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] Network devices parameters 4270 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4271 Note that mem_start is often overloaded to mean 4272 something different and driver-specific. 4273 This usage is only documented in each driver source 4274 file if at all. 4275 4276 netpoll.carrier_timeout= 4277 [NET] Specifies amount of time (in seconds) that 4278 netpoll should wait for a carrier. By default netpoll 4279 waits 4 seconds. 4280 4281 nf_conntrack.acct= 4282 [NETFILTER] Enable connection tracking flow accounting 4283 0 to disable accounting 4284 1 to enable accounting 4285 Default value is 0. 4286 4287 nfs.cache_getent= 4288 [NFS] sets the pathname to the program which is used 4289 to update the NFS client cache entries. 4290 4291 nfs.cache_getent_timeout= 4292 [NFS] sets the timeout after which an attempt to 4293 update a cache entry is deemed to have failed. 4294 4295 nfs.callback_nr_threads= 4296 [NFSv4] set the total number of threads that the 4297 NFS client will assign to service NFSv4 callback 4298 requests. 4299 4300 nfs.callback_tcpport= 4301 [NFS] set the TCP port on which the NFSv4 callback 4302 channel should listen. 4303 4304 nfs.delay_retrans= 4305 [NFS] specifies the number of times the NFSv4 client 4306 retries the request before returning an EAGAIN error, 4307 after a reply of NFS4ERR_DELAY from the server. 4308 Only applies if the softerr mount option is enabled, 4309 and the specified value is >= 0. 4310 4311 nfs.enable_ino64= 4312 [NFS] enable 64-bit inode numbers. 4313 If zero, the NFS client will fake up a 32-bit inode 4314 number for the readdir() and stat() syscalls instead 4315 of returning the full 64-bit number. 4316 The default is to return 64-bit inode numbers. 4317 4318 nfs.idmap_cache_timeout= 4319 [NFS] set the maximum lifetime for idmapper cache 4320 entries. 4321 4322 nfs.max_session_cb_slots= 4323 [NFSv4.1] Sets the maximum number of session 4324 slots the client will assign to the callback 4325 channel. This determines the maximum number of 4326 callbacks the client will process in parallel for 4327 a particular server. 4328 4329 nfs.max_session_slots= 4330 [NFSv4.1] Sets the maximum number of session slots 4331 the client will attempt to negotiate with the server. 4332 This limits the number of simultaneous RPC requests 4333 that the client can send to the NFSv4.1 server. 4334 Note that there is little point in setting this 4335 value higher than the max_tcp_slot_table_limit. 4336 4337 nfs.nfs4_disable_idmapping= 4338 [NFSv4] When set to the default of '1', this option 4339 ensures that both the RPC level authentication 4340 scheme and the NFS level operations agree to use 4341 numeric uids/gids if the mount is using the 4342 'sec=sys' security flavour. In effect it is 4343 disabling idmapping, which can make migration from 4344 legacy NFSv2/v3 systems to NFSv4 easier. 4345 Servers that do not support this mode of operation 4346 will be autodetected by the client, and it will fall 4347 back to using the idmapper. 4348 To turn off this behaviour, set the value to '0'. 4349 4350 nfs.nfs4_unique_id= 4351 [NFS4] Specify an additional fixed unique ident- 4352 ification string that NFSv4 clients can insert into 4353 their nfs_client_id4 string. This is typically a 4354 UUID that is generated at system install time. 4355 4356 nfs.recover_lost_locks= 4357 [NFSv4] Attempt to recover locks that were lost due 4358 to a lease timeout on the server. Please note that 4359 doing this risks data corruption, since there are 4360 no guarantees that the file will remain unchanged 4361 after the locks are lost. 4362 If you want to enable the kernel legacy behaviour of 4363 attempting to recover these locks, then set this 4364 parameter to '1'. 4365 The default parameter value of '0' causes the kernel 4366 not to attempt recovery of lost locks. 4367 4368 nfs.send_implementation_id= 4369 [NFSv4.1] Send client implementation identification 4370 information in exchange_id requests. 4371 If zero, no implementation identification information 4372 will be sent. 4373 The default is to send the implementation identification 4374 information. 4375 4376 nfs4.layoutstats_timer= 4377 [NFSv4.2] Change the rate at which the kernel sends 4378 layoutstats to the pNFS metadata server. 4379 4380 Setting this to value to 0 causes the kernel to use 4381 whatever value is the default set by the layout 4382 driver. A non-zero value sets the minimum interval 4383 in seconds between layoutstats transmissions. 4384 4385 nfsd.inter_copy_offload_enable= 4386 [NFSv4.2] When set to 1, the server will support 4387 server-to-server copies for which this server is 4388 the destination of the copy. 4389 4390 nfsd.nfs4_disable_idmapping= 4391 [NFSv4] When set to the default of '1', the NFSv4 4392 server will return only numeric uids and gids to 4393 clients using auth_sys, and will accept numeric uids 4394 and gids from such clients. This is intended to ease 4395 migration from NFSv2/v3. 4396 4397 nfsd.nfsd4_ssc_umount_timeout= 4398 [NFSv4.2] When used as the destination of a 4399 server-to-server copy, knfsd temporarily mounts 4400 the source server. It caches the mount in case 4401 it will be needed again, and discards it if not 4402 used for the number of milliseconds specified by 4403 this parameter. 4404 4405 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4406 See Documentation/admin-guide/nfs/nfsroot.rst. 4407 4408 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4409 See Documentation/admin-guide/nfs/nfsroot.rst. 4410 4411 nfsrootdebug [NFS] enable nfsroot debugging messages. 4412 See Documentation/admin-guide/nfs/nfsroot.rst. 4413 4414 nmi_backtrace.backtrace_idle [KNL] 4415 Dump stacks even of idle CPUs in response to an 4416 NMI stack-backtrace request. 4417 4418 nmi_debug= [KNL,SH] Specify one or more actions to take 4419 when a NMI is triggered. 4420 Format: [state][,regs][,debounce][,die] 4421 4422 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4423 Format: [panic,][nopanic,][rNNN,][num] 4424 Valid num: 0 or 1 4425 0 - turn hardlockup detector in nmi_watchdog off 4426 1 - turn hardlockup detector in nmi_watchdog on 4427 rNNN - configure the watchdog with raw perf event 0xNNN 4428 4429 When panic is specified, panic when an NMI watchdog 4430 timeout occurs (or 'nopanic' to not panic on an NMI 4431 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4432 To disable both hard and soft lockup detectors, 4433 please see 'nowatchdog'. 4434 This is useful when you use a panic=... timeout and 4435 need the box quickly up again. 4436 4437 These settings can be accessed at runtime via 4438 the nmi_watchdog and hardlockup_panic sysctls. 4439 4440 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4441 emulation library even if a 387 maths coprocessor 4442 is present. 4443 4444 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4445 Forces kernel to use 3-level paging instead. 4446 4447 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4448 kernel to use 4-level paging instead. 4449 4450 noalign [KNL,ARM] 4451 4452 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4453 IOAPICs that may be present in the system. 4454 4455 noapictimer [APIC,X86] Don't set up the APIC timer 4456 4457 noautogroup Disable scheduler automatic task group creation. 4458 4459 nocache [ARM,EARLY] 4460 4461 no_console_suspend 4462 [HW] Never suspend the console 4463 Disable suspending of consoles during suspend and 4464 hibernate operations. Once disabled, debugging 4465 messages can reach various consoles while the rest 4466 of the system is being put to sleep (ie, while 4467 debugging driver suspend/resume hooks). This may 4468 not work reliably with all consoles, but is known 4469 to work with serial and VGA consoles. 4470 To facilitate more flexible debugging, we also add 4471 console_suspend, a printk module parameter to control 4472 it. Users could use console_suspend (usually 4473 /sys/module/printk/parameters/console_suspend) to 4474 turn on/off it dynamically. 4475 4476 no_debug_objects 4477 [KNL,EARLY] Disable object debugging 4478 4479 nodsp [SH] Disable hardware DSP at boot time. 4480 4481 noefi [EFI,EARLY] Disable EFI runtime services support. 4482 4483 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4484 4485 noexec32 [X86-64] 4486 This affects only 32-bit executables. 4487 noexec32=on: enable non-executable mappings (default) 4488 read doesn't imply executable mappings 4489 noexec32=off: disable non-executable mappings 4490 read implies executable mappings 4491 4492 no_file_caps Tells the kernel not to honor file capabilities. The 4493 only way then for a file to be executed with privilege 4494 is to be setuid root or executed by root. 4495 4496 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4497 4498 nofsgsbase [X86] Disables FSGSBASE instructions. 4499 4500 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4501 register save and restore. The kernel will only save 4502 legacy floating-point registers on task switch. 4503 4504 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4505 4506 no_hash_pointers 4507 [KNL,EARLY] 4508 Alias for "hash_pointers=never". 4509 4510 nohibernate [HIBERNATION] Disable hibernation and resume. 4511 4512 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4513 busy wait in do_idle() and not use the arch_cpu_idle() 4514 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4515 to be effective. This is useful on platforms where the 4516 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4517 correctly or when doing power measurements to evaluate 4518 the impact of the sleep instructions. This is also 4519 useful when using JTAG debugger. 4520 4521 nohpet [X86] Don't use the HPET timer. 4522 4523 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4524 4525 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4526 4527 nohz= [KNL] Boottime enable/disable dynamic ticks 4528 Valid arguments: on, off 4529 Default: on 4530 4531 nohz_full= [KNL,BOOT,SMP,ISOL] 4532 The argument is a cpu list, as described above. 4533 In kernels built with CONFIG_NO_HZ_FULL=y, set 4534 the specified list of CPUs whose tick will be stopped 4535 whenever possible. The boot CPU will be forced outside 4536 the range to maintain the timekeeping. Any CPUs 4537 in this list will have their RCU callbacks offloaded, 4538 just as if they had also been called out in the 4539 rcu_nocbs= boot parameter. 4540 4541 Note that this argument takes precedence over 4542 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4543 4544 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4545 initial RAM disk. Currently this parameter applies to 4546 initrd only, not to initramfs. But it applies to both 4547 in EFI mode. 4548 4549 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4550 remapping. 4551 [Deprecated - use intremap=off] 4552 4553 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4554 4555 noiotrap [SH] Disables trapped I/O port accesses. 4556 4557 noirqdebug [X86-32] Disables the code which attempts to detect and 4558 disable unhandled interrupt sources. 4559 4560 noisapnp [ISAPNP] Disables ISA PnP code. 4561 4562 nokaslr [KNL,EARLY] 4563 When CONFIG_RANDOMIZE_BASE is set, this disables 4564 kernel and module base offset ASLR (Address Space 4565 Layout Randomization). 4566 4567 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4568 fault handling. 4569 4570 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4571 4572 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4573 4574 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4575 4576 nomce [X86-32] Disable Machine Check Exception 4577 4578 nomfgpt [X86-32] Disable Multi-Function General Purpose 4579 Timer usage (for AMD Geode machines). 4580 4581 nomodeset Disable kernel modesetting. Most systems' firmware 4582 sets up a display mode and provides framebuffer memory 4583 for output. With nomodeset, DRM and fbdev drivers will 4584 not load if they could possibly displace the pre- 4585 initialized output. Only the system framebuffer will 4586 be available for use. The respective drivers will not 4587 perform display-mode changes or accelerated rendering. 4588 4589 Useful as error fallback, or for testing and debugging. 4590 4591 nomodule Disable module load 4592 4593 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4594 shutdown the other cpus. Instead use the REBOOT_VECTOR 4595 irq. 4596 4597 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4598 pagetables) support. 4599 4600 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4601 4602 nopku [X86] Disable Memory Protection Keys CPU feature found 4603 in some Intel CPUs. 4604 4605 nopti [X86-64,EARLY] 4606 Equivalent to pti=off 4607 4608 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4609 Disables the PV optimizations forcing the guest to run 4610 as generic guest with no PV drivers. Currently support 4611 XEN HVM, KVM, HYPER_V and VMWARE guest. 4612 4613 nopvspin [X86,XEN,KVM,EARLY] 4614 Disables the qspinlock slow path using PV optimizations 4615 which allow the hypervisor to 'idle' the guest on lock 4616 contention. 4617 4618 norandmaps Don't use address space randomization. Equivalent to 4619 echo 0 > /proc/sys/kernel/randomize_va_space 4620 4621 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4622 with UP alternatives 4623 4624 noresume [SWSUSP] Disables resume and restores original swap 4625 space. 4626 4627 no-scroll [VGA] Disables scrollback. 4628 This is required for the Braillex ib80-piezo Braille 4629 reader made by F.H. Papenmeier (Germany). 4630 4631 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4632 4633 nosmap [PPC,EARLY] 4634 Disable SMAP (Supervisor Mode Access Prevention) 4635 even if it is supported by processor. 4636 4637 nosmep [PPC64s,EARLY] 4638 Disable SMEP (Supervisor Mode Execution Prevention) 4639 even if it is supported by processor. 4640 4641 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4642 and disable the IO APIC. legacy for "maxcpus=0". 4643 4644 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4645 Equivalent to smt=1. 4646 4647 [KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT). 4648 nosmt=force: Force disable SMT, cannot be undone 4649 via the sysfs control file. 4650 4651 nosoftlockup [KNL] Disable the soft-lockup detector. 4652 4653 nospec_store_bypass_disable 4654 [HW,EARLY] Disable all mitigations for the Speculative 4655 Store Bypass vulnerability 4656 4657 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4658 history injection) vulnerability. System may allow data leaks 4659 with this option. 4660 4661 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4662 (bounds check bypass). With this option data leaks are 4663 possible in the system. 4664 4665 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4666 for the Spectre variant 2 (indirect branch 4667 prediction) vulnerability. System may allow data 4668 leaks with this option. 4669 4670 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4671 Disable paravirtualized steal time accounting. steal time 4672 is computed, but won't influence scheduler behaviour 4673 4674 nosync [HW,M68K] Disables sync negotiation for all devices. 4675 4676 no_timer_check [X86,APIC] Disables the code which tests for broken 4677 timer IRQ sources, i.e., the IO-APIC timer. This can 4678 work around problems with incorrect timer 4679 initialization on some boards. 4680 4681 no_uaccess_flush 4682 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4683 4684 novmcoredd [KNL,KDUMP] 4685 Disable device dump. Device dump allows drivers to 4686 append dump data to vmcore so you can collect driver 4687 specified debug info. Drivers can append the data 4688 without any limit and this data is stored in memory, 4689 so this may cause significant memory stress. Disabling 4690 device dump can help save memory but the driver debug 4691 data will be no longer available. This parameter 4692 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4693 is set. 4694 4695 no-vmw-sched-clock 4696 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4697 scheduler clock and use the default one. 4698 4699 nowatchdog [KNL] Disable both lockup detectors, i.e. 4700 soft-lockup and NMI watchdog (hard-lockup). 4701 4702 nowb [ARM,EARLY] 4703 4704 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4705 4706 NOTE: this parameter will be ignored on systems with the 4707 LEGACY_XAPIC_DISABLED bit set in the 4708 IA32_XAPIC_DISABLE_STATUS MSR. 4709 4710 noxsave [BUGS=X86] Disables x86 extended register state save 4711 and restore using xsave. The kernel will fallback to 4712 enabling legacy floating-point and sse state. 4713 4714 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4715 register states. The kernel will fall back to use 4716 xsave to save the states. By using this parameter, 4717 performance of saving the states is degraded because 4718 xsave doesn't support modified optimization while 4719 xsaveopt supports it on xsaveopt enabled systems. 4720 4721 noxsaves [X86] Disables xsaves and xrstors used in saving and 4722 restoring x86 extended register state in compacted 4723 form of xsave area. The kernel will fall back to use 4724 xsaveopt and xrstor to save and restore the states 4725 in standard form of xsave area. By using this 4726 parameter, xsave area per process might occupy more 4727 memory on xsaves enabled systems. 4728 4729 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4730 could support. nr_cpus=n : n >= 1 limits the kernel to 4731 support 'n' processors. It could be larger than the 4732 number of already plugged CPU during bootup, later in 4733 runtime you can physically add extra cpu until it reaches 4734 n. So during boot up some boot time memory for per-cpu 4735 variables need be pre-allocated for later physical cpu 4736 hot plugging. 4737 4738 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4739 4740 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4741 Disable NUMA, Only set up a single NUMA node 4742 spanning all memory. 4743 4744 numa=fake=<size>[MG] 4745 [KNL, ARM64, RISCV, X86, EARLY] 4746 If given as a memory unit, fills all system RAM with 4747 nodes of size interleaved over physical nodes. 4748 4749 numa=fake=<N> 4750 [KNL, ARM64, RISCV, X86, EARLY] 4751 If given as an integer, fills all system RAM with N 4752 fake nodes interleaved over physical nodes. 4753 4754 numa=fake=<N>U 4755 [KNL, ARM64, RISCV, X86, EARLY] 4756 If given as an integer followed by 'U', it will 4757 divide each physical node into N emulated nodes. 4758 4759 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4760 4761 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4762 soft-reserved memory partitioning. 4763 4764 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4765 NUMA balancing. 4766 Allowed values are enable and disable 4767 4768 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4769 'node', 'default' can be specified 4770 This can be set from sysctl after boot. 4771 See Documentation/admin-guide/sysctl/vm.rst for details. 4772 4773 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4774 nvme quirk list. List entries are separated by a 4775 '-' character. 4776 Each entry has the form VendorID:ProductID:quirk_names. 4777 The IDs are 4-digits hex numbers and quirk_names is a 4778 list of quirk names separated by commas. A quirk name 4779 can be prefixed by '^', meaning that the specified 4780 quirk must be disabled. 4781 4782 Example: 4783 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4784 4785 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4786 See Documentation/core-api/debugging-via-ohci1394.rst for more 4787 info. 4788 4789 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4790 Rather than timing out after 20 ms if an EC 4791 command is not properly ACKed, override the length 4792 of the timeout. We have interrupts disabled while 4793 waiting for the ACK, so if this is set too high 4794 interrupts *may* be lost! 4795 4796 omap_mux= [OMAP] Override bootloader pin multiplexing. 4797 Format: <mux_mode0.mode_name=value>... 4798 For example, to override I2C bus2: 4799 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4800 4801 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4802 4803 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4804 4805 boundary - index of last SLC block on Flex-OneNAND. 4806 The remaining blocks are configured as MLC blocks. 4807 lock - Configure if Flex-OneNAND boundary should be locked. 4808 Once locked, the boundary cannot be changed. 4809 1 indicates lock status, 0 indicates unlock status. 4810 4811 oops=panic [KNL,EARLY] 4812 Always panic on oopses. Default is to just kill the 4813 process, but there is a small probability of 4814 deadlocking the machine. 4815 This will also cause panics on machine check exceptions. 4816 Useful together with panic=30 to trigger a reboot. 4817 4818 page_alloc.shuffle= 4819 [KNL] Boolean flag to control whether the page allocator 4820 should randomize its free lists. This parameter can be 4821 used to enable/disable page randomization. The state of 4822 the flag can be read from sysfs at: 4823 /sys/module/page_alloc/parameters/shuffle. 