selftests/mm: allow uffd test to skip properly with no privilege

Allow skip a unit test properly due to no privilege (e.g.  sigbus and
events tests).

[colin.i.king@gmail.com: fix spelling mistake "priviledge" -> "privilege"]
  Link: https://lkml.kernel.org/r/20230414081506.1678998-1-colin.i.king@gmail.com
Link: https://lkml.kernel.org/r/20230412164520.329163-1-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Colin Ian King <colin.i.king@gmail.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-common.c

@@ -232,7 +232,7 @@ void uffd_stats_report(struct uffd_args *args, int n_cpus)
 	printf("\n");
 }
 
-void userfaultfd_open(uint64_t *features)
+int userfaultfd_open(uint64_t *features)
 {
 	struct uffdio_api uffdio_api;
 
@@ -241,18 +241,19 @@ void userfaultfd_open(uint64_t *features)
 	else
 		uffd = uffd_open_sys(UFFD_FLAGS);
 	if (uffd < 0)
-		err("uffd open failed (dev=%d)", test_dev_userfaultfd);
+		return -1;
 	uffd_flags = fcntl(uffd, F_GETFD, NULL);
 
 	uffdio_api.api = UFFD_API;
 	uffdio_api.features = *features;
 	if (ioctl(uffd, UFFDIO_API, &uffdio_api))
-		err("UFFDIO_API failed.\nPlease make sure to "
-		    "run with either root or ptrace capability.");
+		/* Probably lack of CAP_PTRACE? */
+		return -1;
 	if (uffdio_api.api != UFFD_API)
 		err("UFFDIO_API error: %" PRIu64, (uint64_t)uffdio_api.api);
 
 	*features = uffdio_api.features;
+	return 0;
 }
 
 static inline void munmap_area(void **area)
@@ -295,7 +296,7 @@ static void uffd_test_ctx_clear(void)
 	munmap_area((void **)&area_remap);
 }
 
-int uffd_test_ctx_init(uint64_t features)
+int uffd_test_ctx_init(uint64_t features, const char **errmsg)
 {
 	unsigned long nr, cpu;
 	int ret;
@@ -303,13 +304,19 @@ int uffd_test_ctx_init(uint64_t features)
 	uffd_test_ctx_clear();
 
 	ret = uffd_test_ops->allocate_area((void **)&area_src, true);
-	if (ret)
-		return ret;
-	ret = uffd_test_ops->allocate_area((void **)&area_dst, false);
-	if (ret)
+	ret |= uffd_test_ops->allocate_area((void **)&area_dst, false);
+	if (ret) {
+		if (errmsg)
+			*errmsg = "memory allocation failed";
 		return ret;
+	}
 
-	userfaultfd_open(&features);
+	ret = userfaultfd_open(&features);
+	if (ret) {
+		if (errmsg)
+			*errmsg = "possible lack of priviledge";
+		return ret;
+	}
 
 	count_verify = malloc(nr_pages * sizeof(unsigned long long));
 	if (!count_verify)

tools/testing/selftests/mm/uffd-common.h

@@ -101,8 +101,8 @@ extern uffd_test_ops_t hugetlb_uffd_test_ops;
 extern uffd_test_ops_t *uffd_test_ops;
 
 void uffd_stats_report(struct uffd_args *args, int n_cpus);
-int uffd_test_ctx_init(uint64_t features);
-void userfaultfd_open(uint64_t *features);
+int uffd_test_ctx_init(uint64_t features, const char **errmsg);
+int userfaultfd_open(uint64_t *features);
 int uffd_read_msg(int ufd, struct uffd_msg *msg);
 void wp_range(int ufd, __u64 start, __u64 len, bool wp);
 void uffd_handle_page_fault(struct uffd_msg *msg, struct uffd_args *args);

tools/testing/selftests/mm/uffd-stress.c

@@ -271,7 +271,8 @@ static int userfaultfd_stress(void)
 	struct uffd_args args[nr_cpus];
 	uint64_t mem_size = nr_pages * page_size;
 
-	uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED);
+	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
+		err("context init failed");
 
 	if (posix_memalign(&area, page_size, page_size))
 		err("out of memory");
@@ -435,7 +436,8 @@ static void parse_test_type_arg(const char *raw_type)
 	 * feature.
 	 */
 
-	userfaultfd_open(&features);
+	if (userfaultfd_open(&features))
+		err("Userfaultfd open failed");
 
 	test_uffdio_wp = test_uffdio_wp &&
 		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);

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

@@ -172,7 +172,8 @@ static int test_uffd_api(bool use_dev)
  * This function initializes the global variables.  TODO: remove global
  * vars and then remove this.
  */
-static int uffd_setup_environment(uffd_test_case_t *test, mem_type_t *mem_type)
+static int uffd_setup_environment(uffd_test_case_t *test, mem_type_t *mem_type,
+				  const char **errmsg)
 {
 	map_shared = mem_type->shared;
 	uffd_test_ops = mem_type->mem_ops;
@@ -186,7 +187,7 @@ static int uffd_setup_environment(uffd_test_case_t *test, mem_type_t *mem_type)
 	/* TODO: remove this global var.. it's so ugly */
 	nr_cpus = 1;
 
-	return uffd_test_ctx_init(test->uffd_feature_required);
+	return uffd_test_ctx_init(test->uffd_feature_required, errmsg);
 }
 
 static bool uffd_feature_supported(uffd_test_case_t *test)
@@ -835,6 +836,7 @@ int main(int argc, char *argv[])
 	uffd_test_case_t *test;
 	mem_type_t *mem_type;
 	char test_name[128];
+	const char *errmsg;
 	int has_uffd;
 	int i, j;
 
@@ -860,8 +862,8 @@ int main(int argc, char *argv[])
 				uffd_test_skip("feature missing");
 				continue;
 			}
-			if (uffd_setup_environment(test, mem_type)) {
-				uffd_test_skip("environment setup failed");
+			if (uffd_setup_environment(test, mem_type, &errmsg)) {
+				uffd_test_skip(errmsg);
 				continue;
 			}
 			test->uffd_fn();