linux-kernel - [RFC PATCH 06/14] KVM: arm64: Use PERF_COUNT_HW_CPU

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Message-Id: <20241203193220.1070811-7-oliver.upton@linux.dev>
Date: Tue,  3 Dec 2024 11:32:12 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: kvmarm@...ts.linux.dev
Cc: Marc Zyngier <maz@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Mingwei Zhang <mizhang@...gle.com>,
	Colton Lewis <coltonlewis@...gle.com>,
	Raghavendra Rao Ananta <rananta@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Oliver Upton <oliver.upton@...ux.dev>
Subject: [RFC PATCH 06/14] KVM: arm64: Use PERF_COUNT_HW_CPU_CYCLES for fixed cycle counter

KVM will soon be able to emulate PMUv3 on non-PMUv3 hardware. Use the
generic event for CPU cycles to allow a non-PMUv3 driver to map the
event correctly on underlying hardware.

Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
---
 arch/arm64/kvm/pmu-emul.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 3e7091e1a2e4..0b2ad60717e8 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -700,16 +700,27 @@ static void kvm_pmu_create_perf_event(struct kvm_pmc *pmc)
 {
 	struct kvm_vcpu *vcpu = kvm_pmc_to_vcpu(pmc);
 	struct arm_pmu *arm_pmu = vcpu->kvm->arch.arm_pmu;
+	struct perf_event_attr attr = {};
 	struct perf_event *event;
-	struct perf_event_attr attr;
 	u64 eventsel, evtreg;
 
 	evtreg = kvm_pmc_read_evtreg(pmc);
 
 	kvm_pmu_stop_counter(pmc);
 	if (pmc->idx == ARMV8_PMU_CYCLE_IDX) {
-		eventsel = ARMV8_PMUV3_PERFCTR_CPU_CYCLES;
+		/*
+		 * Use the common event space for the cycle counter, allowing
+		 * the underlying PMU driver to map it onto hardware in the
+		 * unlikely case the host doesn't actually have PMUv3.
+		 */
+		attr.type = PERF_TYPE_HARDWARE;
+		eventsel = PERF_COUNT_HW_CPU_CYCLES;
 	} else {
+		/*
+		 * Otherwise, treat the event as a raw event for the selected
+		 * PMU.
+		 */
+		attr.type = arm_pmu->pmu.type;
 		eventsel = evtreg & kvm_pmu_event_mask(vcpu->kvm);
 
 		/*
@@ -729,8 +740,6 @@ static void kvm_pmu_create_perf_event(struct kvm_pmc *pmc)
 			return;
 	}
 
-	memset(&attr, 0, sizeof(struct perf_event_attr));
-	attr.type = arm_pmu->pmu.type;
 	attr.size = sizeof(attr);
 	attr.pinned = 1;
 	attr.disabled = !kvm_pmu_counter_is_enabled(pmc);
-- 
2.39.5