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

Synthetic debugging MSRs (HV_X64_MSR_SYNDBG_CONTROL,
HV_X64_MSR_SYNDBG_STATUS, HV_X64_MSR_SYNDBG_SEND_BUFFER,
HV_X64_MSR_SYNDBG_RECV_BUFFER, HV_X64_MSR_SYNDBG_PENDING_BUFFER,
HV_X64_MSR_SYNDBG_OPTIONS) are only available to guest when
HV_FEATURE_DEBUG_MSRS_AVAILABLE bit is exposed.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210521095204.2161214-18-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -1266,6 +1266,10 @@ static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
 	case HV_X64_MSR_CRASH_CTL:
 		return hv_vcpu->cpuid_cache.features_edx &
 			HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;
+	case HV_X64_MSR_SYNDBG_OPTIONS:
+	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
+		return hv_vcpu->cpuid_cache.features_edx &
+			HV_FEATURE_DEBUG_MSRS_AVAILABLE;
 	default:
 		break;
 	}