Documentation/x86/x86_64/boot-options.txt

   1 AMD64 specific boot options
   2
   3 There are many others (usually documented in driver documentation), but
   4 only the AMD64 specific ones are listed here.
   5
   6 Machine check
   7
   8    Please see Documentation/x86/x86_64/machinecheck for sysfs runtime tunables.
   9
  10    mce=off disable machine check
  11    mce=bootlog Enable logging of machine checks left over from booting.
  12                Disabled by default on AMD because some BIOS leave bogus ones.
  13                If your BIOS doesn't do that it's a good idea to enable though
  14                to make sure you log even machine check events that result
  15                in a reboot. On Intel systems it is enabled by default.
  16    mce=nobootlog
  17                 Disable boot machine check logging.
  18    mce=tolerancelevel (number)
  19                 0: always panic on uncorrected errors, log corrected errors
  20                 1: panic or SIGBUS on uncorrected errors, log corrected errors
  21                 2: SIGBUS or log uncorrected errors, log corrected errors
  22                 3: never panic or SIGBUS, log all errors (for testing only)
  23                 Default is 1
  24                 Can be also set using sysfs which is preferable.
  25
  26    nomce (for compatibility with i386): same as mce=off
  27
  28    Everything else is in sysfs now.
  29
  30 APICs
  31
  32    apic          Use IO-APIC. Default
  33
  34    noapic        Don't use the IO-APIC.
  35
  36    disableapic   Don't use the local APIC
  37
  38    nolapic       Don't use the local APIC (alias for i386 compatibility)
  39
  40    pirq=...      See Documentation/x86/i386/IO-APIC.txt
  41
  42    noapictimer   Don't set up the APIC timer
  43
  44    no_timer_check Don't check the IO-APIC timer. This can work around
  45                  problems with incorrect timer initialization on some boards.
  46
  47    apicmaintimer Run time keeping from the local APIC timer instead
  48                  of using the PIT/HPET interrupt for this. This is useful
  49                  when the PIT/HPET interrupts are unreliable.
  50
  51    noapicmaintimer  Don't do time keeping using the APIC timer.
  52                  Useful when this option was auto selected, but doesn't work.
  53
  54    apicpmtimer
  55                  Do APIC timer calibration using the pmtimer. Implies
  56                  apicmaintimer. Useful when your PIT timer is totally
  57                  broken.
  58
  59 Early Console
  60
  61    syntax: earlyprintk=vga
  62            earlyprintk=serial[,ttySn[,baudrate]]
  63
  64    The early console is useful when the kernel crashes before the
  65    normal console is initialized. It is not enabled by
  66    default because it has some cosmetic problems.
  67    Append ,keep to not disable it when the real console takes over.
  68    Only vga or serial at a time, not both.
  69    Currently only ttyS0 and ttyS1 are supported.
  70    Interaction with the standard serial driver is not very good.
  71    The VGA output is eventually overwritten by the real console.
  72
  73 Timing
  74
  75   notsc
  76   Don't use the CPU time stamp counter to read the wall time.
  77   This can be used to work around timing problems on multiprocessor systems
  78   with not properly synchronized CPUs.
  79
  80   report_lost_ticks
  81   Report when timer interrupts are lost because some code turned off
  82   interrupts for too long.
  83
  84   nohpet
  85   Don't use the HPET timer.
  86
  87 Idle loop
  88
  89   idle=poll
  90   Don't do power saving in the idle loop using HLT, but poll for rescheduling
  91   event. This will make the CPUs eat a lot more power, but may be useful
  92   to get slightly better performance in multiprocessor benchmarks. It also
  93   makes some profiling using performance counters more accurate.
  94   Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
  95   CPUs) this option has no performance advantage over the normal idle loop.
  96   It may also interact badly with hyperthreading.
  97
  98 Rebooting
  99
 100    reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
 101    bios   Use the CPU reboot vector for warm reset
 102    warm   Don't set the cold reboot flag
 103    cold   Set the cold reboot flag
 104    triple Force a triple fault (init)
 105    kbd    Use the keyboard controller. cold reset (default)
 106    acpi   Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
 107           ACPI reset does not work, the reboot path attempts the reset using
 108           the keyboard controller.