4824 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4825 4826 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4827 Storage of the information about who allocated 4828 each page is disabled in default. With this switch, 4829 we can turn it on. 4830 on: enable the feature 4831 4832 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4833 poisoning on the buddy allocator, available with 4834 CONFIG_PAGE_POISONING=y. 4835 off: turn off poisoning (default) 4836 on: turn on poisoning 4837 4838 page_reporting.page_reporting_order= 4839 [KNL] Minimal page reporting order 4840 Format: <integer> 4841 Adjust the minimal page reporting order. The page 4842 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4843 4844 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4845 timeout > 0: seconds before rebooting 4846 timeout = 0: wait forever 4847 timeout < 0: reboot immediately 4848 Format: <timeout> 4849 4850 panic_on_taint= [KNL,EARLY] 4851 Bitmask for conditionally calling panic() in add_taint() 4852 Format: <hex>[,nousertaint] 4853 Hexadecimal bitmask representing the set of TAINT flags 4854 that will cause the kernel to panic when add_taint() is 4855 called with any of the flags in this set. 4856 The optional switch "nousertaint" can be utilized to 4857 prevent userspace forced crashes by writing to sysctl 4858 /proc/sys/kernel/tainted any flagset matching with the 4859 bitmask set on panic_on_taint. 4860 See Documentation/admin-guide/tainted-kernels.rst for 4861 extra details on the taint flags that users can pick 4862 to compose the bitmask to assign to panic_on_taint. 4863 4864 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4865 on a WARN(). 4866 4867 panic_force_cpu= 4868 [KNL,SMP] Force panic handling to execute on a specific CPU. 4869 Format: <cpu number> 4870 Some platforms require panic handling to occur on a 4871 specific CPU for the crash kernel to function correctly. 4872 This can be due to firmware limitations, interrupt routing 4873 constraints, or platform-specific requirements where only 4874 a particular CPU can safely enter the crash kernel. 4875 When set, panic() will redirect execution to the specified 4876 CPU before proceeding with the normal panic and kexec flow. 4877 If the target CPU is offline or unavailable, panic proceeds 4878 on the current CPU. 4879 This option should only be used for systems with the above 4880 constraints as it might cause the panic operation to be less reliable. 4881 4882 panic_print= Bitmask for printing system info when panic happens. 4883 User can chose combination of the following bits: 4884 bit 0: print all tasks info 4885 bit 1: print system memory info 4886 bit 2: print timer info 4887 bit 3: print locks info if CONFIG_LOCKDEP is on 4888 bit 4: print ftrace buffer 4889 bit 5: replay all kernel messages on consoles at the end of panic 4890 bit 6: print all CPUs backtrace (if available in the arch) 4891 bit 7: print only tasks in uninterruptible (blocked) state 4892 *Be aware* that this option may print a _lot_ of lines, 4893 so there are risks of losing older messages in the log. 4894 Use this option carefully, maybe worth to setup a 4895 bigger log buffer with "log_buf_len" along with this. 4896 4897 panic_sys_info= A comma separated list of extra information to be dumped 4898 on panic. 4899 Format: val[,val...] 4900 Where @val can be any of the following: 4901 4902 tasks: print all tasks info 4903 mem: print system memory info 4904 timers: print timers info 4905 locks: print locks info if CONFIG_LOCKDEP is on 4906 ftrace: print ftrace buffer 4907 all_bt: print all CPUs backtrace (if available in the arch) 4908 blocked_tasks: print only tasks in uninterruptible (blocked) state 4909 4910 This is a human readable alternative to the 'panic_print' option. 4911 4912 panic_console_replay 4913 When panic happens, replay all kernel messages on 4914 consoles at the end of panic. 4915 4916 parkbd.port= [HW] Parallel port number the keyboard adapter is 4917 connected to, default is 0. 4918 Format: <parport#> 4919 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4920 0 for XT, 1 for AT (default is AT). 4921 Format: <mode> 4922 4923 parport= [HW,PPT] Specify parallel ports. 0 disables. 4924 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4925 Use 'auto' to force the driver to use any 4926 IRQ/DMA settings detected (the default is to 4927 ignore detected IRQ/DMA settings because of 4928 possible conflicts). You can specify the base 4929 address, IRQ, and DMA settings; IRQ and DMA 4930 should be numbers, or 'auto' (for using detected 4931 settings on that particular port), or 'nofifo' 4932 (to avoid using a FIFO even if it is detected). 4933 Parallel ports are assigned in the order they 4934 are specified on the command line, starting 4935 with parport0. 4936 4937 parport_init_mode= [HW,PPT] 4938 Configure VIA parallel port to operate in 4939 a specific mode. This is necessary on Pegasos 4940 computer where firmware has no options for setting 4941 up parallel port mode and sets it to spp. 4942 Currently this function knows 686a and 8231 chips. 4943 Format: [spp|ps2|epp|ecp|ecpepp] 4944 4945 pata_legacy.all= [HW,LIBATA] 4946 Format: <int> 4947 Set to non-zero to probe primary and secondary ISA 4948 port ranges on PCI systems where no PCI PATA device 4949 has been found at either range. Disabled by default. 4950 4951 pata_legacy.autospeed= [HW,LIBATA] 4952 Format: <int> 4953 Set to non-zero if a chip is present that snoops speed 4954 changes. Disabled by default. 4955 4956 pata_legacy.ht6560a= [HW,LIBATA] 4957 Format: <int> 4958 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4959 the secondary channel, or both channels respectively. 4960 Disabled by default. 4961 4962 pata_legacy.ht6560b= [HW,LIBATA] 4963 Format: <int> 4964 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4965 the secondary channel, or both channels respectively. 4966 Disabled by default. 4967 4968 pata_legacy.iordy_mask= [HW,LIBATA] 4969 Format: <int> 4970 IORDY enable mask. Set individual bits to allow IORDY 4971 for the respective channel. Bit 0 is for the first 4972 legacy channel handled by this driver, bit 1 is for 4973 the second channel, and so on. The sequence will often 4974 correspond to the primary legacy channel, the secondary 4975 legacy channel, and so on, but the handling of a PCI 4976 bus and the use of other driver options may interfere 4977 with the sequence. By default IORDY is allowed across 4978 all channels. 4979 4980 pata_legacy.opti82c46x= [HW,LIBATA] 4981 Format: <int> 4982 Set to 1, 2, or 3 for Opti 82c611A on the primary 4983 channel, the secondary channel, or both channels 4984 respectively. Disabled by default. 4985 4986 pata_legacy.opti82c611a= [HW,LIBATA] 4987 Format: <int> 4988 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4989 channel, the secondary channel, or both channels 4990 respectively. Disabled by default. 4991 4992 pata_legacy.pio_mask= [HW,LIBATA] 4993 Format: <int> 4994 PIO mode mask for autospeed devices. Set individual 4995 bits to allow the use of the respective PIO modes. 4996 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4997 All modes allowed by default. 4998 4999 pata_legacy.probe_all= [HW,LIBATA] 5000 Format: <int> 5001 Set to non-zero to probe tertiary and further ISA 5002 port ranges on PCI systems. Disabled by default. 5003 5004 pata_legacy.probe_mask= [HW,LIBATA] 5005 Format: <int> 5006 Probe mask for legacy ISA PATA ports. Depending on 5007 platform configuration and the use of other driver 5008 options up to 6 legacy ports are supported: 0x1f0, 5009 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5010 of individual ports can be disabled by setting the 5011 corresponding bits in the mask to 1. Bit 0 is for 5012 the first port in the list above (0x1f0), and so on. 5013 By default all supported ports are probed. 5014 5015 pata_legacy.qdi= [HW,LIBATA] 5016 Format: <int> 5017 Set to non-zero to probe QDI controllers. By default 5018 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5019 5020 pata_legacy.winbond= [HW,LIBATA] 5021 Format: <int> 5022 Set to non-zero to probe Winbond controllers. Use 5023 the standard I/O port (0x130) if 1, otherwise the 5024 value given is the I/O port to use (typically 0x1b0). 5025 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5026 0 otherwise. 5027 5028 pata_platform.pio_mask= [HW,LIBATA] 5029 Format: <int> 5030 Supported PIO mode mask. Set individual bits to allow 5031 the use of the respective PIO modes. Bit 0 is for 5032 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5033 allowed by default. 5034 5035 pause_on_oops=<int> 5036 Halt all CPUs after the first oops has been printed for 5037 the specified number of seconds. This is to be used if 5038 your oopses keep scrolling off the screen. 5039 5040 pcbit= [HW,ISDN] 5041 5042 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5043 5044 Some options herein operate on a specific device 5045 or a set of devices (<pci_dev>). These are 5046 specified in one of the following formats: 5047 5048 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5049 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5050 5051 Note: the first format specifies a PCI 5052 bus/device/function address which may change 5053 if new hardware is inserted, if motherboard 5054 firmware changes, or due to changes caused 5055 by other kernel parameters. If the 5056 domain is left unspecified, it is 5057 taken to be zero. Optionally, a path 5058 to a device through multiple device/function 5059 addresses can be specified after the base 5060 address (this is more robust against 5061 renumbering issues). The second format 5062 selects devices using IDs from the 5063 configuration space which may match multiple 5064 devices in the system. 5065 5066 earlydump dump PCI config space before the kernel 5067 changes anything 5068 off [X86] don't probe for the PCI bus 5069 bios [X86-32] force use of PCI BIOS, don't access 5070 the hardware directly. Use this if your machine 5071 has a non-standard PCI host bridge. 5072 nobios [X86-32] disallow use of PCI BIOS, only direct 5073 hardware access methods are allowed. Use this 5074 if you experience crashes upon bootup and you 5075 suspect they are caused by the BIOS. 5076 conf1 [X86] Force use of PCI Configuration Access 5077 Mechanism 1 (config address in IO port 0xCF8, 5078 data in IO port 0xCFC, both 32-bit). 5079 conf2 [X86] Force use of PCI Configuration Access 5080 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5081 the function, IO port 0xCFA, also 8-bit, sets 5082 bus number. The config space is then accessed 5083 through ports 0xC000-0xCFFF). 5084 See http://wiki.osdev.org/PCI for more info 5085 on the configuration access mechanisms. 5086 noaer [PCIE] If the PCIEAER kernel config parameter is 5087 enabled, this kernel boot option can be used to 5088 disable the use of PCIE advanced error reporting. 5089 nodomains [PCI] Disable support for multiple PCI 5090 root domains (aka PCI segments, in ACPI-speak). 5091 nommconf [X86] Disable use of MMCONFIG for PCI 5092 Configuration 5093 check_enable_amd_mmconf [X86] check for and enable 5094 properly configured MMIO access to PCI 5095 config space on AMD family 10h CPU 5096 nomsi [MSI] If the PCI_MSI kernel config parameter is 5097 enabled, this kernel boot option can be used to 5098 disable the use of MSI interrupts system-wide. 5099 noioapicquirk [APIC] Disable all boot interrupt quirks. 5100 Safety option to keep boot IRQs enabled. This 5101 should never be necessary. 5102 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5103 primary IO-APIC for bridges that cannot disable 5104 boot IRQs. This fixes a source of spurious IRQs 5105 when the system masks IRQs. 5106 noioapicreroute [APIC] Disable workaround that uses the 5107 boot IRQ equivalent of an IRQ that connects to 5108 a chipset where boot IRQs cannot be disabled. 5109 The opposite of ioapicreroute. 5110 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5111 routing table. These calls are known to be buggy 5112 on several machines and they hang the machine 5113 when used, but on other computers it's the only 5114 way to get the interrupt routing table. Try 5115 this option if the kernel is unable to allocate 5116 IRQs or discover secondary PCI buses on your 5117 motherboard. 5118 rom [X86] Assign address space to expansion ROMs. 5119 Use with caution as certain devices share 5120 address decoders between ROMs and other 5121 resources. 5122 norom [X86] Do not assign address space to 5123 expansion ROMs that do not already have 5124 BIOS assigned address ranges. 5125 nobar [X86] Do not assign address space to the 5126 BARs that weren't assigned by the BIOS. 5127 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5128 assigned automatically to PCI devices. You can 5129 make the kernel exclude IRQs of your ISA cards 5130 this way. 5131 pirqaddr=0xAAAAA [X86] Specify the physical address 5132 of the PIRQ table (normally generated 5133 by the BIOS) if it is outside the 5134 F0000h-100000h range. 5135 lastbus=N [X86] Scan all buses thru bus #N. Can be 5136 useful if the kernel is unable to find your 5137 secondary buses and you want to tell it 5138 explicitly which ones they are. 5139 assign-busses [X86] Always assign all PCI bus 5140 numbers ourselves, overriding 5141 whatever the firmware may have done. 5142 usepirqmask [X86] Honor the possible IRQ mask stored 5143 in the BIOS $PIR table. This is needed on 5144 some systems with broken BIOSes, notably 5145 some HP Pavilion N5400 and Omnibook XE3 5146 notebooks. This will have no effect if ACPI 5147 IRQ routing is enabled. 5148 noacpi [X86] Do not use ACPI for IRQ routing 5149 or for PCI scanning. 5150 use_crs [X86] Use PCI host bridge window information 5151 from ACPI. On BIOSes from 2008 or later, this 5152 is enabled by default. If you need to use this, 5153 please report a bug. 5154 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5155 If you need to use this, please report a bug. 5156 use_e820 [X86] Use E820 reservations to exclude parts of 5157 PCI host bridge windows. This is a workaround 5158 for BIOS defects in host bridge _CRS methods. 5159 If you need to use this, please report a bug to 5160 <linux-pci@vger.kernel.org>. 5161 no_e820 [X86] Ignore E820 reservations for PCI host 5162 bridge windows. This is the default on modern 5163 hardware. If you need to use this, please report 5164 a bug to <linux-pci@vger.kernel.org>. 5165 routeirq Do IRQ routing for all PCI devices. 5166 This is normally done in pci_enable_device(), 5167 so this option is a temporary workaround 5168 for broken drivers that don't call it. 5169 skip_isa_align [X86] do not align io start addr, so can 5170 handle more pci cards 5171 noearly [X86] Don't do any early type 1 scanning. 5172 This might help on some broken boards which 5173 machine check when some devices' config space 5174 is read. But various workarounds are disabled 5175 and some IOMMU drivers will not work. 5176 bfsort Sort PCI devices into breadth-first order. 5177 This sorting is done to get a device 5178 order compatible with older (<= 2.4) kernels. 5179 nobfsort Don't sort PCI devices into breadth-first order. 5180 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5181 tuning and use the BIOS-configured MPS defaults. 5182 pcie_bus_safe Set every device's MPS to the largest value 5183 supported by all devices below the root complex. 5184 pcie_bus_perf Set device MPS to the largest allowable MPS 5185 based on its parent bus. Also set MRRS (Max 5186 Read Request Size) to the largest supported 5187 value (no larger than the MPS that the device 5188 or bus can support) for best performance. 5189 pcie_bus_peer2peer Set every device's MPS to 128B, which 5190 every device is guaranteed to support. This 5191 configuration allows peer-to-peer DMA between 5192 any pair of devices, possibly at the cost of 5193 reduced performance. This also guarantees 5194 that hot-added devices will work. 5195 cbiosize=nn[KMG] The fixed amount of bus space which is 5196 reserved for the CardBus bridge's IO window. 5197 The default value is 256 bytes. 5198 cbmemsize=nn[KMG] The fixed amount of bus space which is 5199 reserved for the CardBus bridge's memory 5200 window. The default value is 64 megabytes. 5201 resource_alignment= 5202 Format: 5203 [<order of align>@]<pci_dev>[; ...] 5204 Specifies alignment and device to reassign 5205 aligned memory resources. How to 5206 specify the device is described above. 5207 If <order of align> is not specified, 5208 PAGE_SIZE is used as alignment. 5209 A PCI-PCI bridge can be specified if resource 5210 windows need to be expanded. 5211 To specify the alignment for several 5212 instances of a device, the PCI vendor, 5213 device, subvendor, and subdevice may be 5214 specified, e.g., 12@pci:8086:9c22:103c:198f 5215 for 4096-byte alignment. 5216 ecrc= Enable/disable PCIe ECRC (transaction layer 5217 end-to-end CRC checking). Only effective if 5218 OS has native AER control (either granted by 5219 ACPI _OSC or forced via "pcie_ports=native") 5220 bios: Use BIOS/firmware settings. This is the 5221 the default. 5222 off: Turn ECRC off 5223 on: Turn ECRC on. 5224 hpiosize=nn[KMG] The fixed amount of bus space which is 5225 reserved for hotplug bridge's IO window. 5226 Default size is 256 bytes. 5227 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5228 reserved for hotplug bridge's MMIO window. 5229 Default size is 2 megabytes. 5230 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5231 reserved for hotplug bridge's MMIO_PREF window. 5232 Default size is 2 megabytes. 5233 hpmemsize=nn[KMG] The fixed amount of bus space which is 5234 reserved for hotplug bridge's MMIO and 5235 MMIO_PREF window. 5236 Default size is 2 megabytes. 5237 hpbussize=nn The minimum amount of additional bus numbers 5238 reserved for buses below a hotplug bridge. 5239 Default is 1. 5240 realloc= Enable/disable reallocating PCI bridge resources 5241 if allocations done by BIOS are too small to 5242 accommodate resources required by all child 5243 devices. 5244 off: Turn realloc off 5245 on: Turn realloc on 5246 realloc same as realloc=on 5247 noari do not use PCIe ARI. 5248 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5249 do not use PCIe ATS (and IOMMU device IOTLB). 5250 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5251 only look for one device below a PCIe downstream 5252 port. 5253 big_root_window Try to add a big 64bit memory window to the PCIe 5254 root complex on AMD CPUs. Some GFX hardware 5255 can resize a BAR to allow access to all VRAM. 5256 Adding the window is slightly risky (it may 5257 conflict with unreported devices), so this 5258 taints the kernel. 5259 disable_acs_redir=<pci_dev>[; ...] 5260 Specify one or more PCI devices (in the format 5261 specified above) separated by semicolons. 5262 Each device specified will have the PCI ACS 5263 redirect capabilities forced off which will 5264 allow P2P traffic between devices through 5265 bridges without forcing it upstream. Note: 5266 this removes isolation between devices and 5267 may put more devices in an IOMMU group. 5268 config_acs= 5269 Format: 5270 <ACS flags>@<pci_dev>[; ...] 5271 Specify one or more PCI devices (in the format 5272 specified above) optionally prepended with flags 5273 and separated by semicolons. The respective 5274 capabilities will be enabled, disabled or 5275 unchanged based on what is specified in 5276 flags. 5277 5278 ACS Flags is defined as follows: 5279 bit-0 : ACS Source Validation 5280 bit-1 : ACS Translation Blocking 5281 bit-2 : ACS P2P Request Redirect 5282 bit-3 : ACS P2P Completion Redirect 5283 bit-4 : ACS Upstream Forwarding 5284 bit-5 : ACS P2P Egress Control 5285 bit-6 : ACS Direct Translated P2P 5286 Each bit can be marked as: 5287 '0' – force disabled 5288 '1' – force enabled 5289 'x' – unchanged 5290 For example, 5291 pci=config_acs=10x@pci:0:0 5292 would configure all devices that support 5293 ACS to enable P2P Request Redirect, disable 5294 Translation Blocking, and leave Source 5295 Validation unchanged from whatever power-up 5296 or firmware set it to. 5297 5298 Note: this may remove isolation between devices 5299 and may put more devices in an IOMMU group. 5300 force_floating [S390] Force usage of floating interrupts. 5301 nomio [S390] Do not use MIO instructions. 5302 norid [S390] ignore the RID field and force use of 5303 one PCI domain per PCI function 5304 notph [PCIE] If the PCIE_TPH kernel config parameter 5305 is enabled, this kernel boot option can be used 5306 to disable PCIe TLP Processing Hints support 5307 system-wide. 5308 5309 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5310 Management. 5311 off Don't touch ASPM configuration at all. Leave any 5312 configuration done by firmware unchanged. 5313 force Enable ASPM even on devices that claim not to support it. 5314 WARNING: Forcing ASPM on may cause system lockups. 5315 5316 pcie_ports= [PCIE] PCIe port services handling: 5317 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5318 even if the platform doesn't give the OS permission to 5319 use them. This may cause conflicts if the platform 5320 also tries to use these services. 5321 dpc-native Use native PCIe service for DPC only. May 5322 cause conflicts if firmware uses AER or DPC. 5323 compat Disable native PCIe services (PME, AER, DPC, PCIe 5324 hotplug). 