[PATCH 4/6] selftests/mm: Extend and rename uffd pagemap test

Peter Xu
2023-04-13T23:12:40Z

Extend it to all types of mem, meanwhile add one parallel test when
EVENT_FORK is enabled, where uffd-wp bits should be persisted rather than
dropped.

Since at it, rename the test to "wp-fork" to better show what it means.
Making the new test called "wp-fork-with-event".

Before:

Testing pagemap on anon... done

After:

Testing wp-fork on anon... done
Testing wp-fork on shmem... done
Testing wp-fork on shmem-private... done
Testing wp-fork on hugetlb... done
Testing wp-fork on hugetlb-private... done
Testing wp-fork-with-event on anon... done
Testing wp-fork-with-event on shmem... done
Testing wp-fork-with-event on shmem-private... done
Testing wp-fork-with-event on hugetlb... done
Testing wp-fork-with-event on hugetlb-private... done

Signed-off-by: Peter Xu <peterx@redhat.com>
---
tools/testing/selftests/mm/uffd-unit-tests.c | 130 +++++++++++++++----
1 file changed, 106 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 452ca05a829d..739fc4d30342 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -227,25 +227,65 @@ static int pagemap_open(void)
err("pagemap uffd-wp bit error: 0x%"PRIx64, value); \
} while (0)

-static int pagemap_test_fork(bool present)
+typedef struct {
+ int parent_uffd, child_uffd;
+} fork_event_args;
+
+static void *fork_event_consumer(void *data)
{
- pid_t child = fork();
+ fork_event_args *args = data;
+ struct uffd_msg msg = { 0 };
+
+ /* Read until a full msg received */
+ while (uffd_read_msg(args->parent_uffd, &msg));
+
+ if (msg.event != UFFD_EVENT_FORK)
+ err("wrong message: %u\n", msg.event);
+
+ /* Just to be properly freed later */
+ args->child_uffd = msg.arg.fork.ufd;
+ return NULL;
+}
+
+static int pagemap_test_fork(int uffd, bool with_event)
+{
+ fork_event_args args = { .parent_uffd = uffd, .child_uffd = -1 };
+ pthread_t thread;
+ pid_t child;
uint64_t value;
int fd, result;

+ /* Prepare a thread to resolve EVENT_FORK */
+ if (with_event) {
+ if (pthread_create(&thread, NULL, fork_event_consumer, &args))
+ err("pthread_create()");
+ }
+
+ child = fork();
if (!child) {
/* Open the pagemap fd of the child itself */
fd = pagemap_open();
value = pagemap_get_entry(fd, area_dst);
/*
- * After fork() uffd-wp bit should be gone as long as we're
- * without UFFD_FEATURE_EVENT_FORK
+ * After fork(), we should handle uffd-wp bit differently:
+ *
+ * (1) when with EVENT_FORK, it should persist
+ * (2) when without EVENT_FORK, it should be dropped
*/
- pagemap_check_wp(value, false);
+ pagemap_check_wp(value, with_event);
/* Succeed */
exit(0);
}
waitpid(child, &result, 0);
+
+ if (with_event) {
+ if (pthread_join(thread, NULL))
+ err("pthread_join()");
+ if (args.child_uffd < 0)
+ err("Didn't receive child uffd");
+ close(args.child_uffd);
+ }
+
return result;
}

@@ -295,7 +335,8 @@ static void uffd_wp_unpopulated_test(uffd_test_args_t *args)
uffd_test_pass();
}

