.. 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: series board detected. Selecting 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. 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. : use no hardware/software IOMMU at all (e.g. because you have < 3 GB memory). Kernel boot message: "PCI-DMA: Disabling IOMMU" 2. : AMD GART based hardware IOMMU. Kernel boot message: "PCI-DMA: using GART IOMMU" 3. : 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=[][,noagp][,off][,force][,noforce] [,memaper[=]][,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: 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[=] Allocate an own aperture over RAM with size 32MB<[,force,noforce] 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. nosnp Do not enable SEV-SNP (applies to host/hypervisor only). Setting 'nosnp' avoids the RMP check overhead in memory accesses when users do not want to run SEV-SNP guests.