 109    efi    Use efi reset_system runtime service. If EFI is not configured or the
 110           EFI reset does not work, the reboot path attempts the reset using
 111           the keyboard controller.
 112
 113    Using warm reset will be much faster especially on big memory
 114    systems because the BIOS will not go through the memory check.
 115    Disadvantage is that not all hardware will be completely reinitialized
 116    on reboot so there may be boot problems on some systems.
 117
 118    reboot=force
 119
 120    Don't stop other CPUs on reboot. This can make reboot more reliable
 121    in some cases.
 122
 123 Non Executable Mappings
 124
 125   noexec=on|off
 126
 127   on      Enable(default)
 128   off     Disable
 129
 130 SMP
 131
 132   additional_cpus=NUM Allow NUM more CPUs for hotplug
 133                  (defaults are specified by the BIOS, see Documentation/x86/x86_64/cpu-hotplug-spec)
 134
 135 NUMA
 136
 137   numa=off      Only set up a single NUMA node spanning all memory.
 138
 139   numa=noacpi   Don't parse the SRAT table for NUMA setup
 140
 141   numa=fake=CMDLINE
 142                 If a number, fakes CMDLINE nodes and ignores NUMA setup of the
 143                 actual machine.  Otherwise, system memory is configured
 144                 depending on the sizes and coefficients listed.  For example:
 145                         numa=fake=2*512,1024,4*256,*128
 146                 gives two 512M nodes, a 1024M node, four 256M nodes, and the
 147                 rest split into 128M chunks.  If the last character of CMDLINE
 148                 is a *, the remaining memory is divided up equally among its
 149                 coefficient:
 150                         numa=fake=2*512,2*
 151                 gives two 512M nodes and the rest split into two nodes.
 152                 Otherwise, the remaining system RAM is allocated to an
 153                 additional node.
 154
 155   numa=hotadd=percent
 156                 Only allow hotadd memory to preallocate page structures upto
 157                 percent of already available memory.
 158                 numa=hotadd=0 will disable hotadd memory.
 159
 160 ACPI
 161
 162   acpi=off      Don't enable ACPI
 163   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 164                 interpreter
 165   acpi=force    Force ACPI on (currently not needed)
 166
 167   acpi=strict   Disable out of spec ACPI workarounds.
 168
 169   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 170
 171   acpi=noirq    Don't route interrupts
 172
 173 PCI
 174
 175   pci=off       Don't use PCI
 176   pci=conf1     Use conf1 access.
 177   pci=conf2     Use conf2 access.
 178   pci=rom       Assign ROMs.
 179   pci=assign-busses    Assign busses
 180   pci=irqmask=MASK             Set PCI interrupt mask to MASK
 181   pci=lastbus=NUMBER           Scan upto NUMBER busses, no matter what the mptable says.
 182   pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 183
 184 IOMMU (input/output memory management unit)
 185
 186  Currently four x86-64 PCI-DMA mapping implementations exist:
 187
 188    1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
 189       (e.g. because you have < 3 GB memory).
 190       Kernel boot message: "PCI-DMA: Disabling IOMMU"
 191
 192    2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
 193       Kernel boot message: "PCI-DMA: using GART IOMMU"
 194
 195    3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
 196       e.g. if there is no hardware IOMMU in the system and it is need because
 197       you have >3GB memory or told the kernel to us it (iommu=soft))
 198       Kernel boot message: "PCI-DMA: Using software bounce buffering
 199       for IO (SWIOTLB)"
 200
 201    4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
 202       pSeries and xSeries servers. This hardware IOMMU supports DMA address
 203       mapping with memory protection, etc.
 204       Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
 205
 206  iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
 207         [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
 208         [,noaperture][,calgary]
 209
 210   General iommu options:
 211     off                Don't initialize and use any kind of IOMMU.
 212     noforce            Don't force hardware IOMMU usage when it is not needed.
