selftests/mm: UFFDIO_API test

Add one simple test for UFFDIO_API.  With that, I also added a bunch of
small but handy helpers along the way.

Link: https://lkml.kernel.org/r/20230412164257.328375-1-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/uffd-unit-tests.c

@@ -9,9 +9,116 @@
 
 #ifdef __NR_userfaultfd
 
+static void uffd_test_report(void)
+{
+	printf("Userfaults unit tests: pass=%u, skip=%u, fail=%u (total=%u)\n",
+	       ksft_get_pass_cnt(),
+	       ksft_get_xskip_cnt(),
+	       ksft_get_fail_cnt(),
+	       ksft_test_num());
+}
+
+static void uffd_test_pass(void)
+{
+	printf("done\n");
+	ksft_inc_pass_cnt();
+}
+
+#define  uffd_test_start(...)  do {		\
+		printf("Testing ");		\
+		printf(__VA_ARGS__);		\
+		printf("... ");			\
+		fflush(stdout);			\
+	} while (0)
+
+#define  uffd_test_fail(...)  do {		\
+		printf("failed [reason: ");	\
+		printf(__VA_ARGS__);		\
+		printf("]\n");			\
+		ksft_inc_fail_cnt();		\
+	} while (0)
+
+#define  uffd_test_skip(...)  do {		\
+		printf("skipped [reason: ");	\
+		printf(__VA_ARGS__);		\
+		printf("]\n");			\
+		ksft_inc_xskip_cnt();		\
+	} while (0)
+
+/*
+ * Returns 1 if specific userfaultfd supported, 0 otherwise.  Note, we'll
+ * return 1 even if some test failed as long as uffd supported, because in
+ * that case we still want to proceed with the rest uffd unit tests.
+ */
+static int test_uffd_api(bool use_dev)
+{
+	struct uffdio_api uffdio_api;
+	int uffd;
+
+	uffd_test_start("UFFDIO_API (with %s)",
+			use_dev ? "/dev/userfaultfd" : "syscall");
+
+	if (use_dev)
+		uffd = uffd_open_dev(UFFD_FLAGS);
+	else
+		uffd = uffd_open_sys(UFFD_FLAGS);
+	if (uffd < 0) {
+		uffd_test_skip("cannot open userfaultfd handle");
+		return 0;
+	}
+
+	/* Test wrong UFFD_API */
+	uffdio_api.api = 0xab;
+	uffdio_api.features = 0;
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api) == 0) {
+		uffd_test_fail("UFFDIO_API should fail with wrong api but didn't");
+		goto out;
+	}
+
+	/* Test wrong feature bit */
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = BIT_ULL(63);
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api) == 0) {
+		uffd_test_fail("UFFDIO_API should fail with wrong feature but didn't");
+		goto out;
+	}
+
+	/* Test normal UFFDIO_API */
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = 0;
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api)) {
+		uffd_test_fail("UFFDIO_API should succeed but failed");
+		goto out;
+	}
+
+	/* Test double requests of UFFDIO_API with a random feature set */
+	uffdio_api.features = BIT_ULL(0);
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api) == 0) {
+		uffd_test_fail("UFFDIO_API should reject initialized uffd");
+		goto out;
+	}
+
+	uffd_test_pass();
+out:
+	close(uffd);
+	/* We have a valid uffd handle */
+	return 1;
+}
+
 int main(int argc, char *argv[])
 {
-	return KSFT_PASS;
+	int has_uffd;
+
+	has_uffd = test_uffd_api(false);
+	has_uffd |= test_uffd_api(true);
+
+	if (!has_uffd) {
+		printf("Userfaultfd not supported or unprivileged, skip all tests\n");
+		exit(KSFT_SKIP);
+	}
+	uffd_test_report();
+
+	return ksft_get_fail_cnt() ? KSFT_FAIL : KSFT_PASS;
 }
 
 #else /* __NR_userfaultfd */