Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 KVM CPUID bits 2 Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010 3 ===================================================== 4 5 A guest running on a kvm host, can check some of its features using 6 cpuid. This is not always guaranteed to work, since userspace can 7 mask-out some, or even all KVM-related cpuid features before launching 8 a guest. 9 10 KVM cpuid functions are: 11 12 function: KVM_CPUID_SIGNATURE (0x40000000) 13 returns : eax = 0x40000001, 14 ebx = 0x4b4d564b, 15 ecx = 0x564b4d56, 16 edx = 0x4d. 17 Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM". 18 The value in eax corresponds to the maximum cpuid function present in this leaf, 19 and will be updated if more functions are added in the future. 20 Note also that old hosts set eax value to 0x0. This should 21 be interpreted as if the value was 0x40000001. 22 This function queries the presence of KVM cpuid leafs. 23 24 25 function: define KVM_CPUID_FEATURES (0x40000001) 26 returns : ebx, ecx, edx = 0 27 eax = and OR'ed group of (1 << flag), where each flags is: 28 29 30 flag || value || meaning 31 ============================================================================= 32 KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs 33 || || 0x11 and 0x12. 34 ------------------------------------------------------------------------------ 35 KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays 36 || || on PIO operations. 37 ------------------------------------------------------------------------------ 38 KVM_FEATURE_MMU_OP || 2 || deprecated. 39 ------------------------------------------------------------------------------ 40 KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs 41 || || 0x4b564d00 and 0x4b564d01 42 ------------------------------------------------------------------------------ 43 KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by 44 || || writing to msr 0x4b564d02 45 ------------------------------------------------------------------------------ 46 KVM_FEATURE_STEAL_TIME || 5 || steal time can be enabled by 47 || || writing to msr 0x4b564d03. 48 ------------------------------------------------------------------------------ 49 KVM_FEATURE_PV_EOI || 6 || paravirtualized end of interrupt 50 || || handler can be enabled by writing 51 || || to msr 0x4b564d04. 52 ------------------------------------------------------------------------------ 53 KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit 54 || || before enabling paravirtualized 55 || || spinlock support. 56 ------------------------------------------------------------------------------ 57 KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit 58 || || before enabling paravirtualized 59 || || tlb flush. 60 ------------------------------------------------------------------------------ 61 KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit 62 || || can be enabled by setting bit 2 63 || || when writing to msr 0x4b564d02 64 ------------------------------------------------------------------------------ 65 KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side 66 || || per-cpu warps are expected in 67 || || kvmclock. 68 ------------------------------------------------------------------------------