diff --git a/Documentation/virtual/kvm/cpuid.rst b/Documentation/virtual/kvm/cpuid.rst new file mode 100644 index 0000000000000000000000000000000000000000..01b081f6e7eae2ca395c71fd3136fc16fc29b632 --- /dev/null +++ b/Documentation/virtual/kvm/cpuid.rst @@ -0,0 +1,107 @@ +.. 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_UNHAULT 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 + sebd IPIs + +KVM_FEATURE_PV_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_CLOCSOURCE_STABLE_BIT 24 host will warn if no guest-side + per-cpu warps are expeced 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 +================== ============ ================================= diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt deleted file mode 100644 index 2bdac528e4a2a41b334060e0d973acb70c67eb60..0000000000000000000000000000000000000000 --- a/Documentation/virtual/kvm/cpuid.txt +++ /dev/null @@ -1,91 +0,0 @@ -KVM CPUID bits -Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010 -===================================================== - -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 each flags is: - - -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 using paravirtualized - || || send IPIs. ------------------------------------------------------------------------------- -KVM_FEATURE_PV_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_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 each flags is: - - -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 -----------------------------------------------------------------------------------