale.gp_exp= [KNL] 5881 Measure performance of expedited synchronous 5882 grace-period primitives. 5883 5884 rcuscale.holdoff= [KNL] 5885 Set test-start holdoff period. The purpose of 5886 this parameter is to delay the start of the 5887 test until boot completes in order to avoid 5888 interference. 5889 5890 rcuscale.kfree_by_call_rcu= [KNL] 5891 In kernels built with CONFIG_RCU_LAZY=y, test 5892 call_rcu() instead of kfree_rcu(). 5893 5894 rcuscale.kfree_mult= [KNL] 5895 Instead of allocating an object of size kfree_obj, 5896 allocate one of kfree_mult * sizeof(kfree_obj). 5897 Defaults to 1. 5898 5899 rcuscale.kfree_rcu_test= [KNL] 5900 Set to measure performance of kfree_rcu() flooding. 5901 5902 rcuscale.kfree_rcu_test_double= [KNL] 5903 Test the double-argument variant of kfree_rcu(). 5904 If this parameter has the same value as 5905 rcuscale.kfree_rcu_test_single, both the single- 5906 and double-argument variants are tested. 5907 5908 rcuscale.kfree_rcu_test_single= [KNL] 5909 Test the single-argument variant of kfree_rcu(). 5910 If this parameter has the same value as 5911 rcuscale.kfree_rcu_test_double, both the single- 5912 and double-argument variants are tested. 5913 5914 rcuscale.kfree_nthreads= [KNL] 5915 The number of threads running loops of kfree_rcu(). 5916 5917 rcuscale.kfree_alloc_num= [KNL] 5918 Number of allocations and frees done in an iteration. 5919 5920 rcuscale.kfree_loops= [KNL] 5921 Number of loops doing rcuscale.kfree_alloc_num number 5922 of allocations and frees. 5923 5924 rcuscale.minruntime= [KNL] 5925 Set the minimum test run time in seconds. This 5926 does not affect the data-collection interval, 5927 but instead allows better measurement of things 5928 like CPU consumption. 5929 5930 rcuscale.nreaders= [KNL] 5931 Set number of RCU readers. The value -1 selects 5932 N, where N is the number of CPUs. A value 5933 "n" less than -1 selects N-n+1, where N is again 5934 the number of CPUs. For example, -2 selects N 5935 (the number of CPUs), -3 selects N+1, and so on. 5936 A value of "n" less than or equal to -N selects 5937 a single reader. 5938 5939 rcuscale.nwriters= [KNL] 5940 Set number of RCU writers. The values operate 5941 the same as for rcuscale.nreaders. 5942 N, where N is the number of CPUs 5943 5944 rcuscale.scale_type= [KNL] 5945 Specify the RCU implementation to test. 5946 5947 rcuscale.shutdown= [KNL] 5948 Shut the system down after performance tests 5949 complete. This is useful for hands-off automated 5950 testing. 5951 5952 rcuscale.verbose= [KNL] 5953 Enable additional printk() statements. 5954 5955 rcuscale.writer_holdoff= [KNL] 5956 Write-side holdoff between grace periods, 5957 in microseconds. The default of zero says 5958 no holdoff. 5959 5960 rcuscale.writer_holdoff_jiffies= [KNL] 5961 Additional write-side holdoff between grace 5962 periods, but in jiffies. The default of zero 5963 says no holdoff. 5964 5965 rcutorture.fqs_duration= [KNL] 5966 Set duration of force_quiescent_state bursts 5967 in microseconds. 5968 5969 rcutorture.fqs_holdoff= [KNL] 5970 Set holdoff time within force_quiescent_state bursts 5971 in microseconds. 5972 5973 rcutorture.fqs_stutter= [KNL] 5974 Set wait time between force_quiescent_state bursts 5975 in seconds. 5976 5977 rcutorture.fwd_progress= [KNL] 5978 Specifies the number of kthreads to be used 5979 for RCU grace-period forward-progress testing 5980 for the types of RCU supporting this notion. 5981 Defaults to 1 kthread, values less than zero or 5982 greater than the number of CPUs cause the number 5983 of CPUs to be used. 5984 5985 rcutorture.fwd_progress_div= [KNL] 5986 Specify the fraction of a CPU-stall-warning 5987 period to do tight-loop forward-progress testing. 5988 5989 rcutorture.fwd_progress_holdoff= [KNL] 5990 Number of seconds to wait between successive 5991 forward-progress tests. 5992 5993 rcutorture.fwd_progress_need_resched= [KNL] 5994 Enclose cond_resched() calls within checks for 5995 need_resched() during tight-loop forward-progress 5996 testing. 5997 5998 rcutorture.gp_cond= [KNL] 5999 Use conditional/asynchronous update-side 6000 normal-grace-period primitives, if available. 6001 6002 rcutorture.gp_cond_exp= [KNL] 6003 Use conditional/asynchronous update-side 6004 expedited-grace-period primitives, if available. 6005 6006 rcutorture.gp_cond_full= [KNL] 6007 Use conditional/asynchronous update-side 6008 normal-grace-period primitives that also take 6009 concurrent expedited grace periods into account, 6010 if available. 6011 6012 rcutorture.gp_cond_exp_full= [KNL] 6013 Use conditional/asynchronous update-side 6014 expedited-grace-period primitives that also take 6015 concurrent normal grace periods into account, 6016 if available. 6017 6018 rcutorture.gp_cond_wi= [KNL] 6019 Nominal wait interval for normal conditional 6020 grace periods (specified by rcutorture's 6021 gp_cond and gp_cond_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_cond_wi_exp= [KNL] 6029 Nominal wait interval for expedited conditional 6030 grace periods (specified by rcutorture's 6031 gp_cond_exp and gp_cond_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_exp= [KNL] 6038 Use expedited update-side primitives, if available. 6039 6040 rcutorture.gp_normal= [KNL] 6041 Use normal (non-expedited) asynchronous 6042 update-side primitives, if available. 6043 6044 rcutorture.gp_poll= [KNL] 6045 Use polled update-side normal-grace-period 6046 primitives, if available. 6047 6048 rcutorture.gp_poll_exp= [KNL] 6049 Use polled update-side expedited-grace-period 6050 primitives, if available. 6051 6052 rcutorture.gp_poll_full= [KNL] 6053 Use polled update-side normal-grace-period 6054 primitives that also take concurrent expedited 6055 grace periods into account, if available. 6056 6057 rcutorture.gp_poll_exp_full= [KNL] 6058 Use polled update-side expedited-grace-period 6059 primitives that also take concurrent normal 6060 grace periods into account, if available. 6061 6062 rcutorture.gp_poll_wi= [KNL] 6063 Nominal wait interval for normal conditional 6064 grace periods (specified by rcutorture's 6065 gp_poll and gp_poll_full module parameters), 6066 in microseconds. The actual wait interval will 6067 be randomly selected to nanosecond granularity up 6068 to this wait interval. Defaults to 16 jiffies, 6069 for example, 16,000 microseconds on a system 6070 with HZ=1000. 6071 6072 rcutorture.gp_poll_wi_exp= [KNL] 6073 Nominal wait interval for expedited conditional 6074 grace periods (specified by rcutorture's 6075 gp_poll_exp and gp_poll_exp_full module 6076 parameters), in microseconds. The actual wait 6077 interval will be randomly selected to nanosecond 6078 granularity up to this wait interval. Defaults to 6079 128 microseconds. 6080 6081 rcutorture.gp_sync= [KNL] 6082 Use normal (non-expedited) synchronous 6083 update-side primitives, if available. If all 6084 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6085 rcutorture.gp_normal=, and rcutorture.gp_sync= 6086 are zero, rcutorture acts as if is interpreted 6087 they are all non-zero. 6088 6089 rcutorture.gpwrap_lag= [KNL] 6090 Enable grace-period wrap lag testing. Setting 6091 to false prevents the gpwrap lag test from 6092 running. Default is true. 6093 6094 rcutorture.gpwrap_lag_gps= [KNL] 6095 Set the value for grace-period wrap lag during 6096 active lag testing periods. This controls how many 6097 grace periods differences we tolerate between 6098 rdp and rnp's gp_seq before setting overflow flag. 6099 The default is always set to 8. 6100 6101 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6102 Set the total cycle duration for gpwrap lag 6103 testing in minutes. This is the total time for 6104 one complete cycle of active and inactive 6105 testing periods. Default is 30 minutes. 6106 6107 rcutorture.gpwrap_lag_active_mins= [KNL] 6108 Set the duration for which gpwrap lag is active 6109 within each cycle, in minutes. During this time, 6110 the grace-period wrap lag will be set to the 6111 value specified by gpwrap_lag_gps. Default is 6112 5 minutes. 6113 6114 rcutorture.irqreader= [KNL] 6115 Run RCU readers from irq handlers, or, more 6116 accurately, from a timer handler. Not all RCU 6117 flavors take kindly to this sort of thing. 6118 6119 rcutorture.leakpointer= [KNL] 6120 Leak an RCU-protected pointer out of the reader. 6121 This can of course result in splats, and is 6122 intended to test the ability of things like 6123 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6124 such leaks. 6125 6126 rcutorture.n_barrier_cbs= [KNL] 6127 Set callbacks/threads for rcu_barrier() testing. 6128 6129 rcutorture.nfakewriters= [KNL] 6130 Set number of concurrent RCU writers. These just 6131 stress RCU, they don't participate in the actual 6132 test, hence the "fake". 6133 6134 rcutorture.nocbs_nthreads= [KNL] 6135 Set number of RCU callback-offload togglers. 6136 Zero (the default) disables toggling. 6137 6138 rcutorture.nocbs_toggle= [KNL] 6139 Set the delay in milliseconds between successive 6140 callback-offload toggling attempts. 6141 6142 rcutorture.nreaders= [KNL] 6143 Set number of RCU readers. The value -1 selects 6144 N-1, where N is the number of CPUs. A value 6145 "n" less than -1 selects N-n-2, where N is again 6146 the number of CPUs. For example, -2 selects N 6147 (the number of CPUs), -3 selects N+1, and so on. 6148 6149 rcutorture.object_debug= [KNL] 6150 Enable debug-object double-call_rcu() testing. 6151 6152 rcutorture.onoff_holdoff= [KNL] 6153 Set time (s) after boot for CPU-hotplug testing. 6154 6155 rcutorture.onoff_interval= [KNL] 6156 Set time (jiffies) between CPU-hotplug operations, 6157 or zero to disable CPU-hotplug testing. 6158 6159 rcutorture.preempt_duration= [KNL] 6160 Set duration (in milliseconds) of preemptions 6161 by a high-priority FIFO real-time task. Set to 6162 zero (the default) to disable. The CPUs to 6163 preempt are selected randomly from the set that 6164 are online at a given point in time. Races with 6165 CPUs going offline are ignored, with that attempt 6166 at preemption skipped. 6167 6168 rcutorture.preempt_interval= [KNL] 6169 Set interval (in milliseconds, defaulting to one 6170 second) between preemptions by a high-priority 6171 FIFO real-time task. This delay is mediated 6172 by an hrtimer and is further fuzzed to avoid 6173 inadvertent synchronizations. 6174 6175 rcutorture.read_exit_burst= [KNL] 6176 The number of times in a given read-then-exit 6177 episode that a set of read-then-exit kthreads 6178 is spawned. 6179 6180 rcutorture.read_exit_delay= [KNL] 6181 The delay, in seconds, between successive 6182 read-then-exit testing episodes. 6183 6184 rcutorture.reader_flavor= [KNL] 6185 A bit mask indicating which readers to use. 6186 If there is more than one bit set, the readers 6187 are entered from low-order bit up, and are 6188 exited in the opposite order. For SRCU, the 6189 0x1 bit is normal readers, 0x2 NMI-safe readers, 6190 and 0x4 light-weight readers. 6191 6192 rcutorture.shuffle_interval= [KNL] 6193 Set task-shuffle interval (s). Shuffling tasks 6194 allows some CPUs to go into dyntick-idle mode 6195 during the rcutorture test. 6196 6197 rcutorture.shutdown_secs= [KNL] 6198 Set time (s) after boot system shutdown. This 6199 is useful for hands-off automated testing. 6200 6201 rcutorture.stall_cpu= [KNL] 6202 Duration of CPU stall (s) to test RCU CPU stall 6203 warnings, zero to disable. 6204 6205 rcutorture.stall_cpu_block= [KNL] 6206 Sleep while stalling if set. This will result 6207 in warnings from preemptible RCU in addition to 6208 any other stall-related activity. Note that 6209 in kernels built with CONFIG_PREEMPTION=n and 6210 CONFIG_PREEMPT_COUNT=y, this parameter will 6211 cause the CPU to pass through a quiescent state. 6212 Given CONFIG_PREEMPTION=n, this will suppress 6213 RCU CPU stall warnings, but will instead result 6214 in scheduling-while-atomic splats. 6215 6216 Use of this module parameter results in splats. 6217 6218 6219 rcutorture.stall_cpu_holdoff= [KNL] 6220 Time to wait (s) after boot before inducing stall. 6221 6222 rcutorture.stall_cpu_irqsoff= [KNL] 6223 Disable interrupts while stalling if set, but only 6224 on the first stall in the set. 6225 6226 rcutorture.stall_cpu_repeat= [KNL] 6227 Number of times to repeat the stall sequence, 6228 so that rcutorture.stall_cpu_repeat=3 will result 6229 in four stall sequences. 6230 6231 rcutorture.stall_gp_kthread= [KNL] 6232 Duration (s) of forced sleep within RCU 6233 grace-period kthread to test RCU CPU stall 6234 warnings, zero to disable. If both stall_cpu 6235 and stall_gp_kthread are specified, the 6236 kthread is starved first, then the CPU. 6237 6238 rcutorture.stat_interval= [KNL] 6239 Time (s) between statistics printk()s. 6240 6241 rcutorture.stutter= [KNL] 6242 Time (s) to stutter testing, for example, specifying 6243 five seconds causes the test to run for five seconds, 6244 wait for five seconds, and so on. This tests RCU's 6245 ability to transition abruptly to and from idle. 6246 6247 rcutorture.test_boost= [KNL] 6248 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6249 "Maybe" means test if the RCU implementation 6250 under test support RCU priority boosting. 