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From:   Like Xu <like.xu.linux@gmail.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v6 06/10] KVM: x86/pmu: Forget PERFCTR_CORE if the min num of counters isn't met
Date:   Tue, 30 May 2023 14:04:19 +0800
Message-Id: <20230530060423.32361-7-likexu@tencent.com>
In-Reply-To: <20230530060423.32361-1-likexu@tencent.com>
References: <20230530060423.32361-1-likexu@tencent.com>
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From: Like Xu <likexu@tencent.com>

A sanity check on the number of counters enumerated by perf is added.
PERFCTR_CORE support is explicitly dropped if the min number isn't met.
E.g. if KVM needs 6 counters and perf says there are 4, then something
is wrong and enumerating 6 to a guest is only going to cause more issues.

Opportunistically, the kvm_cpu_cap_check_and_set() is applied to simplify
the host check before setting the PERFCTR_CORE flag.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Like Xu <likexu@tencent.com>
---
 arch/x86/kvm/svm/svm.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ca32389f3c36..d9669e3cc00a 100644
--- 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();
-- 
2.40.1