5325 5326 pcie_port_pm= [PCIE] PCIe port power management handling: 5327 off Disable power management of all PCIe ports 5328 force Forcibly enable power management of all PCIe ports 5329 5330 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5331 nomsi Do not use MSI for native PCIe PME signaling (this makes 5332 all PCIe root ports use INTx for all services). 5333 5334 pcmv= [HW,PCMCIA] BadgePAD 4 5335 5336 pd_ignore_unused 5337 [PM] 5338 Keep all power-domains already enabled by bootloader on, 5339 even if no driver has claimed them. This is useful 5340 for debug and development, but should not be 5341 needed on a platform with proper driver support. 5342 5343 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5344 boot time. 5345 Format: { 0 | 1 } 5346 See arch/parisc/kernel/pdc_chassis.c 5347 5348 percpu_alloc= [MM,EARLY] 5349 Select which percpu first chunk allocator to use. 5350 Currently supported values are "embed" and "page". 5351 Archs may support subset or none of the selections. 5352 See comments in mm/percpu.c for details on each 5353 allocator. This parameter is primarily for debugging 5354 and performance comparison. 5355 5356 pirq= [SMP,APIC] Manual mp-table setup 5357 See Documentation/arch/x86/i386/IO-APIC.rst. 5358 5359 plip= [PPT,NET] Parallel port network link 5360 Format: { parport<nr> | timid | 0 } 5361 See also Documentation/admin-guide/parport.rst. 5362 5363 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5364 Override pmtimer IOPort with a hex value. 5365 e.g. pmtmr=0x508 5366 5367 pmu_override= [PPC] Override the PMU. 5368 This option takes over the PMU facility, so it is no 5369 longer usable by perf. Setting this option starts the 5370 PMU counters by setting MMCR0 to 0 (the FC bit is 5371 cleared). If a number is given, then MMCR1 is set to 5372 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5373 remains 0. 5374 5375 pm_async= [PM] 5376 Format: off 5377 This parameter sets the initial value of the 5378 /sys/power/pm_async sysfs knob at boot time. 5379 If set to "off", disables asynchronous suspend and 5380 resume of devices during system-wide power transitions. 5381 This can be useful on platforms where device 5382 dependencies are not well-defined, or for debugging 5383 power management issues. Asynchronous operations are 5384 enabled by default. 5385 5386 5387 pm_debug_messages [SUSPEND,KNL] 5388 Enable suspend/resume debug messages during boot up. 5389 5390 pnp.debug=1 [PNP] 5391 Enable PNP debug messages (depends on the 5392 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5393 via /sys/module/pnp/parameters/debug. We always show 5394 current resource usage; turning this on also shows 5395 possible settings and some assignment information. 5396 5397 pnpacpi= [ACPI] 5398 { off } 5399 5400 pnpbios= [ISAPNP] 5401 { on | off | curr | res | no-curr | no-res } 5402 5403 pnp_reserve_irq= 5404 [ISAPNP] Exclude IRQs for the autoconfiguration 5405 5406 pnp_reserve_dma= 5407 [ISAPNP] Exclude DMAs for the autoconfiguration 5408 5409 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5410 Ranges are in pairs (I/O port base and size). 5411 5412 pnp_reserve_mem= 5413 [ISAPNP] Exclude memory regions for the 5414 autoconfiguration. 5415 Ranges are in pairs (memory base and size). 5416 5417 ports= [IP_VS_FTP] IPVS ftp helper module 5418 Default is 21. 5419 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5420 may be specified. 5421 Format: <port>,<port>.... 5422 5423 possible_cpus= [SMP,S390,X86] 5424 Format: <unsigned int> 5425 Set the number of possible CPUs, overriding the 5426 regular discovery mechanisms (such as ACPI/FW, etc). 5427 5428 powersave=off [PPC] This option disables power saving features. 5429 It specifically disables cpuidle and sets the 5430 platform machine description specific power_save 5431 function to NULL. On Idle the CPU just reduces 5432 execution priority. 5433 5434 ppc_strict_facility_enable 5435 [PPC,ENABLE] This option catches any kernel floating point, 5436 Altivec, VSX and SPE outside of regions specifically 5437 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5438 There is some performance impact when enabling this. 5439 5440 ppc_tm= [PPC,EARLY] 5441 Format: {"off"} 5442 Disable Hardware Transactional Memory 5443 5444 preempt= [KNL] 5445 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5446 none - Limited to cond_resched() calls 5447 voluntary - Limited to cond_resched() and might_sleep() calls 5448 full - Any section that isn't explicitly preempt disabled 5449 can be preempted anytime. Tasks will also yield 5450 contended spinlocks (if the critical section isn't 5451 explicitly preempt disabled beyond the lock itself). 5452 lazy - Scheduler controlled. Similar to full but instead 5453 of preempting the task immediately, the task gets 5454 one HZ tick time to yield itself before the 5455 preemption will be forced. One preemption is when the 5456 task returns to user space. 5457 5458 print-fatal-signals= 5459 [KNL] debug: print fatal signals 5460 5461 If enabled, warn about various signal handling 5462 related application anomalies: too many signals, 5463 too many POSIX.1 timers, fatal signals causing a 5464 coredump - etc. 5465 5466 If you hit the warning due to signal overflow, 5467 you might want to try "ulimit -i unlimited". 5468 5469 default: off. 5470 5471 printk.always_kmsg_dump= 5472 Trigger kmsg_dump for cases other than kernel oops or 5473 panics 5474 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5475 default: disabled 5476 5477 printk.console_no_auto_verbose= 5478 Disable console loglevel raise on oops, panic 5479 or lockdep-detected issues (only if lock debug is on). 5480 With an exception to setups with low baudrate on 5481 serial console, keeping this 0 is a good choice 5482 in order to provide more debug information. 5483 Format: <bool> 5484 default: 0 (auto_verbose is enabled) 5485 5486 printk.debug_non_panic_cpus= 5487 Allows storing messages from non-panic CPUs into 5488 the printk log buffer during panic(). They are 5489 flushed to consoles by the panic-CPU on 5490 a best-effort basis. 5491 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5492 Default: disabled 5493 5494 printk.devkmsg={on,off,ratelimit} 5495 Control writing to /dev/kmsg. 5496 on - unlimited logging to /dev/kmsg from userspace 5497 off - logging to /dev/kmsg disabled 5498 ratelimit - ratelimit the logging 5499 Default: ratelimit 5500 5501 printk.time= Show timing data prefixed to each printk message line 5502 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5503 5504 proc_mem.force_override= [KNL] 5505 Format: {always | ptrace | never} 5506 Traditionally /proc/pid/mem allows memory permissions to be 5507 overridden without restrictions. This option may be set to 5508 restrict that. Can be one of: 5509 - 'always': traditional behavior always allows mem overrides. 5510 - 'ptrace': only allow mem overrides for active ptracers. 5511 - 'never': never allow mem overrides. 5512 If not specified, default is the CONFIG_PROC_MEM_* choice. 5513 5514 processor.max_cstate= [HW,ACPI] 5515 Limit processor to maximum C-state 5516 max_cstate=9 overrides any DMI blacklist limit. 5517 5518 processor.nocst [HW,ACPI] 5519 Ignore the _CST method to determine C-states, 5520 instead using the legacy FADT method 5521 5522 profile= [KNL] Enable kernel profiling via /proc/profile 5523 Format: [<profiletype>,]<number> 5524 Param: <profiletype>: "schedule" or "kvm" 5525 [defaults to kernel profiling] 5526 Param: "schedule" - profile schedule points. 5527 Param: "kvm" - profile VM exits. 5528 Param: <number> - step/bucket size as a power of 2 for 5529 statistical time based profiling. 5530 5531 prot_virt= [S390] enable hosting protected virtual machines 5532 isolated from the hypervisor (if hardware supports 5533 that). If enabled, the default kernel base address 5534 might be overridden even when Kernel Address Space 5535 Layout Randomization is disabled. 5536 Format: <bool> 5537 5538 psi= [KNL] Enable or disable pressure stall information 5539 tracking. 5540 Format: <bool> 5541 5542 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5543 probe for; one of (bare|imps|exps|lifebook|any). 5544 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5545 per second. 5546 psmouse.resetafter= [HW,MOUSE] 5547 Try to reset the device after so many bad packets 5548 (0 = never). 5549 psmouse.resolution= 5550 [HW,MOUSE] Set desired mouse resolution, in dpi. 5551 psmouse.smartscroll= 5552 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5553 0 = disabled, 1 = enabled (default). 5554 5555 pstore.backend= Specify the name of the pstore backend to use 5556 5557 pti= [X86-64] Control Page Table Isolation of user and 5558 kernel address spaces. Disabling this feature 5559 removes hardening, but improves performance of 5560 system calls and interrupts. 5561 5562 on - unconditionally enable 5563 off - unconditionally disable 5564 auto - kernel detects whether your CPU model is 5565 vulnerable to issues that PTI mitigates 5566 5567 Not specifying this option is equivalent to pti=auto. 5568 5569 pty.legacy_count= 5570 [KNL] Number of legacy pty's. Overwrites compiled-in 5571 default number. 5572 5573 quiet [KNL,EARLY] Disable most log messages 5574 5575 r128= [HW,DRM] 5576 5577 radix_hcall_invalidate=on [PPC/PSERIES] 5578 Disable RADIX GTSE feature and use hcall for TLB 5579 invalidate. 5580 5581 raid= [HW,RAID] 5582 See Documentation/admin-guide/md.rst. 5583 5584 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5585 See Documentation/admin-guide/blockdev/ramdisk.rst. 5586 5587 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5588 5589 random.trust_cpu=off 5590 [KNL,EARLY] Disable trusting the use of the CPU's 5591 random number generator (if available) to 5592 initialize the kernel's RNG. 5593 5594 random.trust_bootloader=off 5595 [KNL,EARLY] Disable trusting the use of the a seed 5596 passed by the bootloader (if available) to 5597 initialize the kernel's RNG. 5598 5599 randomize_kstack_offset= 5600 [KNL,EARLY] Enable or disable kernel stack offset 5601 randomization, which provides roughly 5 bits of 5602 entropy, frustrating memory corruption attacks 5603 that depend on stack address determinism or 5604 cross-syscall address exposures. This is only 5605 available on architectures that have defined 5606 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5607 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5608 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5609 5610 ras=option[,option,...] [KNL] RAS-specific options 5611 5612 cec_disable [X86] 5613 Disable the Correctable Errors Collector, 5614 see CONFIG_RAS_CEC help text. 5615 5616 rcu_nocbs[=cpu-list] 5617 [KNL] The optional argument is a cpu list, 5618 as described above. 5619 5620 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5621 enable the no-callback CPU mode, which prevents 5622 such CPUs' callbacks from being invoked in 5623 softirq context. Invocation of such CPUs' RCU 5624 callbacks will instead be offloaded to "rcuox/N" 5625 kthreads created for that purpose, where "x" is 5626 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5627 for the kthreads that mediate grace periods; and 5628 "N" is the CPU number. This reduces OS jitter on 5629 the offloaded CPUs, which can be useful for HPC 5630 and real-time workloads. It can also improve 5631 energy efficiency for asymmetric multiprocessors. 5632 5633 If a cpulist is passed as an argument, the specified 5634 list of CPUs is set to no-callback mode from boot. 5635 5636 Otherwise, if the '=' sign and the cpulist 5637 arguments are omitted, no CPU will be set to 5638 no-callback mode from boot but the mode may be 5639 toggled at runtime via cpusets. 5640 5641 Note that this argument takes precedence over 5642 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5643 5644 rcu_nocb_poll [KNL] 5645 Rather than requiring that offloaded CPUs 5646 (specified by rcu_nocbs= above) explicitly 5647 awaken the corresponding "rcuoN" kthreads, 5648 make these kthreads poll for callbacks. 5649 This improves the real-time response for the 5650 offloaded CPUs by relieving them of the need to 5651 wake up the corresponding kthread, but degrades 5652 energy efficiency by requiring that the kthreads 5653 periodically wake up to do the polling. 5654 5655 rcutree.blimit= [KNL] 5656 Set maximum number of finished RCU callbacks to 5657 process in one batch. 5658 5659 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5660 Do only a one-line RCU CPU stall warning when 5661 there is an ongoing too-long CSD-lock wait. 5662 5663 rcutree.do_rcu_barrier= [KNL] 5664 Request a call to rcu_barrier(). This is 5665 throttled so that userspace tests can safely 5666 hammer on the sysfs variable if they so choose. 5667 If triggered before the RCU grace-period machinery 5668 is fully active, this will error out with EAGAIN. 5669 5670 rcutree.dump_tree= [KNL] 5671 Dump the structure of the rcu_node combining tree 5672 out at early boot. This is used for diagnostic 5673 purposes, to verify correct tree setup. 5674 5675 rcutree.gp_cleanup_delay= [KNL] 5676 Set the number of jiffies to delay each step of 5677 RCU grace-period cleanup. 5678 5679 rcutree.gp_init_delay= [KNL] 5680 Set the number of jiffies to delay each step of 5681 RCU grace-period initialization. 5682 5683 rcutree.gp_preinit_delay= [KNL] 5684 Set the number of jiffies to delay each step of 5685 RCU grace-period pre-initialization, that is, 5686 the propagation of recent CPU-hotplug changes up 5687 the rcu_node combining tree. 5688 5689 rcutree.jiffies_till_first_fqs= [KNL] 5690 Set delay from grace-period initialization to 5691 first attempt to force quiescent states. 5692 Units are jiffies, minimum value is zero, 5693 and maximum value is HZ. 5694 5695 rcutree.jiffies_till_next_fqs= [KNL] 5696 Set delay between subsequent attempts to force 5697 quiescent states. Units are jiffies, minimum 5698 value is one, and maximum value is HZ. 5699 5700 rcutree.jiffies_till_sched_qs= [KNL] 5701 Set required age in jiffies for a 5702 given grace period before RCU starts 5703 soliciting quiescent-state help from 5704 rcu_note_context_switch() and cond_resched(). 5705 If not specified, the kernel will calculate 5706 a value based on the most recent settings 5707 of rcutree.jiffies_till_first_fqs 5708 and rcutree.jiffies_till_next_fqs. 5709 This calculated value may be viewed in 5710 rcutree.jiffies_to_sched_qs. Any attempt to set 5711 rcutree.jiffies_to_sched_qs will be cheerfully 5712 overwritten. 5713 5714 rcutree.kthread_prio= [KNL,BOOT] 5715 Set the SCHED_FIFO priority of the RCU per-CPU 5716 kthreads (rcuc/N). This value is also used for 5717 the priority of the RCU boost threads (rcub/N) 5718 and for the RCU grace-period kthreads (rcu_bh, 5719 rcu_preempt, and rcu_sched). If RCU_BOOST is 5720 set, valid values are 1-99 and the default is 1 5721 (the least-favored priority). Otherwise, when 5722 RCU_BOOST is not set, valid values are 0-99 and 5723 the default is zero (non-realtime operation). 5724 When RCU_NOCB_CPU is set, also adjust the 5725 priority of NOCB callback kthreads. 5726 5727 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5728 On callback-offloaded (rcu_nocbs) CPUs, 5729 RCU reduces the lock contention that would 5730 otherwise be caused by callback floods through 5731 use of the ->nocb_bypass list. However, in the 5732 common non-flooded case, RCU queues directly to 5733 the main ->cblist in order to avoid the extra 5734 overhead of the ->nocb_bypass list and its lock. 5735 But if there are too many callbacks queued during 5736 a single jiffy, RCU pre-queues the callbacks into 5737 the ->nocb_bypass queue. The definition of "too 5738 many" is supplied by this kernel boot parameter. 5739 5740 rcutree.nohz_full_patience_delay= [KNL] 5741 On callback-offloaded (rcu_nocbs) CPUs, avoid 5742 disturbing RCU unless the grace period has 5743 reached the specified age in milliseconds. 5744 Defaults to zero. Large values will be capped 5745 at five seconds. All values will be rounded down 5746 to the nearest value representable by jiffies. 5747 5748 rcutree.qhimark= [KNL] 5749 Set threshold of queued RCU callbacks beyond which 5750 batch limiting is disabled. 5751 5752 rcutree.qlowmark= [KNL] 5753 Set threshold of queued RCU callbacks below which 5754 batch limiting is re-enabled. 5755 5756 rcutree.qovld= [KNL] 5757 Set threshold of queued RCU callbacks beyond which 5758 RCU's force-quiescent-state scan will aggressively 5759 enlist help from cond_resched() and sched IPIs to 5760 help CPUs more quickly reach quiescent states. 5761 Set to less than zero to make this be set based 5762 on rcutree.qhimark at boot time and to zero to 5763 disable more aggressive help enlistment. 5764 5765 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5766 Set the page-cache refill delay (in milliseconds) 5767 in response to low-memory conditions. The range 5768 of permitted values is in the range 0:100000. 5769 5770 rcutree.rcu_divisor= [KNL] 5771 Set the shift-right count to use to compute 5772 the callback-invocation batch limit bl from 5773 the number of callbacks queued on this CPU. 5774 The result will be bounded below by the value of 5775 the rcutree.blimit kernel parameter. Every bl 5776 callbacks, the softirq handler will exit in 5777 order to allow the CPU to do other work. 5778 5779 Please note that this callback-invocation batch 5780 limit applies only to non-offloaded callback 5781 invocation. Offloaded callbacks are instead 5782 invoked in the context of an rcuoc kthread, which 5783 scheduler will preempt as it does any other task. 5784 5785 rcutree.rcu_fanout_exact= [KNL] 5786 Disable autobalancing of the rcu_node combining 5787 tree. This is used by rcutorture, and might 5788 possibly be useful for architectures having high 5789 cache-to-cache transfer latencies. 5790 5791 rcutree.rcu_fanout_leaf= [KNL] 5792 Change the number of CPUs assigned to each 5793 leaf rcu_node structure. Useful for very 5794 large systems, which will choose the value 64, 5795 and for NUMA systems with large remote-access 5796 latencies, which will choose a value aligned 5797 with the appropriate hardware boundaries. 5798 5799 rcutree.rcu_min_cached_objs= [KNL] 5800 Minimum number of objects which are cached and 5801 maintained per one CPU. Object size is equal 5802 to PAGE_SIZE. The cache allows to reduce the 5803 pressure to page allocator, also it makes the 5804 whole algorithm to behave better in low memory 5805 condition. 5806 5807 rcutree.rcu_nocb_gp_stride= [KNL] 5808 Set the number of NOCB callback kthreads in 5809 each group, which defaults to the square root 5810 of the number of CPUs. Larger numbers reduce 5811 the wakeup overhead on the global grace-period 5812 kthread, but increases that same overhead on 5813 each group's NOCB grace-period kthread. 5814 5815 rcutree.rcu_kick_kthreads= [KNL] 5816 Cause the grace-period kthread to get an extra 5817 wake_up() if it sleeps three times longer than 5818 it should at force-quiescent-state time. 5819 This wake_up() will be accompanied by a 5820 WARN_ONCE() splat and an ftrace_dump(). 5821 5822 rcutree.rcu_resched_ns= [KNL] 5823 Limit the time spend invoking a batch of RCU 5824 callbacks to the specified number of nanoseconds. 5825 By default, this limit is checked only once 5826 every 32 callbacks in order to limit the pain 5827 inflicted by local_clock() overhead. 5828 5829 rcutree.rcu_unlock_delay= [KNL] 5830 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5831 this specifies an rcu_read_unlock()-time delay 5832 in microseconds. This defaults to zero. 5833 Larger delays increase the probability of 5834 catching RCU pointer leaks, that is, buggy use 5835 of RCU-protected pointers after the relevant 5836 rcu_read_unlock() has completed. 5837 5838 rcutree.sysrq_rcu= [KNL] 5839 Commandeer a sysrq key to dump out Tree RCU's 5840 rcu_node tree with an eye towards determining 5841 why a new grace period has not yet started. 5842 5843 rcutree.use_softirq= [KNL] 5844 If set to zero, move all RCU_SOFTIRQ processing to 5845 per-CPU rcuc kthreads. Defaults to a non-zero 5846 value, meaning that RCU_SOFTIRQ is used by default. 5847 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5848 5849 But note that CONFIG_PREEMPT_RT=y kernels disable 5850 this kernel boot parameter, forcibly setting it 5851 to zero. 5852 5853 rcutree.enable_rcu_lazy= [KNL] 5854 To save power, batch RCU callbacks and flush after 5855 delay, memory pressure or callback list growing too 5856 big. 5857 5858 rcutree.rcu_normal_wake_from_gp= [KNL] 5859 Reduces a latency of synchronize_rcu() call. This approach 5860 maintains its own track of synchronize_rcu() callers, so it 5861 does not interact with regular callbacks because it does not 5862 use a call_rcu[_hurry]() path. Please note, this is for a 5863 normal grace period. 5864 5865 How to enable it: 5866 5867 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5868 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5869 5870 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5871 disabled by the boot parameter passing 0. 