1 .. SPDX-License-Identifier: GPL-2.0
3 ===========================
4 AMD64 Specific Boot Options
5 ===========================
7 There are many others (usually documented in driver documentation), but
8 only the AMD64 specific ones are listed here.
12 Please see Documentation/x86/x86_64/machinecheck.rst for sysfs runtime tunables.
17 Disable CMCI(Corrected Machine Check Interrupt) that
18 Intel processor supports. Usually this disablement is
19 not recommended, but it might be handy if your hardware
21 Note that you'll get more problems without CMCI than with
22 due to the shared banks, i.e. you might get duplicated
25 Don't make logs for corrected errors. All events reported
26 as corrected are silently cleared by OS.
27 This option will be useful if you have no interest in any
30 Disable features for corrected errors, e.g. polling timer
31 and CMCI. All events reported as corrected are not cleared
32 by OS and remained in its error banks.
33 Usually this disablement is not recommended, however if
34 there is an agent checking/clearing corrected errors
35 (e.g. BIOS or hardware monitoring applications), conflicting
36 with OS's error handling, and you cannot deactivate the agent,
37 then this option will be a help.
39 Do not opt-in to Local MCE delivery. Use legacy method
42 Enable logging of machine checks left over from booting.
43 Disabled by default on AMD Fam10h and older because some BIOS
45 If your BIOS doesn't do that it's a good idea to enable though
46 to make sure you log even machine check events that result
47 in a reboot. On Intel systems it is enabled by default.
49 Disable boot machine check logging.
50 mce=tolerancelevel[,monarchtimeout] (number,number)
52 0: always panic on uncorrected errors, log corrected errors
53 1: panic or SIGBUS on uncorrected errors, log corrected errors
54 2: SIGBUS or log uncorrected errors, log corrected errors
55 3: never panic or SIGBUS, log all errors (for testing only)
57 Can be also set using sysfs which is preferable.
59 Sets the time in us to wait for other CPUs on machine checks. 0
61 mce=bios_cmci_threshold
62 Don't overwrite the bios-set CMCI threshold. This boot option
63 prevents Linux from overwriting the CMCI threshold set by the
64 bios. Without this option, Linux always sets the CMCI
65 threshold to 1. Enabling this may make memory predictive failure
66 analysis less effective if the bios sets thresholds for memory
67 errors since we will not see details for all errors.
69 Force-enable recoverable machine check code paths
71 nomce (for compatibility with i386)
74 Everything else is in sysfs now.
83 Don't use the IO-APIC.
86 Don't use the local APIC
89 Don't use the local APIC (alias for i386 compatibility)
92 See Documentation/x86/i386/IO-APIC.rst
95 Don't set up the APIC timer
98 Don't check the IO-APIC timer. This can work around
99 problems with incorrect timer initialization on some boards.
102 Do APIC timer calibration using the pmtimer. Implies
103 apicmaintimer. Useful when your PIT timer is totally broken.
109 Deprecated, use tsc=unstable instead.
112 Don't use the HPET timer.
118 Don't do power saving in the idle loop using HLT, but poll for rescheduling
119 event. This will make the CPUs eat a lot more power, but may be useful
120 to get slightly better performance in multiprocessor benchmarks. It also
121 makes some profiling using performance counters more accurate.
122 Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
123 CPUs) this option has no performance advantage over the normal idle loop.
124 It may also interact badly with hyperthreading.
129 reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] | p[ci] [, [w]arm | [c]old]
131 Use the CPU reboot vector for warm reset
133 Don't set the cold reboot flag
135 Set the cold reboot flag
137 Force a triple fault (init)
139 Use the keyboard controller. cold reset (default)
141 Use the ACPI RESET_REG in the FADT. If ACPI is not configured or
142 the ACPI reset does not work, the reboot path attempts the reset
143 using the keyboard controller.
145 Use efi reset_system runtime service. If EFI is not configured or
146 the EFI reset does not work, the reboot path attempts the reset using
147 the keyboard controller.
