[PATCH 1/3] userfaultfd/selftests: fix feature support detection

[Axel Rasmussen]

Currently, the test decides whether or not to test certain features
(e.g., writeprotect support) essentially by examining command-line
arguments. For example, if we're testing anonymous memory, then we
should test writeprotect support as well (since it generally is
supported for anonymous).

This is broken, however. Take writeprotect support as an example: sure
it's supported for anon, but it also requires that we have
CONFIG_HAVE_ARCH_USERFAULTFD_WP. I.e., it is not supported at all on
aarch64. So, running the test on such an arch fails: it tries to test
writeprotect for anon, but since it isn't *actually* supported, it
fails.

So, instead of checking command-line arguments to the test, check the
features the way the UFFD API intends: when we open a new userfaultfd,
pass in the feature(s) this test case would like to try to exercise. The
kernel reports back a subset of those features which are actually
supported: check these returned flags to see if the features are
*actually* supported.

(For a couple of cases, where *registration* would fail [with -EINVAL]
even though UFFDIO_API reports the feature as supported, we have to
check test_type as well as the feature flag.)

In some cases, we check immediately after opening the userfaultfd, and
if the features are missing, we skip the entire test. In some other
cases, we can proceed with "most" of the test, only skipping a few
pieces.

This lets us remove the global test_uffdio_wp and test_uffdio_minor
variables entirely.

Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
---
 tools/testing/selftests/vm/userfaultfd.c | 94 +++++++++++-------------
 1 file changed, 43 insertions(+), 51 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 10ab56c2484a..2366caf90435 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -79,10 +79,6 @@ static int test_type;
 #define ALARM_INTERVAL_SECS 10
 static volatile bool test_uffdio_copy_eexist = true;
 static volatile bool test_uffdio_zeropage_eexist = true;
-/* Whether to test uffd write-protection */
-static bool test_uffdio_wp = false;
-/* Whether to test uffd minor faults */
-static bool test_uffdio_minor = false;
 
 static bool map_shared;
 static int shm_fd;
@@ -90,6 +86,7 @@ static int huge_fd;
 static char *huge_fd_off0;
 static unsigned long long *count_verify;
 static int uffd = -1;
+static uint64_t uffd_features;
 static int uffd_flags, finished, *pipefd;
 static char *area_src, *area_src_alias, *area_dst, *area_dst_alias;
 static char *zeropage;
@@ -345,7 +342,7 @@ static struct uffd_test_ops hugetlb_uffd_test_ops = {
 
 static struct uffd_test_ops *uffd_test_ops;
 
-static void userfaultfd_open(uint64_t *features)
+static void userfaultfd_open(uint64_t features)
 {
 	struct uffdio_api uffdio_api;
 
@@ -355,14 +352,20 @@ static void userfaultfd_open(uint64_t *features)
 	uffd_flags = fcntl(uffd, F_GETFD, NULL);
 
 	uffdio_api.api = UFFD_API;
-	uffdio_api.features = *features;
+	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.");
 	if (uffdio_api.api != UFFD_API)
 		err("UFFDIO_API error: %" PRIu64, (uint64_t)uffdio_api.api);
 
-	*features = uffdio_api.features;
+	uffd_features = uffdio_api.features;
+}
+
+static inline bool uffd_wp_supported(void)
+{
+	return test_type == TEST_ANON &&
+		(uffd_features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 }
 
 static inline void munmap_area(void **area)
@@ -397,6 +400,7 @@ static void uffd_test_ctx_clear(void)
 			err("close uffd");
 		uffd = -1;
 	}
+	uffd_features = 0;
 
 	huge_fd_off0 = NULL;
 	munmap_area((void **)&area_src);
@@ -405,7 +409,7 @@ static void uffd_test_ctx_clear(void)
 	munmap_area((void **)&area_dst_alias);
 }
 
-static void uffd_test_ctx_init_ext(uint64_t *features)
+static void uffd_test_ctx_init(uint64_t features)
 {
 	unsigned long nr, cpu;
 
@@ -445,11 +449,6 @@ static void uffd_test_ctx_init_ext(uint64_t *features)
 			err("pipe");
 }
 