5872 5873 rcuscale.gp_async= [KNL] 5874 Measure performance of asynchronous 5875 grace-period primitives such as call_rcu(). 5876 5877 rcuscale.gp_async_max= [KNL] 5878 Specify the maximum number of outstanding 5879 callbacks per writer thread. When a writer 5880 thread exceeds this limit, it invokes the 5881 corresponding flavor of rcu_barrier() to allow 5882 previously posted callbacks to drain. 5883 5884 rcuscale.gp_exp= [KNL] 5885 Measure performance of expedited synchronous 5886 grace-period primitives. 5887 5888 rcuscale.holdoff= [KNL] 5889 Set test-start holdoff period. The purpose of 5890 this parameter is to delay the start of the 5891 test until boot completes in order to avoid 5892 interference. 5893 5894 rcuscale.kfree_by_call_rcu= [KNL] 5895 In kernels built with CONFIG_RCU_LAZY=y, test 5896 call_rcu() instead of kfree_rcu(). 5897 5898 rcuscale.kfree_mult= [KNL] 5899 Instead of allocating an object of size kfree_obj, 5900 allocate one of kfree_mult * sizeof(kfree_obj). 5901 Defaults to 1. 5902 5903 rcuscale.kfree_rcu_test= [KNL] 5904 Set to measure performance of kfree_rcu() flooding. 5905 5906 rcuscale.kfree_rcu_test_double= [KNL] 5907 Test the double-argument variant of kfree_rcu(). 5908 If this parameter has the same value as 5909 rcuscale.kfree_rcu_test_single, both the single- 5910 and double-argument variants are tested. 5911 5912 rcuscale.kfree_rcu_test_single= [KNL] 5913 Test the single-argument variant of kfree_rcu(). 5914 If this parameter has the same value as 5915 rcuscale.kfree_rcu_test_double, both the single- 5916 and double-argument variants are tested. 5917 5918 rcuscale.kfree_nthreads= [KNL] 5919 The number of threads running loops of kfree_rcu(). 5920 5921 rcuscale.kfree_alloc_num= [KNL] 5922 Number of allocations and frees done in an iteration. 5923 5924 rcuscale.kfree_loops= [KNL] 5925 Number of loops doing rcuscale.kfree_alloc_num number 5926 of allocations and frees. 5927 5928 rcuscale.minruntime= [KNL] 5929 Set the minimum test run time in seconds. This 5930 does not affect the data-collection interval, 5931 but instead allows better measurement of things 5932 like CPU consumption. 5933 5934 rcuscale.nreaders= [KNL] 5935 Set number of RCU readers. The value -1 selects 5936 N, where N is the number of CPUs. A value 5937 "n" less than -1 selects N-n+1, where N is again 5938 the number of CPUs. For example, -2 selects N 5939 (the number of CPUs), -3 selects N+1, and so on. 5940 A value of "n" less than or equal to -N selects 5941 a single reader. 5942 5943 rcuscale.nwriters= [KNL] 5944 Set number of RCU writers. The values operate 5945 the same as for rcuscale.nreaders. 5946 N, where N is the number of CPUs 5947 5948 rcuscale.scale_type= [KNL] 5949 Specify the RCU implementation to test. 5950 5951 rcuscale.shutdown= [KNL] 5952 Shut the system down after performance tests 5953 complete. This is useful for hands-off automated 5954 testing. 5955 5956 rcuscale.verbose= [KNL] 5957 Enable additional printk() statements. 5958 5959 rcuscale.writer_holdoff= [KNL] 5960 Write-side holdoff between grace periods, 5961 in microseconds. The default of zero says 5962 no holdoff. 5963 5964 rcuscale.writer_holdoff_jiffies= [KNL] 5965 Additional write-side holdoff between grace 5966 periods, but in jiffies. The default of zero 5967 says no holdoff. 5968 5969 rcutorture.fqs_duration= [KNL] 5970 Set duration of force_quiescent_state bursts 5971 in microseconds. 5972 5973 rcutorture.fqs_holdoff= [KNL] 5974 Set holdoff time within force_quiescent_state bursts 5975 in microseconds. 5976 5977 rcutorture.fqs_stutter= [KNL] 5978 Set wait time between force_quiescent_state bursts 5979 in seconds. 5980 5981 rcutorture.fwd_progress= [KNL] 5982 Specifies the number of kthreads to be used 5983 for RCU grace-period forward-progress testing 5984 for the types of RCU supporting this notion. 5985 Defaults to 1 kthread, values less than zero or 5986 greater than the number of CPUs cause the number 5987 of CPUs to be used. 5988 5989 rcutorture.fwd_progress_div= [KNL] 5990 Specify the fraction of a CPU-stall-warning 5991 period to do tight-loop forward-progress testing. 5992 5993 rcutorture.fwd_progress_holdoff= [KNL] 5994 Number of seconds to wait between successive 5995 forward-progress tests. 5996 5997 rcutorture.fwd_progress_need_resched= [KNL] 5998 Enclose cond_resched() calls within checks for 5999 need_resched() during tight-loop forward-progress 6000 testing. 6001 6002 rcutorture.gp_cond= [KNL] 6003 Use conditional/asynchronous update-side 6004 normal-grace-period primitives, if available. 6005 6006 rcutorture.gp_cond_exp= [KNL] 6007 Use conditional/asynchronous update-side 6008 expedited-grace-period primitives, if available. 6009 6010 rcutorture.gp_cond_full= [KNL] 6011 Use conditional/asynchronous update-side 6012 normal-grace-period primitives that also take 6013 concurrent expedited grace periods into account, 6014 if available. 6015 6016 rcutorture.gp_cond_exp_full= [KNL] 6017 Use conditional/asynchronous update-side 6018 expedited-grace-period primitives that also take 6019 concurrent normal grace periods into account, 6020 if available. 6021 6022 rcutorture.gp_cond_wi= [KNL] 6023 Nominal wait interval for normal conditional 6024 grace periods (specified by rcutorture's 6025 gp_cond and gp_cond_full module parameters), 6026 in microseconds. The actual wait interval will 6027 be randomly selected to nanosecond granularity up 6028 to this wait interval. Defaults to 16 jiffies, 6029 for example, 16,000 microseconds on a system 6030 with HZ=1000. 6031 6032 rcutorture.gp_cond_wi_exp= [KNL] 6033 Nominal wait interval for expedited conditional 6034 grace periods (specified by rcutorture's 6035 gp_cond_exp and gp_cond_exp_full module 6036 parameters), in microseconds. The actual wait 6037 interval will be randomly selected to nanosecond 6038 granularity up to this wait interval. Defaults to 6039 128 microseconds. 6040 6041 rcutorture.gp_exp= [KNL] 6042 Use expedited update-side primitives, if available. 6043 6044 rcutorture.gp_normal= [KNL] 6045 Use normal (non-expedited) asynchronous 6046 update-side primitives, if available. 6047 6048 rcutorture.gp_poll= [KNL] 6049 Use polled update-side normal-grace-period 6050 primitives, if available. 6051 6052 rcutorture.gp_poll_exp= [KNL] 6053 Use polled update-side expedited-grace-period 6054 primitives, if available. 6055 6056 rcutorture.gp_poll_full= [KNL] 6057 Use polled update-side normal-grace-period 6058 primitives that also take concurrent expedited 6059 grace periods into account, if available. 6060 6061 rcutorture.gp_poll_exp_full= [KNL] 6062 Use polled update-side expedited-grace-period 6063 primitives that also take concurrent normal 6064 grace periods into account, if available. 6065 6066 rcutorture.gp_poll_wi= [KNL] 6067 Nominal wait interval for normal conditional 6068 grace periods (specified by rcutorture's 6069 gp_poll and gp_poll_full module parameters), 6070 in microseconds. The actual wait interval will 6071 be randomly selected to nanosecond granularity up 6072 to this wait interval. Defaults to 16 jiffies, 6073 for example, 16,000 microseconds on a system 6074 with HZ=1000. 6075 6076 rcutorture.gp_poll_wi_exp= [KNL] 6077 Nominal wait interval for expedited conditional 6078 grace periods (specified by rcutorture's 6079 gp_poll_exp and gp_poll_exp_full module 6080 parameters), in microseconds. The actual wait 6081 interval will be randomly selected to nanosecond 6082 granularity up to this wait interval. Defaults to 6083 128 microseconds. 6084 6085 rcutorture.gp_sync= [KNL] 6086 Use normal (non-expedited) synchronous 6087 update-side primitives, if available. If all 6088 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6089 rcutorture.gp_normal=, and rcutorture.gp_sync= 6090 are zero, rcutorture acts as if is interpreted 6091 they are all non-zero. 6092 6093 rcutorture.gpwrap_lag= [KNL] 6094 Enable grace-period wrap lag testing. Setting 6095 to false prevents the gpwrap lag test from 6096 running. Default is true. 6097 6098 rcutorture.gpwrap_lag_gps= [KNL] 6099 Set the value for grace-period wrap lag during 6100 active lag testing periods. This controls how many 6101 grace periods differences we tolerate between 6102 rdp and rnp's gp_seq before setting overflow flag. 6103 The default is always set to 8. 6104 6105 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6106 Set the total cycle duration for gpwrap lag 6107 testing in minutes. This is the total time for 6108 one complete cycle of active and inactive 6109 testing periods. Default is 30 minutes. 6110 6111 rcutorture.gpwrap_lag_active_mins= [KNL] 6112 Set the duration for which gpwrap lag is active 6113 within each cycle, in minutes. During this time, 6114 the grace-period wrap lag will be set to the 6115 value specified by gpwrap_lag_gps. Default is 6116 5 minutes. 6117 6118 rcutorture.irqreader= [KNL] 6119 Run RCU readers from irq handlers, or, more 6120 accurately, from a timer handler. Not all RCU 6121 flavors take kindly to this sort of thing. 6122 6123 rcutorture.leakpointer= [KNL] 6124 Leak an RCU-protected pointer out of the reader. 6125 This can of course result in splats, and is 6126 intended to test the ability of things like 6127 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6128 such leaks. 6129 6130 rcutorture.n_barrier_cbs= [KNL] 6131 Set callbacks/threads for rcu_barrier() testing. 6132 6133 rcutorture.nfakewriters= [KNL] 6134 Set number of concurrent RCU writers. These just 6135 stress RCU, they don't participate in the actual 6136 test, hence the "fake". 6137 6138 rcutorture.nocbs_nthreads= [KNL] 6139 Set number of RCU callback-offload togglers. 6140 Zero (the default) disables toggling. 6141 6142 rcutorture.nocbs_toggle= [KNL] 6143 Set the delay in milliseconds between successive 6144 callback-offload toggling attempts. 6145 6146 rcutorture.nreaders= [KNL] 6147 Set number of RCU readers. The value -1 selects 6148 N-1, where N is the number of CPUs. A value 6149 "n" less than -1 selects N-n-2, where N is again 6150 the number of CPUs. For example, -2 selects N 6151 (the number of CPUs), -3 selects N+1, and so on. 6152 6153 rcutorture.object_debug= [KNL] 6154 Enable debug-object double-call_rcu() testing. 6155 6156 rcutorture.onoff_holdoff= [KNL] 6157 Set time (s) after boot for CPU-hotplug testing. 6158 6159 rcutorture.onoff_interval= [KNL] 6160 Set time (jiffies) between CPU-hotplug operations, 6161 or zero to disable CPU-hotplug testing. 6162 6163 rcutorture.preempt_duration= [KNL] 6164 Set duration (in milliseconds) of preemptions 6165 by a high-priority FIFO real-time task. Set to 6166 zero (the default) to disable. The CPUs to 6167 preempt are selected randomly from the set that 6168 are online at a given point in time. Races with 6169 CPUs going offline are ignored, with that attempt 6170 at preemption skipped. 6171 6172 rcutorture.preempt_interval= [KNL] 6173 Set interval (in milliseconds, defaulting to one 6174 second) between preemptions by a high-priority 6175 FIFO real-time task. This delay is mediated 6176 by an hrtimer and is further fuzzed to avoid 6177 inadvertent synchronizations. 6178 6179 rcutorture.read_exit_burst= [KNL] 6180 The number of times in a given read-then-exit 6181 episode that a set of read-then-exit kthreads 6182 is spawned. 6183 6184 rcutorture.read_exit_delay= [KNL] 6185 The delay, in seconds, between successive 6186 read-then-exit testing episodes. 6187 6188 rcutorture.reader_flavor= [KNL] 6189 A bit mask indicating which readers to use. 6190 If there is more than one bit set, the readers 6191 are entered from low-order bit up, and are 6192 exited in the opposite order. For SRCU, the 6193 0x1 bit is normal readers, 0x2 NMI-safe readers, 6194 and 0x4 light-weight readers. 6195 6196 rcutorture.shuffle_interval= [KNL] 6197 Set task-shuffle interval (s). Shuffling tasks 6198 allows some CPUs to go into dyntick-idle mode 6199 during the rcutorture test. 6200 6201 rcutorture.shutdown_secs= [KNL] 6202 Set time (s) after boot system shutdown. This 6203 is useful for hands-off automated testing. 6204 6205 rcutorture.stall_cpu= [KNL] 6206 Duration of CPU stall (s) to test RCU CPU stall 6207 warnings, zero to disable. 6208 6209 rcutorture.stall_cpu_block= [KNL] 6210 Sleep while stalling if set. This will result 6211 in warnings from preemptible RCU in addition to 6212 any other stall-related activity. Note that 6213 in kernels built with CONFIG_PREEMPTION=n and 6214 CONFIG_PREEMPT_COUNT=y, this parameter will 6215 cause the CPU to pass through a quiescent state. 6216 Given CONFIG_PREEMPTION=n, this will suppress 6217 RCU CPU stall warnings, but will instead result 6218 in scheduling-while-atomic splats. 6219 6220 Use of this module parameter results in splats. 6221 6222 6223 rcutorture.stall_cpu_holdoff= [KNL] 6224 Time to wait (s) after boot before inducing stall. 6225 6226 rcutorture.stall_cpu_irqsoff= [KNL] 6227 Disable interrupts while stalling if set, but only 6228 on the first stall in the set. 6229 6230 rcutorture.stall_cpu_repeat= [KNL] 6231 Number of times to repeat the stall sequence, 6232 so that rcutorture.stall_cpu_repeat=3 will result 6233 in four stall sequences. 6234 6235 rcutorture.stall_gp_kthread= [KNL] 6236 Duration (s) of forced sleep within RCU 6237 grace-period kthread to test RCU CPU stall 6238 warnings, zero to disable. If both stall_cpu 6239 and stall_gp_kthread are specified, the 6240 kthread is starved first, then the CPU. 6241 6242 rcutorture.stat_interval= [KNL] 6243 Time (s) between statistics printk()s. 6244 6245 rcutorture.stutter= [KNL] 6246 Time (s) to stutter testing, for example, specifying 6247 five seconds causes the test to run for five seconds, 6248 wait for five seconds, and so on. This tests RCU's 6249 ability to transition abruptly to and from idle. 6250 6251 rcutorture.test_boost= [KNL] 6252 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6253 "Maybe" means test if the RCU implementation 6254 under test support RCU priority boosting. 6255 6256 rcutorture.test_boost_duration= [KNL] 6257 Duration (s) of each individual boost test. 6258 6259 rcutorture.test_boost_holdoff= [KNL] 6260 Holdoff time (s) from start of test to the start 6261 of RCU priority-boost testing. Defaults to zero, 6262 that is, no holdoff. 6263 6264 rcutorture.test_boost_interval= [KNL] 6265 Interval (s) between each boost test. 6266 6267 rcutorture.test_no_idle_hz= [KNL] 6268 Test RCU's dyntick-idle handling. See also the 6269 rcutorture.shuffle_interval parameter. 6270 6271 rcutorture.torture_type= [KNL] 6272 Specify the RCU implementation to test. 6273 6274 rcutorture.verbose= [KNL] 6275 Enable additional printk() statements. 6276 6277 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6278 Dump ftrace buffer after reporting RCU CPU 6279 stall warning. 6280 6281 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6282 Provide RCU CPU stall notifiers, but see the 6283 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6284 option's help text. TL;DR: You almost certainly 6285 do not want rcupdate.rcu_cpu_stall_notifiers. 6286 6287 rcupdate.rcu_cpu_stall_suppress= [KNL] 6288 Suppress RCU CPU stall warning messages. 6289 6290 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6291 Suppress RCU CPU stall warning messages and 6292 rcutorture writer stall warnings that occur 6293 during early boot, that is, during the time 6294 before the init task is spawned. 6295 6296 rcupdate.rcu_cpu_stall_timeout= [KNL] 6297 Set timeout for RCU CPU stall warning messages. 6298 The value is in seconds and the maximum allowed 6299 value is 300 seconds. 6300 6301 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6302 Set timeout for expedited RCU CPU stall warning 6303 messages. The value is in milliseconds 6304 and the maximum allowed value is 21000 6305 milliseconds. Please note that this value is 6306 adjusted to an arch timer tick resolution. 6307 Setting this to zero causes the value from 6308 rcupdate.rcu_cpu_stall_timeout to be used (after 6309 conversion from seconds to milliseconds). 6310 6311 rcupdate.rcu_cpu_stall_cputime= [KNL] 6312 Provide statistics on the cputime and count of 6313 interrupts and tasks during the sampling period. For 6314 multiple continuous RCU stalls, all sampling periods 6315 begin at half of the first RCU stall timeout. 6316 6317 rcupdate.rcu_exp_stall_task_details= [KNL] 6318 Print stack dumps of any tasks blocking the 6319 current expedited RCU grace period during an 6320 expedited RCU CPU stall warning. 6321 6322 rcupdate.rcu_expedited= [KNL] 6323 Use expedited grace-period primitives, for 6324 example, synchronize_rcu_expedited() instead 6325 of synchronize_rcu(). This reduces latency, 6326 but can increase CPU utilization, degrade 6327 real-time latency, and degrade energy efficiency. 6328 No effect on CONFIG_TINY_RCU kernels. 6329 6330 rcupdate.rcu_normal= [KNL] 6331 Use only normal grace-period primitives, 6332 for example, synchronize_rcu() instead of 6333 synchronize_rcu_expedited(). This improves 6334 real-time latency, CPU utilization, and 6335 energy efficiency, but can expose users to 6336 increased grace-period latency. This parameter 6337 overrides rcupdate.rcu_expedited. No effect on 6338 CONFIG_TINY_RCU kernels. 6339 6340 rcupdate.rcu_normal_after_boot= [KNL] 6341 Once boot has completed (that is, after 6342 rcu_end_inkernel_boot() has been invoked), use 6343 only normal grace-period primitives. No effect 6344 on CONFIG_TINY_RCU kernels. 6345 6346 But note that CONFIG_PREEMPT_RT=y kernels enables 6347 this kernel boot parameter, forcibly setting 6348 it to the value one, that is, converting any 6349 post-boot attempt at an expedited RCU grace 6350 period to instead use normal non-expedited 6351 grace-period processing. 6352 6353 rcupdate.rcu_task_collapse_lim= [KNL] 6354 Set the maximum number of callbacks present 6355 at the beginning of a grace period that allows 6356 the RCU Tasks flavors to collapse back to using 6357 a single callback queue. This switching only 6358 occurs when rcupdate.rcu_task_enqueue_lim is 6359 set to the default value of -1. 6360 6361 rcupdate.rcu_task_contend_lim= [KNL] 6362 Set the minimum number of callback-queuing-time 6363 lock-contention events per jiffy required to 6364 cause the RCU Tasks flavors to switch to per-CPU 6365 callback queuing. This switching only occurs 6366 when rcupdate.rcu_task_enqueue_lim is set to 6367 the default value of -1. 6368 6369 rcupdate.rcu_task_enqueue_lim= [KNL] 6370 Set the number of callback queues to use for the 6371 RCU Tasks family of RCU flavors. The default 6372 of -1 allows this to be automatically (and 6373 dynamically) adjusted. This parameter is intended 6374 for use in testing. 6375 6376 rcupdate.rcu_task_lazy_lim= [KNL] 6377 Number of callbacks on a given CPU that will 6378 cancel laziness on that CPU. Use -1 to disable 6379 cancellation of laziness, but be advised that 6380 doing so increases the danger of OOM due to 6381 callback flooding. 6382 6383 rcupdate.rcu_task_stall_info= [KNL] 6384 Set initial timeout in jiffies for RCU task stall 6385 informational messages, which give some indication 6386 of the problem for those not patient enough to 6387 wait for ten minutes. Informational messages are 6388 only printed prior to the stall-warning message 6389 for a given grace period. Disable with a value 6390 less than or equal to zero. Defaults to ten 6391 seconds. A change in value does not take effect 6392 until the beginning of the next grace period. 6393 6394 rcupdate.rcu_task_stall_info_mult= [KNL] 6395 Multiplier for time interval between successive 6396 RCU task stall informational messages for a given 6397 RCU tasks grace period. This value is clamped 6398 to one through ten, inclusive. It defaults to 6399 the value three, so that the first informational 6400 message is printed 10 seconds into the grace 6401 period, the second at 40 seconds, the third at 6402 160 seconds, and then the stall warning at 600 6403 seconds would prevent a fourth at 640 seconds. 6404 6405 rcupdate.rcu_task_stall_timeout= [KNL] 6406 Set timeout in jiffies for RCU task stall 6407 warning messages. Disable with a value less 6408 than or equal to zero. Defaults to ten minutes. 6409 A change in value does not take effect until 6410 the beginning of the next grace period. 6411 6412 rcupdate.rcu_tasks_lazy_ms= [KNL] 6413 Set timeout in milliseconds RCU Tasks asynchronous 6414 callback batching for call_rcu_tasks(). 6415 A negative value will take the default. A value 6416 of zero will disable batching. Batching is 6417 always disabled for synchronize_rcu_tasks(). 6418 6419 rcupdate.rcu_self_test= [KNL] 6420 Run the RCU early boot self tests 6421 6422 rdinit= [KNL] 6423 Format: <full_path> 6424 Run specified binary instead of /init from the ramdisk, 6425 used for early userspace startup. See initrd. 6426 6427 rdrand= [X86,EARLY] 6428 force - Override the decision by the kernel to hide the 6429 advertisement of RDRAND support (this affects 6430 certain AMD processors because of buggy BIOS 6431 support, specifically around the suspend/resume 6432 path). 6433 6434 rdt= [HW,X86,RDT] 6435 Turn on/off individual RDT features. List is: 6436 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6437 mba, smba, bmec, abmc, sdciae, energy[:guid], 6438 perf[:guid]. 