linux-kernel - [PATCH v5 35/44] KVM: x86/pmu: Reprogram mediated PMU event selectors on event filter updates

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Message-ID: <20250806195706.1650976-36-seanjc@google.com>
Date: Wed,  6 Aug 2025 12:56:57 -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 35/44] KVM: x86/pmu: Reprogram mediated PMU event selectors
 on event filter updates

From: Dapeng Mi <dapeng1.mi@...ux.intel.com>

Refresh the event selectors that are programmed into hardware when a PMC
is "reprogrammed" for a mediated PMU, i.e. if userspace changes the PMU
event filters

Note, KVM doesn't utilize the reprogramming infrastructure to handle
counter overflow for mediated PMUs, as there's no need to reprogram a
non-existent perf event.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Co-developed-by: Mingwei Zhang <mizhang@...gle.com>
Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
[sean: add a helper to document behavior, split patch and rewrite changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/pmu.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index e39ae37f0280..b4c6a7704a01 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -518,6 +518,25 @@ static bool pmc_is_event_allowed(struct kvm_pmc *pmc)
 	return is_fixed_event_allowed(filter, pmc->idx);
 }
 
+static void kvm_mediated_pmu_refresh_event_filter(struct kvm_pmc *pmc)
+{
+	bool allowed = pmc_is_event_allowed(pmc);
+	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
+
+	if (pmc_is_gp(pmc)) {
+		pmc->eventsel_hw &= ~ARCH_PERFMON_EVENTSEL_ENABLE;
+		if (allowed)
+			pmc->eventsel_hw |= pmc->eventsel &
+					    ARCH_PERFMON_EVENTSEL_ENABLE;
+	} else {
+		u64 mask = intel_fixed_bits_by_idx(pmc->idx - KVM_FIXED_PMC_BASE_IDX, 0xf);
+
+		pmu->fixed_ctr_ctrl_hw &= ~mask;
+		if (allowed)
+			pmu->fixed_ctr_ctrl_hw |= pmu->fixed_ctr_ctrl & mask;
+	}
+}
+
 static int reprogram_counter(struct kvm_pmc *pmc)
 {
 	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
@@ -526,6 +545,11 @@ static int reprogram_counter(struct kvm_pmc *pmc)
 	bool emulate_overflow;
 	u8 fixed_ctr_ctrl;
 
+	if (kvm_vcpu_has_mediated_pmu(pmu_to_vcpu(pmu))) {
+		kvm_mediated_pmu_refresh_event_filter(pmc);
+		return 0;
+	}
+
 	emulate_overflow = pmc_pause_counter(pmc);
 
 	if (!pmc_is_globally_enabled(pmc) || !pmc_is_locally_enabled(pmc) ||
-- 
2.50.1.565.gc32cd1483b-goog