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