-static inline void uffd_test_ctx_init(uint64_t features)
-{
-	uffd_test_ctx_init_ext(&features);
-}
-
 static int my_bcmp(char *str1, char *str2, size_t n)
 {
 	unsigned long i;
@@ -587,7 +586,7 @@ static int __copy_page(int ufd, unsigned long offset, bool retry)
 	uffdio_copy.dst = (unsigned long) area_dst + offset;
 	uffdio_copy.src = (unsigned long) area_src + offset;
 	uffdio_copy.len = page_size;
-	if (test_uffdio_wp)
+	if (uffd_wp_supported())
 		uffdio_copy.mode = UFFDIO_COPY_MODE_WP;
 	else
 		uffdio_copy.mode = 0;
@@ -778,7 +777,7 @@ static void *background_thread(void *arg)
 	 * at least the first half of the pages mapped already which
 	 * can be write-protected for testing
 	 */
-	if (test_uffdio_wp)
+	if (uffd_wp_supported())
 		wp_range(uffd, (unsigned long)area_dst + start_nr * page_size,
 			nr_pages_per_cpu * page_size, true);
 
@@ -1062,12 +1061,12 @@ static int userfaultfd_zeropage_test(void)
 	printf("testing UFFDIO_ZEROPAGE: ");
 	fflush(stdout);
 
-	uffd_test_ctx_init(0);
+	uffd_test_ctx_init(UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 
 	uffdio_register.range.start = (unsigned long) area_dst;
 	uffdio_register.range.len = nr_pages * page_size;
 	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
-	if (test_uffdio_wp)
+	if (uffd_wp_supported())
 		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
 	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
 		err("register failure");
@@ -1089,7 +1088,7 @@ static int userfaultfd_events_test(void)
 	struct uffdio_register uffdio_register;
 	unsigned long expected_ioctls;
 	pthread_t uffd_mon;
-	int err, features;
+	int err;
 	pid_t pid;
 	char c;
 	struct uffd_stats stats = { 0 };
@@ -1097,16 +1096,15 @@ static int userfaultfd_events_test(void)
 	printf("testing events (fork, remap, remove): ");
 	fflush(stdout);
 
-	features = UFFD_FEATURE_EVENT_FORK | UFFD_FEATURE_EVENT_REMAP |
-		UFFD_FEATURE_EVENT_REMOVE;
-	uffd_test_ctx_init(features);
+	uffd_test_ctx_init(UFFD_FEATURE_EVENT_FORK | UFFD_FEATURE_EVENT_REMAP |
+			   UFFD_FEATURE_EVENT_REMOVE | UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 
 	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 
 	uffdio_register.range.start = (unsigned long) area_dst;
 	uffdio_register.range.len = nr_pages * page_size;
 	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
-	if (test_uffdio_wp)
+	if (uffd_wp_supported())
 		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
 	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
 		err("register failure");
@@ -1144,7 +1142,7 @@ static int userfaultfd_sig_test(void)
 	unsigned long expected_ioctls;
 	unsigned long userfaults;
 	pthread_t uffd_mon;
-	int err, features;
+	int err;
 	pid_t pid;
 	char c;
 	struct uffd_stats stats = { 0 };
@@ -1152,15 +1150,15 @@ static int userfaultfd_sig_test(void)
 	printf("testing signal delivery: ");
 	fflush(stdout);
 
-	features = UFFD_FEATURE_EVENT_FORK|UFFD_FEATURE_SIGBUS;
-	uffd_test_ctx_init(features);
+	uffd_test_ctx_init(UFFD_FEATURE_EVENT_FORK | UFFD_FEATURE_SIGBUS |
+			   UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 
 	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 
 	uffdio_register.range.start = (unsigned long) area_dst;
 	uffdio_register.range.len = nr_pages * page_size;
 	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
-	if (test_uffdio_wp)
+	if (uffd_wp_supported())
 		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
 	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
 		err("register failure");
@@ -1209,25 +1207,23 @@ static int userfaultfd_minor_test(void)
 	void *expected_page;
 	char c;
 	struct uffd_stats stats = { 0 };
-	uint64_t req_features, features_out;
-
-	if (!test_uffdio_minor)
-		return 0;
+	uint64_t features;
 
 	printf("testing minor faults: ");
 	fflush(stdout);
 
