Revert "KVM: x86/pmu: Accept 0 for absent PMU MSRs when host-initiated if !enable_pmu"

Eating reads and writes to all "PMU" MSRs when there is no PMU is wildly
broken as it results in allowing accesses to _any_ MSR on Intel CPUs
as intel_is_valid_msr() returns true for all host_initiated accesses.

A revert of commit d1c88a40 ("KVM: x86: always allow host-initiated
writes to PMU MSRs") will soon follow.

This reverts commit 8e6a58e2.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220611005755.753273-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/pmu.c

@@ -442,19 +442,11 @@ static void kvm_pmu_mark_pmc_in_use(struct kvm_vcpu *vcpu, u32 msr)
 
 int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
-	if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu) {
-		msr_info->data = 0;
-		return 0;
-	}
-
 	return static_call(kvm_x86_pmu_get_msr)(vcpu, msr_info);
 }
 
 int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
-	if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu)
-		return !!msr_info->data;
-
 	kvm_pmu_mark_pmc_in_use(vcpu, msr_info->index);
 	return static_call(kvm_x86_pmu_set_msr)(vcpu, msr_info);
 }

arch/x86/kvm/svm/pmu.c

@@ -182,16 +182,7 @@ static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
 static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr, bool host_initiated)
 {
 	/* All MSRs refer to exactly one PMC, so msr_idx_to_pmc is enough.  */
-	if (!host_initiated)
-		return false;
-
-	switch (msr) {
-	case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
-	case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
-		return true;
-	default:
-		return false;
-	}
+	return false;
 }
 
 static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)