linux-kernel - [PATCH v5 18/24] KVM: arm64: Enforce PMU event filter at vcpu

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Message-ID: <20251209205121.1871534-19-coltonlewis@google.com>
Date: Tue,  9 Dec 2025 20:51:15 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
	Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Mingwei Zhang <mizhang@...gle.com>, Joey Gouly <joey.gouly@....com>, 
	Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>, 
	Mark Rutland <mark.rutland@....com>, Shuah Khan <shuah@...nel.org>, 
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-perf-users@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Colton Lewis <coltonlewis@...gle.com>
Subject: [PATCH v5 18/24] KVM: arm64: Enforce PMU event filter at vcpu_load()

The KVM API for event filtering says that counters do not count when
blocked by the event filter. To enforce that, the event filter must be
rechecked on every load since it might have changed since the last
time the guest wrote a value. If the event is filtered, exclude
counting at all exception levels before writing the hardware.

Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
---
 arch/arm64/kvm/pmu-direct.c | 44 +++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/arch/arm64/kvm/pmu-direct.c b/arch/arm64/kvm/pmu-direct.c
index 71977d24f489a..8d0d6d1a0d851 100644
--- a/arch/arm64/kvm/pmu-direct.c
+++ b/arch/arm64/kvm/pmu-direct.c
@@ -221,6 +221,49 @@ u8 kvm_pmu_hpmn(struct kvm_vcpu *vcpu)
 	return nr_host_cnt_max;
 }
 
+/**
+ * kvm_pmu_apply_event_filter()
+ * @vcpu: Pointer to vcpu struct
+ *
+ * To uphold the guarantee of the KVM PMU event filter, we must ensure
+ * no counter counts if the event is filtered. Accomplish this by
+ * filtering all exception levels if the event is filtered.
+ */
+static void kvm_pmu_apply_event_filter(struct kvm_vcpu *vcpu)
+{
+	struct arm_pmu *pmu = vcpu->kvm->arch.arm_pmu;
+	u64 evtyper_set = ARMV8_PMU_EXCLUDE_EL0 |
+		ARMV8_PMU_EXCLUDE_EL1;
+	u64 evtyper_clr = ARMV8_PMU_INCLUDE_EL2;
+	u8 i;
+	u64 val;
+	u64 evsel;
+
+	if (!pmu)
+		return;
+
+	for (i = 0; i < pmu->hpmn_max; i++) {
+		val = __vcpu_sys_reg(vcpu, PMEVTYPER0_EL0 + i);
+		evsel = val & kvm_pmu_event_mask(vcpu->kvm);
+
+		if (vcpu->kvm->arch.pmu_filter &&
+		    !test_bit(evsel, vcpu->kvm->arch.pmu_filter))
+			val |= evtyper_set;
+
+		val &= ~evtyper_clr;
+		write_pmevtypern(i, val);
+	}
+
+	val = __vcpu_sys_reg(vcpu, PMCCFILTR_EL0);
+
+	if (vcpu->kvm->arch.pmu_filter &&
+	    !test_bit(ARMV8_PMUV3_PERFCTR_CPU_CYCLES, vcpu->kvm->arch.pmu_filter))
+		val |= evtyper_set;
+
+	val &= ~evtyper_clr;
+	write_pmccfiltr(val);
+}
+
 /**
  * kvm_pmu_load() - Load untrapped PMU registers
  * @vcpu: Pointer to struct kvm_vcpu
@@ -244,6 +287,7 @@ void kvm_pmu_load(struct kvm_vcpu *vcpu)
 		return;
 
 	pmu = vcpu->kvm->arch.arm_pmu;
+	kvm_pmu_apply_event_filter(vcpu);
 
 	for (i = 0; i < pmu->hpmn_max; i++) {
 		val = __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i);
-- 
2.52.0.239.gd5f0c6e74e-goog