6251 6252 rcutorture.test_boost_duration= [KNL] 6253 Duration (s) of each individual boost test. 6254 6255 rcutorture.test_boost_holdoff= [KNL] 6256 Holdoff time (s) from start of test to the start 6257 of RCU priority-boost testing. Defaults to zero, 6258 that is, no holdoff. 6259 6260 rcutorture.test_boost_interval= [KNL] 6261 Interval (s) between each boost test. 6262 6263 rcutorture.test_no_idle_hz= [KNL] 6264 Test RCU's dyntick-idle handling. See also the 6265 rcutorture.shuffle_interval parameter. 6266 6267 rcutorture.torture_type= [KNL] 6268 Specify the RCU implementation to test. 6269 6270 rcutorture.verbose= [KNL] 6271 Enable additional printk() statements. 6272 6273 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6274 Dump ftrace buffer after reporting RCU CPU 6275 stall warning. 6276 6277 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6278 Provide RCU CPU stall notifiers, but see the 6279 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6280 option's help text. TL;DR: You almost certainly 6281 do not want rcupdate.rcu_cpu_stall_notifiers. 6282 6283 rcupdate.rcu_cpu_stall_suppress= [KNL] 6284 Suppress RCU CPU stall warning messages. 6285 6286 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6287 Suppress RCU CPU stall warning messages and 6288 rcutorture writer stall warnings that occur 6289 during early boot, that is, during the time 6290 before the init task is spawned. 6291 6292 rcupdate.rcu_cpu_stall_timeout= [KNL] 6293 Set timeout for RCU CPU stall warning messages. 6294 The value is in seconds and the maximum allowed 6295 value is 300 seconds. 6296 6297 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6298 Set timeout for expedited RCU CPU stall warning 6299 messages. The value is in milliseconds 6300 and the maximum allowed value is 21000 6301 milliseconds. Please note that this value is 6302 adjusted to an arch timer tick resolution. 6303 Setting this to zero causes the value from 6304 rcupdate.rcu_cpu_stall_timeout to be used (after 6305 conversion from seconds to milliseconds). 6306 6307 rcupdate.rcu_cpu_stall_cputime= [KNL] 6308 Provide statistics on the cputime and count of 6309 interrupts and tasks during the sampling period. For 6310 multiple continuous RCU stalls, all sampling periods 6311 begin at half of the first RCU stall timeout. 6312 6313 rcupdate.rcu_exp_stall_task_details= [KNL] 6314 Print stack dumps of any tasks blocking the 6315 current expedited RCU grace period during an 6316 expedited RCU CPU stall warning. 6317 6318 rcupdate.rcu_expedited= [KNL] 6319 Use expedited grace-period primitives, for 6320 example, synchronize_rcu_expedited() instead 6321 of synchronize_rcu(). This reduces latency, 6322 but can increase CPU utilization, degrade 6323 real-time latency, and degrade energy efficiency. 6324 No effect on CONFIG_TINY_RCU kernels. 6325 6326 rcupdate.rcu_normal= [KNL] 6327 Use only normal grace-period primitives, 6328 for example, synchronize_rcu() instead of 6329 synchronize_rcu_expedited(). This improves 6330 real-time latency, CPU utilization, and 6331 energy efficiency, but can expose users to 6332 increased grace-period latency. This parameter 6333 overrides rcupdate.rcu_expedited. No effect on 6334 CONFIG_TINY_RCU kernels. 6335 6336 rcupdate.rcu_normal_after_boot= [KNL] 6337 Once boot has completed (that is, after 6338 rcu_end_inkernel_boot() has been invoked), use 6339 only normal grace-period primitives. No effect 6340 on CONFIG_TINY_RCU kernels. 6341 6342 But note that CONFIG_PREEMPT_RT=y kernels enables 6343 this kernel boot parameter, forcibly setting 6344 it to the value one, that is, converting any 6345 post-boot attempt at an expedited RCU grace 6346 period to instead use normal non-expedited 6347 grace-period processing. 6348 6349 rcupdate.rcu_task_collapse_lim= [KNL] 6350 Set the maximum number of callbacks present 6351 at the beginning of a grace period that allows 6352 the RCU Tasks flavors to collapse back to using 6353 a single callback queue. This switching only 6354 occurs when rcupdate.rcu_task_enqueue_lim is 6355 set to the default value of -1. 6356 6357 rcupdate.rcu_task_contend_lim= [KNL] 6358 Set the minimum number of callback-queuing-time 6359 lock-contention events per jiffy required to 6360 cause the RCU Tasks flavors to switch to per-CPU 6361 callback queuing. This switching only occurs 6362 when rcupdate.rcu_task_enqueue_lim is set to 6363 the default value of -1. 6364 6365 rcupdate.rcu_task_enqueue_lim= [KNL] 6366 Set the number of callback queues to use for the 6367 RCU Tasks family of RCU flavors. The default 6368 of -1 allows this to be automatically (and 6369 dynamically) adjusted. This parameter is intended 6370 for use in testing. 6371 6372 rcupdate.rcu_task_lazy_lim= [KNL] 6373 Number of callbacks on a given CPU that will 6374 cancel laziness on that CPU. Use -1 to disable 6375 cancellation of laziness, but be advised that 6376 doing so increases the danger of OOM due to 6377 callback flooding. 6378 6379 rcupdate.rcu_task_stall_info= [KNL] 6380 Set initial timeout in jiffies for RCU task stall 6381 informational messages, which give some indication 6382 of the problem for those not patient enough to 6383 wait for ten minutes. Informational messages are 6384 only printed prior to the stall-warning message 6385 for a given grace period. Disable with a value 6386 less than or equal to zero. Defaults to ten 6387 seconds. A change in value does not take effect 6388 until the beginning of the next grace period. 6389 6390 rcupdate.rcu_task_stall_info_mult= [KNL] 6391 Multiplier for time interval between successive 6392 RCU task stall informational messages for a given 6393 RCU tasks grace period. This value is clamped 6394 to one through ten, inclusive. It defaults to 6395 the value three, so that the first informational 6396 message is printed 10 seconds into the grace 6397 period, the second at 40 seconds, the third at 6398 160 seconds, and then the stall warning at 600 6399 seconds would prevent a fourth at 640 seconds. 6400 6401 rcupdate.rcu_task_stall_timeout= [KNL] 6402 Set timeout in jiffies for RCU task stall 6403 warning messages. Disable with a value less 6404 than or equal to zero. Defaults to ten minutes. 6405 A change in value does not take effect until 6406 the beginning of the next grace period. 6407 6408 rcupdate.rcu_tasks_lazy_ms= [KNL] 6409 Set timeout in milliseconds RCU Tasks asynchronous 6410 callback batching for call_rcu_tasks(). 6411 A negative value will take the default. A value 6412 of zero will disable batching. Batching is 6413 always disabled for synchronize_rcu_tasks(). 6414 6415 rcupdate.rcu_self_test= [KNL] 6416 Run the RCU early boot self tests 6417 6418 rdinit= [KNL] 6419 Format: <full_path> 6420 Run specified binary instead of /init from the ramdisk, 6421 used for early userspace startup. See initrd. 6422 6423 rdrand= [X86,EARLY] 6424 force - Override the decision by the kernel to hide the 6425 advertisement of RDRAND support (this affects 6426 certain AMD processors because of buggy BIOS 6427 support, specifically around the suspend/resume 6428 path). 6429 6430 rdt= [HW,X86,RDT] 6431 Turn on/off individual RDT features. List is: 6432 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6433 mba, smba, bmec, abmc, sdciae, energy[:guid], 6434 perf[:guid]. 6435 E.g. to turn on cmt and turn off mba use: 6436 rdt=cmt,!mba 6437 To turn off all energy telemetry monitoring and ensure that 6438 perf telemetry monitoring associated with guid 0x12345 6439 is enabled use: 6440 rdt=!energy,perf:0x12345 6441 6442 reboot= [KNL] 6443 Format (x86 or x86_64): 6444 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6445 [[,]s[mp]#### \ 6446 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6447 [[,]f[orce] 6448 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6449 (prefix with 'panic_' to set mode for panic 6450 reboot only), 6451 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6452 reboot_force is either force or not specified, 6453 reboot_cpu is s[mp]#### with #### being the processor 6454 to be used for rebooting. 6455 6456 acpi 6457 Use the ACPI RESET_REG in the FADT. If ACPI is not 6458 configured or the ACPI reset does not work, the reboot 6459 path attempts the reset using the keyboard controller. 6460 6461 bios 6462 Use the CPU reboot vector for warm reset 6463 6464 cold 6465 Set the cold reboot flag 6466 6467 default 6468 There are some built-in platform specific "quirks" 6469 - you may see: "reboot: <name> series board detected. 6470 Selecting <type> for reboots." In the case where you 6471 think the quirk is in error (e.g. you have newer BIOS, 6472 or newer board) using this option will ignore the 6473 built-in quirk table, and use the generic default 6474 reboot actions. 6475 6476 efi 6477 Use efi reset_system runtime service. If EFI is not 6478 configured or the EFI reset does not work, the reboot 6479 path attempts the reset using the keyboard controller. 6480 6481 force 6482 Don't stop other CPUs on reboot. This can make reboot 6483 more reliable in some cases. 6484 6485 kbd 6486 Use the keyboard controller. cold reset (default) 6487 6488 pci 6489 Use a write to the PCI config space register 0xcf9 to 6490 trigger reboot. 6491 6492 triple 6493 Force a triple fault (init) 6494 6495 warm 6496 Don't set the cold reboot flag 6497 6498 Using warm reset will be much faster especially on big 6499 memory systems because the BIOS will not go through 6500 the memory check. Disadvantage is that not all 6501 hardware will be completely reinitialized on reboot so 6502 there may be boot problems on some systems. 6503 6504 6505 refscale.holdoff= [KNL] 6506 Set test-start holdoff period. The purpose of 6507 this parameter is to delay the start of the 6508 test until boot completes in order to avoid 6509 interference. 6510 6511 refscale.lookup_instances= [KNL] 6512 Number of data elements to use for the forms of 6513 SLAB_TYPESAFE_BY_RCU testing. A negative number 6514 is negated and multiplied by nr_cpu_ids, while 6515 zero specifies nr_cpu_ids. 6516 6517 refscale.loops= [KNL] 6518 Set the number of loops over the synchronization 6519 primitive under test. Increasing this number 6520 reduces noise due to loop start/end overhead, 6521 but the default has already reduced the per-pass 6522 noise to a handful of picoseconds on ca. 2020 6523 x86 laptops. 6524 6525 refscale.nreaders= [KNL] 6526 Set number of readers. The default value of -1 6527 selects N, where N is roughly 75% of the number 6528 of CPUs. A value of zero is an interesting choice. 6529 6530 refscale.nruns= [KNL] 6531 Set number of runs, each of which is dumped onto 6532 the console log. 6533 6534 refscale.readdelay= [KNL] 6535 Set the read-side critical-section duration, 6536 measured in microseconds. 6537 6538 refscale.scale_type= [KNL] 6539 Specify the read-protection implementation to test. 6540 6541 refscale.shutdown= [KNL] 6542 Shut down the system at the end of the performance 6543 test. This defaults to 1 (shut it down) when 6544 refscale is built into the kernel and to 0 (leave 6545 it running) when refscale is built as a module. 6546 6547 refscale.verbose= [KNL] 6548 Enable additional printk() statements. 6549 6550 refscale.verbose_batched= [KNL] 6551 Batch the additional printk() statements. If zero 6552 (the default) or negative, print everything. Otherwise, 6553 print every Nth verbose statement, where N is the value 6554 specified. 6555 6556 regulator_ignore_unused 6557 [REGULATOR] 6558 Prevents regulator framework from disabling regulators 6559 that are unused, due no driver claiming them. This may 6560 be useful for debug and development, but should not be 6561 needed on a platform with proper driver support. 6562 6563 relax_domain_level= 6564 [KNL, SMP] Set scheduler's default relax_domain_level. 6565 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6566 6567 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6568 Format: <base1>,<size1>[,<base2>,<size2>,...] 6569 Reserve I/O ports or memory so the kernel won't use 6570 them. If <base> is less than 0x10000, the region 6571 is assumed to be I/O ports; otherwise it is memory. 6572 6573 reserve_mem= [RAM] 6574 Format: nn[KMG]:<align>:<label> 6575 Reserve physical memory and label it with a name that 6576 other subsystems can use to access it. This is typically 6577 used for systems that do not wipe the RAM, and this command 6578 line will try to reserve the same physical memory on 6579 soft reboots. Note, it is not guaranteed to be the same 6580 location. For example, if anything about the system changes 6581 or if booting a different kernel. It can also fail if KASLR 6582 places the kernel at the location of where the RAM reservation 6583 was from a previous boot, the new reservation will be at a 6584 different location. 6585 Any subsystem using this feature must add a way to verify 6586 that the contents of the physical memory is from a previous 6587 boot, as there may be cases where the memory will not be 6588 located at the same location. 6589 6590 The format is size:align:label for example, to request 6591 12 megabytes of 4096 alignment for ramoops: 6592 6593 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6594 6595 reservetop= [X86-32,EARLY] 6596 Format: nn[KMG] 6597 Reserves a hole at the top of the kernel virtual 6598 address space. 