Documentation/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/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    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.
  60
  61 Early Console
  62
  63    syntax: earlyprintk=vga
  64            earlyprintk=serial[,ttySn[,baudrate]]
  65
  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.
  74
  75 Timing
  76
  77   notsc
  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.
  81
  82   report_lost_ticks
  83   Report when timer interrupts are lost because some code turned off
  84   interrupts for too long.
  85
  86   nmi_watchdog=NUMBER[,panic]
  87   NUMBER can be:
  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
  92   vector.
  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
  95   quickly up again.
  96
  97   nohpet
  98   Don't use the HPET timer.
  99
 100 Idle loop
 101
 102   idle=poll
 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.
 110
 111 Rebooting
 112
 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.
 125
 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.
 130
 131    reboot=force
 132
 133    Don't stop other CPUs on reboot. This can make reboot more reliable
 134    in some cases.
 135
 136 Non Executable Mappings
 137
 138   noexec=on|off
 139
 140   on      Enable(default)
 141   off     Disable
 142
 143 SMP
 144
 145   additional_cpus=NUM Allow NUM more CPUs for hotplug
 146                  (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
 147
 148 NUMA
 149
 150   numa=off      Only set up a single NUMA node spanning all memory.
 151
 152   numa=noacpi   Don't parse the SRAT table for NUMA setup
 153
 154   numa=fake=CMDLINE
 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
 162                 coefficient:
 163                         numa=fake=2*512,2*
 164                 gives two 512M nodes and the rest split into two nodes.
 165                 Otherwise, the remaining system RAM is allocated to an
 166                 additional node.
 167
 168   numa=hotadd=percent
 169                 Only allow hotadd memory to preallocate page structures upto
 170                 percent of already available memory.
 171                 numa=hotadd=0 will disable hotadd memory.
 172
 173 ACPI
 174
 175   acpi=off      Don't enable ACPI
 176   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 177                 interpreter
 178   acpi=force    Force ACPI on (currently not needed)
 179
 180   acpi=strict   Disable out of spec ACPI workarounds.
 181
 182   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 183
 184   acpi=noirq    Don't route interrupts
 185
 186 PCI
 187
 188   pci=off       Don't use PCI
 189   pci=conf1     Use conf1 access.
 190   pci=conf2     Use conf2 access.
 191   pci=rom       Assign ROMs.
 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.
 196
 197 IOMMU (input/output memory management unit)
 198
 199  Currently four x86-64 PCI-DMA mapping implementations exist:
 200
 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"
 204
 205    2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
 206       Kernel boot message: "PCI-DMA: using GART IOMMU"
 207
 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
 212       for IO (SWIOTLB)"
 213
 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"
 218
 219  iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
 220         [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
 221         [,noaperture][,calgary]
 222
 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.
 226                        (default).
 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.
 232
 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     fullflush          Flush IOMMU on each allocation (default).
 237     nofullflush        Don't use IOMMU fullflush.
 238     leak               Turn on simple iommu leak tracing (only when
 239                        CONFIG_IOMMU_LEAK is on). Default number of leak pages
 240                        is 20.
 241     memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.
 242                        (default: order=1, i.e. 64MB)
 243     merge              Do scatter-gather (SG) merging. Implies "force"
 244                        (experimental).
 245     nomerge            Don't do scatter-gather (SG) merging.
 246     noaperture         Ask the IOMMU not to touch the aperture for AGP.
 247     forcesac           Force single-address cycle (SAC) mode for masks <40bits
 248                        (experimental).
 249     noagp              Don't initialize the AGP driver and use full aperture.
 250     allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
 251                        DAC is used with 32-bit PCI to push a 64-bit address in
 252                        two cycles. When off all DMA over >4GB is forced through
 253                        an IOMMU or software bounce buffering.
 254     nodac              Forbid DAC mode, i.e. DMA >4GB.
 255     panic              Always panic when IOMMU overflows.
 256     calgary            Use the Calgary IOMMU if it is available
 257
 258   iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
 259   implementation:
 260     swiotlb=<pages>[,force]
 261     <pages>            Prereserve that many 128K pages for the software IO
 262                        bounce buffering.
 263     force              Force all IO through the software TLB.
 264
 265   Settings for the IBM Calgary hardware IOMMU currently found in IBM
 266   pSeries and xSeries machines:
 267
 268     calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
 269     calgary=[translate_empty_slots]
 270     calgary=[disable=<PCI bus number>]
 271     panic              Always panic when IOMMU overflows
 272
 273     64k,...,8M - Set the size of each PCI slot's translation table
 274     when using the Calgary IOMMU. This is the size of the translation
 275     table itself in main memory. The smallest table, 64k, covers an IO
 276     space of 32MB; the largest, 8MB table, can cover an IO space of
 277     4GB. Normally the kernel will make the right choice by itself.
 278
 279     translate_empty_slots - Enable translation even on slots that have
 280     no devices attached to them, in case a device will be hotplugged
 281     in the future.
 282
 283     disable=<PCI bus number> - Disable translation on a given PHB. For
 284     example, the built-in graphics adapter resides on the first bridge
 285     (PCI bus number 0); if translation (isolation) is enabled on this
 286     bridge, X servers that access the hardware directly from user
 287     space might stop working. Use this option if you have devices that
 288     are accessed from userspace directly on some PCI host bridge.
 289
 290 Debugging
 291
 292   oops=panic    Always panic on oopses. Default is to just kill the process,
 293                 but there is a small probability of deadlocking the machine.
 294                 This will also cause panics on machine check exceptions.
 295                 Useful together with panic=30 to trigger a reboot.
 296
 297   kstack=N      Print N words from the kernel stack in oops dumps.
 298
 299   pagefaulttrace  Dump all page faults. Only useful for extreme debugging
 300                 and will create a lot of output.
 301
 302   call_trace=[old|both|newfallback|new]
 303                 old: use old inexact backtracer
 304                 new: use new exact dwarf2 unwinder
 305                 both: print entries from both
 306                 newfallback: use new unwinder but fall back to old if it gets
 307                         stuck (default)
 308
 309 Miscellaneous
 310
 311         nogbpages
 312                 Do not use GB pages for kernel direct mappings.
 313         gbpages
 314                 Use GB pages for kernel direct mappings.