Documentation/arch/x86/x86_64/boot-options.rst - linux - Git at Google

 .. SPDX-License-Identifier: GPL-2.0

 ===========================
 AMD64 Specific Boot Options
 ===========================

 There are many others (usually documented in driver documentation), but
 only the AMD64 specific ones are listed here.

 Machine check
 =============
 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.

    mce=off
 		Disable machine check
    mce=no_cmci
 		Disable CMCI(Corrected Machine Check Interrupt) that
 		Intel processor supports.  Usually this disablement is
 		not recommended, but it might be handy if your hardware
 		is misbehaving.
 		Note that you'll get more problems without CMCI than with
 		due to the shared banks, i.e. you might get duplicated
 		error logs.
    mce=dont_log_ce
 		Don't make logs for corrected errors.  All events reported
 		as corrected are silently cleared by OS.
 		This option will be useful if you have no interest in any
 		of corrected errors.
    mce=ignore_ce
 		Disable features for corrected errors, e.g. polling timer
 		and CMCI.  All events reported as corrected are not cleared
 		by OS and remained in its error banks.
 		Usually this disablement is not recommended, however if
 		there is an agent checking/clearing corrected errors
 		(e.g. BIOS or hardware monitoring applications), conflicting
 		with OS's error handling, and you cannot deactivate the agent,
 		then this option will be a help.
    mce=no_lmce
 		Do not opt-in to Local MCE delivery. Use legacy method
 		to broadcast MCEs.
    mce=bootlog
 		Enable logging of machine checks left over from booting.
 		Disabled by default on AMD Fam10h and older because some BIOS
 		leave bogus ones.
 		If your BIOS doesn't do that it's a good idea to enable though
 		to make sure you log even machine check events that result
 		in a reboot. On Intel systems it is enabled by default.
    mce=nobootlog
 		Disable boot machine check logging.
    mce=monarchtimeout (number)
 		monarchtimeout:
 		Sets the time in us to wait for other CPUs on machine checks. 0
 		to disable.
    mce=bios_cmci_threshold
 		Don't overwrite the bios-set CMCI threshold. This boot option
 		prevents Linux from overwriting the CMCI threshold set by the
 		bios. Without this option, Linux always sets the CMCI
 		threshold to 1. Enabling this may make memory predictive failure
 		analysis less effective if the bios sets thresholds for memory
 		errors since we will not see details for all errors.
    mce=recovery
 		Force-enable recoverable machine check code paths

    nomce (for compatibility with i386)
 		same as mce=off

    Everything else is in sysfs now.

 APICs
 =====

    apic
 	Use IO-APIC. Default

    noapic
 	Don't use the IO-APIC.

    disableapic
 	Don't use the local APIC

    nolapic
      Don't use the local APIC (alias for i386 compatibility)

    pirq=...
 	See Documentation/arch/x86/i386/IO-APIC.rst

    noapictimer
 	Don't set up the APIC timer

    no_timer_check
 	Don't check the IO-APIC timer. This can work around
 	problems with incorrect timer initialization on some boards.

    apicpmtimer
 	Do APIC timer calibration using the pmtimer. Implies
 	apicmaintimer. Useful when your PIT timer is totally broken.

 Timing
 ======

   notsc
     Deprecated, use tsc=unstable instead.

   nohpet
     Don't use the HPET timer.

 Idle loop
 =========

   idle=poll
     Don't do power saving in the idle loop using HLT, but poll for rescheduling
     event. This will make the CPUs eat a lot more power, but may be useful
     to get slightly better performance in multiprocessor benchmarks. It also
     makes some profiling using performance counters more accurate.
     Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
     CPUs) this option has no performance advantage over the normal idle loop.
     It may also interact badly with hyperthreading.

 Rebooting
 =========

    reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] | p[ci] [, [w]arm | [c]old]
       bios
         Use the CPU reboot vector for warm reset
       warm
         Don't set the cold reboot flag
       cold
         Set the cold reboot flag
       triple
         Force a triple fault (init)
       kbd
         Use the keyboard controller. cold reset (default)
       acpi
         Use the ACPI RESET_REG in the FADT. If ACPI is not configured or
         the ACPI reset does not work, the reboot path attempts the reset
         using the keyboard controller.
       efi
         Use efi reset_system runtime service. If EFI is not configured or
         the EFI reset does not work, the reboot path attempts the reset using
         the keyboard controller.
       pci
         Use a write to the PCI config space register 0xcf9 to trigger reboot.