6599 6600 reset_devices [KNL] Force drivers to reset the underlying device 6601 during initialization. 6602 6603 resume= [SWSUSP] 6604 Specify the partition device for software suspend 6605 Format: 6606 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6607 6608 resume_offset= [SWSUSP] 6609 Specify the offset from the beginning of the partition 6610 given by "resume=" at which the swap header is located, 6611 in <PAGE_SIZE> units (needed only for swap files). 6612 See Documentation/power/swsusp-and-swap-files.rst 6613 6614 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6615 read the resume files 6616 6617 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6618 Useful for devices that are detected asynchronously 6619 (e.g. USB and MMC devices). 6620 6621 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6622 be accessible via /sys/firmware/initrd. 6623 6624 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6625 Speculative Code Execution with Return Instructions) 6626 vulnerability. 6627 6628 AMD-based UNRET and IBPB mitigations alone do not stop 6629 sibling threads from influencing the predictions of other 6630 sibling threads. For that reason, STIBP is used on pro- 6631 cessors that support it, and mitigate SMT on processors 6632 that don't. 6633 6634 off - no mitigation 6635 auto - automatically select a mitigation 6636 auto,nosmt - automatically select a mitigation, 6637 disabling SMT if necessary for 6638 the full mitigation (only on Zen1 6639 and older without STIBP). 6640 ibpb - On AMD, mitigate short speculation 6641 windows on basic block boundaries too. 6642 Safe, highest perf impact. It also 6643 enables STIBP if present. Not suitable 6644 on Intel. 6645 ibpb,nosmt - Like "ibpb" above but will disable SMT 6646 when STIBP is not available. This is 6647 the alternative for systems which do not 6648 have STIBP. 6649 unret - Force enable untrained return thunks, 6650 only effective on AMD f15h-f17h based 6651 systems. 6652 unret,nosmt - Like unret, but will disable SMT when STIBP 6653 is not available. This is the alternative for 6654 systems which do not have STIBP. 6655 6656 Selecting 'auto' will choose a mitigation method at run 6657 time according to the CPU. 6658 6659 Not specifying this option is equivalent to retbleed=auto. 6660 6661 rfkill.default_state= 6662 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6663 etc. communication is blocked by default. 6664 1 Unblocked. 6665 6666 rfkill.master_switch_mode= 6667 0 The "airplane mode" button does nothing. 6668 1 The "airplane mode" button toggles between everything 6669 blocked and the previous configuration. 6670 2 The "airplane mode" button toggles between everything 6671 blocked and everything unblocked. 6672 6673 ring3mwait=disable 6674 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6675 CPUs. 6676 6677 riscv_isa_fallback [RISCV,EARLY] 6678 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6679 falling back to detecting extension support by parsing 6680 "riscv,isa" property on devicetree systems when the 6681 replacement properties are not found. See the Kconfig 6682 entry for RISCV_ISA_FALLBACK. 6683 6684 riscv_nousercfi= 6685 all Disable user CFI ABI to userspace even if cpu extension 6686 are available. 6687 bcfi Disable user backward CFI ABI to userspace even if 6688 the shadow stack extension is available. 6689 fcfi Disable user forward CFI ABI to userspace even if the 6690 landing pad extension is available. 6691 6692 ro [KNL] Mount root device read-only on boot 6693 6694 rodata= [KNL,EARLY] 6695 on Mark read-only kernel memory as read-only (default). 6696 off Leave read-only kernel memory writable for debugging. 6697 noalias Mark read-only kernel memory as read-only but retain 6698 writable aliases in the direct map for regions outside 6699 of the kernel image. [arm64] 6700 6701 rockchip.usb_uart 6702 [EARLY] 6703 Enable the uart passthrough on the designated usb port 6704 on Rockchip SoCs. When active, the signals of the 6705 debug-uart get routed to the D+ and D- pins of the usb 6706 port and the regular usb controller gets disabled. 6707 6708 root= [KNL] Root filesystem 6709 Usually this is a block device specifier of some kind, 6710 see the early_lookup_bdev comment in 6711 block/early-lookup.c for details. 6712 Alternatively this can be "ram" for the legacy initial 6713 ramdisk, "nfs" and "cifs" for root on a network file 6714 system, or "mtd" and "ubi" for mounting from raw flash. 6715 6716 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6717 mount the root filesystem 6718 6719 rootflags= [KNL] Set root filesystem mount option string 6720 6721 rseq_slice_ext= [KNL] RSEQ based time slice extension 6722 Format: boolean 6723 Control enablement of RSEQ based time slice extension. 6724 Default is 'on'. 6725 6726 initramfs_options= [KNL] 6727 Specify mount options for the initramfs mount. 6728 6729 rootfstype= [KNL] Set root filesystem type 6730 6731 rootwait [KNL] Wait (indefinitely) for root device to show up. 6732 Useful for devices that are detected asynchronously 6733 (e.g. USB and MMC devices). 6734 6735 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6736 to show up before attempting to mount the root 6737 filesystem. 6738 6739 rproc_mem=nn[KMG][@address] 6740 [KNL,ARM,CMA] Remoteproc physical memory block. 6741 Memory area to be used by remote processor image, 6742 managed by CMA. 6743 6744 rseq_debug= [KNL] Enable or disable restartable sequence 6745 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6746 Format: <bool> 6747 6748 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6749 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6750 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6751 Format: <bool> 6752 6753 rw [KNL] Mount root device read-write on boot 6754 6755 S [KNL] Run init in single mode 6756 6757 s390_iommu= [HW,S390] 6758 Set s390 IOTLB flushing mode 6759 strict 6760 With strict flushing every unmap operation will result 6761 in an IOTLB flush. Default is lazy flushing before 6762 reuse, which is faster. Deprecated, equivalent to 6763 iommu.strict=1. 6764 6765 s390_iommu_aperture= [KNL,S390] 6766 Specifies the size of the per device DMA address space 6767 accessible through the DMA and IOMMU APIs as a decimal 6768 factor of the size of main memory. 6769 The default is 1 meaning that one can concurrently use 6770 as many DMA addresses as physical memory is installed, 6771 if supported by hardware, and thus map all of memory 6772 once. With a value of 2 one can map all of memory twice 6773 and so on. As a special case a factor of 0 imposes no 6774 restrictions other than those given by hardware at the 6775 cost of significant additional memory use for tables. 6776 6777 sa1100ir [NET] 6778 See drivers/net/irda/sa1100_ir.c. 6779 6780 sched_proxy_exec= [KNL] 6781 Enables or disables "proxy execution" style 6782 solution to mutex-based priority inversion. 6783 Format: <bool> 6784 6785 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6786 6787 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6788 Allowed values are enable and disable. This feature 6789 incurs a small amount of overhead in the scheduler 6790 but is useful for debugging and performance tuning. 6791 6792 sched_thermal_decay_shift= 6793 [Deprecated] 6794 [KNL, SMP] Set a decay shift for scheduler thermal 6795 pressure signal. Thermal pressure signal follows the 6796 default decay period of other scheduler pelt 6797 signals(usually 32 ms but configurable). Setting 6798 sched_thermal_decay_shift will left shift the decay 6799 period for the thermal pressure signal by the shift 6800 value. 6801 i.e. with the default pelt decay period of 32 ms 6802 sched_thermal_decay_shift thermal pressure decay pr 6803 1 64 ms 6804 2 128 ms 6805 and so on. 6806 Format: integer between 0 and 10 6807 Default is 0. 6808 6809 scftorture.holdoff= [KNL] 6810 Number of seconds to hold off before starting 6811 test. Defaults to zero for module insertion and 6812 to 10 seconds for built-in smp_call_function() 6813 tests. 6814 6815 scftorture.longwait= [KNL] 6816 Request ridiculously long waits randomly selected 6817 up to the chosen limit in seconds. Zero (the 6818 default) disables this feature. Please note 6819 that requesting even small non-zero numbers of 6820 seconds can result in RCU CPU stall warnings, 6821 softlockup complaints, and so on. 6822 6823 scftorture.nthreads= [KNL] 6824 Number of kthreads to spawn to invoke the 6825 smp_call_function() family of functions. 6826 The default of -1 specifies a number of kthreads 6827 equal to the number of CPUs. 6828 6829 scftorture.onoff_holdoff= [KNL] 6830 Number seconds to wait after the start of the 6831 test before initiating CPU-hotplug operations. 6832 6833 scftorture.onoff_interval= [KNL] 6834 Number seconds to wait between successive 6835 CPU-hotplug operations. Specifying zero (which 6836 is the default) disables CPU-hotplug operations. 6837 6838 scftorture.shutdown_secs= [KNL] 6839 The number of seconds following the start of the 6840 test after which to shut down the system. The 6841 default of zero avoids shutting down the system. 6842 Non-zero values are useful for automated tests. 6843 6844 scftorture.stat_interval= [KNL] 6845 The number of seconds between outputting the 6846 current test statistics to the console. A value 6847 of zero disables statistics output. 6848 6849 scftorture.stutter_cpus= [KNL] 6850 The number of jiffies to wait between each change 6851 to the set of CPUs under test. 6852 6853 scftorture.use_cpus_read_lock= [KNL] 6854 Use use_cpus_read_lock() instead of the default 6855 preempt_disable() to disable CPU hotplug 6856 while invoking one of the smp_call_function*() 6857 functions. 6858 6859 scftorture.verbose= [KNL] 6860 Enable additional printk() statements. 6861 6862 scftorture.weight_single= [KNL] 6863 The probability weighting to use for the 6864 smp_call_function_single() function with a zero 6865 "wait" parameter. A value of -1 selects the 6866 default if all other weights are -1. However, 6867 if at least one weight has some other value, a 6868 value of -1 will instead select a weight of zero. 6869 6870 scftorture.weight_single_wait= [KNL] 6871 The probability weighting to use for the 6872 smp_call_function_single() function with a 6873 non-zero "wait" parameter. See weight_single. 6874 6875 scftorture.weight_many= [KNL] 6876 The probability weighting to use for the 6877 smp_call_function_many() function with a zero 6878 "wait" parameter. See weight_single. 6879 Note well that setting a high probability for 6880 this weighting can place serious IPI load 6881 on the system. 6882 6883 scftorture.weight_many_wait= [KNL] 6884 The probability weighting to use for the 6885 smp_call_function_many() function with a 6886 non-zero "wait" parameter. See weight_single 6887 and weight_many. 6888 6889 scftorture.weight_all= [KNL] 6890 The probability weighting to use for the 6891 smp_call_function_all() function with a zero 6892 "wait" parameter. See weight_single and 6893 weight_many. 6894 6895 scftorture.weight_all_wait= [KNL] 6896 The probability weighting to use for the 6897 smp_call_function_all() function with a 6898 non-zero "wait" parameter. See weight_single 6899 and weight_many. 6900 6901 sdw_mclk_divider=[SDW] 6902 Specify the MCLK divider for Intel SoundWire buses in 6903 case the BIOS does not provide the clock rate properly. 6904 6905 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6906 xtime_lock contention on larger systems, and/or RCU lock 6907 contention on all systems with CONFIG_MAXSMP set. 6908 Format: { "0" | "1" } 6909 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6910 1 -- enable. 6911 Note: increases power consumption, thus should only be 6912 enabled if running jitter sensitive (HPC/RT) workloads. 6913 6914 security= [SECURITY] Choose a legacy "major" security module to 6915 enable at boot. This has been deprecated by the 6916 "lsm=" parameter. 6917 6918 selinux= [SELINUX] Disable or enable SELinux at boot time. 6919 Format: { "0" | "1" } 6920 See security/selinux/Kconfig help text. 6921 0 -- disable. 6922 1 -- enable. 6923 Default value is 1. 6924 6925 serialnumber [BUGS=X86-32] 6926 6927 sev=option[,option...] [X86-64] 6928 6929 debug 6930 Enable debug messages. 6931 6932 nosnp 6933 Do not enable SEV-SNP (applies to host/hypervisor 6934 only). Setting 'nosnp' avoids the RMP check overhead 6935 in memory accesses when users do not want to run 6936 SEV-SNP guests. 6937 6938 shapers= [NET] 6939 Maximal number of shapers. 6940 6941 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6942 Limit apic dumping. The parameter defines the maximal 6943 number of local apics being dumped. Also it is possible 6944 to set it to "all" by meaning -- no limit here. 6945 Format: { 1 (default) | 2 | ... | all }. 6946 The parameter valid if only apic=debug or 6947 apic=verbose is specified. 