Commit 0f4a7185 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: VMX: Give host userspace full control of MSR_IA32_PERF_CAPABILITIES 



Do not clear manipulate MSR_IA32_PERF_CAPABILITIES in intel_pmu_refresh(),
i.e. give userspace full control over capability/read-only MSRs.  KVM is
not a babysitter, it is userspace's responsiblity to provide a valid and
coherent vCPU model.

Attempting to "help" the guest by forcing a consistent model creates edge
cases, and ironicially leads to inconsistent behavior.

Example #1:  KVM doesn't do intel_pmu_refresh() when userspace writes
the MSR.

Example #2: KVM doesn't clear the bits when the PMU is disabled, or when
there's no architectural PMU.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220611005755.753273-3-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 9fc22296

arch/x86/kvm/vmx/pmu_intel.c

+0 −2
Original line number Diff line number Diff line
@@ -619,8 +619,6 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu) 
			pmu->pebs_enable_mask =

				~((1ull << pmu->nr_arch_gp_counters) - 1);

		}

	} else {

		vcpu->arch.perf_capabilities &= ~PERF_CAP_PEBS_MASK;

	}

}