linux/Documentation/x86/x86_64/boot-options.txt
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   1AMD64 specific boot options
   2
   3There are many others (usually documented in driver documentation), but
   4only the AMD64 specific ones are listed here.
   5
   6Machine check
   7
   8   Please see Documentation/x86/x86_64/machinecheck for sysfs runtime tunables.
   9
  10   mce=off
  11                Disable machine check
  12   mce=no_cmci
  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
  16                is misbehaving.
  17                Note that you'll get more problems without CMCI than with
  18                due to the shared banks, i.e. you might get duplicated
  19                error logs.
  20   mce=dont_log_ce
  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
  24                of corrected errors.
  25   mce=ignore_ce
  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.
  34   mce=no_lmce
  35                Do not opt-in to Local MCE delivery. Use legacy method
  36                to broadcast MCEs.
  37   mce=bootlog
  38                Enable logging of machine checks left over from booting.
  39                Disabled by default on AMD Fam10h and older because some BIOS
  40                leave bogus ones.
  41                If your BIOS doesn't do that it's a good idea to enable though
  42                to make sure you log even machine check events that result
  43                in a reboot. On Intel systems it is enabled by default.
  44   mce=nobootlog
  45                Disable boot machine check logging.
  46   mce=tolerancelevel[,monarchtimeout] (number,number)
  47                tolerance levels:
  48                0: always panic on uncorrected errors, log corrected errors
  49                1: panic or SIGBUS on uncorrected errors, log corrected errors
  50                2: SIGBUS or log uncorrected errors, log corrected errors
  51                3: never panic or SIGBUS, log all errors (for testing only)
  52                Default is 1
  53                Can be also set using sysfs which is preferable.
  54                monarchtimeout:
  55                Sets the time in us to wait for other CPUs on machine checks. 0
  56                to disable.
  57   mce=bios_cmci_threshold
  58                Don't overwrite the bios-set CMCI threshold. This boot option
  59                prevents Linux from overwriting the CMCI threshold set by the
  60                bios. Without this option, Linux always sets the CMCI
  61                threshold to 1. Enabling this may make memory predictive failure
  62                analysis less effective if the bios sets thresholds for memory
  63                errors since we will not see details for all errors.
  64   mce=recovery
  65                Force-enable recoverable machine check code paths
  66
  67   nomce (for compatibility with i386): same as mce=off
  68
  69   Everything else is in sysfs now.
  70
  71APICs
  72
  73   apic          Use IO-APIC. Default
  74
  75   noapic        Don't use the IO-APIC.
  76
  77   disableapic   Don't use the local APIC
  78
  79   nolapic       Don't use the local APIC (alias for i386 compatibility)
  80
  81   pirq=...      See Documentation/x86/i386/IO-APIC.txt
  82
  83   noapictimer   Don't set up the APIC timer
  84
  85   no_timer_check Don't check the IO-APIC timer. This can work around
  86                 problems with incorrect timer initialization on some boards.
  87   apicpmtimer
  88                 Do APIC timer calibration using the pmtimer. Implies
  89                 apicmaintimer. Useful when your PIT timer is totally
  90                 broken.
  91
  92Timing
  93
  94  notsc
  95  Don't use the CPU time stamp counter to read the wall time.
  96  This can be used to work around timing problems on multiprocessor systems
  97  with not properly synchronized CPUs.
  98
  99  nohpet
 100  Don't use the HPET timer.
 101
 102Idle loop
 103
 104  idle=poll
 105  Don't do power saving in the idle loop using HLT, but poll for rescheduling
 106  event. This will make the CPUs eat a lot more power, but may be useful
 107  to get slightly better performance in multiprocessor benchmarks. It also
 108  makes some profiling using performance counters more accurate.
 109  Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
 110  CPUs) this option has no performance advantage over the normal idle loop.
 111  It may also interact badly with hyperthreading.
 112
 113Rebooting
 114
 115   reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
 116   bios   Use the CPU reboot vector for warm reset
 117   warm   Don't set the cold reboot flag
 118   cold   Set the cold reboot flag
 119   triple Force a triple fault (init)
 120   kbd    Use the keyboard controller. cold reset (default)
 121   acpi   Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
 122          ACPI reset does not work, the reboot path attempts the reset using
 123          the keyboard controller.
 124   efi    Use efi reset_system runtime service. If EFI is not configured or the
 125          EFI reset does not work, the reboot path attempts the reset using
 126          the keyboard controller.
 127
 128   Using warm reset will be much faster especially on big memory
 129   systems because the BIOS will not go through the memory check.
 130   Disadvantage is that not all hardware will be completely reinitialized
 131   on reboot so there may be boot problems on some systems.
 132
 133   reboot=force
 134
 135   Don't stop other CPUs on reboot. This can make reboot more reliable
 136   in some cases.
 137
 138Non Executable Mappings
 139
 140  noexec=on|off
 141
 142  on      Enable(default)
 143  off     Disable
 144
 145NUMA
 146
 147  numa=off      Only set up a single NUMA node spanning all memory.
 148
 149  numa=noacpi   Don't parse the SRAT table for NUMA setup
 150
 151  numa=fake=<size>[MG]
 152                If given as a memory unit, fills all system RAM with nodes of
 153                size interleaved over physical nodes.
 154
 155  numa=fake=<N>
 156                If given as an integer, fills all system RAM with N fake nodes
 157                interleaved over physical nodes.