6948 Example: apic=debug show_lapic=all 6949 6950 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6951 Enabling slab_debug allows one to determine the 6952 culprit if slab objects become corrupted. Enabling 6953 slab_debug can create guard zones around objects and 6954 may poison objects when not in use. Also tracks the 6955 last alloc / free. For more information see 6956 Documentation/admin-guide/mm/slab.rst. 6957 (slub_debug legacy name also accepted for now) 6958 6959 Using this option implies the "no_hash_pointers" 6960 option which can be undone by adding the 6961 "hash_pointers=always" option. 6962 6963 slab_max_order= [MM] 6964 Determines the maximum allowed order for slabs. 6965 A high setting may cause OOMs due to memory 6966 fragmentation. For more information see 6967 Documentation/admin-guide/mm/slab.rst. 6968 (slub_max_order legacy name also accepted for now) 6969 6970 slab_merge [MM] 6971 Enable merging of slabs with similar size when the 6972 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6973 (slub_merge legacy name also accepted for now) 6974 6975 slab_min_objects= [MM] 6976 The minimum number of objects per slab. SLUB will 6977 increase the slab order up to slab_max_order to 6978 generate a sufficiently large slab able to contain 6979 the number of objects indicated. The higher the number 6980 of objects the smaller the overhead of tracking slabs 6981 and the less frequently locks need to be acquired. 6982 For more information see 6983 Documentation/admin-guide/mm/slab.rst. 6984 (slub_min_objects legacy name also accepted for now) 6985 6986 slab_min_order= [MM] 6987 Determines the minimum page order for slabs. Must be 6988 lower or equal to slab_max_order. For more information see 6989 Documentation/admin-guide/mm/slab.rst. 6990 (slub_min_order legacy name also accepted for now) 6991 6992 slab_nomerge [MM] 6993 Disable merging of slabs with similar size. May be 6994 necessary if there is some reason to distinguish 6995 allocs to different slabs, especially in hardened 6996 environments where the risk of heap overflows and 6997 layout control by attackers can usually be 6998 frustrated by disabling merging. This will reduce 6999 most of the exposure of a heap attack to a single 7000 cache (risks via metadata attacks are mostly 7001 unchanged). Debug options disable merging on their 7002 own. 7003 For more information see 7004 Documentation/admin-guide/mm/slab.rst. 7005 (slub_nomerge legacy name also accepted for now) 7006 7007 slab_strict_numa [MM] 7008 Support memory policies on a per object level 7009 in the slab allocator. The default is for memory 7010 policies to be applied at the folio level when 7011 a new folio is needed or a partial folio is 7012 retrieved from the lists. Increases overhead 7013 in the slab fastpaths but gains more accurate 7014 NUMA kernel object placement which helps with slow 7015 interconnects in NUMA systems. 7016 7017 slram= [HW,MTD] 7018 7019 smart2= [HW] 7020 Format: <io1>[,<io2>[,...,<io8>]] 7021 7022 smp.csd_lock_timeout= [KNL] 7023 Specify the period of time in milliseconds 7024 that smp_call_function() and friends will wait 7025 for a CPU to release the CSD lock. This is 7026 useful when diagnosing bugs involving CPUs 7027 disabling interrupts for extended periods 7028 of time. Defaults to 5,000 milliseconds, and 7029 setting a value of zero disables this feature. 7030 This feature may be more efficiently disabled 7031 using the csdlock_debug- kernel parameter. 7032 7033 smp.panic_on_ipistall= [KNL] 7034 If a csd_lock_timeout extends for more than 7035 the specified number of milliseconds, panic the 7036 system. By default, let CSD-lock acquisition 7037 take as long as they take. Specifying 300,000 7038 for this value provides a 5-minute timeout. 7039 7040 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7041 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7042 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7043 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7044 smsc-ircc2.ircc_irq= [HW] IRQ line 7045 smsc-ircc2.ircc_dma= [HW] DMA channel 7046 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7047 0: Toshiba Satellite 1800 (GP data pin select) 7048 1: Fast pin select (default) 7049 2: ATC IRMode 7050 7051 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7052 (logical CPUs) to use per physical CPU on systems 7053 capable of symmetric multithreading (SMT). Will 7054 be capped to the actual hardware limit. 7055 Format: <integer> 7056 Default: -1 (no limit) 7057 7058 softlockup_panic= 7059 [KNL] Should the soft-lockup detector generate panics. 7060 Format: <int> 7061 7062 A value of non-zero instructs the soft-lockup detector 7063 to panic the machine when a soft-lockup duration exceeds 7064 N thresholds. It is also controlled by the kernel.softlockup_panic 7065 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7066 respective build-time switch to that functionality. 7067 7068 softlockup_all_cpu_backtrace= 7069 [KNL] Should the soft-lockup detector generate 7070 backtraces on all cpus. 7071 Format: 0 | 1 7072 7073 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7074 See Documentation/admin-guide/laptops/sonypi.rst 7075 7076 spectre_bhi= [X86] Control mitigation of Branch History Injection 7077 (BHI) vulnerability. This setting affects the 7078 deployment of the HW BHI control and the SW BHB 7079 clearing sequence. 7080 7081 on - (default) Enable the HW or SW mitigation as 7082 needed. This protects the kernel from 7083 both syscalls and VMs. 7084 vmexit - On systems which don't have the HW mitigation 7085 available, enable the SW mitigation on vmexit 7086 ONLY. On such systems, the host kernel is 7087 protected from VM-originated BHI attacks, but 7088 may still be vulnerable to syscall attacks. 7089 off - Disable the mitigation. 7090 7091 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7092 (indirect branch speculation) vulnerability. 7093 The default operation protects the kernel from 7094 user space attacks. 7095 7096 on - unconditionally enable, implies 7097 spectre_v2_user=on 7098 off - unconditionally disable, implies 7099 spectre_v2_user=off 7100 auto - kernel detects whether your CPU model is 7101 vulnerable 7102 7103 Selecting 'on' will, and 'auto' may, choose a 7104 mitigation method at run time according to the 7105 CPU, the available microcode, the setting of the 7106 CONFIG_MITIGATION_RETPOLINE configuration option, 7107 and the compiler with which the kernel was built. 7108 7109 Selecting 'on' will also enable the mitigation 7110 against user space to user space task attacks. 7111 Selecting specific mitigation does not force enable 7112 user mitigations. 7113 7114 Selecting 'off' will disable both the kernel and 7115 the user space protections. 7116 7117 Specific mitigations can also be selected manually: 7118 7119 retpoline - replace indirect branches 7120 retpoline,generic - Retpolines 7121 retpoline,lfence - LFENCE; indirect branch 7122 retpoline,amd - alias for retpoline,lfence 7123 eibrs - Enhanced/Auto IBRS 7124 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7125 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7126 ibrs - use IBRS to protect kernel 7127 7128 Not specifying this option is equivalent to 7129 spectre_v2=auto. 7130 7131 spectre_v2_user= 7132 [X86] Control mitigation of Spectre variant 2 7133 (indirect branch speculation) vulnerability between 7134 user space tasks 7135 7136 on - Unconditionally enable mitigations. Is 7137 enforced by spectre_v2=on 7138 7139 off - Unconditionally disable mitigations. Is 7140 enforced by spectre_v2=off 7141 7142 prctl - Indirect branch speculation is enabled, 7143 but mitigation can be enabled via prctl 7144 per thread. The mitigation control state 7145 is inherited on fork. 7146 7147 prctl,ibpb 7148 - Like "prctl" above, but only STIBP is 7149 controlled per thread. IBPB is issued 7150 always when switching between different user 7151 space processes. 7152 7153 seccomp 7154 - Same as "prctl" above, but all seccomp 7155 threads will enable the mitigation unless 7156 they explicitly opt out. 7157 7158 seccomp,ibpb 7159 - Like "seccomp" above, but only STIBP is 7160 controlled per thread. IBPB is issued 7161 always when switching between different 7162 user space processes. 7163 7164 auto - Kernel selects the mitigation depending on 7165 the available CPU features and vulnerability. 7166 7167 Default mitigation: "prctl" 7168 7169 Not specifying this option is equivalent to 7170 spectre_v2_user=auto. 7171 7172 spec_rstack_overflow= 7173 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7174 7175 off - Disable mitigation 7176 microcode - Enable microcode mitigation only 7177 safe-ret - Enable sw-only safe RET mitigation (default) 7178 ibpb - Enable mitigation by issuing IBPB on 7179 kernel entry 7180 ibpb-vmexit - Issue IBPB only on VMEXIT 7181 (cloud-specific mitigation) 7182 7183 spec_store_bypass_disable= 7184 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7185 (Speculative Store Bypass vulnerability) 7186 7187 Certain CPUs are vulnerable to an exploit against a 7188 a common industry wide performance optimization known 7189 as "Speculative Store Bypass" in which recent stores 7190 to the same memory location may not be observed by 7191 later loads during speculative execution. The idea 7192 is that such stores are unlikely and that they can 7193 be detected prior to instruction retirement at the 7194 end of a particular speculation execution window. 7195 7196 In vulnerable processors, the speculatively forwarded 7197 store can be used in a cache side channel attack, for 7198 example to read memory to which the attacker does not 7199 directly have access (e.g. inside sandboxed code). 7200 7201 This parameter controls whether the Speculative Store 7202 Bypass optimization is used. 7203 7204 On x86 the options are: 7205 7206 on - Unconditionally disable Speculative Store Bypass 7207 off - Unconditionally enable Speculative Store Bypass 7208 auto - Kernel detects whether the CPU model contains an 7209 implementation of Speculative Store Bypass and 7210 picks the most appropriate mitigation. If the 7211 CPU is not vulnerable, "off" is selected. If the 7212 CPU is vulnerable the default mitigation is 7213 architecture and Kconfig dependent. See below. 7214 prctl - Control Speculative Store Bypass per thread 7215 via prctl. Speculative Store Bypass is enabled 7216 for a process by default. The state of the control 7217 is inherited on fork. 7218 seccomp - Same as "prctl" above, but all seccomp threads 7219 will disable SSB unless they explicitly opt out. 7220 7221 Default mitigations: 7222 X86: "prctl" 7223 7224 On powerpc the options are: 7225 7226 on,auto - On Power8 and Power9 insert a store-forwarding 7227 barrier on kernel entry and exit. On Power7 7228 perform a software flush on kernel entry and 7229 exit. 7230 off - No action. 7231 7232 Not specifying this option is equivalent to 7233 spec_store_bypass_disable=auto. 7234 7235 split_lock_detect= 7236 [X86] Enable split lock detection or bus lock detection 7237 7238 When enabled (and if hardware support is present), atomic 7239 instructions that access data across cache line 7240 boundaries will result in an alignment check exception 7241 for split lock detection or a debug exception for 7242 bus lock detection. 7243 7244 off - not enabled 7245 7246 warn - the kernel will emit rate-limited warnings 7247 about applications triggering the #AC 7248 exception or the #DB exception. This mode is 7249 the default on CPUs that support split lock 7250 detection or bus lock detection. Default 7251 behavior is by #AC if both features are 7252 enabled in hardware. 7253 7254 fatal - the kernel will send SIGBUS to applications 7255 that trigger the #AC exception or the #DB 7256 exception. Default behavior is by #AC if 7257 both features are enabled in hardware. 7258 7259 ratelimit:N - 7260 Set system wide rate limit to N bus locks 7261 per second for bus lock detection. 7262 0 < N <= 1000. 7263 7264 N/A for split lock detection. 7265 7266 7267 If an #AC exception is hit in the kernel or in 7268 firmware (i.e. not while executing in user mode) 7269 the kernel will oops in either "warn" or "fatal" 7270 mode. 7271 7272 #DB exception for bus lock is triggered only when 7273 CPL > 0. 7274 7275 srbds= [X86,INTEL,EARLY] 7276 Control the Special Register Buffer Data Sampling 7277 (SRBDS) mitigation. 7278 7279 Certain CPUs are vulnerable to an MDS-like 7280 exploit which can leak bits from the random 7281 number generator. 7282 7283 By default, this issue is mitigated by 7284 microcode. However, the microcode fix can cause 7285 the RDRAND and RDSEED instructions to become 7286 much slower. Among other effects, this will 7287 result in reduced throughput from /dev/urandom. 7288 7289 The microcode mitigation can be disabled with 7290 the following option: 7291 7292 off: Disable mitigation and remove 7293 performance impact to RDRAND and RDSEED 7294 7295 srcutree.big_cpu_lim [KNL] 7296 Specifies the number of CPUs constituting a 7297 large system, such that srcu_struct structures 7298 should immediately allocate an srcu_node array. 7299 This kernel-boot parameter defaults to 128, 7300 but takes effect only when the low-order four 7301 bits of srcutree.convert_to_big is equal to 3 7302 (decide at boot). 