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

From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	 Tianrui Zhao <zhaotianrui@loongson.cn>,
	Bibo Mao <maobibo@loongson.cn>,
	 Huacai Chen <chenhuacai@kernel.org>,
	Anup Patel <anup@brainfault.org>,
	 Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	 Albert Ou <aou@eecs.berkeley.edu>, Xin Li <xin@zytor.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	 Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	 Arnaldo Carvalho de Melo <acme@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	 Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	 kvm@vger.kernel.org, loongarch@lists.linux.dev,
	kvm-riscv@lists.infradead.org,  linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org,  linux-perf-users@vger.kernel.org,
	Kan Liang <kan.liang@linux.intel.com>,
	 Yongwei Ma <yongwei.ma@intel.com>,
	Mingwei Zhang <mizhang@google.com>,
	 Xiong Zhang <xiong.y.zhang@linux.intel.com>,
	Sandipan Das <sandipan.das@amd.com>,
	 Dapeng Mi <dapeng1.mi@linux.intel.com>
Subject: [PATCH v5 35/44] KVM: x86/pmu: Reprogram mediated PMU event selectors on event filter updates
Date: Wed,  6 Aug 2025 12:56:57 -0700	[thread overview]
Message-ID: <20250806195706.1650976-36-seanjc@google.com> (raw)
In-Reply-To: <20250806195706.1650976-1-seanjc@google.com>

From: Dapeng Mi <dapeng1.mi@linux.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@google.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Co-developed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
[sean: add a helper to document behavior, split patch and rewrite changelog]
Signed-off-by: Sean Christopherson <seanjc@google.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


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