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=bootlog 35 Enable logging of machine checks left over from booting. 36 Disabled by default on AMD because some BIOS leave bogus ones. 37 If your BIOS doesn't do that it's a good idea to enable though 38 to make sure you log even machine check events that result 39 in a reboot. On Intel systems it is enabled by default. 40 mce=nobootlog 41 Disable boot machine check logging. 42 mce=tolerancelevel[,monarchtimeout] (number,number) 43 tolerance levels: 44 0: always panic on uncorrected errors, log corrected errors 45 1: panic or SIGBUS on uncorrected errors, log corrected errors 46 2: SIGBUS or log uncorrected errors, log corrected errors 47 3: never panic or SIGBUS, log all errors (for testing only) 48 Default is 1 49 Can be also set using sysfs which is preferable. 50 monarchtimeout: 51 Sets the time in us to wait for other CPUs on machine checks. 0 52 to disable. 53 54 nomce (for compatibility with i386): same as mce=off 55 56 Everything else is in sysfs now. 57 58APICs 59 60 apic Use IO-APIC. Default 61 62 noapic Don't use the IO-APIC. 63 64 disableapic Don't use the local APIC 65 66 nolapic Don't use the local APIC (alias for i386 compatibility) 67 68 pirq=... See Documentation/x86/i386/IO-APIC.txt 69 70 noapictimer Don't set up the APIC timer 71 72 no_timer_check Don't check the IO-APIC timer. This can work around 73 problems with incorrect timer initialization on some boards. 74 75 apicmaintimer Run time keeping from the local APIC timer instead 76 of using the PIT/HPET interrupt for this. This is useful 77 when the PIT/HPET interrupts are unreliable. 78 79 noapicmaintimer Don't do time keeping using the APIC timer. 80 Useful when this option was auto selected, but doesn't work. 81 82 apicpmtimer 83 Do APIC timer calibration using the pmtimer. Implies 84 apicmaintimer. Useful when your PIT timer is totally 85 broken. 86 87Early Console 88 89 syntax: earlyprintk=vga 90 earlyprintk=serial[,ttySn[,baudrate]] 91 92 The early console is useful when the kernel crashes before the 93 normal console is initialized. It is not enabled by 94 default because it has some cosmetic problems. 95 Append ,keep to not disable it when the real console takes over. 96 Only vga or serial at a time, not both. 97 Currently only ttyS0 and ttyS1 are supported. 98 Interaction with the standard serial driver is not very good. 99 The VGA output is eventually overwritten by the real console. 100 101Timing 102 103 notsc 104 Don't use the CPU time stamp counter to read the wall time. 105 This can be used to work around timing problems on multiprocessor systems 106 with not properly synchronized CPUs. 107 108 report_lost_ticks 109 Report when timer interrupts are lost because some code turned off 110 interrupts for too long. 111 112 nohpet 113 Don't use the HPET timer. 114 115Idle loop 116 117 idle=poll 118 Don't do power saving in the idle loop using HLT, but poll for rescheduling 119 event. This will make the CPUs eat a lot more power, but may be useful 120 to get slightly better performance in multiprocessor benchmarks. It also 121 makes some profiling using performance counters more accurate. 122 Please note that on systems with MONITOR/MWAIT support (like Intel EM64T 123 CPUs) this option has no performance advantage over the normal idle loop. 124 It may also interact badly with hyperthreading. 125 126Rebooting 127 128 reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old] 129 bios Use the CPU reboot vector for warm reset 130 warm Don't set the cold reboot flag 131 cold Set the cold reboot flag 132 triple Force a triple fault (init) 133 kbd Use the keyboard controller. cold reset (default) 134 acpi Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the 135 ACPI reset does not work, the reboot path attempts the reset using 136 the keyboard controller. 137 efi Use efi reset_system runtime service. If EFI is not configured or the 138 EFI reset does not work, the reboot path attempts the reset using 139 the keyboard controller. 140 141 Using warm reset will be much faster especially on big memory 142 systems because the BIOS will not go through the memory check. 143 Disadvantage is that not all hardware will be completely reinitialized 144 on reboot so there may be boot problems on some systems. 145 146 reboot=force 147 148 Don't stop other CPUs on reboot. This can make reboot more reliable 149 in some cases. 150 151Non Executable Mappings 152 153 noexec=on|off 154 155 on Enable(default) 156 off Disable 157 158SMP 159 160 additional_cpus=NUM Allow NUM more CPUs for hotplug 161 (defaults are specified by the BIOS, see Documentation/x86/x86_64/cpu-hotplug-spec) 162 163NUMA 164 165 numa=off Only set up a single NUMA node spanning all memory. 166 167 numa=noacpi Don't parse the SRAT table for NUMA setup 168 169 numa=fake=<size>[MG] 170 If given as a memory unit, fills all system RAM with nodes of 171 size interleaved over physical nodes. 172 173 numa=fake=<N> 174 If given as an integer, fills all system RAM with N fake nodes 175 interleaved over physical nodes. 176 177ACPI 178 179 acpi=off Don't enable ACPI 180 acpi=ht Use ACPI boot table parsing, but don't enable ACPI 181 interpreter 182 acpi=force Force ACPI on (currently not needed) 183 184 acpi=strict Disable out of spec ACPI workarounds. 185 186 acpi_sci={edge,level,high,low} Set up ACPI SCI interrupt. 