linux-kernel - [PATCH v2 13/14] KVM: arm64: Provide 1 event counter on IMPDEF hardware

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Message-Id: <20250203183111.191519-14-oliver.upton@linux.dev>
Date: Mon,  3 Feb 2025 10:31:10 -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>,
	Janne Grunau <j@...nau.net>
Subject: [PATCH v2 13/14] KVM: arm64: Provide 1 event counter on IMPDEF hardware

PMUv3 requires that all programmable event counters are capable of
counting any event. The Apple M* PMU is quite a bit different, and
events have affinities for particular PMCs.

Expose 1 event counter on IMPDEF hardware, allowing the guest to do
something useful with its PMU while also upholding the requirements of
the architecture.

Tested-by: Janne Grunau <j@...nau.net>
Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
---
 arch/arm64/kvm/pmu-emul.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 97f29153193f..e7b732bcaaa2 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1027,6 +1027,13 @@ u8 kvm_arm_pmu_get_max_counters(struct kvm *kvm)
 {
 	struct arm_pmu *arm_pmu = kvm->arch.arm_pmu;
 
+	/*
+	 * PMUv3 requires that all event counters are capable of counting any
+	 * event, though the same may not be true of non-PMUv3 hardware.
+	 */
+	if (cpus_have_final_cap(ARM64_WORKAROUND_PMUV3_IMPDEF_TRAPS))
+		return 1;
+
 	/*
 	 * The arm_pmu->cntr_mask considers the fixed counter(s) as well.
 	 * Ignore those and return only the general-purpose counters.
-- 
2.39.5