7303 7304 srcutree.convert_to_big [KNL] 7305 Specifies under what conditions an SRCU tree 7306 srcu_struct structure will be converted to big 7307 form, that is, with an rcu_node tree: 7308 7309 0: Never. 7310 1: At init_srcu_struct() time. 7311 2: When rcutorture decides to. 7312 3: Decide at boot time (default). 7313 0x1X: Above plus if high contention. 7314 7315 Either way, the srcu_node tree will be sized based 7316 on the actual runtime number of CPUs (nr_cpu_ids) 7317 instead of the compile-time CONFIG_NR_CPUS. 7318 7319 srcutree.counter_wrap_check [KNL] 7320 Specifies how frequently to check for 7321 grace-period sequence counter wrap for the 7322 srcu_data structure's ->srcu_gp_seq_needed field. 7323 The greater the number of bits set in this kernel 7324 parameter, the less frequently counter wrap will 7325 be checked for. Note that the bottom two bits 7326 are ignored. 7327 7328 srcutree.exp_holdoff [KNL] 7329 Specifies how many nanoseconds must elapse 7330 since the end of the last SRCU grace period for 7331 a given srcu_struct until the next normal SRCU 7332 grace period will be considered for automatic 7333 expediting. Set to zero to disable automatic 7334 expediting. 7335 7336 srcutree.srcu_max_nodelay [KNL] 7337 Specifies the number of no-delay instances 7338 per jiffy for which the SRCU grace period 7339 worker thread will be rescheduled with zero 7340 delay. Beyond this limit, worker thread will 7341 be rescheduled with a sleep delay of one jiffy. 7342 7343 srcutree.srcu_max_nodelay_phase [KNL] 7344 Specifies the per-grace-period phase, number of 7345 non-sleeping polls of readers. Beyond this limit, 7346 grace period worker thread will be rescheduled 7347 with a sleep delay of one jiffy, between each 7348 rescan of the readers, for a grace period phase. 7349 7350 srcutree.srcu_retry_check_delay [KNL] 7351 Specifies number of microseconds of non-sleeping 7352 delay between each non-sleeping poll of readers. 7353 7354 srcutree.small_contention_lim [KNL] 7355 Specifies the number of update-side contention 7356 events per jiffy will be tolerated before 7357 initiating a conversion of an srcu_struct 7358 structure to big form. Note that the value of 7359 srcutree.convert_to_big must have the 0x10 bit 7360 set for contention-based conversions to occur. 7361 7362 ssbd= [ARM64,HW,EARLY] 7363 Speculative Store Bypass Disable control 7364 7365 On CPUs that are vulnerable to the Speculative 7366 Store Bypass vulnerability and offer a 7367 firmware based mitigation, this parameter 7368 indicates how the mitigation should be used: 7369 7370 force-on: Unconditionally enable mitigation for 7371 for both kernel and userspace 7372 force-off: Unconditionally disable mitigation for 7373 for both kernel and userspace 7374 kernel: Always enable mitigation in the 7375 kernel, and offer a prctl interface 7376 to allow userspace to register its 7377 interest in being mitigated too. 7378 7379 stack_guard_gap= [MM] 7380 override the default stack gap protection. The value 7381 is in page units and it defines how many pages prior 7382 to (for stacks growing down) resp. after (for stacks 7383 growing up) the main stack are reserved for no other 7384 mapping. Default value is 256 pages. 7385 7386 stack_depot_disable= [KNL,EARLY] 7387 Setting this to true through kernel command line will 7388 disable the stack depot thereby saving the static memory 7389 consumed by the stack hash table. By default this is set 7390 to false. 7391 7392 stack_depot_max_pools= [KNL,EARLY] 7393 Specify the maximum number of pools to use for storing 7394 stack traces. Pools are allocated on-demand up to this 7395 limit. Default value is 8191 pools. 7396 7397 stacktrace [FTRACE] 7398 Enable the stack tracer on boot up. 7399 7400 stacktrace_filter=[function-list] 7401 [FTRACE] Limit the functions that the stack tracer 7402 will trace at boot up. function-list is a comma-separated 7403 list of functions. This list can be changed at run 7404 time by the stack_trace_filter file in the debugfs 7405 tracing directory. Note, this enables stack tracing 7406 and the stacktrace above is not needed. 7407 7408 sti= [PARISC,HW] 7409 Format: <num> 7410 Set the STI (builtin display/keyboard on the HP-PARISC 7411 machines) console (graphic card) which should be used 7412 as the initial boot-console. 7413 See also comment in drivers/video/console/sticore.c. 7414 7415 sti_font= [HW] 7416 See comment in drivers/video/console/sticore.c. 7417 7418 stifb= [HW] 7419 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7420 7421 strict_sas_size= 7422 [X86] 7423 Format: <bool> 7424 Enable or disable strict sigaltstack size checks 7425 against the required signal frame size which 7426 depends on the supported FPU features. This can 7427 be used to filter out binaries which have 7428 not yet been made aware of AT_MINSIGSTKSZ. 7429 7430 stress_hpt [PPC,EARLY] 7431 Limits the number of kernel HPT entries in the hash 7432 page table to increase the rate of hash page table 7433 faults on kernel addresses. 7434 7435 stress_slb [PPC,EARLY] 7436 Limits the number of kernel SLB entries, and flushes 7437 them frequently to increase the rate of SLB faults 7438 on kernel addresses. 7439 7440 no_slb_preload [PPC,EARLY] 7441 Disables slb preloading for userspace. 7442 7443 sunrpc.min_resvport= 7444 sunrpc.max_resvport= 7445 [NFS,SUNRPC] 7446 SunRPC servers often require that client requests 7447 originate from a privileged port (i.e. a port in the 7448 range 0 < portnr < 1024). 7449 An administrator who wishes to reserve some of these 7450 ports for other uses may adjust the range that the 7451 kernel's sunrpc client considers to be privileged 7452 using these two parameters to set the minimum and 7453 maximum port values. 7454 7455 sunrpc.svc_rpc_per_connection_limit= 7456 [NFS,SUNRPC] 7457 Limit the number of requests that the server will 7458 process in parallel from a single connection. 7459 The default value is 0 (no limit). 7460 7461 sunrpc.pool_mode= 7462 [NFS] 7463 Control how the NFS server code allocates CPUs to 7464 service thread pools. Depending on how many NICs 7465 you have and where their interrupts are bound, this 7466 option will affect which CPUs will do NFS serving. 7467 Note: this parameter cannot be changed while the 7468 NFS server is running. 7469 7470 auto the server chooses an appropriate mode 7471 automatically using heuristics 7472 global a single global pool contains all CPUs 7473 percpu one pool for each CPU 7474 pernode one pool for each NUMA node (equivalent 7475 to global on non-NUMA machines) 7476 7477 sunrpc.tcp_slot_table_entries= 7478 sunrpc.udp_slot_table_entries= 7479 [NFS,SUNRPC] 7480 Sets the upper limit on the number of simultaneous 7481 RPC calls that can be sent from the client to a 7482 server. Increasing these values may allow you to 7483 improve throughput, but will also increase the 7484 amount of memory reserved for use by the client. 7485 7486 suspend.pm_test_delay= 7487 [SUSPEND] 7488 Sets the number of seconds to remain in a suspend test 7489 mode before resuming the system (see 7490 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7491 is set. Default value is 5. 7492 7493 svm= [PPC] 7494 Format: { on | off | y | n | 1 | 0 } 7495 This parameter controls use of the Protected 7496 Execution Facility on pSeries. 7497 7498 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7499 Format: { <int> [,<int>] | force | noforce } 7500 <int> -- Number of I/O TLB slabs 7501 <int> -- Second integer after comma. Number of swiotlb 7502 areas with their own lock. Will be rounded up 7503 to a power of 2. 7504 force -- force using of bounce buffers even if they 7505 wouldn't be automatically used by the kernel 7506 noforce -- Never use bounce buffers (for debugging) 7507 7508 switches= [HW,M68k,EARLY] 7509 7510 sysctl.*= [KNL] 7511 Set a sysctl parameter, right before loading the init 7512 process, as if the value was written to the respective 7513 /proc/sys/... file. Both '.' and '/' are recognized as 7514 separators. Unrecognized parameters and invalid values 7515 are reported in the kernel log. Sysctls registered 7516 later by a loaded module cannot be set this way. 7517 Example: sysctl.vm.swappiness=40 7518 7519 sysrq_always_enabled 7520 [KNL] 7521 Ignore sysrq setting - this boot parameter will 7522 neutralize any effect of /proc/sys/kernel/sysrq. 7523 Useful for debugging. 7524 7525 tcpmhash_entries= [KNL,NET] 7526 Set the number of tcp_metrics_hash slots. 7527 Default value is 8192 or 16384 depending on total 7528 ram pages. This is used to specify the TCP metrics 7529 cache size. See Documentation/networking/ip-sysctl.rst 7530 "tcp_no_metrics_save" section for more details. 7531 7532 tdfx= [HW,DRM] 7533 7534 test_suspend= [SUSPEND] 7535 Format: { "mem" | "standby" | "freeze" }[,N] 7536 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7537 standby suspend) or "freeze" (for suspend type freeze) 7538 as the system sleep state during system startup with 7539 the optional capability to repeat N number of times. 7540 The system is woken from this state using a 7541 wakeup-capable RTC alarm. 7542 7543 thash_entries= [KNL,NET] 7544 Set number of hash buckets for TCP connection 7545 7546 thermal.act= [HW,ACPI] 7547 -1: disable all active trip points in all thermal zones 7548 <degrees C>: override all lowest active trip points 7549 7550 thermal.crt= [HW,ACPI] 7551 -1: disable all critical trip points in all thermal zones 7552 <degrees C>: override all critical trip points 7553 7554 thermal.off= [HW,ACPI] 7555 1: disable ACPI thermal control 7556 7557 thermal.psv= [HW,ACPI] 7558 -1: disable all passive trip points 7559 <degrees C>: override all passive trip points to this 7560 value 7561 7562 thermal.tzp= [HW,ACPI] 7563 Specify global default ACPI thermal zone polling rate 7564 <deci-seconds>: poll all this frequency 7565 0: no polling (default) 7566 7567 thp_anon= [KNL] 7568 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7569 state is one of "always", "madvise", "never" or "inherit". 7570 Control the default behavior of the system with respect 7571 to anonymous transparent hugepages. 7572 Can be used multiple times for multiple anon THP sizes. 7573 See Documentation/admin-guide/mm/transhuge.rst for more 7574 details. 7575 7576 threadirqs [KNL,EARLY] 7577 Force threading of all interrupt handlers except those 7578 marked explicitly IRQF_NO_THREAD. 7579 7580 thp_shmem= [KNL] 7581 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7582 Control the default policy of each hugepage size for the 7583 internal shmem mount. <policy> is one of policies available 7584 for the shmem mount ("always", "inherit", "never", "within_size", 7585 and "advise"). 7586 It can be used multiple times for multiple shmem THP sizes. 7587 See Documentation/admin-guide/mm/transhuge.rst for more 7588 details. 7589 7590 topology= [S390,EARLY] 7591 Format: {off | on} 7592 Specify if the kernel should make use of the cpu 7593 topology information if the hardware supports this. 7594 The scheduler will make use of this information and 7595 e.g. base its process migration decisions on it. 7596 Default is on. 7597 7598 torture.disable_onoff_at_boot= [KNL] 7599 Prevent the CPU-hotplug component of torturing 7600 until after init has spawned. 7601 7602 torture.ftrace_dump_at_shutdown= [KNL] 7603 Dump the ftrace buffer at torture-test shutdown, 7604 even if there were no errors. This can be a 7605 very costly operation when many torture tests 7606 are running concurrently, especially on systems 7607 with rotating-rust storage. 7608 7609 torture.verbose_sleep_frequency= [KNL] 7610 Specifies how many verbose printk()s should be 7611 emitted between each sleep. The default of zero 7612 disables verbose-printk() sleeping. 7613 7614 torture.verbose_sleep_duration= [KNL] 7615 Duration of each verbose-printk() sleep in jiffies. 7616 7617 tpm.disable_pcr_integrity= [HW,TPM] 7618 Do not protect PCR registers from unintended physical 7619 access, or interposers in the bus by the means of 7620 having an integrity protected session wrapped around 7621 TPM2_PCR_Extend command. Consider this in a situation 7622 where TPM is heavily utilized by IMA, thus protection 7623 causing a major performance hit, and the space where 7624 machines are deployed is by other means guarded. 7625 7626 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7627 Maximum time in milliseconds to retry sending a message 7628 to the TPM service before giving up. This parameter controls 7629 how long the system will continue retrying when the TPM 7630 service is busy. 7631 Format: <unsigned int> 7632 Default: 2000 (2 seconds) 7633 7634 tpm_suspend_pcr=[HW,TPM] 7635 Format: integer pcr id 7636 Specify that at suspend time, the tpm driver 7637 should extend the specified pcr with zeros, 7638 as a workaround for some chips which fail to 7639 flush the last written pcr on TPM_SaveState. 7640 This will guarantee that all the other pcrs 7641 are saved. 