1 AMD64 specific boot options
3 There are many others (usually documented in driver documentation), but
4 only the AMD64 specific ones are listed here.
8 Please see Documentation/x86/x86_64/machinecheck for sysfs runtime tunables.
13 Disable CMCI(Corrected Machine Check Interrupt) that
14 Intel processor supports. Usually this disablement is
15 not recommended, but it might be handy if your hardware
17 Note that you'll get more problems without CMCI than with
18 due to the shared banks, i.e. you might get duplicated
21 Don't make logs for corrected errors. All events reported
22 as corrected are silently cleared by OS.
23 This option will be useful if you have no interest in any
26 Disable features for corrected errors, e.g. polling timer
27 and CMCI. All events reported as corrected are not cleared
28 by OS and remained in its error banks.
29 Usually this disablement is not recommended, however if
30 there is an agent checking/clearing corrected errors
31 (e.g. BIOS or hardware monitoring applications), conflicting
32 with OS's error handling, and you cannot deactivate the agent,
33 then this option will be a help.
35 Enable logging of machine checks left over from booting.
36 Disabled by default on AMD because some BIOS leave bogus ones.
37 If your BIOS doesn't do that it's a good idea to enable though
38 to make sure you log even machine check events that result
39 in a reboot. On Intel systems it is enabled by default.
41 Disable boot machine check logging.
42 mce=tolerancelevel[,monarchtimeout] (number,number)
44 0: always panic on uncorrected errors, log corrected errors
45 1: panic or SIGBUS on uncorrected errors, log corrected errors
46 2: SIGBUS or log uncorrected errors, log corrected errors
47 3: never panic or SIGBUS, log all errors (for testing only)
49 Can be also set using sysfs which is preferable.
51 Sets the time in us to wait for other CPUs on machine checks. 0
53 mce=bios_cmci_threshold
54 Don't overwrite the bios-set CMCI threshold. This boot option
55 prevents Linux from overwriting the CMCI threshold set by the
56 bios. Without this option, Linux always sets the CMCI
57 threshold to 1. Enabling this may make memory predictive failure
58 analysis less effective if the bios sets thresholds for memory
59 errors since we will not see details for all errors.
61 nomce (for compatibility with i386): same as mce=off
63 Everything else is in sysfs now.
67 apic Use IO-APIC. Default
69 noapic Don't use the IO-APIC.
71 disableapic Don't use the local APIC
73 nolapic Don't use the local APIC (alias for i386 compatibility)
75 pirq=... See Documentation/x86/i386/IO-APIC.txt
77 noapictimer Don't set up the APIC timer
79 no_timer_check Don't check the IO-APIC timer. This can work around
80 problems with incorrect timer initialization on some boards.
82 apicmaintimer Run time keeping from the local APIC timer instead
83 of using the PIT/HPET interrupt for this. This is useful
84 when the PIT/HPET interrupts are unreliable.
86 noapicmaintimer Don't do time keeping using the APIC timer.
87 Useful when this option was auto selected, but doesn't work.
90 Do APIC timer calibration using the pmtimer. Implies
91 apicmaintimer. Useful when your PIT timer is totally
97 Don't use the CPU time stamp counter to read the wall time.
98 This can be used to work around timing problems on multiprocessor systems
99 with not properly synchronized CPUs.
102 Don't use the HPET timer.
107 Don't do power saving in the idle loop using HLT, but poll for rescheduling
108 event. This will make the CPUs eat a lot more power, but may be useful
109 to get slightly better performance in multiprocessor benchmarks. It also
110 makes some profiling using performance counters more accurate.
111 Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
112 CPUs) this option has no performance advantage over the normal idle loop.
113 It may also interact badly with hyperthreading.
117 reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
118 bios Use the CPU reboot vector for warm reset
119 warm Don't set the cold reboot flag
120 cold Set the cold reboot flag
121 triple Force a triple fault (init)
122 kbd Use the keyboard controller. cold reset (default)
123 acpi Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
124 ACPI reset does not work, the reboot path attempts the reset using
125 the keyboard controller.
126 efi Use efi reset_system runtime service. If EFI is not configured or the
127 EFI reset does not work, the reboot path attempts the reset using
128 the keyboard controller.
130 Using warm reset will be much faster especially on big memory
131 systems because the BIOS will not go through the memory check.
132 Disadvantage is that not all hardware will be completely reinitialized
133 on reboot so there may be boot problems on some systems.
137 Don't stop other CPUs on reboot. This can make reboot more reliable
140 Non Executable Mappings
149 additional_cpus=NUM Allow NUM more CPUs for hotplug
150 (defaults are specified by the BIOS, see Documentation/x86/x86_64/cpu-hotplug-spec)
154 numa=off Only set up a single NUMA node spanning all memory.
156 numa=noacpi Don't parse the SRAT table for NUMA setup
159 If given as a memory unit, fills all system RAM with nodes of
160 size interleaved over physical nodes.
163 If given as an integer, fills all system RAM with N fake nodes
164 interleaved over physical nodes.
