KVM: x86: expose MSR_PLATFORM_INFO as a feature MSR

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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8637bc00109659bf69ec208ee0701bca08b80434..2e713480933a1378398d5cab50db8e40396502d6 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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;