KVM: do not #GP on perf MSR writes when vPMU is disabled

Return to behaviour perf MSR had before introducing vPMU in case vPMU
is disabled. Some guests access those registers unconditionally and do
not expect it to fail.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/x86.c

@@ -1495,6 +1495,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 
 int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
+	bool pr = false;
+
 	switch (msr) {
 	case MSR_EFER:
 		return set_efer(vcpu, data);
@@ -1635,6 +1637,18 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		pr_unimpl(vcpu, "unimplemented perfctr wrmsr: "
 			"0x%x data 0x%llx\n", msr, data);
 		break;
+	case MSR_P6_PERFCTR0:
+	case MSR_P6_PERFCTR1:
+		pr = true;
+	case MSR_P6_EVNTSEL0:
+	case MSR_P6_EVNTSEL1:
+		if (kvm_pmu_msr(vcpu, msr))
+			return kvm_pmu_set_msr(vcpu, msr, data);
+
+		if (pr || data != 0)
+			pr_unimpl(vcpu, "disabled perfctr wrmsr: "
+				"0x%x data 0x%llx\n", msr, data);
+		break;
 	case MSR_K7_CLK_CTL:
 		/*
 		 * Ignore all writes to this no longer documented MSR.
@@ -1835,6 +1849,14 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 	case MSR_FAM10H_MMIO_CONF_BASE:
 		data = 0;
 		break;
+	case MSR_P6_PERFCTR0:
+	case MSR_P6_PERFCTR1:
+	case MSR_P6_EVNTSEL0:
+	case MSR_P6_EVNTSEL1:
+		if (kvm_pmu_msr(vcpu, msr))
+			return kvm_pmu_get_msr(vcpu, msr, pdata);
+		data = 0;
+		break;
 	case MSR_IA32_UCODE_REV:
 		data = 0x100000000ULL;
 		break;