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From: Sean Christopherson <seanjc@google.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, Like Xu <like.xu.linux@gmail.com>
Subject: [PATCH v5 2/8] KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs
Date: Thu,  6 Oct 2022 00:03:08 +0000	[thread overview]
Message-ID: <20221006000314.73240-3-seanjc@google.com> (raw)
In-Reply-To: <20221006000314.73240-1-seanjc@google.com>

Advertise LBR support to userspace via MSR_IA32_PERF_CAPABILITIES if and
only if perf fully supports LBRs.  Perf may disable LBRs (by zeroing the
number of LBRs) even on platforms the allegedly support LBRs, e.g. if
probing any LBR MSRs during setup fails.

Fixes: be635e34c284 ("KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES")
Reported-by: Like Xu <like.xu.linux@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/capabilities.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 87c4e46daf37..a6689bf06542 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -400,6 +400,7 @@ static inline bool vmx_pebs_supported(void)
 static inline u64 vmx_get_perf_capabilities(void)
 {
 	u64 perf_cap = PMU_CAP_FW_WRITES;
+	struct x86_pmu_lbr lbr;
 	u64 host_perf_cap = 0;
 
 	if (!enable_pmu)
@@ -408,7 +409,9 @@ static inline u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
 
-	perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
+	x86_perf_get_lbr(&lbr);
+	if (lbr.nr)
+		perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
 
 	if (vmx_pebs_supported()) {
 		perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
-- 
2.38.0.rc1.362.ged0d419d3c-goog


  parent reply	other threads:[~2022-10-06  0:03 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-06  0:03 [PATCH v5 0/8] KVM: x86: Intel LBR related perf cleanups Sean Christopherson
2022-10-06  0:03 ` [PATCH v5 1/8] perf/x86/core: Zero @lbr instead of returning -1 in x86_perf_get_lbr() stub Sean Christopherson
2022-10-06  0:03 ` Sean Christopherson [this message]
2022-10-06  0:03 ` [PATCH v5 3/8] KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl() Sean Christopherson
2022-10-06  0:03 ` [PATCH v5 4/8] KVM: VMX: Ignore guest CPUID for host userspace writes to DEBUGCTL Sean Christopherson
2022-10-06  0:03 ` [PATCH v5 5/8] KVM: x86: Track supported PERF_CAPABILITIES in kvm_caps Sean Christopherson
2022-10-14  9:25   ` Like Xu
2022-10-06  0:03 ` [PATCH v5 6/8] KVM: x86: Init vcpu->arch.perf_capabilities in common x86 code Sean Christopherson
2022-10-06  0:03 ` [PATCH v5 7/8] KVM: x86: Handle PERF_CAPABILITIES in common x86's kvm_get_msr_feature() Sean Christopherson
2022-10-06  0:03 ` [PATCH v5 8/8] KVM: x86: Directly query supported PERF_CAPABILITIES for WRMSR checks Sean Christopherson
2022-11-02 17:18 ` [PATCH v5 0/8] KVM: x86: Intel LBR related perf cleanups Paolo Bonzini

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