[RFC,2/4] KVM: arm64: Make guests see only counters they can access

Commit Message

Colton Lewis Jan. 27, 2025, 10:20 p.m. UTC

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 <[e-mail]>
---
 arch/arm64/kvm/pmu-emul.c                                 | 8 +++++++-
 tools/testing/selftests/kvm/aarch64/vpmu_counter_access.c | 2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

Patch

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();