KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled

The bit 12 represents "Processor Event Based Sampling Unavailable (RO)" :
	1 = PEBS is not supported.
	0 = PEBS is supported.

A write to this PEBS_UNAVL available bit will bring #GP(0) when guest PEBS
is enabled. Some PEBS drivers in guest may care about this bit.

Signed-off-by: Like Xu <like.xu@linux.intel.com>
Message-Id: <20220411101946.20262-13-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/pmu_intel.c

@@ -605,6 +605,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 		bitmap_set(pmu->all_valid_pmc_idx, INTEL_PMC_IDX_FIXED_VLBR, 1);
 
 	if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_FORMAT) {
+		vcpu->arch.ia32_misc_enable_msr &= ~MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
 		if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_BASELINE) {
 			pmu->pebs_enable_mask = ~pmu->global_ctrl;
 			pmu->reserved_bits &= ~ICL_EVENTSEL_ADAPTIVE;
@@ -618,6 +619,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 				~((1ull << pmu->nr_arch_gp_counters) - 1);
 		}
 	} else {
+		vcpu->arch.ia32_misc_enable_msr |= MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
 		vcpu->arch.perf_capabilities &= ~PERF_CAP_PEBS_MASK;
 	}
 }

arch/x86/kvm/x86.c

@@ -3561,7 +3561,13 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_MISC_ENABLE: {
 		u64 old_val = vcpu->arch.ia32_misc_enable_msr;
-		u64 pmu_mask = MSR_IA32_MISC_ENABLE_EMON;
+		u64 pmu_mask = MSR_IA32_MISC_ENABLE_EMON |
+			MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
+
+		/* RO bits */
+		if (!msr_info->host_initiated &&
+		    ((old_val ^ data) & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
+			return 1;
 
 		/*
 		 * For a dummy user space, the order of setting vPMU capabilities and