168 acpi=off Don't enable ACPI
169 acpi=ht Use ACPI boot table parsing, but don't enable ACPI
171 acpi=force Force ACPI on (currently not needed)
173 acpi=strict Disable out of spec ACPI workarounds.
175 acpi_sci={edge,level,high,low} Set up ACPI SCI interrupt.
177 acpi=noirq Don't route interrupts
179 acpi=nocmcff Disable firmware first mode for corrected errors. This
180 disables parsing the HEST CMC error source to check if
181 firmware has set the FF flag. This may result in
182 duplicate corrected error reports.
186 pci=off Don't use PCI
187 pci=conf1 Use conf1 access.
188 pci=conf2 Use conf2 access.
190 pci=assign-busses Assign busses
191 pci=irqmask=MASK Set PCI interrupt mask to MASK
192 pci=lastbus=NUMBER Scan up to NUMBER busses, no matter what the mptable says.
193 pci=noacpi Don't use ACPI to set up PCI interrupt routing.
195 IOMMU (input/output memory management unit)
197 Currently four x86-64 PCI-DMA mapping implementations exist:
199 1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
200 (e.g. because you have < 3 GB memory).
201 Kernel boot message: "PCI-DMA: Disabling IOMMU"
203 2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
204 Kernel boot message: "PCI-DMA: using GART IOMMU"
206 3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
207 e.g. if there is no hardware IOMMU in the system and it is need because
208 you have >3GB memory or told the kernel to us it (iommu=soft))
209 Kernel boot message: "PCI-DMA: Using software bounce buffering
212 4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
213 pSeries and xSeries servers. This hardware IOMMU supports DMA address
214 mapping with memory protection, etc.
215 Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
217 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
218 [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
219 [,noaperture][,calgary]
221 General iommu options:
222 off Don't initialize and use any kind of IOMMU.
223 noforce Don't force hardware IOMMU usage when it is not needed.
225 force Force the use of the hardware IOMMU even when it is
226 not actually needed (e.g. because < 3 GB memory).
227 soft Use software bounce buffering (SWIOTLB) (default for
228 Intel machines). This can be used to prevent the usage
229 of an available hardware IOMMU.
231 iommu options only relevant to the AMD GART hardware IOMMU:
232 <size> Set the size of the remapping area in bytes.
233 allowed Overwrite iommu off workarounds for specific chipsets.
234 fullflush Flush IOMMU on each allocation (default).
235 nofullflush Don't use IOMMU fullflush.
236 leak Turn on simple iommu leak tracing (only when
237 CONFIG_IOMMU_LEAK is on). Default number of leak pages
239 memaper[=<order>] Allocate an own aperture over RAM with size 32MB<<order.
240 (default: order=1, i.e. 64MB)
241 merge Do scatter-gather (SG) merging. Implies "force"
243 nomerge Don't do scatter-gather (SG) merging.
244 noaperture Ask the IOMMU not to touch the aperture for AGP.
245 forcesac Force single-address cycle (SAC) mode for masks <40bits
247 noagp Don't initialize the AGP driver and use full aperture.
248 allowdac Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
249 DAC is used with 32-bit PCI to push a 64-bit address in
250 two cycles. When off all DMA over >4GB is forced through
251 an IOMMU or software bounce buffering.
252 nodac Forbid DAC mode, i.e. DMA >4GB.
253 panic Always panic when IOMMU overflows.
254 calgary Use the Calgary IOMMU if it is available
256 iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
258 swiotlb=<pages>[,force]
259 <pages> Prereserve that many 128K pages for the software IO
261 force Force all IO through the software TLB.
263 Settings for the IBM Calgary hardware IOMMU currently found in IBM
264 pSeries and xSeries machines:
266 calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
267 calgary=[translate_empty_slots]
268 calgary=[disable=<PCI bus number>]
269 panic Always panic when IOMMU overflows
271 64k,...,8M - Set the size of each PCI slot's translation table
272 when using the Calgary IOMMU. This is the size of the translation
273 table itself in main memory. The smallest table, 64k, covers an IO
274 space of 32MB; the largest, 8MB table, can cover an IO space of
275 4GB. Normally the kernel will make the right choice by itself.
277 translate_empty_slots - Enable translation even on slots that have
278 no devices attached to them, in case a device will be hotplugged
281 disable=<PCI bus number> - Disable translation on a given PHB. For
282 example, the built-in graphics adapter resides on the first bridge
283 (PCI bus number 0); if translation (isolation) is enabled on this
284 bridge, X servers that access the hardware directly from user
285 space might stop working. Use this option if you have devices that
286 are accessed from userspace directly on some PCI host bridge.
290 kstack=N Print N words from the kernel stack in oops dumps.
292 pagefaulttrace Dump all page faults. Only useful for extreme debugging
293 and will create a lot of output.
295 call_trace=[old|both|newfallback|new]
296 old: use old inexact backtracer
297 new: use new exact dwarf2 unwinder
298 both: print entries from both
299 newfallback: use new unwinder but fall back to old if it gets
305 Do not use GB pages for kernel direct mappings.
307 Use GB pages for kernel direct mappings.