149 Use a write to the PCI config space register 0xcf9 to trigger reboot.
151 Using warm reset will be much faster especially on big memory
152 systems because the BIOS will not go through the memory check.
153 Disadvantage is that not all hardware will be completely reinitialized
154 on reboot so there may be boot problems on some systems.
157 Don't stop other CPUs on reboot. This can make reboot more reliable
161 There are some built-in platform specific "quirks" - you may see:
162 "reboot: <name> series board detected. Selecting <type> for reboots."
163 In the case where you think the quirk is in error (e.g. you have
164 newer BIOS, or newer board) using this option will ignore the built-in
165 quirk table, and use the generic default reboot actions.
167 Non Executable Mappings
168 =======================
180 Only set up a single NUMA node spanning all memory.
183 Don't parse the SRAT table for NUMA setup
186 Don't parse the HMAT table for NUMA setup, or soft-reserved memory
190 If given as a memory unit, fills all system RAM with nodes of
191 size interleaved over physical nodes.
194 If given as an integer, fills all system RAM with N fake nodes
195 interleaved over physical nodes.
198 If given as an integer followed by 'U', it will divide each
199 physical node into N emulated nodes.
207 Use ACPI boot table parsing, but don't enable ACPI interpreter
209 Force ACPI on (currently not needed)
211 Disable out of spec ACPI workarounds.
212 acpi_sci={edge,level,high,low}
213 Set up ACPI SCI interrupt.
215 Don't route interrupts
217 Disable firmware first mode for corrected errors. This
218 disables parsing the HEST CMC error source to check if
219 firmware has set the FF flag. This may result in
220 duplicate corrected error reports.
236 Set PCI interrupt mask to MASK
238 Scan up to NUMBER busses, no matter what the mptable says.
240 Don't use ACPI to set up PCI interrupt routing.
242 IOMMU (input/output memory management unit)
243 ===========================================
244 Multiple x86-64 PCI-DMA mapping implementations exist, for example:
246 1. <kernel/dma/direct.c>: use no hardware/software IOMMU at all
247 (e.g. because you have < 3 GB memory).
248 Kernel boot message: "PCI-DMA: Disabling IOMMU"
250 2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
251 Kernel boot message: "PCI-DMA: using GART IOMMU"
253 3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
254 e.g. if there is no hardware IOMMU in the system and it is need because
255 you have >3GB memory or told the kernel to us it (iommu=soft))
256 Kernel boot message: "PCI-DMA: Using software bounce buffering
261 iommu=[<size>][,noagp][,off][,force][,noforce]
262 [,memaper[=<order>]][,merge][,fullflush][,nomerge]
265 General iommu options:
268 Don't initialize and use any kind of IOMMU.
270 Don't force hardware IOMMU usage when it is not needed. (default).
272 Force the use of the hardware IOMMU even when it is
273 not actually needed (e.g. because < 3 GB memory).
275 Use software bounce buffering (SWIOTLB) (default for
276 Intel machines). This can be used to prevent the usage
277 of an available hardware IOMMU.
279 iommu options only relevant to the AMD GART hardware IOMMU:
282 Set the size of the remapping area in bytes.
284 Overwrite iommu off workarounds for specific chipsets.
286 Flush IOMMU on each allocation (default).
288 Don't use IOMMU fullflush.
290 Allocate an own aperture over RAM with size 32MB<<order.
291 (default: order=1, i.e. 64MB)
293 Do scatter-gather (SG) merging. Implies "force" (experimental).
295 Don't do scatter-gather (SG) merging.
297 Ask the IOMMU not to touch the aperture for AGP.
299 Don't initialize the AGP driver and use full aperture.
301 Always panic when IOMMU overflows.
303 iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
306 swiotlb=<pages>[,force]
308 Prereserve that many 128K pages for the software IO bounce buffering.
310 Force all IO through the software TLB.
317 Do not use GB pages for kernel direct mappings.
319 Use GB pages for kernel direct mappings.