1.. SPDX-License-Identifier: GPL-2.0
2
3===========================
4AMD64 Specific Boot Options
5===========================
6
7There are many others (usually documented in driver documentation), but
8only the AMD64 specific ones are listed here.
9
10Machine check
11=============
12Please see Documentation/x86/x86_64/machinecheck.rst for sysfs runtime tunables.
13
14   mce=off
15		Disable machine check
16   mce=no_cmci
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
20		is misbehaving.
21		Note that you'll get more problems without CMCI than with
22		due to the shared banks, i.e. you might get duplicated
23		error logs.
24   mce=dont_log_ce
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
28		of corrected errors.
29   mce=ignore_ce
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.
38   mce=no_lmce
39		Do not opt-in to Local MCE delivery. Use legacy method
40		to broadcast MCEs.
41   mce=bootlog
42		Enable logging of machine checks left over from booting.
43		Disabled by default on AMD Fam10h and older because some BIOS
44		leave bogus ones.
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.
48   mce=nobootlog
49		Disable boot machine check logging.
50   mce=monarchtimeout (number)
51		monarchtimeout:
52		Sets the time in us to wait for other CPUs on machine checks. 0
53		to disable.
54   mce=bios_cmci_threshold
55		Don't overwrite the bios-set CMCI threshold. This boot option
56		prevents Linux from overwriting the CMCI threshold set by the
57		bios. Without this option, Linux always sets the CMCI
58		threshold to 1. Enabling this may make memory predictive failure
59		analysis less effective if the bios sets thresholds for memory
60		errors since we will not see details for all errors.
61   mce=recovery
62		Force-enable recoverable machine check code paths
63
64   nomce (for compatibility with i386)
65		same as mce=off
66
67   Everything else is in sysfs now.
68
69APICs
70=====
71
72   apic
73	Use IO-APIC. Default
74
75   noapic
76	Don't use the IO-APIC.
77
78   disableapic
79	Don't use the local APIC
80
81   nolapic
82     Don't use the local APIC (alias for i386 compatibility)
83
84   pirq=...
85	See Documentation/x86/i386/IO-APIC.rst
86
87   noapictimer
88	Don't set up the APIC timer
89
90   no_timer_check
91	Don't check the IO-APIC timer. This can work around
92	problems with incorrect timer initialization on some boards.
93
94   apicpmtimer
95	Do APIC timer calibration using the pmtimer. Implies
96	apicmaintimer. Useful when your PIT timer is totally broken.
97
98Timing
99======
100
101  notsc
102    Deprecated, use tsc=unstable instead.
103
104  nohpet
105    Don't use the HPET timer.
106
107Idle loop
108=========
109
110  idle=poll
111    Don't do power saving in the idle loop using HLT, but poll for rescheduling
112    event. This will make the CPUs eat a lot more power, but may be useful
113    to get slightly better performance in multiprocessor benchmarks. It also
114    makes some profiling using performance counters more accurate.
115    Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
116    CPUs) this option has no performance advantage over the normal idle loop.
117    It may also interact badly with hyperthreading.
118
119Rebooting
120=========
121
122   reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] | p[ci] [, [w]arm | [c]old]
123      bios
124        Use the CPU reboot vector for warm reset
125      warm
126        Don't set the cold reboot flag
127      cold
128        Set the cold reboot flag
129      triple
130        Force a triple fault (init)
131      kbd
132        Use the keyboard controller. cold reset (default)
133      acpi
134        Use the ACPI RESET_REG in the FADT. If ACPI is not configured or
135        the ACPI reset does not work, the reboot path attempts the reset
136        using the keyboard controller.
137      efi
138        Use efi reset_system runtime service. If EFI is not configured or
139        the EFI reset does not work, the reboot path attempts the reset using
140        the keyboard controller.
141      pci
142        Use a write to the PCI config space register 0xcf9 to trigger reboot.
143
144   Using warm reset will be much faster especially on big memory
145   systems because the BIOS will not go through the memory check.
146   Disadvantage is that not all hardware will be completely reinitialized
147   on reboot so there may be boot problems on some systems.
148
149   reboot=force
150     Don't stop other CPUs on reboot. This can make reboot more reliable
151     in some cases.
152
153   reboot=default
154     There are some built-in platform specific "quirks" - you may see:
155     "reboot: <name> series board detected. Selecting <type> for reboots."
156     In the case where you think the quirk is in error (e.g. you have
157     newer BIOS, or newer board) using this option will ignore the built-in
158     quirk table, and use the generic default reboot actions.
159
160NUMA
161====
162
163  numa=off
164    Only set up a single NUMA node spanning all memory.
165
166  numa=noacpi
167    Don't parse the SRAT table for NUMA setup
168
169  numa=nohmat
170    Don't parse the HMAT table for NUMA setup, or soft-reserved memory
171    partitioning.