    Using warm reset will be much faster especially on big memory
    systems because the BIOS will not go through the memory check.
    Disadvantage is that not all hardware will be completely reinitialized
    on reboot so there may be boot problems on some systems.

    reboot=force
      Don't stop other CPUs on reboot. This can make reboot more reliable
      in some cases.

    reboot=default
      There are some built-in platform specific "quirks" - you may see:
      "reboot: <name> series board detected. Selecting <type> for reboots."
      In the case where you think the quirk is in error (e.g. you have
      newer BIOS, or newer board) using this option will ignore the built-in
      quirk table, and use the generic default reboot actions.

 NUMA
 ====

   numa=off
     Only set up a single NUMA node spanning all memory.

   numa=noacpi
     Don't parse the SRAT table for NUMA setup

   numa=nohmat
     Don't parse the HMAT table for NUMA setup, or soft-reserved memory
     partitioning.

   numa=fake=<size>[MG]
     If given as a memory unit, fills all system RAM with nodes of
     size interleaved over physical nodes.

   numa=fake=<N>
     If given as an integer, fills all system RAM with N fake nodes
     interleaved over physical nodes.

   numa=fake=<N>U
     If given as an integer followed by 'U', it will divide each
     physical node into N emulated nodes.

 ACPI
 ====

   acpi=off
     Don't enable ACPI
   acpi=ht
     Use ACPI boot table parsing, but don't enable ACPI interpreter
   acpi=force
     Force ACPI on (currently not needed)
   acpi=strict
     Disable out of spec ACPI workarounds.
   acpi_sci={edge,level,high,low}
     Set up ACPI SCI interrupt.
   acpi=noirq
     Don't route interrupts
   acpi=nocmcff
     Disable firmware first mode for corrected errors. This
     disables parsing the HEST CMC error source to check if
     firmware has set the FF flag. This may result in
     duplicate corrected error reports.

 PCI
 ===

   pci=off
     Don't use PCI
   pci=conf1
     Use conf1 access.
   pci=conf2
     Use conf2 access.
   pci=rom
     Assign ROMs.
   pci=assign-busses
     Assign busses
   pci=irqmask=MASK
     Set PCI interrupt mask to MASK
   pci=lastbus=NUMBER
     Scan up to NUMBER busses, no matter what the mptable says.
   pci=noacpi
     Don't use ACPI to set up PCI interrupt routing.

 IOMMU (input/output memory management unit)
 ===========================================
 Multiple x86-64 PCI-DMA mapping implementations exist, for example:

    1. <kernel/dma/direct.c>: use no hardware/software IOMMU at all
       (e.g. because you have < 3 GB memory).
       Kernel boot message: "PCI-DMA: Disabling IOMMU"

    2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
       Kernel boot message: "PCI-DMA: using GART IOMMU"

    3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
       e.g. if there is no hardware IOMMU in the system and it is need because
       you have >3GB memory or told the kernel to us it (iommu=soft))
       Kernel boot message: "PCI-DMA: Using software bounce buffering
       for IO (SWIOTLB)"

 ::

   iommu=[<size>][,noagp][,off][,force][,noforce]
   [,memaper[=<order>]][,merge][,fullflush][,nomerge]
   [,noaperture]

 General iommu options:

     off
       Don't initialize and use any kind of IOMMU.
     noforce
       Don't force hardware IOMMU usage when it is not needed. (default).
     force
       Force the use of the hardware IOMMU even when it is
       not actually needed (e.g. because < 3 GB memory).
     soft
       Use software bounce buffering (SWIOTLB) (default for
       Intel machines). This can be used to prevent the usage
       of an available hardware IOMMU.

 iommu options only relevant to the AMD GART hardware IOMMU:

     <size>
       Set the size of the remapping area in bytes.
     allowed
       Overwrite iommu off workarounds for specific chipsets.
     fullflush
       Flush IOMMU on each allocation (default).
     nofullflush
       Don't use IOMMU fullflush.
     memaper[=<order>]
       Allocate an own aperture over RAM with size 32MB<<order.
       (default: order=1, i.e. 64MB)
     merge
       Do scatter-gather (SG) merging. Implies "force" (experimental).
     nomerge
       Don't do scatter-gather (SG) merging.
     noaperture
       Ask the IOMMU not to touch the aperture for AGP.
     noagp
       Don't initialize the AGP driver and use full aperture.
     panic
       Always panic when IOMMU overflows.

 iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
 implementation:

     swiotlb=<slots>[,force,noforce]
       <slots>
         Prereserve that many 2K slots for the software IO bounce buffering.
       force
         Force all IO through the software TLB.
       noforce
         Do not initialize the software TLB.


 Miscellaneous
 =============

   nogbpages
     Do not use GB pages for kernel direct mappings.
   gbpages
     Use GB pages for kernel direct mappings.


