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 v4 08/12] KVM: x86/pmu: Disable vPMU if the minimum num of counters isn't met
Date:   Tue, 14 Feb 2023 13:07:53 +0800
Message-Id: <20230214050757.9623-9-likexu@tencent.com>
In-Reply-To: <20230214050757.9623-1-likexu@tencent.com>
References: <20230214050757.9623-1-likexu@tencent.com>
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From: Like Xu <likexu@tencent.com>

For compatibility with old software, KVM/AMD should never report less
than four counters if vPMU is supported. Thus KVM should sanity check
the number of counters enumerated by perf and explicitly disable vPMU
support if the min isn't met. E.g. if KVM needs 4 counters and perf says
there are 3, then something is wrong and enumerating 4 to the guest
is only going to cause more troubles.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Like Xu <likexu@tencent.com>
---
 arch/x86/kvm/pmu.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index d1cc02c8da88..46db5404894e 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -170,6 +170,12 @@ static inline void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops)
 	if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp)
 		enable_pmu = false;
 
+	/*
+	 * For AMD, disable vPMU if the minimum number of counters isn't met.
+	 */
+	if (!is_intel && kvm_pmu_cap.num_counters_gp < AMD64_NUM_COUNTERS)
+		enable_pmu = false;
+
 	if (!enable_pmu) {
 		memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
 		return;
-- 
2.39.1