172
173  numa=fake=<size>[MG]
174    If given as a memory unit, fills all system RAM with nodes of
175    size interleaved over physical nodes.
176
177  numa=fake=<N>
178    If given as an integer, fills all system RAM with N fake nodes
179    interleaved over physical nodes.
180
181  numa=fake=<N>U
182    If given as an integer followed by 'U', it will divide each
183    physical node into N emulated nodes.
184
185ACPI
186====
187
188  acpi=off
189    Don't enable ACPI
190  acpi=ht
191    Use ACPI boot table parsing, but don't enable ACPI interpreter
192  acpi=force
193    Force ACPI on (currently not needed)
194  acpi=strict
195    Disable out of spec ACPI workarounds.
196  acpi_sci={edge,level,high,low}
197    Set up ACPI SCI interrupt.
198  acpi=noirq
199    Don't route interrupts
200  acpi=nocmcff
201    Disable firmware first mode for corrected errors. This
202    disables parsing the HEST CMC error source to check if
203    firmware has set the FF flag. This may result in
204    duplicate corrected error reports.
205
206PCI
207===
208
209  pci=off
210    Don't use PCI
211  pci=conf1
212    Use conf1 access.
213  pci=conf2
214    Use conf2 access.
215  pci=rom
216    Assign ROMs.
217  pci=assign-busses
218    Assign busses
219  pci=irqmask=MASK
220    Set PCI interrupt mask to MASK
221  pci=lastbus=NUMBER
222    Scan up to NUMBER busses, no matter what the mptable says.
223  pci=noacpi
224    Don't use ACPI to set up PCI interrupt routing.
225
226IOMMU (input/output memory management unit)
227===========================================
228Multiple x86-64 PCI-DMA mapping implementations exist, for example:
229
230   1. <kernel/dma/direct.c>: use no hardware/software IOMMU at all
231      (e.g. because you have < 3 GB memory).
232      Kernel boot message: "PCI-DMA: Disabling IOMMU"
233
234   2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
235      Kernel boot message: "PCI-DMA: using GART IOMMU"
236
237   3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
238      e.g. if there is no hardware IOMMU in the system and it is need because
239      you have >3GB memory or told the kernel to us it (iommu=soft))
240      Kernel boot message: "PCI-DMA: Using software bounce buffering
241      for IO (SWIOTLB)"
242
243::
244
245  iommu=[<size>][,noagp][,off][,force][,noforce]
246  [,memaper[=<order>]][,merge][,fullflush][,nomerge]
247  [,noaperture]
248
249General iommu options:
250
251    off
252      Don't initialize and use any kind of IOMMU.
253    noforce
254      Don't force hardware IOMMU usage when it is not needed. (default).
255    force
256      Force the use of the hardware IOMMU even when it is
257      not actually needed (e.g. because < 3 GB memory).
258    soft
259      Use software bounce buffering (SWIOTLB) (default for
260      Intel machines). This can be used to prevent the usage
261      of an available hardware IOMMU.
262
263iommu options only relevant to the AMD GART hardware IOMMU:
264
265    <size>
266      Set the size of the remapping area in bytes.
267    allowed
268      Overwrite iommu off workarounds for specific chipsets.
269    fullflush
270      Flush IOMMU on each allocation (default).
271    nofullflush
272      Don't use IOMMU fullflush.
273    memaper[=<order>]
274      Allocate an own aperture over RAM with size 32MB<<order.
275      (default: order=1, i.e. 64MB)
276    merge
277      Do scatter-gather (SG) merging. Implies "force" (experimental).
278    nomerge
279      Don't do scatter-gather (SG) merging.
280    noaperture
281      Ask the IOMMU not to touch the aperture for AGP.
282    noagp
283      Don't initialize the AGP driver and use full aperture.
284    panic
285      Always panic when IOMMU overflows.
286
287iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
288implementation:
289
290    swiotlb=<slots>[,force,noforce]
291      <slots>
292        Prereserve that many 2K slots for the software IO bounce buffering.
293      force
294        Force all IO through the software TLB.
295      noforce
296        Do not initialize the software TLB.
297
298
299Miscellaneous
300=============
301
302  nogbpages
303    Do not use GB pages for kernel direct mappings.
304  gbpages
305    Use GB pages for kernel direct mappings.
306
307
308AMD SEV (Secure Encrypted Virtualization)
309=========================================
310Options relating to AMD SEV, specified via the following format:
311
312::
313
314   sev=option1[,option2]
315
316The available options are:
317
318   debug
319     Enable debug messages.
320