-static void uffd_pagemap_test(uffd_test_args_t *args)
+static void uffd_wp_fork_test_common(uffd_test_args_t *args,
+ bool with_event)
{
int pagemap_fd;
uint64_t value;
@@ -311,23 +352,42 @@ static void uffd_pagemap_test(uffd_test_args_t *args)
wp_range(uffd, (uint64_t)area_dst, page_size, true);
value = pagemap_get_entry(pagemap_fd, area_dst);
pagemap_check_wp(value, true);
- /* Make sure uffd-wp bit dropped when fork */
- if (pagemap_test_fork(true))
- err("Detected stall uffd-wp bit in child");
-
- /* Exclusive required or PAGEOUT won't work */
- if (!(value & PM_MMAP_EXCLUSIVE))
- err("multiple mapping detected: 0x%"PRIx64, value);
+ if (pagemap_test_fork(uffd, with_event)) {
+ uffd_test_fail("Detected %s uffd-wp bit in child in present pte",
+ with_event ? "missing" : "stall");
+ goto out;
+ }

- if (madvise(area_dst, page_size, MADV_PAGEOUT))
- err("madvise(MADV_PAGEOUT) failed");
+ /*
+ * This is an attempt for zapping the pgtable so as to test the
+ * markers.
+ *
+ * For private mappings, PAGEOUT will only work on exclusive ptes
+ * (PM_MMAP_EXCLUSIVE) which we should satisfy.
+ *
+ * For shared, PAGEOUT may not work. Use DONTNEED instead which
+ * plays a similar role of zapping (rather than freeing the page)
+ * to expose pte markers.
+ */
+ if (args->mem_type->shared) {
+ if (madvise(area_dst, page_size, MADV_DONTNEED))
+ err("MADV_DONTNEED");
+ } else {
+ /*
+ * NOTE: ignore retval because private-hugetlb doesn't yet
+ * support swapping, so it could fail.
+ */
+ madvise(area_dst, page_size, MADV_PAGEOUT);
+ }

/* Uffd-wp should persist even swapped out */
value = pagemap_get_entry(pagemap_fd, area_dst);
pagemap_check_wp(value, true);
- /* Make sure uffd-wp bit dropped when fork */
- if (pagemap_test_fork(false))
- err("Detected stall uffd-wp bit in child");
+ if (pagemap_test_fork(uffd, with_event)) {
+ uffd_test_fail("Detected %s uffd-wp bit in child in zapped pte",
+ with_event ? "missing" : "stall");
+ goto out;
+ }

/* Unprotect; this tests swap pte modifications */
wp_range(uffd, (uint64_t)area_dst, page_size, false);
@@ -338,9 +398,21 @@ static void uffd_pagemap_test(uffd_test_args_t *args)
*area_dst = 2;
value = pagemap_get_entry(pagemap_fd, area_dst);
pagemap_check_wp(value, false);
-
- close(pagemap_fd);
uffd_test_pass();
+out:
+ if (uffd_unregister(uffd, area_dst, nr_pages * page_size))
+ err("unregister failed");
+ close(pagemap_fd);
+}
+
+static void uffd_wp_fork_test(uffd_test_args_t *args)
+{
+ uffd_wp_fork_test_common(args, false);
+}
+
+static void uffd_wp_fork_with_event_test(uffd_test_args_t *args)
+{
+ uffd_wp_fork_test_common(args, true);
}

static void check_memory_contents(char *p)
@@ -836,10 +908,20 @@ uffd_test_case_t uffd_tests[] = {
.uffd_feature_required = 0,
},
{
- .name = "pagemap",
- .uffd_fn = uffd_pagemap_test,
- .mem_targets = MEM_ANON,
- .uffd_feature_required = UFFD_FEATURE_PAGEFAULT_FLAG_WP,
+ .name = "wp-fork",
+ .uffd_fn = uffd_wp_fork_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required = UFFD_FEATURE_PAGEFAULT_FLAG_WP |
+ UFFD_FEATURE_WP_HUGETLBFS_SHMEM,
+ },
+ {
+ .name = "wp-fork-with-event",
+ .uffd_fn = uffd_wp_fork_with_event_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required = UFFD_FEATURE_PAGEFAULT_FLAG_WP |
+ UFFD_FEATURE_WP_HUGETLBFS_SHMEM |
+ /* when set, child process should inherit uffd-wp bits */
+ UFFD_FEATURE_EVENT_FORK,
},
{
.name = "wp-unpopulated",
--
2.39.1