KVM: selftests: Verify userspace can create "redundant" binary stats files

Verify that KVM doesn't artificially limit KVM_GET_STATS_FD to a single
file per VM/vCPU.  There's no known use case for getting multiple stats
fds, but it should work, and more importantly creating multiple files will
make it easier to test that KVM correct manages VM refcounts for stats
files.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230711230131.648752-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: sean-jc

tools/testing/selftests/kvm/kvm_binary_stats_test.c

@@ -185,6 +185,7 @@ static void stats_test(int stats_fd)
 
 int main(int argc, char *argv[])
 {
+	int vm_stats_fds, *vcpu_stats_fds;
 	int i, j;
 	struct kvm_vcpu **vcpus;
 	struct kvm_vm **vms;
@@ -217,18 +218,37 @@ int main(int argc, char *argv[])
 	vcpus = malloc(sizeof(struct kvm_vcpu *) * max_vm * max_vcpu);
 	TEST_ASSERT(vcpus, "Allocate memory for storing vCPU pointers");
 
+	/*
+	 * Not per-VM as the array is populated, used, and invalidated within a
+	 * single for-loop iteration.
+	 */
+	vcpu_stats_fds = calloc(max_vm, sizeof(*vcpu_stats_fds));
+	TEST_ASSERT(vcpu_stats_fds, "Allocate memory for VM stats fds");
+
 	for (i = 0; i < max_vm; ++i) {
 		vms[i] = vm_create_barebones();
 		for (j = 0; j < max_vcpu; ++j)
 			vcpus[i * max_vcpu + j] = __vm_vcpu_add(vms[i], j);
 	}
 
-	/* Check stats read for every VM and VCPU */
+	/*
+	 * Check stats read for every VM and vCPU, with a variety of testcases.
+	 * Note, stats_test() closes the passed in stats fd.
+	 */
 	for (i = 0; i < max_vm; ++i) {
+		vm_stats_fds = vm_get_stats_fd(vms[i]);
+
+		/* Verify userspace can instantiate multiple stats files. */
 		stats_test(vm_get_stats_fd(vms[i]));
 
-		for (j = 0; j < max_vcpu; ++j)
+		for (j = 0; j < max_vcpu; ++j) {
+			vcpu_stats_fds[j] = vcpu_get_stats_fd(vcpus[i * max_vcpu + j]);
 			stats_test(vcpu_get_stats_fd(vcpus[i * max_vcpu + j]));
+		}
+
+		stats_test(vm_stats_fds);
+		for (j = 0; j < max_vcpu; ++j)
+			stats_test(vcpu_stats_fds[j]);
 
 		ksft_test_result_pass("vm%i\n", i);
 	}
@@ -237,6 +257,7 @@ int main(int argc, char *argv[])
 		kvm_vm_free(vms[i]);
 	free(vms);
 	free(vcpus);
+	free(vcpu_stats_fds);
 
 	ksft_finished();	/* Print results and exit() accordingly */
 }