 AMD SEV (Secure Encrypted Virtualization)
 =========================================
 Options relating to AMD SEV, specified via the following format:

 ::

    sev=option1[,option2]

 The available options are:

    debug
      Enable debug messages.
	.. SPDX-License-Identifier: GPL-2.0

	===========================
	AMD64 Specific Boot Options
	===========================

	There are many others (usually documented in driver documentation), but
	only the AMD64 specific ones are listed here.

	Machine check
	=============
	Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.

	mce=off
	Disable machine check
	mce=no_cmci
	Disable CMCI(Corrected Machine Check Interrupt) that
	Intel processor supports. Usually this disablement is
	not recommended, but it might be handy if your hardware
	is misbehaving.
	Note that you'll get more problems without CMCI than with
	due to the shared banks, i.e. you might get duplicated
	error logs.
	mce=dont_log_ce
	Don't make logs for corrected errors. All events reported
	as corrected are silently cleared by OS.
	This option will be useful if you have no interest in any
	of corrected errors.
	mce=ignore_ce
	Disable features for corrected errors, e.g. polling timer
	and CMCI. All events reported as corrected are not cleared
	by OS and remained in its error banks.
	Usually this disablement is not recommended, however if
	there is an agent checking/clearing corrected errors
	(e.g. BIOS or hardware monitoring applications), conflicting
	with OS's error handling, and you cannot deactivate the agent,
	then this option will be a help.
	mce=no_lmce
	Do not opt-in to Local MCE delivery. Use legacy method
	to broadcast MCEs.
	mce=bootlog
	Enable logging of machine checks left over from booting.
	Disabled by default on AMD Fam10h and older because some BIOS
	leave bogus ones.
	If your BIOS doesn't do that it's a good idea to enable though
	to make sure you log even machine check events that result
	in a reboot. On Intel systems it is enabled by default.
	mce=nobootlog
	Disable boot machine check logging.
	mce=monarchtimeout (number)
	monarchtimeout:
	Sets the time in us to wait for other CPUs on machine checks. 0
	to disable.
	mce=bios_cmci_threshold
	Don't overwrite the bios-set CMCI threshold. This boot option
	prevents Linux from overwriting the CMCI threshold set by the
	bios. Without this option, Linux always sets the CMCI
	threshold to 1. Enabling this may make memory predictive failure
	analysis less effective if the bios sets thresholds for memory
	errors since we will not see details for all errors.
	mce=recovery
	Force-enable recoverable machine check code paths

	nomce (for compatibility with i386)
	same as mce=off

	Everything else is in sysfs now.

	APICs
	=====

	apic
	Use IO-APIC. Default

	noapic
	Don't use the IO-APIC.

	disableapic
	Don't use the local APIC

	nolapic
	Don't use the local APIC (alias for i386 compatibility)

	pirq=...
	See Documentation/arch/x86/i386/IO-APIC.rst

	noapictimer
	Don't set up the APIC timer

	no_timer_check
	Don't check the IO-APIC timer. This can work around
	problems with incorrect timer initialization on some boards.

	apicpmtimer
	Do APIC timer calibration using the pmtimer. Implies
	apicmaintimer. Useful when your PIT timer is totally broken.

	Timing
	======

	notsc
	Deprecated, use tsc=unstable instead.

	nohpet
	Don't use the HPET timer.

	Idle loop
	=========

	idle=poll
	Don't do power saving in the idle loop using HLT, but poll for rescheduling
	event. This will make the CPUs eat a lot more power, but may be useful
	to get slightly better performance in multiprocessor benchmarks. It also
	makes some profiling using performance counters more accurate.
	Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
	CPUs) this option has no performance advantage over the normal idle loop.
	It may also interact badly with hyperthreading.

	Rebooting
	=========

	reboot=b[ios] \| t[riple] \| k[bd] \| a[cpi] \| e[fi] \| p[ci] [, [w]arm \| [c]old]
	bios
	Use the CPU reboot vector for warm reset
	warm
	Don't set the cold reboot flag
	cold
	Set the cold reboot flag
	triple
	Force a triple fault (init)
	kbd
	Use the keyboard controller. cold reset (default)
	acpi
	Use the ACPI RESET_REG in the FADT. If ACPI is not configured or
	the ACPI reset does not work, the reboot path attempts the reset
	using the keyboard controller.
	efi
	Use efi reset_system runtime service. If EFI is not configured or
	the EFI reset does not work, the reboot path attempts the reset using
	the keyboard controller.
	pci
	Use a write to the PCI config space register 0xcf9 to trigger reboot.

