[PATCH v5 07/15] KVM: VMX: Add helper to check if the guest PMU has PERF_GLOBAL_CTRL

Sean Christopherson
2022-06-08T01:09:55Z

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@google.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