KVM: x86/pmu: Advertise PERFCTR_CORE iff the min nr of counters is met

Enable and advertise PERFCTR_CORE if and only if the minimum number of
required counters are available, i.e. if perf says there are less than six
general purpose counters.

Opportunistically, use kvm_cpu_cap_check_and_set() instead of open coding
the check for host support.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Like Xu <likexu@tencent.com>
[sean: massage shortlog and changelog]
Link: https://lore.kernel.org/r/20230603011058.1038821-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ca32389..d9669e3 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5025,9 +5025,18 @@ static __init void svm_set_cpu_caps(void)
            boot_cpu_has(X86_FEATURE_AMD_SSBD))
                kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
 
-       /* AMD PMU PERFCTR_CORE CPUID */
-       if (enable_pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
-               kvm_cpu_cap_set(X86_FEATURE_PERFCTR_CORE);
+       if (enable_pmu) {
+               /*
+                * Enumerate support for PERFCTR_CORE if and only if KVM has
+                * access to enough counters to virtualize "core" support,
+                * otherwise limit vPMU support to the legacy number of counters.
+                */
+               if (kvm_pmu_cap.num_counters_gp < AMD64_NUM_COUNTERS_CORE)
+                       kvm_pmu_cap.num_counters_gp = min(AMD64_NUM_COUNTERS,
+                                                         kvm_pmu_cap.num_counters_gp);
+               else
+                       kvm_cpu_cap_check_and_set(X86_FEATURE_PERFCTR_CORE);
+       }
 
        /* CPUID 0x8000001F (SME/SEV features) */
        sev_set_cpu_caps();