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 mce=off disable machine check
9 mce=bootlog Enable logging of machine checks left over from booting.
10 Disabled by default on AMD because some BIOS leave bogus ones.
11 If your BIOS doesn't do that it's a good idea to enable though
12 to make sure you log even machine check events that result
13 in a reboot. On Intel systems it is enabled by default.
15 Disable boot machine check logging.
16 mce=tolerancelevel (number)
17 0: always panic on uncorrected errors, log corrected errors
18 1: panic or SIGBUS on uncorrected errors, log corrected errors
19 2: SIGBUS or log uncorrected errors, log corrected errors
20 3: never panic or SIGBUS, log all errors (for testing only)
22 Can be also set using sysfs which is preferable.
24 nomce (for compatibility with i386): same as mce=off
26 Everything else is in sysfs now.
30 apic Use IO-APIC. Default
32 noapic Don't use the IO-APIC.
34 disableapic Don't use the local APIC
36 nolapic Don't use the local APIC (alias for i386 compatibility)
38 pirq=... See Documentation/i386/IO-APIC.txt
40 noapictimer Don't set up the APIC timer
42 no_timer_check Don't check the IO-APIC timer. This can work around
43 problems with incorrect timer initialization on some boards.
45 apicmaintimer Run time keeping from the local APIC timer instead
46 of using the PIT/HPET interrupt for this. This is useful
47 when the PIT/HPET interrupts are unreliable.
49 noapicmaintimer Don't do time keeping using the APIC timer.
50 Useful when this option was auto selected, but doesn't work.
53 Do APIC timer calibration using the pmtimer. Implies
54 apicmaintimer. Useful when your PIT timer is totally
57 disable_8254_timer / enable_8254_timer
58 Enable interrupt 0 timer routing over the 8254 in addition to over
59 the IO-APIC. The kernel tries to set a sensible default.
63 syntax: earlyprintk=vga
64 earlyprintk=serial[,ttySn[,baudrate]]
66 The early console is useful when the kernel crashes before the
67 normal console is initialized. It is not enabled by
68 default because it has some cosmetic problems.
69 Append ,keep to not disable it when the real console takes over.
70 Only vga or serial at a time, not both.
71 Currently only ttyS0 and ttyS1 are supported.
72 Interaction with the standard serial driver is not very good.
73 The VGA output is eventually overwritten by the real console.
78 Don't use the CPU time stamp counter to read the wall time.
79 This can be used to work around timing problems on multiprocessor systems
80 with not properly synchronized CPUs.
83 Report when timer interrupts are lost because some code turned off
84 interrupts for too long.
86 nmi_watchdog=NUMBER[,panic]
88 0 don't use an NMI watchdog
89 1 use the IO-APIC timer for the NMI watchdog
90 2 use the local APIC for the NMI watchdog using a performance counter. Note
91 This will use one performance counter and the local APIC's performance
93 When panic is specified panic when an NMI watchdog timeout occurs.
94 This is useful when you use a panic=... timeout and need the box
98 Don't use the HPET timer.
103 Don't do power saving in the idle loop using HLT, but poll for rescheduling
104 event. This will make the CPUs eat a lot more power, but may be useful
105 to get slightly better performance in multiprocessor benchmarks. It also
106 makes some profiling using performance counters more accurate.
107 Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
108 CPUs) this option has no performance advantage over the normal idle loop.
109 It may also interact badly with hyperthreading.
113 reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
114 bios Use the CPU reboot vector for warm reset
115 warm Don't set the cold reboot flag
116 cold Set the cold reboot flag
117 triple Force a triple fault (init)
118 kbd Use the keyboard controller. cold reset (default)
119 acpi Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
120 ACPI reset does not work, the reboot path attempts the reset using
121 the keyboard controller.
122 efi Use efi reset_system runtime service. If EFI is not configured or the
123 EFI reset does not work, the reboot path attempts the reset using
124 the keyboard controller.
126 Using warm reset will be much faster especially on big memory
127 systems because the BIOS will not go through the memory check.
