linux-kernel - [PATCH v5 15/44] KVM: SVM: Check pmu->version, not enable

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Message-ID: <20250806195706.1650976-16-seanjc@google.com>
Date: Wed,  6 Aug 2025 12:56:37 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Anup Patel <anup@...infault.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Xin Li <xin@...or.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, loongarch@...ts.linux.dev, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, Kan Liang <kan.liang@...ux.intel.com>, 
	Yongwei Ma <yongwei.ma@...el.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Xiong Zhang <xiong.y.zhang@...ux.intel.com>, Sandipan Das <sandipan.das@....com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH v5 15/44] KVM: SVM: Check pmu->version, not enable_pmu, when
 getting PMC MSRs

Gate access to PMC MSRs based on pmu->version, not on kvm->arch.enable_pmu,
to more accurately reflect KVM's behavior.  This is a glorified nop, as
pmu->version and pmu->nr_arch_gp_counters can only be non-zero if
amd_pmu_refresh() is reached, kvm_pmu_refresh() invokes amd_pmu_refresh()
if and only if kvm->arch.enable_pmu is true, and amd_pmu_refresh() forces
pmu->version to be 1 or 2.

I.e. the following holds true:

  !pmu->nr_arch_gp_counters || kvm->arch.enable_pmu == (pmu->version > 0)

and so the only way for amd_pmu_get_pmc() to return a non-NULL value is if
both kvm->arch.enable_pmu and pmu->version evaluate to true.

No real functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 288f7f2a46f2..7b8577f3c57a 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -41,7 +41,7 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
 	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
 	unsigned int idx;
 
-	if (!vcpu->kvm->arch.enable_pmu)
+	if (!pmu->version)
 		return NULL;
 
 	switch (msr) {
-- 
2.50.1.565.gc32cd1483b-goog