7642 7643 tpm_tis.interrupts= [HW,TPM] 7644 Enable interrupts for the MMIO based physical layer 7645 for the FIFO interface. By default it is set to false 7646 (0). For more information about TPM hardware interfaces 7647 defined by Trusted Computing Group (TCG) see 7648 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7649 7650 tp_printk [FTRACE] 7651 Have the tracepoints sent to printk as well as the 7652 tracing ring buffer. This is useful for early boot up 7653 where the system hangs or reboots and does not give the 7654 option for reading the tracing buffer or performing a 7655 ftrace_dump_on_oops. 7656 7657 To turn off having tracepoints sent to printk, 7658 echo 0 > /proc/sys/kernel/tracepoint_printk 7659 Note, echoing 1 into this file without the 7660 tp_printk kernel cmdline option has no effect. 7661 7662 The tp_printk_stop_on_boot (see below) can also be used 7663 to stop the printing of events to console at 7664 late_initcall_sync. 7665 7666 ** CAUTION ** 7667 7668 Having tracepoints sent to printk() and activating high 7669 frequency tracepoints such as irq or sched, can cause 7670 the system to live lock. 7671 7672 tp_printk_stop_on_boot [FTRACE] 7673 When tp_printk (above) is set, it can cause a lot of noise 7674 on the console. It may be useful to only include the 7675 printing of events during boot up, as user space may 7676 make the system inoperable. 7677 7678 This command line option will stop the printing of events 7679 to console at the late_initcall_sync() time frame. 7680 7681 trace_buf_size=nn[KMG] 7682 [FTRACE] will set tracing buffer size on each cpu. 7683 7684 trace_clock= [FTRACE] Set the clock used for tracing events 7685 at boot up. 7686 local - Use the per CPU time stamp counter 7687 (converted into nanoseconds). Fast, but 7688 depending on the architecture, may not be 7689 in sync between CPUs. 7690 global - Event time stamps are synchronized across 7691 CPUs. May be slower than the local clock, 7692 but better for some race conditions. 7693 counter - Simple counting of events (1, 2, ..) 7694 note, some counts may be skipped due to the 7695 infrastructure grabbing the clock more than 7696 once per event. 7697 uptime - Use jiffies as the time stamp. 7698 perf - Use the same clock that perf uses. 7699 mono - Use ktime_get_mono_fast_ns() for time stamps. 7700 mono_raw - Use ktime_get_raw_fast_ns() for time 7701 stamps. 7702 boot - Use ktime_get_boot_fast_ns() for time stamps. 7703 Architectures may add more clocks. See 7704 Documentation/trace/ftrace.rst for more details. 7705 7706 trace_event=[event-list] 7707 [FTRACE] Set and start specified trace events in order 7708 to facilitate early boot debugging. The event-list is a 7709 comma-separated list of trace events to enable. See 7710 also Documentation/trace/events.rst 7711 7712 To enable modules, use :mod: keyword: 7713 7714 trace_event=:mod:<module> 7715 7716 The value before :mod: will only enable specific events 7717 that are part of the module. See the above mentioned 7718 document for more information. 7719 7720 trace_instance=[instance-info] 7721 [FTRACE] Create a ring buffer instance early in boot up. 7722 This will be listed in: 7723 7724 /sys/kernel/tracing/instances 7725 7726 Events can be enabled at the time the instance is created 7727 via: 7728 7729 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7730 7731 Note, the "<system*>:" portion is optional if the event is 7732 unique. 7733 7734 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7735 7736 will enable the "sched_switch" event (note, the "sched:" is optional, and 7737 the same thing would happen if it was left off). The irq_handler_entry 7738 event, and all events under the "initcall" system. 7739 7740 Flags can be added to the instance to modify its behavior when it is 7741 created. The flags are separated by '^'. 7742 7743 The available flags are: 7744 7745 traceoff - Have the tracing instance tracing disabled after it is created. 7746 traceprintk - Have trace_printk() write into this trace instance 7747 (note, "printk" and "trace_printk" can also be used) 7748 7749 trace_instance=foo^traceoff^traceprintk,sched,irq 7750 7751 The flags must come before the defined events. 7752 7753 If memory has been reserved (see memmap for x86), the instance 7754 can use that memory: 7755 7756 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7757 7758 The above will create a "boot_map" instance that uses the physical 7759 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7760 instance will be split up accordingly. 7761 7762 Alternatively, the memory can be reserved by the reserve_mem option: 7763 7764 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7765 7766 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7767 and place the ring buffer in this memory. Note that due to KASLR, the 7768 memory may not be the same location each time, which will not preserve 7769 the buffer content. 7770 7771 Also note that the layout of the ring buffer data may change between 7772 kernel versions where the validator will fail and reset the ring buffer 7773 if the layout is not the same as the previous kernel. 7774 7775 If the ring buffer is used for persistent bootups and has events enabled, 7776 it is recommend to disable tracing so that events from a previous boot do not 7777 mix with events of the current boot (unless you are debugging a random crash 7778 at boot up). 7779 7780 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7781 7782 Note, saving the trace buffer across reboots does require that the system 7783 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7784 can force a memory reset on boot which will clear any trace that was stored. 7785 This is just one of many ways that can clear memory. Make sure your system 7786 keeps the content of memory across reboots before relying on this option. 7787 7788 NB: Both the mapped address and size must be page aligned for the architecture. 7789 7790 See also Documentation/trace/debugging.rst 7791 7792 7793 trace_options=[option-list] 7794 [FTRACE] Enable or disable tracer options at boot. 7795 The option-list is a comma delimited list of options 7796 that can be enabled or disabled just as if you were 7797 to echo the option name into 7798 7799 /sys/kernel/tracing/trace_options 7800 7801 For example, to enable stacktrace option (to dump the 7802 stack trace of each event), add to the command line: 7803 7804 trace_options=stacktrace 7805 7806 See also Documentation/trace/ftrace.rst "trace options" 7807 section. 7808 7809 trace_trigger=[trigger-list] 7810 [FTRACE] Add an event trigger on specific events. 7811 Set a trigger on top of a specific event, with an optional 7812 filter. 7813 7814 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7815 Where more than one trigger may be specified that are comma delimited. 7816 7817 For example: 7818 7819 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7820 7821 The above will enable the "stacktrace" trigger on the "sched_switch" 7822 event but only trigger it if the "prev_state" of the "sched_switch" 7823 event is "2" (TASK_UNINTERRUPTIBLE). 7824 7825 See also "Event triggers" in Documentation/trace/events.rst 7826 7827 7828 traceoff_after_boot 7829 [FTRACE] Sometimes tracing is used to debug issues 7830 during the boot process. Since the trace buffer has a 7831 limited amount of storage, it may be prudent to 7832 disable tracing after the boot is finished, otherwise 7833 the critical information may be overwritten. With this 7834 option, the main tracing buffer will be turned off at 7835 the end of the boot process. 7836 7837 traceoff_on_warning 7838 [FTRACE] enable this option to disable tracing when a 7839 warning is hit. This turns off "tracing_on". Tracing can 7840 be enabled again by echoing '1' into the "tracing_on" 7841 file located in /sys/kernel/tracing/ 7842 7843 This option is useful, as it disables the trace before 7844 the WARNING dump is called, which prevents the trace to 7845 be filled with content caused by the warning output. 7846 7847 This option can also be set at run time via the sysctl 7848 option: kernel/traceoff_on_warning 7849 7850 transparent_hugepage= 7851 [KNL] 7852 Format: [always|madvise|never] 7853 Can be used to control the default behavior of the system 7854 with respect to transparent hugepages. 7855 See Documentation/admin-guide/mm/transhuge.rst 7856 for more details. 7857 7858 transparent_hugepage_shmem= [KNL] 7859 Format: [always|within_size|advise|never|deny|force] 7860 Can be used to control the hugepage allocation policy for 7861 the internal shmem mount. 7862 See Documentation/admin-guide/mm/transhuge.rst 7863 for more details. 7864 7865 transparent_hugepage_tmpfs= [KNL] 7866 Format: [always|within_size|advise|never] 7867 Can be used to control the default hugepage allocation policy 7868 for the tmpfs mount. 7869 See Documentation/admin-guide/mm/transhuge.rst 7870 for more details. 7871 7872 trusted.source= [KEYS] 7873 Format: <string> 7874 This parameter identifies the trust source as a backend 7875 for trusted keys implementation. Supported trust 7876 sources: 7877 - "tpm" 7878 - "tee" 7879 - "caam" 7880 - "dcp" 7881 - "pkwm" 7882 If not specified then it defaults to iterating through 7883 the trust source list starting with TPM and assigns the 7884 first trust source as a backend which is initialized 7885 successfully during iteration. 7886 7887 trusted.rng= [KEYS] 7888 Format: <string> 7889 The RNG used to generate key material for trusted keys. 7890 Can be one of: 7891 - "kernel" 7892 - the same value as trusted.source: "tpm" or "tee" 7893 - "default" 7894 If not specified, "default" is used. In this case, 7895 the RNG's choice is left to each individual trust source. 7896 7897 trusted.dcp_use_otp_key 7898 This is intended to be used in combination with 7899 trusted.source=dcp and will select the DCP OTP key 7900 instead of the DCP UNIQUE key blob encryption. 7901 7902 trusted.dcp_skip_zk_test 7903 This is intended to be used in combination with 7904 trusted.source=dcp and will disable the check if the 7905 blob key is all zeros. This is helpful for situations where 7906 having this key zero'ed is acceptable. E.g. in testing 7907 scenarios. 7908 7909 tsa= [X86] Control mitigation for Transient Scheduler 7910 Attacks on AMD CPUs. Search the following in your 7911 favourite search engine for more details: 7912 7913 "Technical guidance for mitigating transient scheduler 7914 attacks". 7915 7916 off - disable the mitigation 7917 on - enable the mitigation (default) 7918 user - mitigate only user/kernel transitions 7919 vm - mitigate only guest/host transitions 7920 7921 7922 tsc= Disable clocksource stability checks for TSC. 7923 Format: <string> 7924 [x86] reliable: mark tsc clocksource as reliable, this 7925 disables clocksource verification at runtime, as well 7926 as the stability checks done at bootup. Used to enable 7927 high-resolution timer mode on older hardware, and in 7928 virtualized environment. 7929 [x86] noirqtime: Do not use TSC to do irq accounting. 7930 Used to run time disable IRQ_TIME_ACCOUNTING on any 7931 platforms where RDTSC is slow and this accounting 7932 can add overhead. 7933 [x86] unstable: mark the TSC clocksource as unstable, this 7934 marks the TSC unconditionally unstable at bootup and 7935 avoids any further wobbles once the TSC watchdog notices. 7936 [x86] nowatchdog: disable clocksource watchdog. Used 7937 in situations with strict latency requirements (where 7938 interruptions from clocksource watchdog are not 7939 acceptable). 7940 [x86] recalibrate: force recalibration against a HW timer 7941 (HPET or PM timer) on systems whose TSC frequency was 7942 obtained from HW or FW using either an MSR or CPUID(0x15). 7943 Warn if the difference is more than 500 ppm. 7944 [x86] watchdog: Enforce the clocksource watchdog on TSC 7945 7946 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7947 value instead. Useful when the early TSC frequency discovery 7948 procedure is not reliable, such as on overclocked systems 7949 with CPUID.16h support and partial CPUID.15h support. 7950 Format: <unsigned int> 7951 7952 tsx= [X86] Control Transactional Synchronization 7953 Extensions (TSX) feature in Intel processors that 7954 support TSX control. 7955 7956 This parameter controls the TSX feature. The options are: 7957 7958 on - Enable TSX on the system. Although there are 7959 mitigations for all known security vulnerabilities, 7960 TSX has been known to be an accelerator for 7961 several previous speculation-related CVEs, and 7962 so there may be unknown security risks associated 7963 with leaving it enabled. 7964 7965 off - Disable TSX on the system. (Note that this 7966 option takes effect only on newer CPUs which are 7967 not vulnerable to MDS, i.e., have 7968 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7969 the new IA32_TSX_CTRL MSR through a microcode 7970 update. This new MSR allows for the reliable 7971 deactivation of the TSX functionality.) 7972 7973 auto - Disable TSX if X86_BUG_TAA is present, 7974 otherwise enable TSX on the system. 7975 7976 Not specifying this option is equivalent to tsx=off. 7977 7978 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7979 for more details. 7980 7981 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7982 Abort (TAA) vulnerability. 