KVM: x86: ensure all MSRs can always be KVM_GET/SET_MSR'd

Some of the MSRs returned by GET_MSR_INDEX_LIST currently cannot be sent back
to KVM_GET_MSR and/or KVM_SET_MSR; either they can never be sent back, or you
they are only accepted under special conditions.  This makes the API a pain to
use.

To avoid this pain, this patch makes it so that the result of the get-list
ioctl can always be used for host-initiated get and set.  Since we don't have
a separate way to check for read-only MSRs, this means some Hyper-V MSRs are
ignored when written.  Arguably they should not even be in the result of
GET_MSR_INDEX_LIST, but I am leaving there in case userspace is using the
outcome of GET_MSR_INDEX_LIST to derive the support for the corresponding
Hyper-V feature.

Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -235,7 +235,7 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
 	struct kvm_vcpu *vcpu = synic_to_vcpu(synic);
 	int ret;
 
-	if (!synic->active)
+	if (!synic->active && !host)
 		return 1;
 
 	trace_kvm_hv_synic_set_msr(vcpu->vcpu_id, msr, data, host);
@@ -295,11 +295,12 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
 	return ret;
 }
 
-static int synic_get_msr(struct kvm_vcpu_hv_synic *synic, u32 msr, u64 *pdata)
+static int synic_get_msr(struct kvm_vcpu_hv_synic *synic, u32 msr, u64 *pdata,
+			 bool host)
 {
 	int ret;
 
-	if (!synic->active)
+	if (!synic->active && !host)
 		return 1;
 
 	ret = 0;
@@ -1014,6 +1015,11 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
 	case HV_X64_MSR_TSC_EMULATION_STATUS:
 		hv->hv_tsc_emulation_status = data;
 		break;
+	case HV_X64_MSR_TIME_REF_COUNT:
+		/* read-only, but still ignore it if host-initiated */
+		if (!host)
+			return 1;
+		break;
 	default:
 		vcpu_unimpl(vcpu, "Hyper-V uhandled wrmsr: 0x%x data 0x%llx\n",
 			    msr, data);
@@ -1101,6 +1107,12 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
 		return stimer_set_count(vcpu_to_stimer(vcpu, timer_index),
 					data, host);
 	}
+	case HV_X64_MSR_TSC_FREQUENCY:
+	case HV_X64_MSR_APIC_FREQUENCY:
+		/* read-only, but still ignore it if host-initiated */
+		if (!host)
+			return 1;
+		break;
 	default:
 		vcpu_unimpl(vcpu, "Hyper-V uhandled wrmsr: 0x%x data 0x%llx\n",
 			    msr, data);
@@ -1156,7 +1168,8 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 	return 0;
 }
 
-static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
+static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
+			  bool host)
 {
 	u64 data = 0;
 	struct kvm_vcpu_hv *hv = &vcpu->arch.hyperv;
@@ -1183,7 +1196,7 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 	case HV_X64_MSR_SIMP:
 	case HV_X64_MSR_EOM:
 	case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
-		return synic_get_msr(vcpu_to_synic(vcpu), msr, pdata);
+		return synic_get_msr(vcpu_to_synic(vcpu), msr, pdata, host);
 	case HV_X64_MSR_STIMER0_CONFIG:
 	case HV_X64_MSR_STIMER1_CONFIG:
 	case HV_X64_MSR_STIMER2_CONFIG:
@@ -1229,7 +1242,7 @@ int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
 		return kvm_hv_set_msr(vcpu, msr, data, host);
 }
 
-int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
+int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host)
 {
 	if (kvm_hv_msr_partition_wide(msr)) {
 		int r;
@@ -1239,7 +1252,7 @@ int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 		mutex_unlock(&vcpu->kvm->arch.hyperv.hv_lock);
 		return r;
 	} else
-		return kvm_hv_get_msr(vcpu, msr, pdata);
+		return kvm_hv_get_msr(vcpu, msr, pdata, host);
 }
 
 static __always_inline int get_sparse_bank_no(u64 valid_bank_mask, int bank_no)

arch/x86/kvm/hyperv.h

@@ -48,7 +48,7 @@ static inline struct kvm_vcpu *synic_to_vcpu(struct kvm_vcpu_hv_synic *synic)
 }
 
 int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host);
-int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
+int kvm_hv_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host);
 
 bool kvm_hv_hypercall_enabled(struct kvm *kvm);
 int kvm_hv_hypercall(struct kvm_vcpu *vcpu);

arch/x86/kvm/x86.c

@@ -2160,10 +2160,11 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vcpu->arch.mcg_status = data;
 		break;
 	case MSR_IA32_MCG_CTL:
-		if (!(mcg_cap & MCG_CTL_P))
+		if (!(mcg_cap & MCG_CTL_P) &&
+		    (data || !msr_info->host_initiated))
 			return 1;
 		if (data != 0 && data != ~(u64)0)
-			return -1;
+			return 1;
 		vcpu->arch.mcg_ctl = data;
 		break;
 	default:
@@ -2551,7 +2552,7 @@ int kvm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 }
 EXPORT_SYMBOL_GPL(kvm_get_msr);
 
-static int get_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
+static int get_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host)
 {
 	u64 data;
 	u64 mcg_cap = vcpu->arch.mcg_cap;
@@ -2566,7 +2567,7 @@ static int get_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 		data = vcpu->arch.mcg_cap;
 		break;
 	case MSR_IA32_MCG_CTL:
-		if (!(mcg_cap & MCG_CTL_P))
+		if (!(mcg_cap & MCG_CTL_P) && !host)
 			return 1;
 		data = vcpu->arch.mcg_ctl;
 		break;
@@ -2699,7 +2700,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_MCG_CTL:
 	case MSR_IA32_MCG_STATUS:
 	case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
-		return get_msr_mce(vcpu, msr_info->index, &msr_info->data);
+		return get_msr_mce(vcpu, msr_info->index, &msr_info->data,
+				   msr_info->host_initiated);
 	case MSR_K7_CLK_CTL:
 		/*
 		 * Provide expected ramp-up count for K7. All other
@@ -2720,7 +2722,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case HV_X64_MSR_TSC_EMULATION_CONTROL:
 	case HV_X64_MSR_TSC_EMULATION_STATUS:
 		return kvm_hv_get_msr_common(vcpu,
-					     msr_info->index, &msr_info->data);
+					     msr_info->index, &msr_info->data,
+					     msr_info->host_initiated);
 		break;
 	case MSR_IA32_BBL_CR_CTL3:
 		/* This legacy MSR exists but isn't fully documented in current