Add a regression test that runs one vCPU and then tries to change the
VM-scoped PMU counter count through an idle sibling. Verify that
SET_NR_COUNTERS fails with EBUSY once any vCPU has run.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
---
 .../selftests/kvm/arm64/vpmu_counter_access.c      | 47 ++++++++++++++++++++--
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
index 22223395969e..05135bcdb462 100644
--- a/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
+++ b/tools/testing/selftests/kvm/arm64/vpmu_counter_access.c
@@ -443,11 +443,10 @@ static void destroy_vpmu_vm(void)
 	kvm_vm_free(vpmu_vm.vm);
 }
 
-static void run_vcpu(struct kvm_vcpu *vcpu, u64 pmcr_n)
+static void run_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct ucall uc;
 
-	vcpu_args_set(vcpu, 1, pmcr_n);
 	vcpu_run(vcpu);
 	switch (get_ucall(vcpu, &uc)) {
 	case UCALL_ABORT:
@@ -461,6 +460,11 @@ static void run_vcpu(struct kvm_vcpu *vcpu, u64 pmcr_n)
 	}
 }
 
+static void guest_code_done(void)
+{
+	GUEST_DONE();
+}
+
 static void test_create_vpmu_vm_with_nr_counters(unsigned int nr_counters, bool expect_fail)
 {
 	struct kvm_vcpu *vcpu;
@@ -503,7 +507,8 @@ static void run_access_test(u64 pmcr_n)
 	/* Save the initial sp to restore them later to run the guest again */
 	sp = vcpu_get_reg(vcpu, ctxt_reg_alias(vcpu, SYS_SP_EL1));
 
-	run_vcpu(vcpu, pmcr_n);
+	vcpu_args_set(vcpu, 1, pmcr_n);
+	run_vcpu(vcpu);
 
 	/*
 	 * Reset and re-initialize the vCPU, and run the guest code again to
@@ -516,7 +521,8 @@ static void run_access_test(u64 pmcr_n)
 	vcpu_set_reg(vcpu, ctxt_reg_alias(vcpu, SYS_SP_EL1), sp);
 	vcpu_set_reg(vcpu, ARM64_CORE_REG(regs.pc), (u64)guest_code);
 
-	run_vcpu(vcpu, pmcr_n);
+	vcpu_args_set(vcpu, 1, pmcr_n);
+	run_vcpu(vcpu);
 
 	destroy_vpmu_vm();
 }
@@ -622,6 +628,37 @@ static bool kvm_supports_nr_counters_attr(void)
 	return supported;
 }
 
+static void test_set_nr_counters_after_vcpu_run(void)
+{
+	struct kvm_vcpu *running_vcpu, *stopped_vcpu;
+	unsigned int nr_counters = 0;
+	struct kvm_vcpu_init init;
+	struct kvm_vm *vm;
+	int ret;
+	u64 irq = 23;
+
+	vm = vm_create(2);
+	vm_ioctl(vm, KVM_ARM_PREFERRED_TARGET, &init);
+	init.features[0] |= BIT(KVM_ARM_VCPU_PMU_V3);
+	running_vcpu = aarch64_vcpu_add(vm, 0, &init, guest_code_done);
+	stopped_vcpu = aarch64_vcpu_add(vm, 1, &init, guest_code_done);
+	kvm_arch_vm_finalize_vcpus(vm);
+
+	vcpu_device_attr_set(running_vcpu, KVM_ARM_VCPU_PMU_V3_CTRL,
+			     KVM_ARM_VCPU_PMU_V3_IRQ, &irq);
+	vcpu_device_attr_set(running_vcpu, KVM_ARM_VCPU_PMU_V3_CTRL,
+			     KVM_ARM_VCPU_PMU_V3_INIT, NULL);
+	run_vcpu(running_vcpu);
+
+	ret = __vcpu_device_attr_set(stopped_vcpu, KVM_ARM_VCPU_PMU_V3_CTRL,
+				     KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS,
+				     &nr_counters);
+	TEST_ASSERT(ret == -1 && errno == EBUSY,
+		    KVM_IOCTL_ERROR(KVM_SET_DEVICE_ATTR, ret));
+
+	kvm_vm_free(vm);
+}
+
 int main(void)
 {
 	u64 i, pmcr_n;
@@ -630,6 +667,8 @@ int main(void)
 	TEST_REQUIRE(kvm_supports_vgic_v3());
 	TEST_REQUIRE(kvm_supports_nr_counters_attr());
 
+	test_set_nr_counters_after_vcpu_run();
+
 	pmcr_n = get_pmcr_n_limit();
 	for (i = 0; i <= pmcr_n; i++) {
 		run_access_test(i);

-- 
2.55.0