7983 7984 Similar to Micro-architectural Data Sampling (MDS) 7985 certain CPUs that support Transactional 7986 Synchronization Extensions (TSX) are vulnerable to an 7987 exploit against CPU internal buffers which can forward 7988 information to a disclosure gadget under certain 7989 conditions. 7990 7991 In vulnerable processors, the speculatively forwarded 7992 data can be used in a cache side channel attack, to 7993 access data to which the attacker does not have direct 7994 access. 7995 7996 This parameter controls the TAA mitigation. The 7997 options are: 7998 7999 full - Enable TAA mitigation on vulnerable CPUs 8000 if TSX is enabled. 8001 8002 full,nosmt - Enable TAA mitigation and disable SMT on 8003 vulnerable CPUs. If TSX is disabled, SMT 8004 is not disabled because CPU is not 8005 vulnerable to cross-thread TAA attacks. 8006 off - Unconditionally disable TAA mitigation 8007 8008 On MDS-affected machines, tsx_async_abort=off can be 8009 prevented by an active MDS mitigation as both vulnerabilities 8010 are mitigated with the same mechanism so in order to disable 8011 this mitigation, you need to specify mds=off too. 8012 8013 Not specifying this option is equivalent to 8014 tsx_async_abort=full. On CPUs which are MDS affected 8015 and deploy MDS mitigation, TAA mitigation is not 8016 required and doesn't provide any additional 8017 mitigation. 8018 8019 For details see: 8020 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8021 8022 turbografx.map[2|3]= [HW,JOY] 8023 TurboGraFX parallel port interface 8024 Format: 8025 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8026 See also Documentation/input/devices/joystick-parport.rst 8027 8028 udbg-immortal [PPC] When debugging early kernel crashes that 8029 happen after console_init() and before a proper 8030 console driver takes over, this boot options might 8031 help "seeing" what's going on. 8032 8033 uhash_entries= [KNL,NET] 8034 Set number of hash buckets for UDP/UDP-Lite connections 8035 8036 uhci-hcd.ignore_oc= 8037 [USB] Ignore overcurrent events (default N). 8038 Some badly-designed motherboards generate lots of 8039 bogus events, for ports that aren't wired to 8040 anything. Set this parameter to avoid log spamming. 8041 Note that genuine overcurrent events won't be 8042 reported either. 8043 8044 unaligned_scalar_speed= 8045 [RISCV] 8046 Format: {slow | fast | unsupported} 8047 Allow skipping scalar unaligned access speed tests. This 8048 is useful for testing alternative code paths and to skip 8049 the tests in environments where they run too slowly. All 8050 CPUs must have the same scalar unaligned access speed. 8051 8052 unaligned_vector_speed= 8053 [RISCV] 8054 Format: {slow | fast | unsupported} 8055 Allow skipping vector unaligned access speed tests. This 8056 is useful for testing alternative code paths and to skip 8057 the tests in environments where they run too slowly. All 8058 CPUs must have the same vector unaligned access speed. 8059 8060 unknown_nmi_panic 8061 [X86] Cause panic on unknown NMI. 8062 8063 unwind_debug [X86-64,EARLY] 8064 Enable unwinder debug output. This can be 8065 useful for debugging certain unwinder error 8066 conditions, including corrupt stacks and 8067 bad/missing unwinder metadata. 8068 8069 usbcore.authorized_default= 8070 [USB] Default USB device authorization: 8071 (default -1 = authorized (same as 1), 8072 0 = not authorized, 1 = authorized, 2 = authorized 8073 if device connected to internal port) 8074 8075 usbcore.autosuspend= 8076 [USB] The autosuspend time delay (in seconds) used 8077 for newly-detected USB devices (default 2). This 8078 is the time required before an idle device will be 8079 autosuspended. Devices for which the delay is set 8080 to a negative value won't be autosuspended at all. 8081 8082 usbcore.usbfs_snoop= 8083 [USB] Set to log all usbfs traffic (default 0 = off). 8084 8085 usbcore.usbfs_snoop_max= 8086 [USB] Maximum number of bytes to snoop in each URB 8087 (default = 65536). 8088 8089 usbcore.blinkenlights= 8090 [USB] Set to cycle leds on hubs (default 0 = off). 8091 8092 usbcore.old_scheme_first= 8093 [USB] Start with the old device initialization 8094 scheme (default 0 = off). 8095 8096 usbcore.usbfs_memory_mb= 8097 [USB] Memory limit (in MB) for buffers allocated by 8098 usbfs (default = 16, 0 = max = 2047). 8099 8100 usbcore.use_both_schemes= 8101 [USB] Try the other device initialization scheme 8102 if the first one fails (default 1 = enabled). 8103 8104 usbcore.initial_descriptor_timeout= 8105 [USB] Specifies timeout for the initial 64-byte 8106 USB_REQ_GET_DESCRIPTOR request in milliseconds 8107 (default 5000 = 5.0 seconds). 8108 8109 usbcore.nousb [USB] Disable the USB subsystem 8110 8111 usbcore.quirks= 8112 [USB] A list of quirk entries to augment the built-in 8113 usb core quirk list. List entries are separated by 8114 commas. Each entry has the form 8115 VendorID:ProductID:Flags. The IDs are 4-digit hex 8116 numbers and Flags is a set of letters. Each letter 8117 will change the built-in quirk; setting it if it is 8118 clear and clearing it if it is set. The letters have 8119 the following meanings: 8120 a = USB_QUIRK_STRING_FETCH_255 (string 8121 descriptors must not be fetched using 8122 a 255-byte read); 8123 b = USB_QUIRK_RESET_RESUME (device can't resume 8124 correctly so reset it instead); 8125 c = USB_QUIRK_NO_SET_INTF (device can't handle 8126 Set-Interface requests); 8127 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8128 handle its Configuration or Interface 8129 strings); 8130 e = USB_QUIRK_RESET (device can't be reset 8131 (e.g morph devices), don't use reset); 8132 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8133 more interface descriptions than the 8134 bNumInterfaces count, and can't handle 8135 talking to these interfaces); 8136 g = USB_QUIRK_DELAY_INIT (device needs a pause 8137 during initialization, after we read 8138 the device descriptor); 8139 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8140 high speed and super speed interrupt 8141 endpoints, the USB 2.0 and USB 3.0 spec 8142 require the interval in microframes (1 8143 microframe = 125 microseconds) to be 8144 calculated as interval = 2 ^ 8145 (bInterval-1). 8146 Devices with this quirk report their 8147 bInterval as the result of this 8148 calculation instead of the exponent 8149 variable used in the calculation); 8150 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8151 handle device_qualifier descriptor 8152 requests); 8153 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8154 generates spurious wakeup, ignore 8155 remote wakeup capability); 8156 k = USB_QUIRK_NO_LPM (device can't handle Link 8157 Power Management); 8158 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8159 (Device reports its bInterval as linear 8160 frames instead of the USB 2.0 8161 calculation); 8162 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8163 to be disconnected before suspend to 8164 prevent spurious wakeup); 8165 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8166 pause after every control message); 8167 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8168 delay after resetting its port); 8169 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8170 (Reduce timeout of the SET_ADDRESS 8171 request from 5000 ms to 500 ms); 8172 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8173 claims zero configurations, 8174 forcing to 1); 8175 Example: quirks=0781:5580:bk,0a5c:5834:gij 8176 8177 usbhid.mousepoll= 8178 [USBHID] The interval which mice are to be polled at. 8179 8180 usbhid.jspoll= 8181 [USBHID] The interval which joysticks are to be polled at. 8182 8183 usbhid.kbpoll= 8184 [USBHID] The interval which keyboards are to be polled at. 8185 8186 usb-storage.delay_use= 8187 [UMS] The delay in seconds before a new device is 8188 scanned for Logical Units (default 1). 8189 Optionally the delay in milliseconds if the value has 8190 suffix with "ms". 8191 Example: delay_use=2567ms 8192 8193 usb-storage.quirks= 8194 [UMS] A list of quirks entries to supplement or 8195 override the built-in unusual_devs list. List 8196 entries are separated by commas. Each entry has 8197 the form VID:PID:Flags where VID and PID are Vendor 8198 and Product ID values (4-digit hex numbers) and 8199 Flags is a set of characters, each corresponding 8200 to a common usb-storage quirk flag as follows: 8201 a = SANE_SENSE (collect more than 18 bytes 8202 of sense data, not on uas); 8203 b = BAD_SENSE (don't collect more than 18 8204 bytes of sense data, not on uas); 8205 c = FIX_CAPACITY (decrease the reported 8206 device capacity by one sector); 8207 d = NO_READ_DISC_INFO (don't use 8208 READ_DISC_INFO command, not on uas); 8209 e = NO_READ_CAPACITY_16 (don't use 8210 READ_CAPACITY_16 command); 8211 f = NO_REPORT_OPCODES (don't use report opcodes 8212 command, uas only); 8213 g = MAX_SECTORS_240 (don't transfer more than 8214 240 sectors at a time, uas only); 8215 h = CAPACITY_HEURISTICS (decrease the 8216 reported device capacity by one 8217 sector if the number is odd); 8218 i = IGNORE_DEVICE (don't bind to this 8219 device); 8220 j = NO_REPORT_LUNS (don't use report luns 8221 command, uas only); 8222 k = NO_SAME (do not use WRITE_SAME, uas only) 8223 l = NOT_LOCKABLE (don't try to lock and 8224 unlock ejectable media, not on uas); 8225 m = MAX_SECTORS_64 (don't transfer more 8226 than 64 sectors = 32 KB at a time, 8227 not on uas); 8228 n = INITIAL_READ10 (force a retry of the 8229 initial READ(10) command, not on uas); 8230 o = CAPACITY_OK (accept the capacity 8231 reported by the device, not on uas); 8232 p = WRITE_CACHE (the device cache is ON 8233 by default, not on uas); 8234 r = IGNORE_RESIDUE (the device reports 8235 bogus residue values, not on uas); 8236 s = SINGLE_LUN (the device has only one 8237 Logical Unit); 8238 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8239 commands, uas only); 8240 u = IGNORE_UAS (don't bind to the uas driver); 8241 w = NO_WP_DETECT (don't test whether the 8242 medium is write-protected). 8243 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8244 even if the device claims no cache, 8245 not on uas) 8246 Example: quirks=0419:aaf5:rl,0421:0433:rc 8247 8248 user_debug= [KNL,ARM] 8249 Format: <int> 8250 See arch/arm/Kconfig.debug help text. 8251 1 - undefined instruction events 8252 2 - system calls 8253 4 - invalid data aborts 8254 8 - SIGSEGV faults 8255 16 - SIGBUS faults 8256 Example: user_debug=31 8257 8258 vdso= [X86,SH,SPARC] 8259 On X86_32, this is an alias for vdso32=. Otherwise: 8260 8261 vdso=1: enable VDSO (the default) 8262 vdso=0: disable VDSO mapping 8263 8264 vdso32= [X86] Control the 32-bit vDSO 8265 vdso32=1: enable 32-bit VDSO 8266 vdso32=0 or vdso32=2: disable 32-bit VDSO 8267 8268 See the help text for CONFIG_COMPAT_VDSO for more 8269 details. If CONFIG_COMPAT_VDSO is set, the default is 8270 vdso32=0; otherwise, the default is vdso32=1. 8271 8272 For compatibility with older kernels, vdso32=2 is an 8273 alias for vdso32=0. 8274 8275 Try vdso32=0 if you encounter an error that says: 8276 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8277 8278 video= [FB,EARLY] Frame buffer configuration 8279 See Documentation/fb/modedb.rst. 8280 8281 video.brightness_switch_enabled= [ACPI] 8282 Format: [0|1] 8283 If set to 1, on receiving an ACPI notify event 8284 generated by hotkey, video driver will adjust brightness 8285 level and then send out the event to user space through 8286 the allocated input device. If set to 0, video driver 8287 will only send out the event without touching backlight 8288 brightness level. 8289 default: 1 8290 8291 virtio_mmio.device= 8292 [VMMIO] Memory mapped virtio (platform) device. 8293 8294 <size>@<baseaddr>:<irq>[:<id>] 8295 where: 8296 <size> := size (can use standard suffixes 8297 like K, M and G) 8298 <baseaddr> := physical base address 8299 <irq> := interrupt number (as passed to 8300 request_irq()) 8301 <id> := (optional) platform device id 8302 example: 8303 virtio_mmio.device=1K@0x100b0000:48:7 8304 8305 Can be used multiple times for multiple devices. 8306 8307 vga= [BOOT,X86-32] Select a particular video mode 8308 See Documentation/arch/x86/boot.rst and 8309 Documentation/admin-guide/svga.rst. 8310 Use vga=ask for menu. 8311 This is actually a boot loader parameter; the value is 8312 passed to the kernel using a special protocol. 8313 8314 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8315 May slow down system boot speed, especially when 8316 enabled on systems with a large amount of memory. 8317 All options are enabled by default, and this 8318 interface is meant to allow for selectively 8319 enabling or disabling specific virtual memory 8320 debugging features. 8321 8322 Available options are: 8323 P Enable page structure init time poisoning 8324 - Disable all of the above options 8325 8326 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8327 exact size of <nn>. This can be used to increase 8328 the minimum size (128MB on x86, arm32 platforms). 8329 It can also be used to decrease the size and leave more room 8330 for directly mapped kernel RAM. Note that this parameter does 8331 not exist on many other platforms (including arm64, alpha, 8332 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8333 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8334 8335 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8336 Sets the memory size reserved for contiguous memory 8337 allocations for the vmcp device driver. 