KVM: selftests: Verify stats fd can be dup()'d and read

Expand the binary stats test to verify that a stats fd can be dup()'d
and read, to (very) roughly simulate userspace passing around the file.
Adding the dup() test is primarily an intermediate step towards verifying
that userspace can read VM/vCPU stats before _and_ after userspace closes
its copy of the VM fd; the dup() test itself is only mildly interesting.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230711230131.648752-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/tools/testing/selftests/kvm/kvm_binary_stats_test.c b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
index 653f10d8fb7c..5317e27b77d0 100644
--- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
+++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
@@ -232,17 +232,23 @@ int main(int argc, char *argv[])
 	}
 
 	/*
-	 * Check stats read for every VM and vCPU, with a variety of testcases.
+	 * Check stats read for every VM and vCPU, with a variety of flavors.
 	 * Note, stats_test() closes the passed in stats fd.
 	 */
 	for (i = 0; i < max_vm; ++i) {
+		/*
+		 * Verify that creating multiple userspace references to a
+		 * single stats file works and doesn't cause explosions.
+		 */
 		vm_stats_fds = vm_get_stats_fd(vms[i]);
+		stats_test(dup(vm_stats_fds));
 
 		/* Verify userspace can instantiate multiple stats files. */
 		stats_test(vm_get_stats_fd(vms[i]));
 
 		for (j = 0; j < max_vcpu; ++j) {
 			vcpu_stats_fds[j] = vcpu_get_stats_fd(vcpus[i * max_vcpu + j]);
+			stats_test(dup(vcpu_stats_fds[j]));
 			stats_test(vcpu_get_stats_fd(vcpus[i * max_vcpu + j]));
 		}