Add MDCR_EL2 coverage to vpmu_counter_access when EL2 is available.

For each configured PMCR_EL0.N value, verify that HPMN tracks the
configured counter count, HPME can be toggled without disturbing HPMN,
and KVM_SET_ONE_REG rejects an out-of-range HPMN without changing
MDCR_EL2. Reset the vCPU and verify that HPMN is restored from the
configured count.

Assisted-by: Codex:gpt-5.5
Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
---
 .../selftests/kvm/arm64/vpmu_counter_access.c      | 76 ++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
index 22223395969e..25203ea117b0 100644
--- a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
@@ -25,6 +25,14 @@
 /* The cycle counter bit position that's common among the PMU registers */
 #define ARMV8_PMU_CYCLE_IDX		31
 
+#ifndef MDCR_EL2_HPMN
+#define MDCR_EL2_HPMN			GENMASK_ULL(4, 0)
+#endif
+
+#ifndef MDCR_EL2_HPME
+#define MDCR_EL2_HPME			BIT_ULL(7)
+#endif
+
 struct vpmu_vm {
 	struct kvm_vm *vm;
 	struct kvm_vcpu *vcpu;
@@ -583,6 +591,73 @@ static void run_pmregs_validity_test(u64 pmcr_n)
 	destroy_vpmu_vm();
 }
 
+static void run_mdcr_el2_validity_test(u64 pmcr_n)
+{
+	struct kvm_vcpu_init init;
+	struct kvm_vcpu *vcpu;
+	u64 mdcr, old_mdcr;
+	int ret;
+
+	pr_debug("MDCR_EL2 test with pmcr_n %lu\n", pmcr_n);
+
+	test_create_vpmu_vm_with_nr_counters(pmcr_n, false);
+	if (!vm_supports_el2(vpmu_vm.vm)) {
+		destroy_vpmu_vm();
+		return;
+	}
+
+	vcpu = vpmu_vm.vcpu;
+
+	mdcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2));
+	TEST_ASSERT(FIELD_GET(MDCR_EL2_HPMN, mdcr) == pmcr_n,
+		    "MDCR_EL2.HPMN is not updated after PMU_V3_SET_NR_COUNTERS (expected %lu, got %lu)",
+		    pmcr_n, FIELD_GET(MDCR_EL2_HPMN, mdcr));
+
+	old_mdcr = mdcr;
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2),
+		     old_mdcr ^ MDCR_EL2_HPME);
+
+	mdcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2));
+	TEST_ASSERT(mdcr == (old_mdcr ^ MDCR_EL2_HPME),
+		    "MDCR_EL2 was not properly updated after HPME write (expected 0x%lx, got 0x%lx)",
+		    old_mdcr ^ MDCR_EL2_HPME, mdcr);
+
+	if (pmcr_n < FIELD_MAX(MDCR_EL2_HPMN)) {
+		errno = 0;
+		old_mdcr = mdcr;
+		ret = __vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2),
+				     u64_replace_bits(mdcr, pmcr_n + 1, MDCR_EL2_HPMN));
+		TEST_ASSERT(ret == -1 && errno == EINVAL,
+			    "Setting MDCR_EL2.HPMN to %lu unexpectedly succeeded",
+			    pmcr_n + 1);
+
+		mdcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2));
+		TEST_ASSERT(mdcr == old_mdcr,
+			    "MDCR_EL2 changed after failed HPMN write (expected 0x%lx, got 0x%lx)",
+			    old_mdcr, mdcr);
+	}
+
+	old_mdcr = mdcr;
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2),
+		     u64_replace_bits(mdcr, 0, MDCR_EL2_HPMN));
+
+	mdcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2));
+	TEST_ASSERT(mdcr == u64_replace_bits(old_mdcr, 0, MDCR_EL2_HPMN),
+		    "MDCR_EL2 was not properly updated after HPMN write (expected 0x%lx, got 0x%lx)",
+		    u64_replace_bits(old_mdcr, 0, MDCR_EL2_HPMN), mdcr);
+
+	kvm_get_default_vcpu_target(vpmu_vm.vm, &init);
+	init.features[0] |= (1 << KVM_ARM_VCPU_PMU_V3);
+	aarch64_vcpu_setup(vcpu, &init);
+
+	mdcr = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MDCR_EL2));
+	TEST_ASSERT(FIELD_GET(MDCR_EL2_HPMN, mdcr) == pmcr_n,
+		    "MDCR_EL2.HPMN is not updated after INIT (expected %lu, got %lu)",
+		    pmcr_n, FIELD_GET(MDCR_EL2_HPMN, mdcr));
+
+	destroy_vpmu_vm();
+}
+
 /*
  * Create a guest with one vCPU, and attempt to set the PMCR_EL0.N for
  * the vCPU to @pmcr_n, which is larger than the host value.
@@ -634,6 +709,7 @@ int main(void)
 	for (i = 0; i <= pmcr_n; i++) {
 		run_access_test(i);
 		run_pmregs_validity_test(i);
+		run_mdcr_el2_validity_test(i);
 	}
 
 	for (i = pmcr_n + 1; i < ARMV8_PMU_MAX_COUNTERS; i++)

-- 
2.55.0