8338 8339 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8340 Format: <command> 8341 8342 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8343 Format: <command> 8344 8345 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8346 Format: <command> 8347 8348 vmscape= [X86] Controls mitigation for VMscape attacks. 8349 VMscape attacks can leak information from a userspace 8350 hypervisor to a guest via speculative side-channels. 8351 8352 off - disable the mitigation 8353 ibpb - use Indirect Branch Prediction Barrier 8354 (IBPB) mitigation (default) 8355 force - force vulnerability detection even on 8356 unaffected processors 8357 8358 vsyscall= [X86-64,EARLY] 8359 Controls the behavior of vsyscalls (i.e. calls to 8360 fixed addresses of 0xffffffffff600x00 from legacy 8361 code). Most statically-linked binaries and older 8362 versions of glibc use these calls. Because these 8363 functions are at fixed addresses, they make nice 8364 targets for exploits that can control RIP. 8365 8366 emulate Vsyscalls turn into traps and are emulated 8367 reasonably safely. The vsyscall page is 8368 readable. This disables the Linear 8369 Address Space Separation (LASS) security 8370 feature and makes the system less secure. 8371 8372 xonly [default] Vsyscalls turn into traps and are 8373 emulated reasonably safely. The vsyscall 8374 page is not readable. 8375 8376 none Vsyscalls don't work at all. This makes 8377 them quite hard to use for exploits but 8378 might break your system. 8379 8380 vt.color= [VT] Default text color. 8381 Format: 0xYX, X = foreground, Y = background. 8382 Default: 0x07 = light gray on black. 8383 8384 vt.cur_default= [VT] Default cursor shape. 8385 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8386 the parameters of the <Esc>[?A;B;Cc escape sequence; 8387 see vga-softcursor.rst. Default: 2 = underline. 8388 8389 vt.default_blu= [VT] 8390 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8391 Change the default blue palette of the console. 8392 This is a 16-member array composed of values 8393 ranging from 0-255. 8394 8395 vt.default_grn= [VT] 8396 Format: <green0>,<green1>,<green2>,...,<green15> 8397 Change the default green palette of the console. 8398 This is a 16-member array composed of values 8399 ranging from 0-255. 8400 8401 vt.default_red= [VT] 8402 Format: <red0>,<red1>,<red2>,...,<red15> 8403 Change the default red palette of the console. 8404 This is a 16-member array composed of values 8405 ranging from 0-255. 8406 8407 vt.default_utf8= 8408 [VT] 8409 Format=<0|1> 8410 Set system-wide default UTF-8 mode for all tty's. 8411 Default is 1, i.e. UTF-8 mode is enabled for all 8412 newly opened terminals. 8413 8414 vt.global_cursor_default= 8415 [VT] 8416 Format=<-1|0|1> 8417 Set system-wide default for whether a cursor 8418 is shown on new VTs. Default is -1, 8419 i.e. cursors will be created by default unless 8420 overridden by individual drivers. 0 will hide 8421 cursors, 1 will display them. 8422 8423 vt.italic= [VT] Default color for italic text; 0-15. 8424 Default: 2 = green. 8425 8426 vt.underline= [VT] Default color for underlined text; 0-15. 8427 Default: 3 = cyan. 8428 8429 watchdog timers [HW,WDT] For information on watchdog timers, 8430 see Documentation/watchdog/watchdog-parameters.rst 8431 or other driver-specific files in the 8432 Documentation/watchdog/ directory. 8433 8434 watchdog_thresh= 8435 [KNL] 8436 Set the hard lockup detector stall duration 8437 threshold in seconds. The soft lockup detector 8438 threshold is set to twice the value. A value of 0 8439 disables both lockup detectors. Default is 10 8440 seconds. 8441 8442 workqueue.unbound_cpus= 8443 [KNL,SMP] Specify to constrain one or some CPUs 8444 to use in unbound workqueues. 8445 Format: <cpu-list> 8446 By default, all online CPUs are available for 8447 unbound workqueues. 8448 8449 workqueue.watchdog_thresh= 8450 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8451 warn stall conditions and dump internal state to 8452 help debugging. 0 disables workqueue stall 8453 detection; otherwise, it's the stall threshold 8454 duration in seconds. The default value is 30 and 8455 it can be updated at runtime by writing to the 8456 corresponding sysfs file. 8457 8458 workqueue.panic_on_stall=<uint> 8459 Panic when workqueue stall is detected by 8460 CONFIG_WQ_WATCHDOG. It sets the number times of the 8461 stall to trigger panic. 8462 8463 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8464 which is 0 (disabled) if not configured. 8465 8466 workqueue.panic_on_stall_time=<uint> 8467 Panic when a workqueue stall has been continuous for 8468 the specified number of seconds. Unlike panic_on_stall 8469 which counts accumulated stall events, this triggers 8470 based on the duration of a single continuous stall. 8471 8472 The default is 0, which disables the time-based panic. 8473 8474 workqueue.cpu_intensive_thresh_us= 8475 Per-cpu work items which run for longer than this 8476 threshold are automatically considered CPU intensive 8477 and excluded from concurrency management to prevent 8478 them from noticeably delaying other per-cpu work 8479 items. Default is 10000 (10ms). 8480 8481 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8482 will report the work functions which violate this 8483 threshold repeatedly. They are likely good 8484 candidates for using WQ_UNBOUND workqueues instead. 8485 8486 workqueue.cpu_intensive_warning_thresh=<uint> 8487 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8488 will report the work functions which violate the 8489 intensive_threshold_us repeatedly. In order to prevent 8490 spurious warnings, start printing only after a work 8491 function has violated this threshold number of times. 8492 8493 The default is 4 times. 0 disables the warning. 8494 8495 workqueue.power_efficient 8496 Per-cpu workqueues are generally preferred because 8497 they show better performance thanks to cache 8498 locality; unfortunately, per-cpu workqueues tend to 8499 be more power hungry than unbound workqueues. 8500 8501 Enabling this makes the per-cpu workqueues which 8502 were observed to contribute significantly to power 8503 consumption unbound, leading to measurably lower 8504 power usage at the cost of small performance 8505 overhead. 8506 8507 The default value of this parameter is determined by 8508 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8509 8510 workqueue.default_affinity_scope= 8511 Select the default affinity scope to use for unbound 8512 workqueues. Can be one of "cpu", "smt", "cache", 8513 "cache_shard", "numa" and "system". Default is 8514 "cache_shard". For more 8515 information, see the Affinity Scopes section in 8516 Documentation/core-api/workqueue.rst. 8517 8518 This can be changed after boot by writing to the 8519 matching /sys/module/workqueue/parameters file. All 8520 workqueues with the "default" affinity scope will be 8521 updated accordingly. 8522 8523 workqueue.debug_force_rr_cpu 8524 Workqueue used to implicitly guarantee that work 8525 items queued without explicit CPU specified are put 8526 on the local CPU. This guarantee is no longer true 8527 and while local CPU is still preferred work items 8528 may be put on foreign CPUs. This debug option 8529 forces round-robin CPU selection to flush out 8530 usages which depend on the now broken guarantee. 8531 When enabled, memory and cache locality will be 8532 impacted. 8533 8534 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8535 Type) of ioremap_wc(). 8536 8537 on - Enable writecombine, use WUC for ioremap_wc() 8538 off - Disable writecombine, use SUC for ioremap_wc() 8539 8540 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8541 default x2apic cluster mode on platforms 8542 supporting x2apic. 8543 8544 xen_512gb_limit [KNL,X86-64,XEN] 8545 Restricts the kernel running paravirtualized under Xen 8546 to use only up to 512 GB of RAM. The reason to do so is 8547 crash analysis tools and Xen tools for doing domain 8548 save/restore/migration must be enabled to handle larger 8549 domains. 8550 8551 xen_console_io [XEN,EARLY] 8552 Boolean option to enable/disable the usage of the Xen 8553 console_io hypercalls to read and write to the console. 8554 Mostly useful for debugging and development. 8555 8556 xen_emul_unplug= [HW,X86,XEN,EARLY] 8557 Unplug Xen emulated devices 8558 Format: [unplug0,][unplug1] 8559 ide-disks -- unplug primary master IDE devices 8560 aux-ide-disks -- unplug non-primary-master IDE devices 8561 nics -- unplug network devices 8562 all -- unplug all emulated devices (NICs and IDE disks) 8563 unnecessary -- unplugging emulated devices is 8564 unnecessary even if the host did not respond to 8565 the unplug protocol 8566 never -- do not unplug even if version check succeeds 8567 8568 xen_legacy_crash [X86,XEN,EARLY] 8569 Crash from Xen panic notifier, without executing late 8570 panic() code such as dumping handler. 8571 8572 xen_mc_debug [X86,XEN,EARLY] 8573 Enable multicall debugging when running as a Xen PV guest. 8574 Enabling this feature will reduce performance a little 8575 bit, so it should only be enabled for obtaining extended 8576 debug data in case of multicall errors. 8577 8578 xen_msr_safe= [X86,XEN,EARLY] 8579 Format: <bool> 8580 Select whether to always use non-faulting (safe) MSR 8581 access functions when running as Xen PV guest. The 8582 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8583 8584 xen_nopv [X86] 8585 Disables the PV optimizations forcing the HVM guest to 8586 run as generic HVM guest with no PV drivers. 8587 This option is obsoleted by the "nopv" option, which 8588 has equivalent effect for XEN platform. 8589 8590 xen_no_vector_callback 8591 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8592 event channel interrupts. 8593 8594 xen_scrub_pages= [XEN] 8595 Boolean option to control scrubbing pages before giving them back 8596 to Xen, for use by other domains. Can be also changed at runtime 8597 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8598 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8599 8600 xen_timer_slop= [X86-64,XEN,EARLY] 8601 Set the timer slop (in nanoseconds) for the virtual Xen 8602 timers (default is 100000). This adjusts the minimum 8603 delta of virtualized Xen timers, where lower values 8604 improve timer resolution at the expense of processing 8605 more timer interrupts. 8606 8607 xen.balloon_boot_timeout= [XEN] 8608 The time (in seconds) to wait before giving up to boot 8609 in case initial ballooning fails to free enough memory. 8610 Applies only when running as HVM or PVH guest and 8611 started with less memory configured than allowed at 8612 max. Default is 180. 8613 8614 xen.event_eoi_delay= [XEN] 8615 How long to delay EOI handling in case of event 8616 storms (jiffies). Default is 10. 8617 8618 xen.event_loop_timeout= [XEN] 8619 After which time (jiffies) the event handling loop 8620 should start to delay EOI handling. Default is 2. 8621 8622 xen.fifo_events= [XEN] 8623 Boolean parameter to disable using fifo event handling 8624 even if available. Normally fifo event handling is 8625 preferred over the 2-level event handling, as it is 8626 fairer and the number of possible event channels is 8627 much higher. Default is on (use fifo events). 8628 8629 xirc2ps_cs= [NET,PCMCIA] 8630 Format: 8631 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8632 8633 xive= [PPC] 8634 By default on POWER9 and above, the kernel will 8635 natively use the XIVE interrupt controller. This option 8636 allows the fallback firmware mode to be used: 8637 8638 off Fallback to firmware control of XIVE interrupt 8639 controller on both pseries and powernv 8640 platforms. Only useful on POWER9 and above. 8641 8642 xive.store-eoi=off [PPC] 8643 By default on POWER10 and above, the kernel will use 8644 stores for EOI handling when the XIVE interrupt mode 8645 is active. This option allows the XIVE driver to use 8646 loads instead, as on POWER9. 8647 8648 xhci-hcd.quirks [USB,KNL] 8649 A hex value specifying bitmask with supplemental xhci 8650 host controller quirks. Meaning of each bit can be 8651 consulted in header drivers/usb/host/xhci.h. 8652 8653 xmon [PPC,EARLY] 8654 Format: { early | on | rw | ro | off } 8655 Controls if xmon debugger is enabled. Default is off. 8656 Passing only "xmon" is equivalent to "xmon=early". 8657 early Call xmon as early as possible on boot; xmon 8658 debugger is called from setup_arch(). 8659 on xmon debugger hooks will be installed so xmon 8660 is only called on a kernel crash. Default mode, 8661 i.e. either "ro" or "rw" mode, is controlled 8662 with CONFIG_XMON_DEFAULT_RO_MODE. 8663 rw xmon debugger hooks will be installed so xmon 8664 is called only on a kernel crash, mode is write, 8665 meaning SPR registers, memory and, other data 8666 can be written using xmon commands. 8667 ro same as "rw" option above but SPR registers, 8668 memory, and other data can't be written using 8669 xmon commands. 8670 off xmon is disabled. 8671