linux-kernel - [PATCH v2 7/7] KVM: VMX: Simplify capability check when handling PERF

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Date:   Wed,  3 Aug 2022 19:26:58 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Like Xu <like.xu.linux@...il.com>
Subject: [PATCH v2 7/7] KVM: VMX: Simplify capability check when handling
 PERF_CAPABILITIES write

Explicitly check for the absence of host support for LBRs or PEBS when
userspace attempts to enable said features by writing PERF_CAPABILITIES.
Comparing host support against the incoming value is unnecessary and
weird since the checks are buried inside an if-statement that verifies
userspace wants to enable the feature.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d7f8331d6f7e..0ada0ee234b7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2323,15 +2323,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (data && !vcpu_to_pmu(vcpu)->version)
 			return 1;
 		if (data & PMU_CAP_LBR_FMT) {
-			if ((data & PMU_CAP_LBR_FMT) !=
-			    (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT))
+			if (!(vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT))
 				return 1;
 			if (!cpuid_model_is_consistent(vcpu))
 				return 1;
 		}
 		if (data & PERF_CAP_PEBS_FORMAT) {
-			if ((data & PERF_CAP_PEBS_MASK) !=
-			    (vmx_get_perf_capabilities() & PERF_CAP_PEBS_MASK))
+			if (!(vmx_get_perf_capabilities() & PERF_CAP_PEBS_MASK))
 				return 1;
 			if (!guest_cpuid_has(vcpu, X86_FEATURE_DS))
 				return 1;
-- 
2.37.1.559.g78731f0fdb-goog