187 188 acpi=noirq Don't route interrupts 189 190PCI 191 192 pci=off Don't use PCI 193 pci=conf1 Use conf1 access. 194 pci=conf2 Use conf2 access. 195 pci=rom Assign ROMs. 196 pci=assign-busses Assign busses 197 pci=irqmask=MASK Set PCI interrupt mask to MASK 198 pci=lastbus=NUMBER Scan upto NUMBER busses, no matter what the mptable says. 199 pci=noacpi Don't use ACPI to set up PCI interrupt routing. 200 201IOMMU (input/output memory management unit) 202 203 Currently four x86-64 PCI-DMA mapping implementations exist: 204 205 1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all 206 (e.g. because you have < 3 GB memory). 207 Kernel boot message: "PCI-DMA: Disabling IOMMU" 208 209 2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU. 210 Kernel boot message: "PCI-DMA: using GART IOMMU" 211 212 3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used 213 e.g. if there is no hardware IOMMU in the system and it is need because 214 you have >3GB memory or told the kernel to us it (iommu=soft)) 215 Kernel boot message: "PCI-DMA: Using software bounce buffering 216 for IO (SWIOTLB)" 217 218 4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM 219 pSeries and xSeries servers. This hardware IOMMU supports DMA address 220 mapping with memory protection, etc. 221 Kernel boot message: "PCI-DMA: Using Calgary IOMMU" 222 223 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>] 224 [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge] 225 [,noaperture][,calgary] 226 227 General iommu options: 228 off Don't initialize and use any kind of IOMMU. 229 noforce Don't force hardware IOMMU usage when it is not needed. 230 (default). 231 force Force the use of the hardware IOMMU even when it is 232 not actually needed (e.g. because < 3 GB memory). 233 soft Use software bounce buffering (SWIOTLB) (default for 234 Intel machines). This can be used to prevent the usage 235 of an available hardware IOMMU. 236 237 iommu options only relevant to the AMD GART hardware IOMMU: 238 <size> Set the size of the remapping area in bytes. 239 allowed Overwrite iommu off workarounds for specific chipsets. 240 fullflush Flush IOMMU on each allocation (default). 241 nofullflush Don't use IOMMU fullflush. 242 leak Turn on simple iommu leak tracing (only when 243 CONFIG_IOMMU_LEAK is on). Default number of leak pages 244 is 20. 245 memaper[=<order>] Allocate an own aperture over RAM with size 32MB<<order. 246 (default: order=1, i.e. 64MB) 247 merge Do scatter-gather (SG) merging. Implies "force" 248 (experimental). 249 nomerge Don't do scatter-gather (SG) merging. 250 noaperture Ask the IOMMU not to touch the aperture for AGP. 251 forcesac Force single-address cycle (SAC) mode for masks <40bits 252 (experimental). 253 noagp Don't initialize the AGP driver and use full aperture. 254 allowdac Allow double-address cycle (DAC) mode, i.e. DMA >4GB. 255 DAC is used with 32-bit PCI to push a 64-bit address in 256 two cycles. When off all DMA over >4GB is forced through 257 an IOMMU or software bounce buffering. 258 nodac Forbid DAC mode, i.e. DMA >4GB. 259 panic Always panic when IOMMU overflows. 260 calgary Use the Calgary IOMMU if it is available 261 262 iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU 263 implementation: 264 swiotlb=<pages>[,force] 265 <pages> Prereserve that many 128K pages for the software IO 266 bounce buffering. 267 force Force all IO through the software TLB. 268 269 Settings for the IBM Calgary hardware IOMMU currently found in IBM 270 pSeries and xSeries machines: 271 272 calgary=[64k,128k,256k,512k,1M,2M,4M,8M] 273 calgary=[translate_empty_slots] 274 calgary=[disable=<PCI bus number>] 275 panic Always panic when IOMMU overflows 276 277 64k,...,8M - Set the size of each PCI slot's translation table 278 when using the Calgary IOMMU. This is the size of the translation 279 table itself in main memory. The smallest table, 64k, covers an IO 280 space of 32MB; the largest, 8MB table, can cover an IO space of 281 4GB. Normally the kernel will make the right choice by itself. 282 283 translate_empty_slots - Enable translation even on slots that have 284 no devices attached to them, in case a device will be hotplugged 285 in the future. 286 287 disable=<PCI bus number> - Disable translation on a given PHB. For 288 example, the built-in graphics adapter resides on the first bridge 289 (PCI bus number 0); if translation (isolation) is enabled on this 290 bridge, X servers that access the hardware directly from user 291 space might stop working. Use this option if you have devices that 292 are accessed from userspace directly on some PCI host bridge. 293 294Debugging 295 296 oops=panic Always panic on oopses. Default is to just kill the process, 297 but there is a small probability of deadlocking the machine. 298 This will also cause panics on machine check exceptions. 299 Useful together with panic=30 to trigger a reboot. 300 301 kstack=N Print N words from the kernel stack in oops dumps. 302 303 pagefaulttrace Dump all page faults. Only useful for extreme debugging 304 and will create a lot of output. 305 306 call_trace=[old|both|newfallback|new] 307 old: use old inexact backtracer 308 new: use new exact dwarf2 unwinder 309 both: print entries from both 310 newfallback: use new unwinder but fall back to old if it gets 311 stuck (default) 312 313Miscellaneous 314 315 nogbpages 316 Do not use GB pages for kernel direct mappings. 317 gbpages 318 Use GB pages for kernel direct mappings. 319