6439 E.g. to turn on cmt and turn off mba use: 6440 rdt=cmt,!mba 6441 To turn off all energy telemetry monitoring and ensure that 6442 perf telemetry monitoring associated with guid 0x12345 6443 is enabled use: 6444 rdt=!energy,perf:0x12345 6445 6446 reboot= [KNL] 6447 Format (x86 or x86_64): 6448 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6449 [[,]s[mp]#### \ 6450 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6451 [[,]f[orce] 6452 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6453 (prefix with 'panic_' to set mode for panic 6454 reboot only), 6455 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6456 reboot_force is either force or not specified, 6457 reboot_cpu is s[mp]#### with #### being the processor 6458 to be used for rebooting. 6459 6460 acpi 6461 Use the ACPI RESET_REG in the FADT. If ACPI is not 6462 configured or the ACPI reset does not work, the reboot 6463 path attempts the reset using the keyboard controller. 6464 6465 bios 6466 Use the CPU reboot vector for warm reset 6467 6468 cold 6469 Set the cold reboot flag 6470 6471 default 6472 There are some built-in platform specific "quirks" 6473 - you may see: "reboot: <name> series board detected. 6474 Selecting <type> for reboots." In the case where you 6475 think the quirk is in error (e.g. you have newer BIOS, 6476 or newer board) using this option will ignore the 6477 built-in quirk table, and use the generic default 6478 reboot actions. 6479 6480 efi 6481 Use efi reset_system runtime service. If EFI is not 6482 configured or the EFI reset does not work, the reboot 6483 path attempts the reset using the keyboard controller. 6484 6485 force 6486 Don't stop other CPUs on reboot. This can make reboot 6487 more reliable in some cases. 6488 6489 kbd 6490 Use the keyboard controller. cold reset (default) 6491 6492 pci 6493 Use a write to the PCI config space register 0xcf9 to 6494 trigger reboot. 6495 6496 triple 6497 Force a triple fault (init) 6498 6499 warm 6500 Don't set the cold reboot flag 6501 6502 Using warm reset will be much faster especially on big 6503 memory systems because the BIOS will not go through 6504 the memory check. Disadvantage is that not all 6505 hardware will be completely reinitialized on reboot so 6506 there may be boot problems on some systems. 6507 6508 6509 refscale.holdoff= [KNL] 6510 Set test-start holdoff period. The purpose of 6511 this parameter is to delay the start of the 6512 test until boot completes in order to avoid 6513 interference. 6514 6515 refscale.lookup_instances= [KNL] 6516 Number of data elements to use for the forms of 6517 SLAB_TYPESAFE_BY_RCU testing. A negative number 6518 is negated and multiplied by nr_cpu_ids, while 6519 zero specifies nr_cpu_ids. 6520 6521 refscale.loops= [KNL] 6522 Set the number of loops over the synchronization 6523 primitive under test. Increasing this number 6524 reduces noise due to loop start/end overhead, 6525 but the default has already reduced the per-pass 6526 noise to a handful of picoseconds on ca. 2020 6527 x86 laptops. 6528 6529 refscale.nreaders= [KNL] 6530 Set number of readers. The default value of -1 6531 selects N, where N is roughly 75% of the number 6532 of CPUs. A value of zero is an interesting choice. 6533 6534 refscale.nruns= [KNL] 6535 Set number of runs, each of which is dumped onto 6536 the console log. 6537 6538 refscale.readdelay= [KNL] 6539 Set the read-side critical-section duration, 6540 measured in microseconds. 6541 6542 refscale.scale_type= [KNL] 6543 Specify the read-protection implementation to test. 6544 6545 refscale.shutdown= [KNL] 6546 Shut down the system at the end of the performance 6547 test. This defaults to 1 (shut it down) when 6548 refscale is built into the kernel and to 0 (leave 6549 it running) when refscale is built as a module. 6550 6551 refscale.verbose= [KNL] 6552 Enable additional printk() statements. 6553 6554 refscale.verbose_batched= [KNL] 6555 Batch the additional printk() statements. If zero 6556 (the default) or negative, print everything. Otherwise, 6557 print every Nth verbose statement, where N is the value 6558 specified. 6559 6560 regulator_ignore_unused 6561 [REGULATOR] 6562 Prevents regulator framework from disabling regulators 6563 that are unused, due no driver claiming them. This may 6564 be useful for debug and development, but should not be 6565 needed on a platform with proper driver support. 6566 6567 relax_domain_level= 6568 [KNL, SMP] Set scheduler's default relax_domain_level. 6569 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6570 6571 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6572 Format: <base1>,<size1>[,<base2>,<size2>,...] 6573 Reserve I/O ports or memory so the kernel won't use 6574 them. If <base> is less than 0x10000, the region 6575 is assumed to be I/O ports; otherwise it is memory. 6576 6577 reserve_mem= [RAM] 6578 Format: nn[KMG]:<align>:<label> 6579 Reserve physical memory and label it with a name that 6580 other subsystems can use to access it. This is typically 6581 used for systems that do not wipe the RAM, and this command 6582 line will try to reserve the same physical memory on 6583 soft reboots. Note, it is not guaranteed to be the same 6584 location. For example, if anything about the system changes 6585 or if booting a different kernel. It can also fail if KASLR 6586 places the kernel at the location of where the RAM reservation 6587 was from a previous boot, the new reservation will be at a 6588 different location. 6589 Any subsystem using this feature must add a way to verify 6590 that the contents of the physical memory is from a previous 6591 boot, as there may be cases where the memory will not be 6592 located at the same location. 6593 6594 The format is size:align:label for example, to request 6595 12 megabytes of 4096 alignment for ramoops: 6596 6597 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6598 6599 reservetop= [X86-32,EARLY] 6600 Format: nn[KMG] 6601 Reserves a hole at the top of the kernel virtual 6602 address space. 6603 6604 reset_devices [KNL] Force drivers to reset the underlying device 6605 during initialization. 6606 6607 resume= [SWSUSP] 6608 Specify the partition device for software suspend 6609 Format: 6610 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6611 6612 resume_offset= [SWSUSP] 6613 Specify the offset from the beginning of the partition 6614 given by "resume=" at which the swap header is located, 6615 in <PAGE_SIZE> units (needed only for swap files). 6616 See Documentation/power/swsusp-and-swap-files.rst 6617 6618 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6619 read the resume files 6620 6621 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6622 Useful for devices that are detected asynchronously 6623 (e.g. USB and MMC devices). 6624 6625 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6626 be accessible via /sys/firmware/initrd. 6627 6628 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6629 Speculative Code Execution with Return Instructions) 6630 vulnerability. 6631 6632 AMD-based UNRET and IBPB mitigations alone do not stop 6633 sibling threads from influencing the predictions of other 6634 sibling threads. For that reason, STIBP is used on pro- 6635 cessors that support it, and mitigate SMT on processors 6636 that don't. 6637 6638 off - no mitigation 6639 auto - automatically select a mitigation 6640 auto,nosmt - automatically select a mitigation, 6641 disabling SMT if necessary for 6642 the full mitigation (only on Zen1 6643 and older without STIBP). 6644 ibpb - On AMD, mitigate short speculation 6645 windows on basic block boundaries too. 6646 Safe, highest perf impact. It also 6647 enables STIBP if present. Not suitable 6648 on Intel. 6649 ibpb,nosmt - Like "ibpb" above but will disable SMT 6650 when STIBP is not available. This is 6651 the alternative for systems which do not 6652 have STIBP. 6653 unret - Force enable untrained return thunks, 6654 only effective on AMD f15h-f17h based 6655 systems. 6656 unret,nosmt - Like unret, but will disable SMT when STIBP 6657 is not available. This is the alternative for 6658 systems which do not have STIBP. 6659 6660 Selecting 'auto' will choose a mitigation method at run 6661 time according to the CPU. 6662 6663 Not specifying this option is equivalent to retbleed=auto. 6664 6665 rfkill.default_state= 6666 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6667 etc. communication is blocked by default. 6668 1 Unblocked. 6669 6670 rfkill.master_switch_mode= 6671 0 The "airplane mode" button does nothing. 6672 1 The "airplane mode" button toggles between everything 6673 blocked and the previous configuration. 6674 2 The "airplane mode" button toggles between everything 6675 blocked and everything unblocked. 6676 6677 ring3mwait=disable 6678 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6679 CPUs. 6680 6681 riscv_isa_fallback [RISCV,EARLY] 6682 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6683 falling back to detecting extension support by parsing 6684 "riscv,isa" property on devicetree systems when the 6685 replacement properties are not found. See the Kconfig 6686 entry for RISCV_ISA_FALLBACK. 6687 6688 riscv_nousercfi= 6689 all Disable user CFI ABI to userspace even if cpu extension 6690 are available. 6691 bcfi Disable user backward CFI ABI to userspace even if 6692 the shadow stack extension is available. 6693 fcfi Disable user forward CFI ABI to userspace even if the 6694 landing pad extension is available. 6695 6696 ro [KNL] Mount root device read-only on boot 6697 6698 rodata= [KNL,EARLY] 6699 on Mark read-only kernel memory as read-only (default). 6700 off Leave read-only kernel memory writable for debugging. 6701 noalias Mark read-only kernel memory as read-only but retain 6702 writable aliases in the direct map for regions outside 6703 of the kernel image. [arm64] 6704 6705 rockchip.usb_uart 6706 [EARLY] 6707 Enable the uart passthrough on the designated usb port 6708 on Rockchip SoCs. When active, the signals of the 6709 debug-uart get routed to the D+ and D- pins of the usb 6710 port and the regular usb controller gets disabled. 6711 6712 root= [KNL] Root filesystem 6713 Usually this is a block device specifier of some kind, 6714 see the early_lookup_bdev comment in 6715 block/early-lookup.c for details. 6716 Alternatively this can be "ram" for the legacy initial 6717 ramdisk, "nfs" and "cifs" for root on a network file 6718 system, or "mtd" and "ubi" for mounting from raw flash. 6719 6720 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6721 mount the root filesystem 6722 6723 rootflags= [KNL] Set root filesystem mount option string 6724 6725 rseq_slice_ext= [KNL] RSEQ based time slice extension 6726 Format: boolean 6727 Control enablement of RSEQ based time slice extension. 6728 Default is 'on'. 6729 6730 initramfs_options= [KNL] 6731 Specify mount options for the initramfs mount. 6732 6733 rootfstype= [KNL] Set root filesystem type 6734 6735 rootwait [KNL] Wait (indefinitely) for root device to show up. 6736 Useful for devices that are detected asynchronously 6737 (e.g. USB and MMC devices). 6738 6739 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6740 to show up before attempting to mount the root 6741 filesystem. 6742 6743 rproc_mem=nn[KMG][@address] 6744 [KNL,ARM,CMA] Remoteproc physical memory block. 6745 Memory area to be used by remote processor image, 6746 managed by CMA. 6747 6748 rseq_debug= [KNL] Enable or disable restartable sequence 6749 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6750 Format: <bool> 6751 6752 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6753 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6754 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6755 Format: <bool> 6756 6757 rw [KNL] Mount root device read-write on boot 6758 6759 S [KNL] Run init in single mode 6760 6761 s390_iommu= [HW,S390] 6762 Set s390 IOTLB flushing mode 6763 strict 6764 With strict flushing every unmap operation will result 6765 in an IOTLB flush. Default is lazy flushing before 6766 reuse, which is faster. Deprecated, equivalent to 6767 iommu.strict=1. 6768 6769 s390_iommu_aperture= [KNL,S390] 6770 Specifies the size of the per device DMA address space 6771 accessible through the DMA and IOMMU APIs as a decimal 6772 factor of the size of main memory. 6773 The default is 1 meaning that one can concurrently use 6774 as many DMA addresses as physical memory is installed, 6775 if supported by hardware, and thus map all of memory 6776 once. With a value of 2 one can map all of memory twice 6777 and so on. As a special case a factor of 0 imposes no 6778 restrictions other than those given by hardware at the 6779 cost of significant additional memory use for tables. 6780 6781 sa1100ir [NET] 6782 See drivers/net/irda/sa1100_ir.c. 6783 6784 sched_proxy_exec= [KNL] 6785 Enables or disables "proxy execution" style 6786 solution to mutex-based priority inversion. 6787 Format: <bool> 6788 6789 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6790 6791 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6792 Allowed values are enable and disable. This feature 6793 incurs a small amount of overhead in the scheduler 6794 but is useful for debugging and performance tuning. 6795 6796 sched_thermal_decay_shift= 6797 [Deprecated] 6798 [KNL, SMP] Set a decay shift for scheduler thermal 6799 pressure signal. Thermal pressure signal follows the 6800 default decay period of other scheduler pelt 6801 signals(usually 32 ms but configurable). Setting 6802 sched_thermal_decay_shift will left shift the decay 6803 period for the thermal pressure signal by the shift 6804 value. 6805 i.e. with the default pelt decay period of 32 ms 6806 sched_thermal_decay_shift thermal pressure decay pr 6807 1 64 ms 6808 2 128 ms 6809 and so on. 6810 Format: integer between 0 and 10 6811 Default is 0. 6812 6813 scftorture.holdoff= [KNL] 6814 Number of seconds to hold off before starting 6815 test. Defaults to zero for module insertion and 6816 to 10 seconds for built-in smp_call_function() 6817 tests. 6818 6819 scftorture.longwait= [KNL] 6820 Request ridiculously long waits randomly selected 6821 up to the chosen limit in seconds. Zero (the 6822 default) disables this feature. Please note 6823 that requesting even small non-zero numbers of 6824 seconds can result in RCU CPU stall warnings, 6825 softlockup complaints, and so on. 6826 6827 scftorture.nthreads= [KNL] 6828 Number of kthreads to spawn to invoke the 6829 smp_call_function() family of functions. 6830 The default of -1 specifies a number of kthreads 6831 equal to the number of CPUs. 6832 6833 scftorture.onoff_holdoff= [KNL] 6834 Number seconds to wait after the start of the 6835 test before initiating CPU-hotplug operations. 6836 6837 scftorture.onoff_interval= [KNL] 6838 Number seconds to wait between successive 6839 CPU-hotplug operations. Specifying zero (which 6840 is the default) disables CPU-hotplug operations. 6841 6842 scftorture.shutdown_secs= [KNL] 6843 The number of seconds following the start of the 6844 test after which to shut down the system. The 6845 default of zero avoids shutting down the system. 6846 Non-zero values are useful for automated tests. 6847 6848 scftorture.stat_interval= [KNL] 6849 The number of seconds between outputting the 6850 current test statistics to the console. A value 6851 of zero disables statistics output. 6852 6853 scftorture.stutter_cpus= [KNL] 6854 The number of jiffies to wait between each change 6855 to the set of CPUs under test. 6856 6857 scftorture.use_cpus_read_lock= [KNL] 6858 Use use_cpus_read_lock() instead of the default 6859 preempt_disable() to disable CPU hotplug 6860 while invoking one of the smp_call_function*() 6861 functions. 6862 6863 scftorture.verbose= [KNL] 6864 Enable additional printk() statements. 6865 6866 scftorture.weight_single= [KNL] 6867 The probability weighting to use for the 6868 smp_call_function_single() function with a zero 6869 "wait" parameter. A value of -1 selects the 6870 default if all other weights are -1. However, 6871 if at least one weight has some other value, a 6872 value of -1 will instead select a weight of zero. 6873 6874 scftorture.weight_single_wait= [KNL] 6875 The probability weighting to use for the 6876 smp_call_function_single() function with a 6877 non-zero "wait" parameter. See weight_single. 6878 6879 scftorture.weight_many= [KNL] 6880 The probability weighting to use for the 6881 smp_call_function_many() function with a zero 6882 "wait" parameter. See weight_single. 6883 Note well that setting a high probability for 6884 this weighting can place serious IPI load 6885 on the system. 6886 6887 scftorture.weight_many_wait= [KNL] 6888 The probability weighting to use for the 6889 smp_call_function_many() function with a 6890 non-zero "wait" parameter. See weight_single 6891 and weight_many. 6892 6893 scftorture.weight_all= [KNL] 6894 The probability weighting to use for the 6895 smp_call_function_all() function with a zero 6896 "wait" parameter. See weight_single and 6897 weight_many. 6898 6899 scftorture.weight_all_wait= [KNL] 6900 The probability weighting to use for the 6901 smp_call_function_all() function with a 6902 non-zero "wait" parameter. See weight_single 6903 and weight_many. 6904 6905 sdw_mclk_divider=[SDW] 6906 Specify the MCLK divider for Intel SoundWire buses in 6907 case the BIOS does not provide the clock rate properly. 6908 6909 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6910 xtime_lock contention on larger systems, and/or RCU lock 6911 contention on all systems with CONFIG_MAXSMP set. 6912 Format: { "0" | "1" } 6913 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6914 1 -- enable. 6915 Note: increases power consumption, thus should only be 6916 enabled if running jitter sensitive (HPC/RT) workloads. 6917 6918 security= [SECURITY] Choose a legacy "major" security module to 6919 enable at boot. This has been deprecated by the 6920 "lsm=" parameter. 6921 6922 selinux= [SELINUX] Disable or enable SELinux at boot time. 6923 Format: { "0" | "1" } 6924 See security/selinux/Kconfig help text. 6925 0 -- disable. 6926 1 -- enable. 6927 Default value is 1. 6928 6929 serialnumber [BUGS=X86-32] 6930 6931 sev=option[,option...] [X86-64] 6932 6933 debug 6934 Enable debug messages. 6935 6936 nosnp 6937 Do not enable SEV-SNP (applies to host/hypervisor 6938 only). Setting 'nosnp' avoids the RMP check overhead 6939 in memory accesses when users do not want to run 6940 SEV-SNP guests. 6941 6942 shapers= [NET] 6943 Maximal number of shapers. 6944 6945 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6946 Limit apic dumping. The parameter defines the maximal 6947 number of local apics being dumped. Also it is possible 6948 to set it to "all" by meaning -- no limit here. 6949 Format: { 1 (default) | 2 | ... | all }. 6950 The parameter valid if only apic=debug or 6951 apic=verbose is specified. 6952 Example: apic=debug show_lapic=all 6953 6954 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6955 Enabling slab_debug allows one to determine the 6956 culprit if slab objects become corrupted. Enabling 6957 slab_debug can create guard zones around objects and 6958 may poison objects when not in use. Also tracks the 6959 last alloc / free. For more information see 6960 Documentation/admin-guide/mm/slab.rst. 6961 (slub_debug legacy name also accepted for now) 6962 6963 Using this option implies the "no_hash_pointers" 6964 option which can be undone by adding the 6965 "hash_pointers=always" option. 6966 6967 slab_max_order= [MM] 6968 Determines the maximum allowed order for slabs. 6969 A high setting may cause OOMs due to memory 6970 fragmentation. For more information see 6971 Documentation/admin-guide/mm/slab.rst. 6972 (slub_max_order legacy name also accepted for now) 6973 6974 slab_merge [MM] 6975 Enable merging of slabs with similar size when the 6976 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6977 (slub_merge legacy name also accepted for now) 6978 6979 slab_min_objects= [MM] 6980 The minimum number of objects per slab. SLUB will 6981 increase the slab order up to slab_max_order to 6982 generate a sufficiently large slab able to contain 6983 the number of objects indicated. The higher the number 6984 of objects the smaller the overhead of tracking slabs 6985 and the less frequently locks need to be acquired. 6986 For more information see 6987 Documentation/admin-guide/mm/slab.rst. 6988 (slub_min_objects legacy name also accepted for now) 6989 6990 slab_min_order= [MM] 6991 Determines the minimum page order for slabs. Must be 6992 lower or equal to slab_max_order. For more information see 6993 Documentation/admin-guide/mm/slab.rst. 6994 (slub_min_order legacy name also accepted for now) 6995 6996 slab_nomerge [MM] 6997 Disable merging of slabs with similar size. May be 6998 necessary if there is some reason to distinguish 6999 allocs to different slabs, especially in hardened 7000 environments where the risk of heap overflows and 7001 layout control by attackers can usually be 7002 frustrated by disabling merging. This will reduce 7003 most of the exposure of a heap attack to a single 7004 cache (risks via metadata attacks are mostly 7005 unchanged). Debug options disable merging on their 7006 own. 7007 For more information see 7008 Documentation/admin-guide/mm/slab.rst. 7009 (slub_nomerge legacy name also accepted for now) 7010 7011 slab_strict_numa [MM] 7012 Support memory policies on a per object level 7013 in the slab allocator. The default is for memory 7014 policies to be applied at the folio level when 7015 a new folio is needed or a partial folio is 7016 retrieved from the lists. Increases overhead 7017 in the slab fastpaths but gains more accurate 7018 NUMA kernel object placement which helps with slow 7019 interconnects in NUMA systems. 