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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 | .. SPDX-License-Identifier: GPL-2.0 ============== KVM CPUID bits ============== :Author: Glauber Costa <glommer@gmail.com> A guest running on a kvm host, can check some of its features using cpuid. This is not always guaranteed to work, since userspace can mask-out some, or even all KVM-related cpuid features before launching a guest. KVM cpuid functions are: function: KVM_CPUID_SIGNATURE (0x40000000) returns:: eax = 0x40000001 ebx = 0x4b4d564b ecx = 0x564b4d56 edx = 0x4d Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM". The value in eax corresponds to the maximum cpuid function present in this leaf, and will be updated if more functions are added in the future. Note also that old hosts set eax value to 0x0. This should be interpreted as if the value was 0x40000001. This function queries the presence of KVM cpuid leafs. function: define KVM_CPUID_FEATURES (0x40000001) returns:: ebx, ecx eax = an OR'ed group of (1 << flag) where ``flag`` is defined as below: ================================== =========== ================================ flag value meaning ================================== =========== ================================ KVM_FEATURE_CLOCKSOURCE 0 kvmclock available at msrs 0x11 and 0x12 KVM_FEATURE_NOP_IO_DELAY 1 not necessary to perform delays on PIO operations KVM_FEATURE_MMU_OP 2 deprecated KVM_FEATURE_CLOCKSOURCE2 3 kvmclock available at msrs 0x4b564d00 and 0x4b564d01 KVM_FEATURE_ASYNC_PF 4 async pf can be enabled by writing to msr 0x4b564d02 KVM_FEATURE_STEAL_TIME 5 steal time can be enabled by writing to msr 0x4b564d03 KVM_FEATURE_PV_EOI 6 paravirtualized end of interrupt handler can be enabled by writing to msr 0x4b564d04 KVM_FEATURE_PV_UNHALT 7 guest checks this feature bit before enabling paravirtualized spinlock support KVM_FEATURE_PV_TLB_FLUSH 9 guest checks this feature bit before enabling paravirtualized tlb flush KVM_FEATURE_ASYNC_PF_VMEXIT 10 paravirtualized async PF VM EXIT can be enabled by setting bit 2 when writing to msr 0x4b564d02 KVM_FEATURE_PV_SEND_IPI 11 guest checks this feature bit before enabling paravirtualized send IPIs KVM_FEATURE_POLL_CONTROL 12 host-side polling on HLT can be disabled by writing to msr 0x4b564d05. KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit before using paravirtualized sched yield. KVM_FEATURE_ASYNC_PF_INT 14 guest checks this feature bit before using the second async pf control msr 0x4b564d06 and async pf acknowledgment msr 0x4b564d07. KVM_FEATURE_MSI_EXT_DEST_ID 15 guest checks this feature bit before using extended destination ID bits in MSI address bits 11-5. KVM_FEATURE_HC_MAP_GPA_RANGE 16 guest checks this feature bit before using the map gpa range hypercall to notify the page state change KVM_FEATURE_MIGRATION_CONTROL 17 guest checks this feature bit before using MSR_KVM_MIGRATION_CONTROL KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24 host will warn if no guest-side per-cpu warps are expected in kvmclock ================================== =========== ================================ :: edx = an OR'ed group of (1 << flag) Where ``flag`` here is defined as below: ================== ============ ================================= flag value meaning ================== ============ ================================= KVM_HINTS_REALTIME 0 guest checks this feature bit to determine that vCPUs are never preempted for an unlimited time allowing optimizations ================== ============ ================================= |