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KVM: x86: expose MSR_PLATFORM_INFO as a feature MSR

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For userspace that wants to disable KVM_X86_QUIRK_STUFF_FEATURE_MSRS, it
is useful to know what bits can be set to 1 in MSR_PLATFORM_INFO (apart
from the TSC ratio).  The right way to do that is via /dev/kvm's
feature MSR mechanism.

In fact, MSR_PLATFORM_INFO is already a feature MSR for the purpose of
blocking updates after the vCPU is run, but KVM_GET_MSRS did not return
a valid value for it.

Just like in a VM that leaves KVM_X86_QUIRK_STUFF_FEATURE_MSRS enabled,
the TSC ratio field is left to 0.  Only bit 31 is set.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-11-13 12:39:45 +01:00
parent a0423af92c
commit b467ab82a9
1 changed files with 3 additions and 0 deletions
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3
arch/x86/kvm/x86.c
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@ -1675,6 +1675,9 @@ static int kvm_get_feature_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
case MSR_IA32_PERF_CAPABILITIES:
*data = kvm_caps.supported_perf_cap;
break;
case MSR_PLATFORM_INFO:
*data = MSR_PLATFORM_INFO_CPUID_FAULT;
break;
case MSR_IA32_UCODE_REV:
rdmsrl_safe(index, data);
break;