-	if (test_type == TEST_HUGETLB)
-		req_features = UFFD_FEATURE_MINOR_HUGETLBFS;
+	if (test_type == TEST_HUGETLB && map_shared)
+		features = UFFD_FEATURE_MINOR_HUGETLBFS;
 	else if (test_type == TEST_SHMEM)
-		req_features = UFFD_FEATURE_MINOR_SHMEM;
-	else
-		return 1;
+		features = UFFD_FEATURE_MINOR_SHMEM;
+	else {
+		printf("skipping test due to unsupported memory type\n");
+		return 0;
+	}
 
-	features_out = req_features;
-	uffd_test_ctx_init_ext(&features_out);
+	uffd_test_ctx_init(features);
 	/* If kernel reports required features aren't supported, skip test. */
-	if ((features_out & req_features) != req_features) {
+	if ((uffd_features & features) != features) {
 		printf("skipping test due to lack of feature support\n");
 		fflush(stdout);
 		return 0;
@@ -1349,10 +1345,6 @@ static void userfaultfd_pagemap_test(unsigned int test_pgsize)
 	int pagemap_fd;
 	uint64_t value;
 
-	/* Pagemap tests uffd-wp only */
-	if (!test_uffdio_wp)
-		return;
-
 	/* Not enough memory to test this page size */
 	if (test_pgsize > nr_pages * page_size)
 		return;
@@ -1361,7 +1353,12 @@ static void userfaultfd_pagemap_test(unsigned int test_pgsize)
 	/* Flush so it doesn't flush twice in parent/child later */
 	fflush(stdout);
 
-	uffd_test_ctx_init(0);
+	uffd_test_ctx_init(UFFD_FEATURE_PAGEFAULT_FLAG_WP);
+	/* Pagemap tests uffd-wp only */
+	if (!uffd_wp_supported()) {
+		printf("skipping test due to lack of feature support\n");
+		return;
+	}
 
 	if (test_pgsize > page_size) {
 		/* This is a thp test */
@@ -1426,7 +1423,7 @@ static int userfaultfd_stress(void)
 	struct uffdio_register uffdio_register;
 	struct uffd_stats uffd_stats[nr_cpus];
 
-	uffd_test_ctx_init(0);
+	uffd_test_ctx_init(UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 
 	if (posix_memalign(&area, page_size, page_size))
 		err("out of memory");
@@ -1464,7 +1461,7 @@ static int userfaultfd_stress(void)
 		uffdio_register.range.start = (unsigned long) area_dst;
 		uffdio_register.range.len = nr_pages * page_size;
 		uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
-		if (test_uffdio_wp)
+		if (uffd_wp_supported())
 			uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
 		if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
 			err("register failure");
@@ -1513,7 +1510,7 @@ static int userfaultfd_stress(void)
 			return 1;
 
 		/* Clear all the write protections if there is any */
-		if (test_uffdio_wp)
+		if (uffd_wp_supported())
 			wp_range(uffd, (unsigned long)area_dst,
 				 nr_pages * page_size, false);
 
@@ -1595,8 +1592,6 @@ static void set_test_type(const char *type)
 	if (!strcmp(type, "anon")) {
 		test_type = TEST_ANON;
 		uffd_test_ops = &anon_uffd_test_ops;
-		/* Only enable write-protect test for anonymous test */
-		test_uffdio_wp = true;
 	} else if (!strcmp(type, "hugetlb")) {
 		test_type = TEST_HUGETLB;
 		uffd_test_ops = &hugetlb_uffd_test_ops;
@@ -1604,13 +1599,10 @@ static void set_test_type(const char *type)
 		map_shared = true;
 		test_type = TEST_HUGETLB;
 		uffd_test_ops = &hugetlb_uffd_test_ops;
-		/* Minor faults require shared hugetlb; only enable here. */
-		test_uffdio_minor = true;
 	} else if (!strcmp(type, "shmem")) {
 		map_shared = true;
 		test_type = TEST_SHMEM;
 		uffd_test_ops = &shmem_uffd_test_ops;
-		test_uffdio_minor = true;
 	} else {
 		err("Unknown test type: %s", type);
 	}
-- 
2.33.0.464.g1972c5931b-goog