128 Disadvantage is that not all hardware will be completely reinitialized
129 on reboot so there may be boot problems on some systems.
133 Don't stop other CPUs on reboot. This can make reboot more reliable
136 Non Executable Mappings
145 additional_cpus=NUM Allow NUM more CPUs for hotplug
146 (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
150 numa=off Only set up a single NUMA node spanning all memory.
152 numa=noacpi Don't parse the SRAT table for NUMA setup
155 If a number, fakes CMDLINE nodes and ignores NUMA setup of the
156 actual machine. Otherwise, system memory is configured
157 depending on the sizes and coefficients listed. For example:
158 numa=fake=2*512,1024,4*256,*128
159 gives two 512M nodes, a 1024M node, four 256M nodes, and the
160 rest split into 128M chunks. If the last character of CMDLINE
161 is a *, the remaining memory is divided up equally among its
164 gives two 512M nodes and the rest split into two nodes.
165 Otherwise, the remaining system RAM is allocated to an
169 Only allow hotadd memory to preallocate page structures upto
170 percent of already available memory.
171 numa=hotadd=0 will disable hotadd memory.
175 acpi=off Don't enable ACPI
176 acpi=ht Use ACPI boot table parsing, but don't enable ACPI
178 acpi=force Force ACPI on (currently not needed)
180 acpi=strict Disable out of spec ACPI workarounds.
182 acpi_sci={edge,level,high,low} Set up ACPI SCI interrupt.
184 acpi=noirq Don't route interrupts
188 pci=off Don't use PCI
189 pci=conf1 Use conf1 access.
190 pci=conf2 Use conf2 access.
192 pci=assign-busses Assign busses
193 pci=irqmask=MASK Set PCI interrupt mask to MASK
194 pci=lastbus=NUMBER Scan upto NUMBER busses, no matter what the mptable says.
195 pci=noacpi Don't use ACPI to set up PCI interrupt routing.
197 IOMMU (input/output memory management unit)
199 Currently four x86-64 PCI-DMA mapping implementations exist:
201 1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
202 (e.g. because you have < 3 GB memory).
203 Kernel boot message: "PCI-DMA: Disabling IOMMU"
205 2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
206 Kernel boot message: "PCI-DMA: using GART IOMMU"
208 3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
209 e.g. if there is no hardware IOMMU in the system and it is need because
210 you have >3GB memory or told the kernel to us it (iommu=soft))
211 Kernel boot message: "PCI-DMA: Using software bounce buffering
214 4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
215 pSeries and xSeries servers. This hardware IOMMU supports DMA address
216 mapping with memory protection, etc.
217 Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
219 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
220 [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
221 [,noaperture][,calgary]
223 General iommu options:
224 off Don't initialize and use any kind of IOMMU.
225 noforce Don't force hardware IOMMU usage when it is not needed.
227 force Force the use of the hardware IOMMU even when it is
228 not actually needed (e.g. because < 3 GB memory).
229 soft Use software bounce buffering (SWIOTLB) (default for
230 Intel machines). This can be used to prevent the usage
231 of an available hardware IOMMU.
233 iommu options only relevant to the AMD GART hardware IOMMU:
234 <size> Set the size of the remapping area in bytes.
235 allowed Overwrite iommu off workarounds for specific chipsets.
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 oops=panic Always panic on oopses. Default is to just kill the process,
291 but there is a small probability of deadlocking the machine.
292 This will also cause panics on machine check exceptions.
293 Useful together with panic=30 to trigger a reboot.
295 kstack=N Print N words from the kernel stack in oops dumps.
297 pagefaulttrace Dump all page faults. Only useful for extreme debugging
298 and will create a lot of output.
300 call_trace=[old|both|newfallback|new]
301 old: use old inexact backtracer
302 new: use new exact dwarf2 unwinder
303 both: print entries from both
304 newfallback: use new unwinder but fall back to old if it gets
310 Do not use GB pages for kernel direct mappings.
312 Use GB pages for kernel direct mappings.