KVM: x86: hyper-v: Honor HV_MSR_HYPERCALL_AVAILABLE privilege bit

HV_X64_MSR_GUEST_OS_ID/HV_X64_MSR_HYPERCALL are only available to guest
when HV_MSR_HYPERCALL_AVAILABLE bit is exposed.
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210521095204.2161214-6-vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -1205,6 +1205,18 @@ void kvm_hv_invalidate_tsc_page(struct kvm *kvm)
 
 static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
 {
+	if (!hv_vcpu->enforce_cpuid)
+		return true;
+
+	switch (msr) {
+	case HV_X64_MSR_GUEST_OS_ID:
+	case HV_X64_MSR_HYPERCALL:
+		return hv_vcpu->cpuid_cache.features_eax &
+			HV_MSR_HYPERCALL_AVAILABLE;
+	default:
+		break;
+	}
+
 	return true;
 }