 213                        (default).
 214     force              Force the use of the hardware IOMMU even when it is
 215                        not actually needed (e.g. because < 3 GB memory).
 216     soft               Use software bounce buffering (SWIOTLB) (default for
 217                        Intel machines). This can be used to prevent the usage
 218                        of an available hardware IOMMU.
 219
 220   iommu options only relevant to the AMD GART hardware IOMMU:
 221     <size>             Set the size of the remapping area in bytes.
 222     allowed            Overwrite iommu off workarounds for specific chipsets.
 223     fullflush          Flush IOMMU on each allocation (default).
 224     nofullflush        Don't use IOMMU fullflush.
 225     leak               Turn on simple iommu leak tracing (only when
 226                        CONFIG_IOMMU_LEAK is on). Default number of leak pages
 227                        is 20.
 228     memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.
 229                        (default: order=1, i.e. 64MB)
 230     merge              Do scatter-gather (SG) merging. Implies "force"
 231                        (experimental).
 232     nomerge            Don't do scatter-gather (SG) merging.
 233     noaperture         Ask the IOMMU not to touch the aperture for AGP.
 234     forcesac           Force single-address cycle (SAC) mode for masks <40bits
 235                        (experimental).
 236     noagp              Don't initialize the AGP driver and use full aperture.
 237     allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
 238                        DAC is used with 32-bit PCI to push a 64-bit address in
 239                        two cycles. When off all DMA over >4GB is forced through
 240                        an IOMMU or software bounce buffering.
 241     nodac              Forbid DAC mode, i.e. DMA >4GB.
 242     panic              Always panic when IOMMU overflows.
 243     calgary            Use the Calgary IOMMU if it is available
 244
 245   iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
 246   implementation:
 247     swiotlb=<pages>[,force]
 248     <pages>            Prereserve that many 128K pages for the software IO
 249                        bounce buffering.
 250     force              Force all IO through the software TLB.
 251
 252   Settings for the IBM Calgary hardware IOMMU currently found in IBM
 253   pSeries and xSeries machines:
 254
 255     calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
 256     calgary=[translate_empty_slots]
 257     calgary=[disable=<PCI bus number>]
 258     panic              Always panic when IOMMU overflows
 259
 260     64k,...,8M - Set the size of each PCI slot's translation table
 261     when using the Calgary IOMMU. This is the size of the translation
 262     table itself in main memory. The smallest table, 64k, covers an IO
 263     space of 32MB; the largest, 8MB table, can cover an IO space of
 264     4GB. Normally the kernel will make the right choice by itself.
 265
 266     translate_empty_slots - Enable translation even on slots that have
 267     no devices attached to them, in case a device will be hotplugged
 268     in the future.
 269
 270     disable=<PCI bus number> - Disable translation on a given PHB. For
 271     example, the built-in graphics adapter resides on the first bridge
 272     (PCI bus number 0); if translation (isolation) is enabled on this
 273     bridge, X servers that access the hardware directly from user
 274     space might stop working. Use this option if you have devices that
 275     are accessed from userspace directly on some PCI host bridge.
 276
 277 Debugging
 278
 279   oops=panic    Always panic on oopses. Default is to just kill the process,
 280                 but there is a small probability of deadlocking the machine.
 281                 This will also cause panics on machine check exceptions.
 282                 Useful together with panic=30 to trigger a reboot.
 283
 284   kstack=N      Print N words from the kernel stack in oops dumps.
 285
 286   pagefaulttrace  Dump all page faults. Only useful for extreme debugging
 287                 and will create a lot of output.
 288
 289   call_trace=[old|both|newfallback|new]
 290                 old: use old inexact backtracer
 291                 new: use new exact dwarf2 unwinder
 292                 both: print entries from both
 293                 newfallback: use new unwinder but fall back to old if it gets
 294                         stuck (default)
 295
 296 Miscellaneous
 297
 298         nogbpages
 299                 Do not use GB pages for kernel direct mappings.
 300         gbpages
 301                 Use GB pages for kernel direct mappings.