 158
 159ACPI
 160
 161  acpi=off      Don't enable ACPI
 162  acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 163                interpreter
 164  acpi=force    Force ACPI on (currently not needed)
 165
 166  acpi=strict   Disable out of spec ACPI workarounds.
 167
 168  acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 169
 170  acpi=noirq    Don't route interrupts
 171
 172  acpi=nocmcff  Disable firmware first mode for corrected errors. This
 173                disables parsing the HEST CMC error source to check if
 174                firmware has set the FF flag. This may result in
 175                duplicate corrected error reports.
 176
 177PCI
 178
 179  pci=off               Don't use PCI
 180  pci=conf1             Use conf1 access.
 181  pci=conf2             Use conf2 access.
 182  pci=rom               Assign ROMs.
 183  pci=assign-busses     Assign busses
 184  pci=irqmask=MASK      Set PCI interrupt mask to MASK
 185  pci=lastbus=NUMBER    Scan up to NUMBER busses, no matter what the mptable says.
 186  pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 187
 188IOMMU (input/output memory management unit)
 189
 190 Currently four x86-64 PCI-DMA mapping implementations exist:
 191
 192   1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
 193      (e.g. because you have < 3 GB memory).
 194      Kernel boot message: "PCI-DMA: Disabling IOMMU"
 195
 196   2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
 197      Kernel boot message: "PCI-DMA: using GART IOMMU"
 198
 199   3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
 200      e.g. if there is no hardware IOMMU in the system and it is need because
 201      you have >3GB memory or told the kernel to us it (iommu=soft))
 202      Kernel boot message: "PCI-DMA: Using software bounce buffering
 203      for IO (SWIOTLB)"
 204
 205   4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
 206      pSeries and xSeries servers. This hardware IOMMU supports DMA address
 207      mapping with memory protection, etc.
 208      Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
 209
 210 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
 211        [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
 212        [,noaperture][,calgary]
 213
 214  General iommu options:
 215    off                Don't initialize and use any kind of IOMMU.
 216    noforce            Don't force hardware IOMMU usage when it is not needed.
 217                       (default).
 218    force              Force the use of the hardware IOMMU even when it is
 219                       not actually needed (e.g. because < 3 GB memory).
 220    soft               Use software bounce buffering (SWIOTLB) (default for
 221                       Intel machines). This can be used to prevent the usage
 222                       of an available hardware IOMMU.
 223
 224  iommu options only relevant to the AMD GART hardware IOMMU:
 225    <size>             Set the size of the remapping area in bytes.
 226    allowed            Overwrite iommu off workarounds for specific chipsets.
 227    fullflush          Flush IOMMU on each allocation (default).
 228    nofullflush        Don't use IOMMU fullflush.
 229    leak               Turn on simple iommu leak tracing (only when
 230                       CONFIG_IOMMU_LEAK is on). Default number of leak pages
 231                       is 20.
 232    memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.
 233                       (default: order=1, i.e. 64MB)
 234    merge              Do scatter-gather (SG) merging. Implies "force"
 235                       (experimental).
 236    nomerge            Don't do scatter-gather (SG) merging.
 237    noaperture         Ask the IOMMU not to touch the aperture for AGP.
 238    forcesac           Force single-address cycle (SAC) mode for masks <40bits
 239                       (experimental).
 240    noagp              Don't initialize the AGP driver and use full aperture.
 241    allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
 242                       DAC is used with 32-bit PCI to push a 64-bit address in
 243                       two cycles. When off all DMA over >4GB is forced through
 244                       an IOMMU or software bounce buffering.
 245    nodac              Forbid DAC mode, i.e. DMA >4GB.
 246    panic              Always panic when IOMMU overflows.
 247    calgary            Use the Calgary IOMMU if it is available
 248
 249  iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
 250  implementation:
 251    swiotlb=<pages>[,force]
 252    <pages>            Prereserve that many 128K pages for the software IO
 253                       bounce buffering.
 254    force              Force all IO through the software TLB.
 255
 256  Settings for the IBM Calgary hardware IOMMU currently found in IBM
 257  pSeries and xSeries machines:
 258
 259    calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
 260    calgary=[translate_empty_slots]
 261    calgary=[disable=<PCI bus number>]
 262    panic              Always panic when IOMMU overflows
 263
 264    64k,...,8M - Set the size of each PCI slot's translation table
 265    when using the Calgary IOMMU. This is the size of the translation
 266    table itself in main memory. The smallest table, 64k, covers an IO
 267    space of 32MB; the largest, 8MB table, can cover an IO space of
 268    4GB. Normally the kernel will make the right choice by itself.
 269
 270    translate_empty_slots - Enable translation even on slots that have
 271    no devices attached to them, in case a device will be hotplugged
 272    in the future.
 273
 274    disable=<PCI bus number> - Disable translation on a given PHB. For
 275    example, the built-in graphics adapter resides on the first bridge
 276    (PCI bus number 0); if translation (isolation) is enabled on this
 277    bridge, X servers that access the hardware directly from user
 278    space might stop working. Use this option if you have devices that
 279    are accessed from userspace directly on some PCI host bridge.
 280
 281Miscellaneous
 282
 283        nogbpages
 284                Do not use GB pages for kernel direct mappings.
 285        gbpages
 286                Use GB pages for kernel direct mappings.
 287
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