KVM: vmx/pmu: Add PMU_CAP_LBR_FMT check when guest LBR is enabled

Usespace could set the bits [0, 5] of the IA32_PERF_CAPABILITIES
MSR which tells about the record format stored in the LBR records.

The LBR will be enabled on the guest if host perf supports LBR
(checked via x86_perf_get_lbr()) and the vcpu model is compatible
with the host one.
Signed-off-by: Like Xu <like.xu@linux.intel.com>
Message-Id: <20210201051039.255478-4-like.xu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/capabilities.h

@@ -387,7 +387,12 @@ static inline u64 vmx_get_perf_capabilities(void)
 
 static inline u64 vmx_supported_debugctl(void)
 {
-	return 0;
+	u64 debugctl = 0;
+
+	if (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT)
+		debugctl |= DEBUGCTLMSR_LBR;
+
+	return debugctl;
 }
 
 #endif /* __KVM_X86_VMX_CAPS_H */

arch/x86/kvm/vmx/pmu_intel.c

@@ -183,6 +183,13 @@ bool intel_pmu_lbr_is_compatible(struct kvm_vcpu *vcpu)
 	return boot_cpu_data.x86_model == guest_cpuid_model(vcpu);
 }
 
+bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
+{
+	struct x86_pmu_lbr *lbr = vcpu_to_lbr_records(vcpu);
+
+	return lbr->nr && (vcpu_get_perf_capabilities(vcpu) & PMU_CAP_LBR_FMT);
+}
+
 static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);

arch/x86/kvm/vmx/vmx.c

@@ -1950,6 +1950,16 @@ static u64 nested_vmx_truncate_sysenter_addr(struct kvm_vcpu *vcpu,
 	return (unsigned long)data;
 }
 
+static u64 vcpu_supported_debugctl(struct kvm_vcpu *vcpu)
+{
+	u64 debugctl = vmx_supported_debugctl();
+
+	if (!intel_pmu_lbr_is_enabled(vcpu))
+		debugctl &= ~DEBUGCTLMSR_LBR;
+
+	return debugctl;
+}
+
 /*
  * Writes msr value into the appropriate "register".
  * Returns 0 on success, non-0 otherwise.
@@ -2001,7 +2011,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vmcs_writel(GUEST_SYSENTER_ESP, data);
 		break;
 	case MSR_IA32_DEBUGCTLMSR: {
-		u64 invalid = data & ~vmx_supported_debugctl();
+		u64 invalid = data & ~vcpu_supported_debugctl(vcpu);
 		if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
 			if (report_ignored_msrs)
 				vcpu_unimpl(vcpu, "%s: BTF|LBR in IA32_DEBUGCTLMSR 0x%llx, nop\n",

arch/x86/kvm/vmx/vmx.h

@@ -97,6 +97,7 @@ union vmx_exit_reason {
 #define vcpu_to_lbr_records(vcpu) (&to_vmx(vcpu)->lbr_desc.records)
 
 bool intel_pmu_lbr_is_compatible(struct kvm_vcpu *vcpu);
+bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu);
 
 struct lbr_desc {
 	/* Basic info about guest LBR records. */