	Using warm reset will be much faster especially on big memory
	systems because the BIOS will not go through the memory check.
	Disadvantage is that not all hardware will be completely reinitialized
	on reboot so there may be boot problems on some systems.

	reboot=force
	Don't stop other CPUs on reboot. This can make reboot more reliable
	in some cases.

	reboot=default
	There are some built-in platform specific "quirks" - you may see:
	"reboot: <name> series board detected. Selecting <type> for reboots."
	In the case where you think the quirk is in error (e.g. you have
	newer BIOS, or newer board) using this option will ignore the built-in
	quirk table, and use the generic default reboot actions.

	NUMA
	====

	numa=off
	Only set up a single NUMA node spanning all memory.

	numa=noacpi
	Don't parse the SRAT table for NUMA setup

	numa=nohmat
	Don't parse the HMAT table for NUMA setup, or soft-reserved memory
	partitioning.

	numa=fake=<size>[MG]
	If given as a memory unit, fills all system RAM with nodes of
	size interleaved over physical nodes.

	numa=fake=<N>
	If given as an integer, fills all system RAM with N fake nodes
	interleaved over physical nodes.

	numa=fake=<N>U
	If given as an integer followed by 'U', it will divide each
	physical node into N emulated nodes.

	ACPI
	====

	acpi=off
	Don't enable ACPI
	acpi=ht
	Use ACPI boot table parsing, but don't enable ACPI interpreter
	acpi=force
	Force ACPI on (currently not needed)
	acpi=strict
	Disable out of spec ACPI workarounds.
	acpi_sci={edge,level,high,low}
	Set up ACPI SCI interrupt.
	acpi=noirq
	Don't route interrupts
	acpi=nocmcff
	Disable firmware first mode for corrected errors. This
	disables parsing the HEST CMC error source to check if
	firmware has set the FF flag. This may result in
	duplicate corrected error reports.

	PCI
	===

	pci=off
	Don't use PCI
	pci=conf1
	Use conf1 access.
	pci=conf2
	Use conf2 access.
	pci=rom
	Assign ROMs.
	pci=assign-busses
	Assign busses
	pci=irqmask=MASK
	Set PCI interrupt mask to MASK
	pci=lastbus=NUMBER
	Scan up to NUMBER busses, no matter what the mptable says.
	pci=noacpi
	Don't use ACPI to set up PCI interrupt routing.

	IOMMU (input/output memory management unit)
	===========================================
	Multiple x86-64 PCI-DMA mapping implementations exist, for example:

	1. <kernel/dma/direct.c>: use no hardware/software IOMMU at all
	(e.g. because you have < 3 GB memory).
	Kernel boot message: "PCI-DMA: Disabling IOMMU"

	2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
	Kernel boot message: "PCI-DMA: using GART IOMMU"

	3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
	e.g. if there is no hardware IOMMU in the system and it is need because
	you have >3GB memory or told the kernel to us it (iommu=soft))
	Kernel boot message: "PCI-DMA: Using software bounce buffering
	for IO (SWIOTLB)"

	::

	iommu=[<size>][,noagp][,off][,force][,noforce]
	[,memaper[=<order>]][,merge][,fullflush][,nomerge]
	[,noaperture]

	General iommu options:

	off
	Don't initialize and use any kind of IOMMU.
	noforce
	Don't force hardware IOMMU usage when it is not needed. (default).
	force
	Force the use of the hardware IOMMU even when it is
	not actually needed (e.g. because < 3 GB memory).
	soft
	Use software bounce buffering (SWIOTLB) (default for
	Intel machines). This can be used to prevent the usage
	of an available hardware IOMMU.

	iommu options only relevant to the AMD GART hardware IOMMU:

	<size>
	Set the size of the remapping area in bytes.
	allowed
	Overwrite iommu off workarounds for specific chipsets.
	fullflush
	Flush IOMMU on each allocation (default).
	nofullflush
	Don't use IOMMU fullflush.
	memaper[=<order>]
	Allocate an own aperture over RAM with size 32MB<<order.
	(default: order=1, i.e. 64MB)
	merge
	Do scatter-gather (SG) merging. Implies "force" (experimental).
	nomerge
	Don't do scatter-gather (SG) merging.
	noaperture
	Ask the IOMMU not to touch the aperture for AGP.
	noagp
	Don't initialize the AGP driver and use full aperture.
	panic
	Always panic when IOMMU overflows.

	iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
	implementation:

	swiotlb=<slots>[,force,noforce]
	<slots>
	Prereserve that many 2K slots for the software IO bounce buffering.
	force
	Force all IO through the software TLB.
	noforce
	Do not initialize the software TLB.


	Miscellaneous
	=============

	nogbpages
	Do not use GB pages for kernel direct mappings.
	gbpages
	Use GB pages for kernel direct mappings.


	AMD SEV (Secure Encrypted Virtualization)
	=========================================
	Options relating to AMD SEV, specified via the following format:

	::

	sev=option1[,option2]

	The available options are:

	debug
	Enable debug messages.