7020 7021 slram= [HW,MTD] 7022 7023 smart2= [HW] 7024 Format: <io1>[,<io2>[,...,<io8>]] 7025 7026 smp.csd_lock_timeout= [KNL] 7027 Specify the period of time in milliseconds 7028 that smp_call_function() and friends will wait 7029 for a CPU to release the CSD lock. This is 7030 useful when diagnosing bugs involving CPUs 7031 disabling interrupts for extended periods 7032 of time. Defaults to 5,000 milliseconds, and 7033 setting a value of zero disables this feature. 7034 This feature may be more efficiently disabled 7035 using the csdlock_debug- kernel parameter. 7036 7037 smp.panic_on_ipistall= [KNL] 7038 If a csd_lock_timeout extends for more than 7039 the specified number of milliseconds, panic the 7040 system. By default, let CSD-lock acquisition 7041 take as long as they take. Specifying 300,000 7042 for this value provides a 5-minute timeout. 7043 7044 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7045 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7046 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7047 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7048 smsc-ircc2.ircc_irq= [HW] IRQ line 7049 smsc-ircc2.ircc_dma= [HW] DMA channel 7050 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7051 0: Toshiba Satellite 1800 (GP data pin select) 7052 1: Fast pin select (default) 7053 2: ATC IRMode 7054 7055 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7056 (logical CPUs) to use per physical CPU on systems 7057 capable of symmetric multithreading (SMT). Will 7058 be capped to the actual hardware limit. 7059 Format: <integer> 7060 Default: -1 (no limit) 7061 7062 softlockup_panic= 7063 [KNL] Should the soft-lockup detector generate panics. 7064 Format: <int> 7065 7066 A value of non-zero instructs the soft-lockup detector 7067 to panic the machine when a soft-lockup duration exceeds 7068 N thresholds. It is also controlled by the kernel.softlockup_panic 7069 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7070 respective build-time switch to that functionality. 7071 7072 softlockup_all_cpu_backtrace= 7073 [KNL] Should the soft-lockup detector generate 7074 backtraces on all cpus. 7075 Format: 0 | 1 7076 7077 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7078 See Documentation/admin-guide/laptops/sonypi.rst 7079 7080 spectre_bhi= [X86] Control mitigation of Branch History Injection 7081 (BHI) vulnerability. This setting affects the 7082 deployment of the HW BHI control and the SW BHB 7083 clearing sequence. 7084 7085 on - (default) Enable the HW or SW mitigation as 7086 needed. This protects the kernel from 7087 both syscalls and VMs. 7088 vmexit - On systems which don't have the HW mitigation 7089 available, enable the SW mitigation on vmexit 7090 ONLY. On such systems, the host kernel is 7091 protected from VM-originated BHI attacks, but 7092 may still be vulnerable to syscall attacks. 7093 off - Disable the mitigation. 7094 7095 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7096 (indirect branch speculation) vulnerability. 7097 The default operation protects the kernel from 7098 user space attacks. 7099 7100 on - unconditionally enable, implies 7101 spectre_v2_user=on 7102 off - unconditionally disable, implies 7103 spectre_v2_user=off 7104 auto - kernel detects whether your CPU model is 7105 vulnerable 7106 7107 Selecting 'on' will, and 'auto' may, choose a 7108 mitigation method at run time according to the 7109 CPU, the available microcode, the setting of the 7110 CONFIG_MITIGATION_RETPOLINE configuration option, 7111 and the compiler with which the kernel was built. 7112 7113 Selecting 'on' will also enable the mitigation 7114 against user space to user space task attacks. 7115 Selecting specific mitigation does not force enable 7116 user mitigations. 7117 7118 Selecting 'off' will disable both the kernel and 7119 the user space protections. 7120 7121 Specific mitigations can also be selected manually: 7122 7123 retpoline - replace indirect branches 7124 retpoline,generic - Retpolines 7125 retpoline,lfence - LFENCE; indirect branch 7126 retpoline,amd - alias for retpoline,lfence 7127 eibrs - Enhanced/Auto IBRS 7128 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7129 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7130 ibrs - use IBRS to protect kernel 7131 7132 Not specifying this option is equivalent to 7133 spectre_v2=auto. 7134 7135 spectre_v2_user= 7136 [X86] Control mitigation of Spectre variant 2 7137 (indirect branch speculation) vulnerability between 7138 user space tasks 7139 7140 on - Unconditionally enable mitigations. Is 7141 enforced by spectre_v2=on 7142 7143 off - Unconditionally disable mitigations. Is 7144 enforced by spectre_v2=off 7145 7146 prctl - Indirect branch speculation is enabled, 7147 but mitigation can be enabled via prctl 7148 per thread. The mitigation control state 7149 is inherited on fork. 7150 7151 prctl,ibpb 7152 - Like "prctl" above, but only STIBP is 7153 controlled per thread. IBPB is issued 7154 always when switching between different user 7155 space processes. 7156 7157 seccomp 7158 - Same as "prctl" above, but all seccomp 7159 threads will enable the mitigation unless 7160 they explicitly opt out. 7161 7162 seccomp,ibpb 7163 - Like "seccomp" above, but only STIBP is 7164 controlled per thread. IBPB is issued 7165 always when switching between different 7166 user space processes. 7167 7168 auto - Kernel selects the mitigation depending on 7169 the available CPU features and vulnerability. 7170 7171 Default mitigation: "prctl" 7172 7173 Not specifying this option is equivalent to 7174 spectre_v2_user=auto. 7175 7176 spec_rstack_overflow= 7177 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7178 7179 off - Disable mitigation 7180 microcode - Enable microcode mitigation only 7181 safe-ret - Enable sw-only safe RET mitigation (default) 7182 ibpb - Enable mitigation by issuing IBPB on 7183 kernel entry 7184 ibpb-vmexit - Issue IBPB only on VMEXIT 7185 (cloud-specific mitigation) 7186 7187 spec_store_bypass_disable= 7188 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7189 (Speculative Store Bypass vulnerability) 7190 7191 Certain CPUs are vulnerable to an exploit against a 7192 a common industry wide performance optimization known 7193 as "Speculative Store Bypass" in which recent stores 7194 to the same memory location may not be observed by 7195 later loads during speculative execution. The idea 7196 is that such stores are unlikely and that they can 7197 be detected prior to instruction retirement at the 7198 end of a particular speculation execution window. 7199 7200 In vulnerable processors, the speculatively forwarded 7201 store can be used in a cache side channel attack, for 7202 example to read memory to which the attacker does not 7203 directly have access (e.g. inside sandboxed code). 7204 7205 This parameter controls whether the Speculative Store 7206 Bypass optimization is used. 7207 7208 On x86 the options are: 7209 7210 on - Unconditionally disable Speculative Store Bypass 7211 off - Unconditionally enable Speculative Store Bypass 7212 auto - Kernel detects whether the CPU model contains an 7213 implementation of Speculative Store Bypass and 7214 picks the most appropriate mitigation. If the 7215 CPU is not vulnerable, "off" is selected. If the 7216 CPU is vulnerable the default mitigation is 7217 architecture and Kconfig dependent. See below. 7218 prctl - Control Speculative Store Bypass per thread 7219 via prctl. Speculative Store Bypass is enabled 7220 for a process by default. The state of the control 7221 is inherited on fork. 7222 seccomp - Same as "prctl" above, but all seccomp threads 7223 will disable SSB unless they explicitly opt out. 7224 7225 Default mitigations: 7226 X86: "prctl" 7227 7228 On powerpc the options are: 7229 7230 on,auto - On Power8 and Power9 insert a store-forwarding 7231 barrier on kernel entry and exit. On Power7 7232 perform a software flush on kernel entry and 7233 exit. 7234 off - No action. 7235 7236 Not specifying this option is equivalent to 7237 spec_store_bypass_disable=auto. 7238 7239 split_lock_detect= 7240 [X86] Enable split lock detection or bus lock detection 7241 7242 When enabled (and if hardware support is present), atomic 7243 instructions that access data across cache line 7244 boundaries will result in an alignment check exception 7245 for split lock detection or a debug exception for 7246 bus lock detection. 7247 7248 off - not enabled 7249 7250 warn - the kernel will emit rate-limited warnings 7251 about applications triggering the #AC 7252 exception or the #DB exception. This mode is 7253 the default on CPUs that support split lock 7254 detection or bus lock detection. Default 7255 behavior is by #AC if both features are 7256 enabled in hardware. 7257 7258 fatal - the kernel will send SIGBUS to applications 7259 that trigger the #AC exception or the #DB 7260 exception. Default behavior is by #AC if 7261 both features are enabled in hardware. 7262 7263 ratelimit:N - 7264 Set system wide rate limit to N bus locks 7265 per second for bus lock detection. 7266 0 < N <= 1000. 7267 7268 N/A for split lock detection. 7269 7270 7271 If an #AC exception is hit in the kernel or in 7272 firmware (i.e. not while executing in user mode) 7273 the kernel will oops in either "warn" or "fatal" 7274 mode. 7275 7276 #DB exception for bus lock is triggered only when 7277 CPL > 0. 7278 7279 srbds= [X86,INTEL,EARLY] 7280 Control the Special Register Buffer Data Sampling 7281 (SRBDS) mitigation. 7282 7283 Certain CPUs are vulnerable to an MDS-like 7284 exploit which can leak bits from the random 7285 number generator. 7286 7287 By default, this issue is mitigated by 7288 microcode. However, the microcode fix can cause 7289 the RDRAND and RDSEED instructions to become 7290 much slower. Among other effects, this will 7291 result in reduced throughput from /dev/urandom. 7292 7293 The microcode mitigation can be disabled with 7294 the following option: 7295 7296 off: Disable mitigation and remove 7297 performance impact to RDRAND and RDSEED 7298 7299 srcutree.big_cpu_lim [KNL] 7300 Specifies the number of CPUs constituting a 7301 large system, such that srcu_struct structures 7302 should immediately allocate an srcu_node array. 7303 This kernel-boot parameter defaults to 128, 7304 but takes effect only when the low-order four 7305 bits of srcutree.convert_to_big is equal to 3 7306 (decide at boot). 7307 7308 srcutree.convert_to_big [KNL] 7309 Specifies under what conditions an SRCU tree 7310 srcu_struct structure will be converted to big 7311 form, that is, with an rcu_node tree: 7312 7313 0: Never. 7314 1: At init_srcu_struct() time. 7315 2: When rcutorture decides to. 7316 3: Decide at boot time (default). 7317 0x1X: Above plus if high contention. 7318 7319 Either way, the srcu_node tree will be sized based 7320 on the actual runtime number of CPUs (nr_cpu_ids) 7321 instead of the compile-time CONFIG_NR_CPUS. 7322 7323 srcutree.counter_wrap_check [KNL] 7324 Specifies how frequently to check for 7325 grace-period sequence counter wrap for the 7326 srcu_data structure's ->srcu_gp_seq_needed field. 7327 The greater the number of bits set in this kernel 7328 parameter, the less frequently counter wrap will 7329 be checked for. Note that the bottom two bits 7330 are ignored. 7331 7332 srcutree.exp_holdoff [KNL] 7333 Specifies how many nanoseconds must elapse 7334 since the end of the last SRCU grace period for 7335 a given srcu_struct until the next normal SRCU 7336 grace period will be considered for automatic 7337 expediting. Set to zero to disable automatic 7338 expediting. 7339 7340 srcutree.srcu_max_nodelay [KNL] 7341 Specifies the number of no-delay instances 7342 per jiffy for which the SRCU grace period 7343 worker thread will be rescheduled with zero 7344 delay. Beyond this limit, worker thread will 7345 be rescheduled with a sleep delay of one jiffy. 7346 7347 srcutree.srcu_max_nodelay_phase [KNL] 7348 Specifies the per-grace-period phase, number of 7349 non-sleeping polls of readers. Beyond this limit, 7350 grace period worker thread will be rescheduled 7351 with a sleep delay of one jiffy, between each 7352 rescan of the readers, for a grace period phase. 7353 7354 srcutree.srcu_retry_check_delay [KNL] 7355 Specifies number of microseconds of non-sleeping 7356 delay between each non-sleeping poll of readers. 7357 7358 srcutree.small_contention_lim [KNL] 7359 Specifies the number of update-side contention 7360 events per jiffy will be tolerated before 7361 initiating a conversion of an srcu_struct 7362 structure to big form. Note that the value of 7363 srcutree.convert_to_big must have the 0x10 bit 7364 set for contention-based conversions to occur. 7365 7366 ssbd= [ARM64,HW,EARLY] 7367 Speculative Store Bypass Disable control 7368 7369 On CPUs that are vulnerable to the Speculative 7370 Store Bypass vulnerability and offer a 7371 firmware based mitigation, this parameter 7372 indicates how the mitigation should be used: 7373 7374 force-on: Unconditionally enable mitigation for 7375 for both kernel and userspace 7376 force-off: Unconditionally disable mitigation for 7377 for both kernel and userspace 7378 kernel: Always enable mitigation in the 7379 kernel, and offer a prctl interface 7380 to allow userspace to register its 7381 interest in being mitigated too. 7382 7383 stack_guard_gap= [MM] 7384 override the default stack gap protection. The value 7385 is in page units and it defines how many pages prior 7386 to (for stacks growing down) resp. after (for stacks 7387 growing up) the main stack are reserved for no other 7388 mapping. Default value is 256 pages. 7389 7390 stack_depot_disable= [KNL,EARLY] 7391 Setting this to true through kernel command line will 7392 disable the stack depot thereby saving the static memory 7393 consumed by the stack hash table. By default this is set 7394 to false. 7395 7396 stack_depot_max_pools= [KNL,EARLY] 7397 Specify the maximum number of pools to use for storing 7398 stack traces. Pools are allocated on-demand up to this 7399 limit. Default value is 8191 pools. 7400 7401 stacktrace [FTRACE] 7402 Enable the stack tracer on boot up. 7403 7404 stacktrace_filter=[function-list] 7405 [FTRACE] Limit the functions that the stack tracer 7406 will trace at boot up. function-list is a comma-separated 7407 list of functions. This list can be changed at run 7408 time by the stack_trace_filter file in the debugfs 7409 tracing directory. Note, this enables stack tracing 7410 and the stacktrace above is not needed. 7411 7412 sti= [PARISC,HW] 7413 Format: <num> 7414 Set the STI (builtin display/keyboard on the HP-PARISC 7415 machines) console (graphic card) which should be used 7416 as the initial boot-console. 7417 See also comment in drivers/video/console/sticore.c. 7418 7419 sti_font= [HW] 7420 See comment in drivers/video/console/sticore.c. 7421 7422 stifb= [HW] 7423 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7424 7425 strict_sas_size= 7426 [X86] 7427 Format: <bool> 7428 Enable or disable strict sigaltstack size checks 7429 against the required signal frame size which 7430 depends on the supported FPU features. This can 7431 be used to filter out binaries which have 7432 not yet been made aware of AT_MINSIGSTKSZ. 7433 7434 stress_hpt [PPC,EARLY] 7435 Limits the number of kernel HPT entries in the hash 7436 page table to increase the rate of hash page table 7437 faults on kernel addresses. 7438 7439 stress_slb [PPC,EARLY] 7440 Limits the number of kernel SLB entries, and flushes 7441 them frequently to increase the rate of SLB faults 7442 on kernel addresses. 7443 7444 no_slb_preload [PPC,EARLY] 7445 Disables slb preloading for userspace. 7446 7447 sunrpc.min_resvport= 7448 sunrpc.max_resvport= 7449 [NFS,SUNRPC] 7450 SunRPC servers often require that client requests 7451 originate from a privileged port (i.e. a port in the 7452 range 0 < portnr < 1024). 7453 An administrator who wishes to reserve some of these 7454 ports for other uses may adjust the range that the 7455 kernel's sunrpc client considers to be privileged 7456 using these two parameters to set the minimum and 7457 maximum port values. 7458 7459 sunrpc.svc_rpc_per_connection_limit= 7460 [NFS,SUNRPC] 7461 Limit the number of requests that the server will 7462 process in parallel from a single connection. 7463 The default value is 0 (no limit). 7464 7465 sunrpc.pool_mode= 7466 [NFS] 7467 Control how the NFS server code allocates CPUs to 7468 service thread pools. Depending on how many NICs 7469 you have and where their interrupts are bound, this 7470 option will affect which CPUs will do NFS serving. 7471 Note: this parameter cannot be changed while the 7472 NFS server is running. 7473 7474 auto the server chooses an appropriate mode 7475 automatically using heuristics 7476 global a single global pool contains all CPUs 7477 percpu one pool for each CPU 7478 pernode one pool for each NUMA node (equivalent 7479 to global on non-NUMA machines) 7480 7481 sunrpc.tcp_slot_table_entries= 7482 sunrpc.udp_slot_table_entries= 7483 [NFS,SUNRPC] 7484 Sets the upper limit on the number of simultaneous 7485 RPC calls that can be sent from the client to a 7486 server. Increasing these values may allow you to 7487 improve throughput, but will also increase the 7488 amount of memory reserved for use by the client. 7489 7490 suspend.pm_test_delay= 7491 [SUSPEND] 7492 Sets the number of seconds to remain in a suspend test 7493 mode before resuming the system (see 7494 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7495 is set. Default value is 5. 7496 7497 svm= [PPC] 7498 Format: { on | off | y | n | 1 | 0 } 7499 This parameter controls use of the Protected 7500 Execution Facility on pSeries. 7501 7502 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7503 Format: { <int> [,<int>] | force | noforce } 7504 <int> -- Number of I/O TLB slabs 7505 <int> -- Second integer after comma. Number of swiotlb 7506 areas with their own lock. Will be rounded up 7507 to a power of 2. 7508 force -- force using of bounce buffers even if they 7509 wouldn't be automatically used by the kernel 7510 noforce -- Never use bounce buffers (for debugging) 7511 7512 switches= [HW,M68k,EARLY] 7513 7514 sysctl.*= [KNL] 7515 Set a sysctl parameter, right before loading the init 7516 process, as if the value was written to the respective 7517 /proc/sys/... file. Both '.' and '/' are recognized as 7518 separators. Unrecognized parameters and invalid values 7519 are reported in the kernel log. Sysctls registered 7520 later by a loaded module cannot be set this way. 7521 Example: sysctl.vm.swappiness=40 7522 7523 sysrq_always_enabled 7524 [KNL] 7525 Ignore sysrq setting - this boot parameter will 7526 neutralize any effect of /proc/sys/kernel/sysrq. 7527 Useful for debugging. 7528 7529 tcpmhash_entries= [KNL,NET] 7530 Set the number of tcp_metrics_hash slots. 7531 Default value is 8192 or 16384 depending on total 7532 ram pages. This is used to specify the TCP metrics 7533 cache size. See Documentation/networking/ip-sysctl.rst 7534 "tcp_no_metrics_save" section for more details. 7535 7536 tdfx= [HW,DRM] 7537 7538 test_suspend= [SUSPEND] 7539 Format: { "mem" | "standby" | "freeze" }[,N] 7540 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7541 standby suspend) or "freeze" (for suspend type freeze) 7542 as the system sleep state during system startup with 7543 the optional capability to repeat N number of times. 7544 The system is woken from this state using a 7545 wakeup-capable RTC alarm. 7546 7547 thash_entries= [KNL,NET] 7548 Set number of hash buckets for TCP connection 7549 7550 thermal.act= [HW,ACPI] 7551 -1: disable all active trip points in all thermal zones 7552 <degrees C>: override all lowest active trip points 7553 7554 thermal.crt= [HW,ACPI] 7555 -1: disable all critical trip points in all thermal zones 7556 <degrees C>: override all critical trip points 7557 7558 thermal.off= [HW,ACPI] 7559 1: disable ACPI thermal control 7560 7561 thermal.psv= [HW,ACPI] 7562 -1: disable all passive trip points 7563 <degrees C>: override all passive trip points to this 7564 value 7565 7566 thermal.tzp= [HW,ACPI] 7567 Specify global default ACPI thermal zone polling rate 7568 <deci-seconds>: poll all this frequency 7569 0: no polling (default) 7570 7571 thp_anon= [KNL] 7572 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7573 state is one of "always", "madvise", "never" or "inherit". 7574 Control the default behavior of the system with respect 7575 to anonymous transparent hugepages. 7576 Can be used multiple times for multiple anon THP sizes. 7577 See Documentation/admin-guide/mm/transhuge.rst for more 7578 details. 