linux-kernel - [RFC PATCH 2/4] KVM: arm64: Make guests see only counters they can access

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Message-ID: <20250127222031.3078945-3-coltonlewis@google.com>
Date: Mon, 27 Jan 2025 22:20:28 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: kvm@...r.kernel.org
Cc: 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>, 
	Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Zenghui Yu <yuzenghui@...wei.com>, Mark Rutland <mark.rutland@....com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	kvmarm@...ts.linux.dev, linux-kselftest@...r.kernel.org, 
	Colton Lewis <coltonlewis@...gle.com>
Subject: [RFC PATCH 2/4] KVM: arm64: Make guests see only counters they can access

The ARM architecture specifies that when MDCR_EL2.HPMN is set, EL1 and
EL0, which includes KVM guests, should read that value for PMCR.N.

Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
---
 arch/arm64/kvm/pmu-emul.c                                 | 8 +++++++-
 tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c | 2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 6c5950b9ceac..052ce8c721fe 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -993,12 +993,18 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
 u8 kvm_arm_pmu_get_max_counters(struct kvm *kvm)
 {
 	struct arm_pmu *arm_pmu = kvm->arch.arm_pmu;
+	u8 limit;
+
+	if (arm_pmu->partitioned)
+		limit = arm_pmu->hpmn - 1;
+	else
+		limit = ARMV8_PMU_MAX_GENERAL_COUNTERS;
 
 	/*
 	 * The arm_pmu->cntr_mask considers the fixed counter(s) as well.
 	 * Ignore those and return only the general-purpose counters.
 	 */
-	return bitmap_weight(arm_pmu->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS);
+	return bitmap_weight(arm_pmu->cntr_mask, limit);
 }
 
 static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
diff --git a/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c b/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c
index f9c0c86d7e85..4d5acdb66bc2 100644
--- a/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c
@@ -610,7 +610,7 @@ static void run_pmregs_validity_test(uint64_t pmcr_n)
  */
 static void run_error_test(uint64_t pmcr_n)
 {
-	pr_debug("Error test with pmcr_n %lu (larger than the host)\n", pmcr_n);
+	pr_debug("Error test with pmcr_n %lu (larger than the host allows)\n", pmcr_n);
 
 	test_create_vpmu_vm_with_pmcr_n(pmcr_n, true);
 	destroy_vpmu_vm();
-- 
2.48.1.262.g85cc9f2d1e-goog