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 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 28APICs 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 61Early 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 75Timing 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 100Idle 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 111Rebooting 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 136Non Executable Mappings 137 138 noexec=on|off 139 140 on Enable(default) 141 off Disable 142 143SMP 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 148NUMA 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 173ACPI 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 186PCI 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 197IOMMU (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 290Debugging 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 309Miscellaneous 310 311 nogbpages 312 Do not use GB pages for kernel direct mappings. 313 gbpages 314 Use GB pages for kernel direct mappings. 315