[PATCH RFC 04/22] KVM: x86: hyper-v: Honor HV_MSR_TIME_REF_COUNT_AVAILABLE privilege bit

[Vitaly Kuznetsov]

HV_X64_MSR_TIME_REF_COUNT is only available to guest when
HV_MSR_TIME_REF_COUNT_AVAILABLE bit is exposed.

Note, writing to HV_X64_MSR_TIME_REF_COUNT is unsupported so
kvm_hv_set_msr_pw() doesn't need an additional check.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/kvm/hyperv.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index b39445aabbc2..efb3d69c98fd 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1440,6 +1440,7 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
 	u64 data = 0;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_hv *hv = to_kvm_hv(kvm);
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 
 	switch (msr) {
 	case HV_X64_MSR_GUEST_OS_ID:
@@ -1449,6 +1450,10 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
 		data = hv->hv_hypercall;
 		break;
 	case HV_X64_MSR_TIME_REF_COUNT:
+		if (unlikely(!host && !(hv_vcpu->cpuid_cache.features_eax &
+					HV_MSR_TIME_REF_COUNT_AVAILABLE)))
+			return 1;
+
 		data = get_time_ref_counter(kvm);
 		break;
 	case HV_X64_MSR_REFERENCE_TSC:
-- 
2.30.2