linux-kernel - [PATCH 3/6] KVM: x86/pmu: Track enabled AMD PMCs with Host-Only xor Guest-Only bits set

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Message-ID: <20260121225438.3908422-4-jmattson@google.com>
Date: Wed, 21 Jan 2026 14:54:01 -0800
From: Jim Mattson <jmattson@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	James Clark <james.clark@...aro.org>, Shuah Khan <shuah@...nel.org>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Cc: Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 3/6] KVM: x86/pmu: Track enabled AMD PMCs with Host-Only xor
 Guest-Only bits set

Add pmc_hostonly and pmc_guestonly bitmaps to struct kvm_pmu to track which
guest-enabled performance counters have just one of the Host-Only and
Guest-Only event selector bits set. PMCs that are disabled, have neither
HG_ONLY bit set, or have both HG_ONLY bits set are not tracked, because
they don't require special handling at vCPU state transitions.

Update the bitmaps when the guest writes to an event selector MSR.

Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  4 ++++
 arch/x86/kvm/pmu.c              |  2 ++
 arch/x86/kvm/svm/pmu.c          | 28 ++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ecd4019b84b7..92050f76f84b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -593,6 +593,10 @@ struct kvm_pmu {
 	DECLARE_BITMAP(pmc_counting_instructions, X86_PMC_IDX_MAX);
 	DECLARE_BITMAP(pmc_counting_branches, X86_PMC_IDX_MAX);
 
+	/* AMD only: track PMCs with Host-Only or Guest-Only bits set */
+	DECLARE_BITMAP(pmc_hostonly, X86_PMC_IDX_MAX);
+	DECLARE_BITMAP(pmc_guestonly, X86_PMC_IDX_MAX);
+
 	u64 ds_area;
 	u64 pebs_enable;
 	u64 pebs_enable_rsvd;
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index bd6b785cf261..833ee2ecd43f 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -921,6 +921,8 @@ static void kvm_pmu_reset(struct kvm_vcpu *vcpu)
 	pmu->need_cleanup = false;
 
 	bitmap_zero(pmu->reprogram_pmi, X86_PMC_IDX_MAX);
+	bitmap_zero(pmu->pmc_hostonly, X86_PMC_IDX_MAX);
+	bitmap_zero(pmu->pmc_guestonly, X86_PMC_IDX_MAX);
 
 	kvm_for_each_pmc(pmu, pmc, i, pmu->all_valid_pmc_idx) {
 		pmc_stop_counter(pmc);
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index f619417557f9..c06013e2b4b1 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -147,6 +147,33 @@ static int amd_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	return 1;
 }
 
+static void amd_pmu_update_hg_bitmaps(struct kvm_pmc *pmc)
+{
+	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
+	u64 eventsel = pmc->eventsel;
+
+	if (!(eventsel & ARCH_PERFMON_EVENTSEL_ENABLE)) {
+		bitmap_clear(pmu->pmc_hostonly, pmc->idx, 1);
+		bitmap_clear(pmu->pmc_guestonly, pmc->idx, 1);
+		return;
+	}
+
+	switch (eventsel & AMD64_EVENTSEL_HG_ONLY) {
+	case AMD64_EVENTSEL_HOSTONLY:
+		bitmap_set(pmu->pmc_hostonly, pmc->idx, 1);
+		bitmap_clear(pmu->pmc_guestonly, pmc->idx, 1);
+		break;
+	case AMD64_EVENTSEL_GUESTONLY:
+		bitmap_clear(pmu->pmc_hostonly, pmc->idx, 1);
+		bitmap_set(pmu->pmc_guestonly, pmc->idx, 1);
+		break;
+	default:
+		bitmap_clear(pmu->pmc_hostonly, pmc->idx, 1);
+		bitmap_clear(pmu->pmc_guestonly, pmc->idx, 1);
+		break;
+	}
+}
+
 static bool amd_pmu_dormant_hg_event(struct kvm_pmc *pmc)
 {
 	u64 hg_only = pmc->eventsel & AMD64_EVENTSEL_HG_ONLY;
@@ -196,6 +223,7 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (data != pmc->eventsel) {
 			pmc->eventsel = data;
 			amd_pmu_set_eventsel_hw(pmc);
+			amd_pmu_update_hg_bitmaps(pmc);
 			kvm_pmu_request_counter_reprogram(pmc);
 		}
 		return 0;
-- 
2.52.0.457.g6b5491de43-goog