7579 7580 threadirqs [KNL,EARLY] 7581 Force threading of all interrupt handlers except those 7582 marked explicitly IRQF_NO_THREAD. 7583 7584 thp_shmem= [KNL] 7585 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7586 Control the default policy of each hugepage size for the 7587 internal shmem mount. <policy> is one of policies available 7588 for the shmem mount ("always", "inherit", "never", "within_size", 7589 and "advise"). 7590 It can be used multiple times for multiple shmem THP sizes. 7591 See Documentation/admin-guide/mm/transhuge.rst for more 7592 details. 7593 7594 topology= [S390,EARLY] 7595 Format: {off | on} 7596 Specify if the kernel should make use of the cpu 7597 topology information if the hardware supports this. 7598 The scheduler will make use of this information and 7599 e.g. base its process migration decisions on it. 7600 Default is on. 7601 7602 torture.disable_onoff_at_boot= [KNL] 7603 Prevent the CPU-hotplug component of torturing 7604 until after init has spawned. 7605 7606 torture.ftrace_dump_at_shutdown= [KNL] 7607 Dump the ftrace buffer at torture-test shutdown, 7608 even if there were no errors. This can be a 7609 very costly operation when many torture tests 7610 are running concurrently, especially on systems 7611 with rotating-rust storage. 7612 7613 torture.verbose_sleep_frequency= [KNL] 7614 Specifies how many verbose printk()s should be 7615 emitted between each sleep. The default of zero 7616 disables verbose-printk() sleeping. 7617 7618 torture.verbose_sleep_duration= [KNL] 7619 Duration of each verbose-printk() sleep in jiffies. 7620 7621 tpm.disable_pcr_integrity= [HW,TPM] 7622 Do not protect PCR registers from unintended physical 7623 access, or interposers in the bus by the means of 7624 having an integrity protected session wrapped around 7625 TPM2_PCR_Extend command. Consider this in a situation 7626 where TPM is heavily utilized by IMA, thus protection 7627 causing a major performance hit, and the space where 7628 machines are deployed is by other means guarded. 7629 7630 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7631 Maximum time in milliseconds to retry sending a message 7632 to the TPM service before giving up. This parameter controls 7633 how long the system will continue retrying when the TPM 7634 service is busy. 7635 Format: <unsigned int> 7636 Default: 2000 (2 seconds) 7637 7638 tpm_suspend_pcr=[HW,TPM] 7639 Format: integer pcr id 7640 Specify that at suspend time, the tpm driver 7641 should extend the specified pcr with zeros, 7642 as a workaround for some chips which fail to 7643 flush the last written pcr on TPM_SaveState. 7644 This will guarantee that all the other pcrs 7645 are saved. 7646 7647 tpm_tis.interrupts= [HW,TPM] 7648 Enable interrupts for the MMIO based physical layer 7649 for the FIFO interface. By default it is set to false 7650 (0). For more information about TPM hardware interfaces 7651 defined by Trusted Computing Group (TCG) see 7652 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7653 7654 tp_printk [FTRACE] 7655 Have the tracepoints sent to printk as well as the 7656 tracing ring buffer. This is useful for early boot up 7657 where the system hangs or reboots and does not give the 7658 option for reading the tracing buffer or performing a 7659 ftrace_dump_on_oops. 7660 7661 To turn off having tracepoints sent to printk, 7662 echo 0 > /proc/sys/kernel/tracepoint_printk 7663 Note, echoing 1 into this file without the 7664 tp_printk kernel cmdline option has no effect. 7665 7666 The tp_printk_stop_on_boot (see below) can also be used 7667 to stop the printing of events to console at 7668 late_initcall_sync. 7669 7670 ** CAUTION ** 7671 7672 Having tracepoints sent to printk() and activating high 7673 frequency tracepoints such as irq or sched, can cause 7674 the system to live lock. 7675 7676 tp_printk_stop_on_boot [FTRACE] 7677 When tp_printk (above) is set, it can cause a lot of noise 7678 on the console. It may be useful to only include the 7679 printing of events during boot up, as user space may 7680 make the system inoperable. 7681 7682 This command line option will stop the printing of events 7683 to console at the late_initcall_sync() time frame. 7684 7685 trace_buf_size=nn[KMG] 7686 [FTRACE] will set tracing buffer size on each cpu. 7687 7688 trace_clock= [FTRACE] Set the clock used for tracing events 7689 at boot up. 7690 local - Use the per CPU time stamp counter 7691 (converted into nanoseconds). Fast, but 7692 depending on the architecture, may not be 7693 in sync between CPUs. 7694 global - Event time stamps are synchronized across 7695 CPUs. May be slower than the local clock, 7696 but better for some race conditions. 7697 counter - Simple counting of events (1, 2, ..) 7698 note, some counts may be skipped due to the 7699 infrastructure grabbing the clock more than 7700 once per event. 7701 uptime - Use jiffies as the time stamp. 7702 perf - Use the same clock that perf uses. 7703 mono - Use ktime_get_mono_fast_ns() for time stamps. 7704 mono_raw - Use ktime_get_raw_fast_ns() for time 7705 stamps. 7706 boot - Use ktime_get_boot_fast_ns() for time stamps. 7707 Architectures may add more clocks. See 7708 Documentation/trace/ftrace.rst for more details. 7709 7710 trace_event=[event-list] 7711 [FTRACE] Set and start specified trace events in order 7712 to facilitate early boot debugging. The event-list is a 7713 comma-separated list of trace events to enable. See 7714 also Documentation/trace/events.rst 7715 7716 To enable modules, use :mod: keyword: 7717 7718 trace_event=:mod:<module> 7719 7720 The value before :mod: will only enable specific events 7721 that are part of the module. See the above mentioned 7722 document for more information. 7723 7724 trace_instance=[instance-info] 7725 [FTRACE] Create a ring buffer instance early in boot up. 7726 This will be listed in: 7727 7728 /sys/kernel/tracing/instances 7729 7730 Events can be enabled at the time the instance is created 7731 via: 7732 7733 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7734 7735 Note, the "<system*>:" portion is optional if the event is 7736 unique. 7737 7738 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7739 7740 will enable the "sched_switch" event (note, the "sched:" is optional, and 7741 the same thing would happen if it was left off). The irq_handler_entry 7742 event, and all events under the "initcall" system. 7743 7744 Flags can be added to the instance to modify its behavior when it is 7745 created. The flags are separated by '^'. 7746 7747 The available flags are: 7748 7749 traceoff - Have the tracing instance tracing disabled after it is created. 7750 traceprintk - Have trace_printk() write into this trace instance 7751 (note, "printk" and "trace_printk" can also be used) 7752 7753 trace_instance=foo^traceoff^traceprintk,sched,irq 7754 7755 The flags must come before the defined events. 7756 7757 If memory has been reserved (see memmap for x86), the instance 7758 can use that memory: 7759 7760 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7761 7762 The above will create a "boot_map" instance that uses the physical 7763 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7764 instance will be split up accordingly. 7765 7766 Alternatively, the memory can be reserved by the reserve_mem option: 7767 7768 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7769 7770 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7771 and place the ring buffer in this memory. Note that due to KASLR, the 7772 memory may not be the same location each time, which will not preserve 7773 the buffer content. 7774 7775 Also note that the layout of the ring buffer data may change between 7776 kernel versions where the validator will fail and reset the ring buffer 7777 if the layout is not the same as the previous kernel. 7778 7779 If the ring buffer is used for persistent bootups and has events enabled, 7780 it is recommend to disable tracing so that events from a previous boot do not 7781 mix with events of the current boot (unless you are debugging a random crash 7782 at boot up). 7783 7784 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7785 7786 Note, saving the trace buffer across reboots does require that the system 7787 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7788 can force a memory reset on boot which will clear any trace that was stored. 7789 This is just one of many ways that can clear memory. Make sure your system 7790 keeps the content of memory across reboots before relying on this option. 7791 7792 NB: Both the mapped address and size must be page aligned for the architecture. 7793 7794 See also Documentation/trace/debugging.rst 7795 7796 7797 trace_options=[option-list] 7798 [FTRACE] Enable or disable tracer options at boot. 7799 The option-list is a comma delimited list of options 7800 that can be enabled or disabled just as if you were 7801 to echo the option name into 7802 7803 /sys/kernel/tracing/trace_options 7804 7805 For example, to enable stacktrace option (to dump the 7806 stack trace of each event), add to the command line: 7807 7808 trace_options=stacktrace 7809 7810 See also Documentation/trace/ftrace.rst "trace options" 7811 section. 7812 7813 trace_trigger=[trigger-list] 7814 [FTRACE] Add an event trigger on specific events. 7815 Set a trigger on top of a specific event, with an optional 7816 filter. 7817 7818 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7819 Where more than one trigger may be specified that are comma delimited. 7820 7821 For example: 7822 7823 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7824 7825 The above will enable the "stacktrace" trigger on the "sched_switch" 7826 event but only trigger it if the "prev_state" of the "sched_switch" 7827 event is "2" (TASK_UNINTERRUPTIBLE). 7828 7829 See also "Event triggers" in Documentation/trace/events.rst 7830 7831 7832 traceoff_after_boot 7833 [FTRACE] Sometimes tracing is used to debug issues 7834 during the boot process. Since the trace buffer has a 7835 limited amount of storage, it may be prudent to 7836 disable tracing after the boot is finished, otherwise 7837 the critical information may be overwritten. With this 7838 option, the main tracing buffer will be turned off at 7839 the end of the boot process. 7840 7841 traceoff_on_warning 7842 [FTRACE] enable this option to disable tracing when a 7843 warning is hit. This turns off "tracing_on". Tracing can 7844 be enabled again by echoing '1' into the "tracing_on" 7845 file located in /sys/kernel/tracing/ 7846 7847 This option is useful, as it disables the trace before 7848 the WARNING dump is called, which prevents the trace to 7849 be filled with content caused by the warning output. 7850 7851 This option can also be set at run time via the sysctl 7852 option: kernel/traceoff_on_warning 7853 7854 transparent_hugepage= 7855 [KNL] 7856 Format: [always|madvise|never] 7857 Can be used to control the default behavior of the system 7858 with respect to transparent hugepages. 7859 See Documentation/admin-guide/mm/transhuge.rst 7860 for more details. 7861 7862 transparent_hugepage_shmem= [KNL] 7863 Format: [always|within_size|advise|never|deny|force] 7864 Can be used to control the hugepage allocation policy for 7865 the internal shmem mount. 7866 See Documentation/admin-guide/mm/transhuge.rst 7867 for more details. 7868 7869 transparent_hugepage_tmpfs= [KNL] 7870 Format: [always|within_size|advise|never] 7871 Can be used to control the default hugepage allocation policy 7872 for the tmpfs mount. 7873 See Documentation/admin-guide/mm/transhuge.rst 7874 for more details. 7875 7876 trusted.source= [KEYS] 7877 Format: <string> 7878 This parameter identifies the trust source as a backend 7879 for trusted keys implementation. Supported trust 7880 sources: 7881 - "tpm" 7882 - "tee" 7883 - "caam" 7884 - "dcp" 7885 - "pkwm" 7886 If not specified then it defaults to iterating through 7887 the trust source list starting with TPM and assigns the 7888 first trust source as a backend which is initialized 7889 successfully during iteration. 7890 7891 trusted.rng= [KEYS] 7892 Format: <string> 7893 The RNG used to generate key material for trusted keys. 7894 Can be one of: 7895 - "kernel" 7896 - the same value as trusted.source: "tpm" or "tee" 7897 - "default" 7898 If not specified, "default" is used. In this case, 7899 the RNG's choice is left to each individual trust source. 7900 7901 trusted.dcp_use_otp_key 7902 This is intended to be used in combination with 7903 trusted.source=dcp and will select the DCP OTP key 7904 instead of the DCP UNIQUE key blob encryption. 7905 7906 trusted.dcp_skip_zk_test 7907 This is intended to be used in combination with 7908 trusted.source=dcp and will disable the check if the 7909 blob key is all zeros. This is helpful for situations where 7910 having this key zero'ed is acceptable. E.g. in testing 7911 scenarios. 7912 7913 tsa= [X86] Control mitigation for Transient Scheduler 7914 Attacks on AMD CPUs. Search the following in your 7915 favourite search engine for more details: 7916 7917 "Technical guidance for mitigating transient scheduler 7918 attacks". 7919 7920 off - disable the mitigation 7921 on - enable the mitigation (default) 7922 user - mitigate only user/kernel transitions 7923 vm - mitigate only guest/host transitions 7924 7925 7926 tsc= Disable clocksource stability checks for TSC. 7927 Format: <string> 7928 [x86] reliable: mark tsc clocksource as reliable, this 7929 disables clocksource verification at runtime, as well 7930 as the stability checks done at bootup. Used to enable 7931 high-resolution timer mode on older hardware, and in 7932 virtualized environment. 7933 [x86] noirqtime: Do not use TSC to do irq accounting. 7934 Used to run time disable IRQ_TIME_ACCOUNTING on any 7935 platforms where RDTSC is slow and this accounting 7936 can add overhead. 7937 [x86] unstable: mark the TSC clocksource as unstable, this 7938 marks the TSC unconditionally unstable at bootup and 7939 avoids any further wobbles once the TSC watchdog notices. 7940 [x86] nowatchdog: disable clocksource watchdog. Used 7941 in situations with strict latency requirements (where 7942 interruptions from clocksource watchdog are not 7943 acceptable). 7944 [x86] recalibrate: force recalibration against a HW timer 7945 (HPET or PM timer) on systems whose TSC frequency was 7946 obtained from HW or FW using either an MSR or CPUID(0x15). 7947 Warn if the difference is more than 500 ppm. 7948 [x86] watchdog: Enforce the clocksource watchdog on TSC 7949 7950 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7951 value instead. Useful when the early TSC frequency discovery 7952 procedure is not reliable, such as on overclocked systems 7953 with CPUID.16h support and partial CPUID.15h support. 7954 Format: <unsigned int> 7955 7956 tsx= [X86] Control Transactional Synchronization 7957 Extensions (TSX) feature in Intel processors that 7958 support TSX control. 7959 7960 This parameter controls the TSX feature. The options are: 7961 7962 on - Enable TSX on the system. Although there are 7963 mitigations for all known security vulnerabilities, 7964 TSX has been known to be an accelerator for 7965 several previous speculation-related CVEs, and 7966 so there may be unknown security risks associated 7967 with leaving it enabled. 7968 7969 off - Disable TSX on the system. (Note that this 7970 option takes effect only on newer CPUs which are 7971 not vulnerable to MDS, i.e., have 7972 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7973 the new IA32_TSX_CTRL MSR through a microcode 7974 update. This new MSR allows for the reliable 7975 deactivation of the TSX functionality.) 7976 7977 auto - Disable TSX if X86_BUG_TAA is present, 7978 otherwise enable TSX on the system. 7979 7980 Not specifying this option is equivalent to tsx=off. 7981 7982 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7983 for more details. 7984 7985 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7986 Abort (TAA) vulnerability. 7987 7988 Similar to Micro-architectural Data Sampling (MDS) 7989 certain CPUs that support Transactional 7990 Synchronization Extensions (TSX) are vulnerable to an 7991 exploit against CPU internal buffers which can forward 7992 information to a disclosure gadget under certain 7993 conditions. 7994 7995 In vulnerable processors, the speculatively forwarded 7996 data can be used in a cache side channel attack, to 7997 access data to which the attacker does not have direct 7998 access. 7999 8000 This parameter controls the TAA mitigation. The 8001 options are: 8002 8003 full - Enable TAA mitigation on vulnerable CPUs 8004 if TSX is enabled. 8005 8006 full,nosmt - Enable TAA mitigation and disable SMT on 8007 vulnerable CPUs. If TSX is disabled, SMT 8008 is not disabled because CPU is not 8009 vulnerable to cross-thread TAA attacks. 8010 off - Unconditionally disable TAA mitigation 8011 8012 On MDS-affected machines, tsx_async_abort=off can be 8013 prevented by an active MDS mitigation as both vulnerabilities 8014 are mitigated with the same mechanism so in order to disable 8015 this mitigation, you need to specify mds=off too. 8016 8017 Not specifying this option is equivalent to 8018 tsx_async_abort=full. On CPUs which are MDS affected 8019 and deploy MDS mitigation, TAA mitigation is not 8020 required and doesn't provide any additional 8021 mitigation. 8022 8023 For details see: 8024 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8025 8026 turbografx.map[2|3]= [HW,JOY] 8027 TurboGraFX parallel port interface 8028 Format: 8029 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8030 See also Documentation/input/devices/joystick-parport.rst 8031 8032 udbg-immortal [PPC] When debugging early kernel crashes that 8033 happen after console_init() and before a proper 8034 console driver takes over, this boot options might 8035 help "seeing" what's going on. 8036 8037 uhash_entries= [KNL,NET] 8038 Set number of hash buckets for UDP/UDP-Lite connections 8039 8040 uhci-hcd.ignore_oc= 8041 [USB] Ignore overcurrent events (default N). 8042 Some badly-designed motherboards generate lots of 8043 bogus events, for ports that aren't wired to 8044 anything. Set this parameter to avoid log spamming. 8045 Note that genuine overcurrent events won't be 8046 reported either. 8047 8048 unaligned_scalar_speed= 8049 [RISCV] 8050 Format: {slow | fast | unsupported} 8051 Allow skipping scalar unaligned access speed tests. This 8052 is useful for testing alternative code paths and to skip 8053 the tests in environments where they run too slowly. All 8054 CPUs must have the same scalar unaligned access speed. 8055 8056 unaligned_vector_speed= 8057 [RISCV] 8058 Format: {slow | fast | unsupported} 8059 Allow skipping vector unaligned access speed tests. This 8060 is useful for testing alternative code paths and to skip 8061 the tests in environments where they run too slowly. All 8062 CPUs must have the same vector unaligned access speed. 8063 8064 unknown_nmi_panic 8065 [X86] Cause panic on unknown NMI. 8066 8067 unwind_debug [X86-64,EARLY] 8068 Enable unwinder debug output. This can be 8069 useful for debugging certain unwinder error 8070 conditions, including corrupt stacks and 8071 bad/missing unwinder metadata. 8072 8073 usbcore.authorized_default= 8074 [USB] Default USB device authorization: 8075 (default -1 = authorized (same as 1), 8076 0 = not authorized, 1 = authorized, 2 = authorized 8077 if device connected to internal port) 8078 8079 usbcore.autosuspend= 8080 [USB] The autosuspend time delay (in seconds) used 8081 for newly-detected USB devices (default 2). This 8082 is the time required before an idle device will be 8083 autosuspended. Devices for which the delay is set 8084 to a negative value won't be autosuspended at all. 8085 8086 usbcore.usbfs_snoop= 8087 [USB] Set to log all usbfs traffic (default 0 = off). 8088 8089 usbcore.usbfs_snoop_max= 8090 [USB] Maximum number of bytes to snoop in each URB 8091 (default = 65536). 8092 8093 usbcore.blinkenlights= 8094 [USB] Set to cycle leds on hubs (default 0 = off). 8095 8096 usbcore.old_scheme_first= 8097 [USB] Start with the old device initialization 8098 scheme (default 0 = off). 8099 8100 usbcore.usbfs_memory_mb= 8101 [USB] Memory limit (in MB) for buffers allocated by 8102 usbfs (default = 16, 0 = max = 2047). 8103 8104 usbcore.use_both_schemes= 8105 [USB] Try the other device initialization scheme 8106 if the first one fails (default 1 = enabled). 8107 8108 usbcore.initial_descriptor_timeout= 8109 [USB] Specifies timeout for the initial 64-byte 8110 USB_REQ_GET_DESCRIPTOR request in milliseconds 8111 (default 5000 = 5.0 seconds). 