linux-kernel - [PATCH v5 07/15] KVM: VMX: Add helper to check if the guest PMU has PERF_GLOBAL

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Message-Id: <20220607213604.3346000-8-seanjc@google.com>
Date:   Tue,  7 Jun 2022 21:35:56 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Li <ercli@...avis.edu>,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: [PATCH v5 07/15] KVM: VMX: Add helper to check if the guest PMU has PERF_GLOBAL_CTRL

Add a helper to check of the guest PMU has PERF_GLOBAL_CTRL, which is
unintuitive _and_ diverges from Intel's architecturally defined behavior.
Even worse, KVM currently implements the check using two different, but
equivalent checksand , _and_ there has been at least one attempt to add a
_third_ flavor.

Link: https://lore.kernel.org/all/Yk4ugOETeo%2FqDRbW@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/pmu_intel.c |  4 ++--
 arch/x86/kvm/vmx/vmx.h       | 12 ++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 5b85320fc9f1..6ce3b066f7d9 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -111,7 +111,7 @@ static bool intel_pmc_is_enabled(struct kvm_pmc *pmc)
 {
 	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
 
-	if (pmu->version < 2)
+	if (!intel_pmu_has_perf_global_ctrl(pmu))
 		return true;
 
 	return test_bit(pmc->idx, (unsigned long *)&pmu->global_ctrl);
@@ -208,7 +208,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr, bool host_initiat
 	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
 		if (host_initiated)
 			return true;
-		return pmu->version > 1;
+		return intel_pmu_has_perf_global_ctrl(pmu);
 		break;
 	case MSR_IA32_PEBS_ENABLE:
 		if (host_initiated)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 576fed7e33de..215f17eb6732 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -91,6 +91,18 @@ union vmx_exit_reason {
 	u32 full;
 };
 
+static inline bool intel_pmu_has_perf_global_ctrl(struct kvm_pmu *pmu)
+{
+	/*
+	 * Architecturally, Intel's SDM states that IA32_PERF_GLOBAL_CTRL is
+	 * supported if "CPUID.0AH: EAX[7:0] > 0", i.e. if the PMU version is
+	 * greater than zero.  However, KVM only exposes and emulates the MSR
+	 * to/for the guest if the guest PMU supports at least "Architectural
+	 * Performance Monitoring Version 2".
+	 */
+	return pmu->version > 1;
+}
+
 #define vcpu_to_lbr_desc(vcpu) (&to_vmx(vcpu)->lbr_desc)
 #define vcpu_to_lbr_records(vcpu) (&to_vmx(vcpu)->lbr_desc.records)
 
-- 
2.36.1.255.ge46751e96f-goog