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) checks, _and_ there has been at least one attempt to add a
_third_ flavor.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220722224409.1336532-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 6e355c5..78f2800 100644 (file)
--- 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);
@@ -207,7 +207,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
        case MSR_CORE_PERF_GLOBAL_STATUS:
        case MSR_CORE_PERF_GLOBAL_CTRL:
        case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
-               ret = pmu->version > 1;
+               return intel_pmu_has_perf_global_ctrl(pmu);
                break;
        case MSR_IA32_PEBS_ENABLE:
                ret = vcpu_get_perf_capabilities(vcpu) & PERF_CAP_PEBS_FORMAT;

diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 286c88e..2a0b94e 100644 (file)
--- 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)