8112 8113 usbcore.nousb [USB] Disable the USB subsystem 8114 8115 usbcore.quirks= 8116 [USB] A list of quirk entries to augment the built-in 8117 usb core quirk list. List entries are separated by 8118 commas. Each entry has the form 8119 VendorID:ProductID:Flags. The IDs are 4-digit hex 8120 numbers and Flags is a set of letters. Each letter 8121 will change the built-in quirk; setting it if it is 8122 clear and clearing it if it is set. The letters have 8123 the following meanings: 8124 a = USB_QUIRK_STRING_FETCH_255 (string 8125 descriptors must not be fetched using 8126 a 255-byte read); 8127 b = USB_QUIRK_RESET_RESUME (device can't resume 8128 correctly so reset it instead); 8129 c = USB_QUIRK_NO_SET_INTF (device can't handle 8130 Set-Interface requests); 8131 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8132 handle its Configuration or Interface 8133 strings); 8134 e = USB_QUIRK_RESET (device can't be reset 8135 (e.g morph devices), don't use reset); 8136 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8137 more interface descriptions than the 8138 bNumInterfaces count, and can't handle 8139 talking to these interfaces); 8140 g = USB_QUIRK_DELAY_INIT (device needs a pause 8141 during initialization, after we read 8142 the device descriptor); 8143 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8144 high speed and super speed interrupt 8145 endpoints, the USB 2.0 and USB 3.0 spec 8146 require the interval in microframes (1 8147 microframe = 125 microseconds) to be 8148 calculated as interval = 2 ^ 8149 (bInterval-1). 8150 Devices with this quirk report their 8151 bInterval as the result of this 8152 calculation instead of the exponent 8153 variable used in the calculation); 8154 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8155 handle device_qualifier descriptor 8156 requests); 8157 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8158 generates spurious wakeup, ignore 8159 remote wakeup capability); 8160 k = USB_QUIRK_NO_LPM (device can't handle Link 8161 Power Management); 8162 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8163 (Device reports its bInterval as linear 8164 frames instead of the USB 2.0 8165 calculation); 8166 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8167 to be disconnected before suspend to 8168 prevent spurious wakeup); 8169 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8170 pause after every control message); 8171 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8172 delay after resetting its port); 8173 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8174 (Reduce timeout of the SET_ADDRESS 8175 request from 5000 ms to 500 ms); 8176 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8177 claims zero configurations, 8178 forcing to 1); 8179 Example: quirks=0781:5580:bk,0a5c:5834:gij 8180 8181 usbhid.mousepoll= 8182 [USBHID] The interval which mice are to be polled at. 8183 8184 usbhid.jspoll= 8185 [USBHID] The interval which joysticks are to be polled at. 8186 8187 usbhid.kbpoll= 8188 [USBHID] The interval which keyboards are to be polled at. 8189 8190 usb-storage.delay_use= 8191 [UMS] The delay in seconds before a new device is 8192 scanned for Logical Units (default 1). 8193 Optionally the delay in milliseconds if the value has 8194 suffix with "ms". 8195 Example: delay_use=2567ms 8196 8197 usb-storage.quirks= 8198 [UMS] A list of quirks entries to supplement or 8199 override the built-in unusual_devs list. List 8200 entries are separated by commas. Each entry has 8201 the form VID:PID:Flags where VID and PID are Vendor 8202 and Product ID values (4-digit hex numbers) and 8203 Flags is a set of characters, each corresponding 8204 to a common usb-storage quirk flag as follows: 8205 a = SANE_SENSE (collect more than 18 bytes 8206 of sense data, not on uas); 8207 b = BAD_SENSE (don't collect more than 18 8208 bytes of sense data, not on uas); 8209 c = FIX_CAPACITY (decrease the reported 8210 device capacity by one sector); 8211 d = NO_READ_DISC_INFO (don't use 8212 READ_DISC_INFO command, not on uas); 8213 e = NO_READ_CAPACITY_16 (don't use 8214 READ_CAPACITY_16 command); 8215 f = NO_REPORT_OPCODES (don't use report opcodes 8216 command, uas only); 8217 g = MAX_SECTORS_240 (don't transfer more than 8218 240 sectors at a time, uas only); 8219 h = CAPACITY_HEURISTICS (decrease the 8220 reported device capacity by one 8221 sector if the number is odd); 8222 i = IGNORE_DEVICE (don't bind to this 8223 device); 8224 j = NO_REPORT_LUNS (don't use report luns 8225 command, uas only); 8226 k = NO_SAME (do not use WRITE_SAME, uas only) 8227 l = NOT_LOCKABLE (don't try to lock and 8228 unlock ejectable media, not on uas); 8229 m = MAX_SECTORS_64 (don't transfer more 8230 than 64 sectors = 32 KB at a time, 8231 not on uas); 8232 n = INITIAL_READ10 (force a retry of the 8233 initial READ(10) command, not on uas); 8234 o = CAPACITY_OK (accept the capacity 8235 reported by the device, not on uas); 8236 p = WRITE_CACHE (the device cache is ON 8237 by default, not on uas); 8238 r = IGNORE_RESIDUE (the device reports 8239 bogus residue values, not on uas); 8240 s = SINGLE_LUN (the device has only one 8241 Logical Unit); 8242 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8243 commands, uas only); 8244 u = IGNORE_UAS (don't bind to the uas driver); 8245 w = NO_WP_DETECT (don't test whether the 8246 medium is write-protected). 8247 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8248 even if the device claims no cache, 8249 not on uas) 8250 Example: quirks=0419:aaf5:rl,0421:0433:rc 8251 8252 user_debug= [KNL,ARM] 8253 Format: <int> 8254 See arch/arm/Kconfig.debug help text. 8255 1 - undefined instruction events 8256 2 - system calls 8257 4 - invalid data aborts 8258 8 - SIGSEGV faults 8259 16 - SIGBUS faults 8260 Example: user_debug=31 8261 8262 vdso= [X86,SH,SPARC] 8263 On X86_32, this is an alias for vdso32=. Otherwise: 8264 8265 vdso=1: enable VDSO (the default) 8266 vdso=0: disable VDSO mapping 8267 8268 vdso32= [X86] Control the 32-bit vDSO 8269 vdso32=1: enable 32-bit VDSO 8270 vdso32=0 or vdso32=2: disable 32-bit VDSO 8271 8272 See the help text for CONFIG_COMPAT_VDSO for more 8273 details. If CONFIG_COMPAT_VDSO is set, the default is 8274 vdso32=0; otherwise, the default is vdso32=1. 8275 8276 For compatibility with older kernels, vdso32=2 is an 8277 alias for vdso32=0. 8278 8279 Try vdso32=0 if you encounter an error that says: 8280 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8281 8282 video= [FB,EARLY] Frame buffer configuration 8283 See Documentation/fb/modedb.rst. 8284 8285 video.brightness_switch_enabled= [ACPI] 8286 Format: [0|1] 8287 If set to 1, on receiving an ACPI notify event 8288 generated by hotkey, video driver will adjust brightness 8289 level and then send out the event to user space through 8290 the allocated input device. If set to 0, video driver 8291 will only send out the event without touching backlight 8292 brightness level. 8293 default: 1 8294 8295 virtio_mmio.device= 8296 [VMMIO] Memory mapped virtio (platform) device. 8297 8298 <size>@<baseaddr>:<irq>[:<id>] 8299 where: 8300 <size> := size (can use standard suffixes 8301 like K, M and G) 8302 <baseaddr> := physical base address 8303 <irq> := interrupt number (as passed to 8304 request_irq()) 8305 <id> := (optional) platform device id 8306 example: 8307 virtio_mmio.device=1K@0x100b0000:48:7 8308 8309 Can be used multiple times for multiple devices. 8310 8311 vga= [BOOT,X86-32] Select a particular video mode 8312 See Documentation/arch/x86/boot.rst and 8313 Documentation/admin-guide/svga.rst. 8314 Use vga=ask for menu. 8315 This is actually a boot loader parameter; the value is 8316 passed to the kernel using a special protocol. 8317 8318 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8319 May slow down system boot speed, especially when 8320 enabled on systems with a large amount of memory. 8321 All options are enabled by default, and this 8322 interface is meant to allow for selectively 8323 enabling or disabling specific virtual memory 8324 debugging features. 8325 8326 Available options are: 8327 P Enable page structure init time poisoning 8328 - Disable all of the above options 8329 8330 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8331 exact size of <nn>. This can be used to increase 8332 the minimum size (128MB on x86, arm32 platforms). 8333 It can also be used to decrease the size and leave more room 8334 for directly mapped kernel RAM. Note that this parameter does 8335 not exist on many other platforms (including arm64, alpha, 8336 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8337 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8338 8339 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8340 Sets the memory size reserved for contiguous memory 8341 allocations for the vmcp device driver. 8342 8343 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8344 Format: <command> 8345 8346 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8347 Format: <command> 8348 8349 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8350 Format: <command> 8351 8352 vmscape= [X86] Controls mitigation for VMscape attacks. 8353 VMscape attacks can leak information from a userspace 8354 hypervisor to a guest via speculative side-channels. 8355 8356 off - disable the mitigation 8357 ibpb - use Indirect Branch Prediction Barrier 8358 (IBPB) mitigation (default) 8359 force - force vulnerability detection even on 8360 unaffected processors 8361 8362 vsyscall= [X86-64,EARLY] 8363 Controls the behavior of vsyscalls (i.e. calls to 8364 fixed addresses of 0xffffffffff600x00 from legacy 8365 code). Most statically-linked binaries and older 8366 versions of glibc use these calls. Because these 8367 functions are at fixed addresses, they make nice 8368 targets for exploits that can control RIP. 8369 8370 emulate Vsyscalls turn into traps and are emulated 8371 reasonably safely. The vsyscall page is 8372 readable. This disables the Linear 8373 Address Space Separation (LASS) security 8374 feature and makes the system less secure. 8375 8376 xonly [default] Vsyscalls turn into traps and are 8377 emulated reasonably safely. The vsyscall 8378 page is not readable. 8379 8380 none Vsyscalls don't work at all. This makes 8381 them quite hard to use for exploits but 8382 might break your system. 8383 8384 vt.color= [VT] Default text color. 8385 Format: 0xYX, X = foreground, Y = background. 8386 Default: 0x07 = light gray on black. 8387 8388 vt.cur_default= [VT] Default cursor shape. 8389 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8390 the parameters of the <Esc>[?A;B;Cc escape sequence; 8391 see vga-softcursor.rst. Default: 2 = underline. 8392 8393 vt.default_blu= [VT] 8394 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8395 Change the default blue palette of the console. 8396 This is a 16-member array composed of values 8397 ranging from 0-255. 8398 8399 vt.default_grn= [VT] 8400 Format: <green0>,<green1>,<green2>,...,<green15> 8401 Change the default green palette of the console. 8402 This is a 16-member array composed of values 8403 ranging from 0-255. 8404 8405 vt.default_red= [VT] 8406 Format: <red0>,<red1>,<red2>,...,<red15> 8407 Change the default red palette of the console. 8408 This is a 16-member array composed of values 8409 ranging from 0-255. 8410 8411 vt.default_utf8= 8412 [VT] 8413 Format=<0|1> 8414 Set system-wide default UTF-8 mode for all tty's. 8415 Default is 1, i.e. UTF-8 mode is enabled for all 8416 newly opened terminals. 8417 8418 vt.global_cursor_default= 8419 [VT] 8420 Format=<-1|0|1> 8421 Set system-wide default for whether a cursor 8422 is shown on new VTs. Default is -1, 8423 i.e. cursors will be created by default unless 8424 overridden by individual drivers. 0 will hide 8425 cursors, 1 will display them. 8426 8427 vt.italic= [VT] Default color for italic text; 0-15. 8428 Default: 2 = green. 8429 8430 vt.underline= [VT] Default color for underlined text; 0-15. 8431 Default: 3 = cyan. 8432 8433 watchdog timers [HW,WDT] For information on watchdog timers, 8434 see Documentation/watchdog/watchdog-parameters.rst 8435 or other driver-specific files in the 8436 Documentation/watchdog/ directory. 8437 8438 watchdog_thresh= 8439 [KNL] 8440 Set the hard lockup detector stall duration 8441 threshold in seconds. The soft lockup detector 8442 threshold is set to twice the value. A value of 0 8443 disables both lockup detectors. Default is 10 8444 seconds. 8445 8446 workqueue.unbound_cpus= 8447 [KNL,SMP] Specify to constrain one or some CPUs 8448 to use in unbound workqueues. 8449 Format: <cpu-list> 8450 By default, all online CPUs are available for 8451 unbound workqueues. 8452 8453 workqueue.watchdog_thresh= 8454 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8455 warn stall conditions and dump internal state to 8456 help debugging. 0 disables workqueue stall 8457 detection; otherwise, it's the stall threshold 8458 duration in seconds. The default value is 30 and 8459 it can be updated at runtime by writing to the 8460 corresponding sysfs file. 8461 8462 workqueue.panic_on_stall=<uint> 8463 Panic when workqueue stall is detected by 8464 CONFIG_WQ_WATCHDOG. It sets the number times of the 8465 stall to trigger panic. 8466 8467 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8468 which is 0 (disabled) if not configured. 8469 8470 workqueue.panic_on_stall_time=<uint> 8471 Panic when a workqueue stall has been continuous for 8472 the specified number of seconds. Unlike panic_on_stall 8473 which counts accumulated stall events, this triggers 8474 based on the duration of a single continuous stall. 8475 8476 The default is 0, which disables the time-based panic. 8477 8478 workqueue.cpu_intensive_thresh_us= 8479 Per-cpu work items which run for longer than this 8480 threshold are automatically considered CPU intensive 8481 and excluded from concurrency management to prevent 8482 them from noticeably delaying other per-cpu work 8483 items. Default is 10000 (10ms). 8484 8485 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8486 will report the work functions which violate this 8487 threshold repeatedly. They are likely good 8488 candidates for using WQ_UNBOUND workqueues instead. 8489 8490 workqueue.cpu_intensive_warning_thresh=<uint> 8491 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8492 will report the work functions which violate the 8493 intensive_threshold_us repeatedly. In order to prevent 8494 spurious warnings, start printing only after a work 8495 function has violated this threshold number of times. 8496 8497 The default is 4 times. 0 disables the warning. 8498 8499 workqueue.power_efficient 8500 Per-cpu workqueues are generally preferred because 8501 they show better performance thanks to cache 8502 locality; unfortunately, per-cpu workqueues tend to 8503 be more power hungry than unbound workqueues. 8504 8505 Enabling this makes the per-cpu workqueues which 8506 were observed to contribute significantly to power 8507 consumption unbound, leading to measurably lower 8508 power usage at the cost of small performance 8509 overhead. 8510 8511 The default value of this parameter is determined by 8512 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8513 8514 workqueue.default_affinity_scope= 8515 Select the default affinity scope to use for unbound 8516 workqueues. Can be one of "cpu", "smt", "cache", 8517 "cache_shard", "numa" and "system". Default is 8518 "cache_shard". For more 8519 information, see the Affinity Scopes section in 8520 Documentation/core-api/workqueue.rst. 8521 8522 This can be changed after boot by writing to the 8523 matching /sys/module/workqueue/parameters file. All 8524 workqueues with the "default" affinity scope will be 8525 updated accordingly. 8526 8527 workqueue.debug_force_rr_cpu 8528 Workqueue used to implicitly guarantee that work 8529 items queued without explicit CPU specified are put 8530 on the local CPU. This guarantee is no longer true 8531 and while local CPU is still preferred work items 8532 may be put on foreign CPUs. This debug option 8533 forces round-robin CPU selection to flush out 8534 usages which depend on the now broken guarantee. 8535 When enabled, memory and cache locality will be 8536 impacted. 8537 8538 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8539 Type) of ioremap_wc(). 8540 8541 on - Enable writecombine, use WUC for ioremap_wc() 8542 off - Disable writecombine, use SUC for ioremap_wc() 8543 8544 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8545 default x2apic cluster mode on platforms 8546 supporting x2apic. 8547 8548 xen_512gb_limit [KNL,X86-64,XEN] 8549 Restricts the kernel running paravirtualized under Xen 8550 to use only up to 512 GB of RAM. The reason to do so is 8551 crash analysis tools and Xen tools for doing domain 8552 save/restore/migration must be enabled to handle larger 8553 domains. 8554 8555 xen_console_io [XEN,EARLY] 8556 Boolean option to enable/disable the usage of the Xen 8557 console_io hypercalls to read and write to the console. 8558 Mostly useful for debugging and development. 8559 8560 xen_emul_unplug= [HW,X86,XEN,EARLY] 8561 Unplug Xen emulated devices 8562 Format: [unplug0,][unplug1] 8563 ide-disks -- unplug primary master IDE devices 8564 aux-ide-disks -- unplug non-primary-master IDE devices 8565 nics -- unplug network devices 8566 all -- unplug all emulated devices (NICs and IDE disks) 8567 unnecessary -- unplugging emulated devices is 8568 unnecessary even if the host did not respond to 8569 the unplug protocol 8570 never -- do not unplug even if version check succeeds 8571 8572 xen_legacy_crash [X86,XEN,EARLY] 8573 Crash from Xen panic notifier, without executing late 8574 panic() code such as dumping handler. 8575 8576 xen_mc_debug [X86,XEN,EARLY] 8577 Enable multicall debugging when running as a Xen PV guest. 8578 Enabling this feature will reduce performance a little 8579 bit, so it should only be enabled for obtaining extended 8580 debug data in case of multicall errors. 8581 8582 xen_msr_safe= [X86,XEN,EARLY] 8583 Format: <bool> 8584 Select whether to always use non-faulting (safe) MSR 8585 access functions when running as Xen PV guest. The 8586 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8587 8588 xen_nopv [X86] 8589 Disables the PV optimizations forcing the HVM guest to 8590 run as generic HVM guest with no PV drivers. 8591 This option is obsoleted by the "nopv" option, which 8592 has equivalent effect for XEN platform. 8593 8594 xen_no_vector_callback 8595 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8596 event channel interrupts. 8597 8598 xen_scrub_pages= [XEN] 8599 Boolean option to control scrubbing pages before giving them back 8600 to Xen, for use by other domains. Can be also changed at runtime 8601 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8602 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8603 8604 xen_timer_slop= [X86-64,XEN,EARLY] 8605 Set the timer slop (in nanoseconds) for the virtual Xen 8606 timers (default is 100000). This adjusts the minimum 8607 delta of virtualized Xen timers, where lower values 8608 improve timer resolution at the expense of processing 8609 more timer interrupts. 8610 8611 xen.balloon_boot_timeout= [XEN] 8612 The time (in seconds) to wait before giving up to boot 8613 in case initial ballooning fails to free enough memory. 8614 Applies only when running as HVM or PVH guest and 8615 started with less memory configured than allowed at 8616 max. Default is 180. 8617 8618 xen.event_eoi_delay= [XEN] 8619 How long to delay EOI handling in case of event 8620 storms (jiffies). Default is 10. 8621 8622 xen.event_loop_timeout= [XEN] 8623 After which time (jiffies) the event handling loop 8624 should start to delay EOI handling. Default is 2. 8625 8626 xen.fifo_events= [XEN] 8627 Boolean parameter to disable using fifo event handling 8628 even if available. Normally fifo event handling is 8629 preferred over the 2-level event handling, as it is 8630 fairer and the number of possible event channels is 8631 much higher. Default is on (use fifo events). 8632 8633 xirc2ps_cs= [NET,PCMCIA] 8634 Format: 8635 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8636 8637 xive= [PPC] 8638 By default on POWER9 and above, the kernel will 8639 natively use the XIVE interrupt controller. This option 8640 allows the fallback firmware mode to be used: 8641 8642 off Fallback to firmware control of XIVE interrupt 8643 controller on both pseries and powernv 8644 platforms. Only useful on POWER9 and above. 8645 8646 xive.store-eoi=off [PPC] 8647 By default on POWER10 and above, the kernel will use 8648 stores for EOI handling when the XIVE interrupt mode 8649 is active. This option allows the XIVE driver to use 8650 loads instead, as on POWER9. 8651 8652 xhci-hcd.quirks [USB,KNL] 8653 A hex value specifying bitmask with supplemental xhci 8654 host controller quirks. Meaning of each bit can be 8655 consulted in header drivers/usb/host/xhci.h. 8656 8657 xmon [PPC,EARLY] 8658 Format: { early | on | rw | ro | off } 8659 Controls if xmon debugger is enabled. Default is off. 8660 Passing only "xmon" is equivalent to "xmon=early". 8661 early Call xmon as early as possible on boot; xmon 8662 debugger is called from setup_arch(). 8663 on xmon debugger hooks will be installed so xmon 8664 is only called on a kernel crash. Default mode, 8665 i.e. either "ro" or "rw" mode, is controlled 8666 with CONFIG_XMON_DEFAULT_RO_MODE. 8667 rw xmon debugger hooks will be installed so xmon 8668 is called only on a kernel crash, mode is write, 8669 meaning SPR registers, memory and, other data 8670 can be written using xmon commands. 8671 ro same as "rw" option above but SPR registers, 8672 memory, and other data can't be written using 8673 xmon commands. 8674 off xmon is disabled. 8675