linux-kernel - [RFC PATCH v2 4/4] KVM: arm64: Make guests see only counters they can access

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Message-ID: <20250208020111.2068239-5-coltonlewis@google.com>
Date: Sat,  8 Feb 2025 02:01:11 +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-perf-users@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Colton Lewis <coltonlewis@...gle.com>
Subject: [RFC PATCH v2 4/4] 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/debug.c                                  | 3 +--
 arch/arm64/kvm/pmu-emul.c                               | 8 +++++++-
 tools/testing/selftests/kvm/arm64/vpmu_counter_access.c | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 0e4c805e7e89..7c04db00bf6c 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -36,8 +36,7 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
 	 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
 	 * to disable guest access to the profiling and trace buffers
 	 */
-	vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN,
-					 *host_data_ptr(nr_event_counters));
+	vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN, read_mdcr());
 	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
 				MDCR_EL2_TPMS |
 				MDCR_EL2_TTRF |
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/arm64/vpmu_counter_access.c b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
index f16b3b27e32e..b5bc18b7528d 100644
--- a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
@@ -609,7 +609,7 @@ 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();
-- 
2.48.1.502.g6dc24dfdaf-goog