[PATCH v1 2/2] selftests/mm: add a test for UFFDIO_MOVE of a write-protected swap entry

[Donggeun Yoo]

Move a swapped-out page out of a write-protected area into a destination
registered for missing faults only, and read pagemap bit 57 at the
destination.  The destination was never write-protected, so the bit must
be clear.

Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@xxxxxxxxx>
---
 tools/testing/selftests/mm/uffd-unit-tests.c | 61 ++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index ef9b3956bdcf..ae8b718f0a27 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -2037,6 +2037,59 @@ static void uffd_move_pmd_split_test(uffd_global_test_opts_t *gopts, uffd_test_a
 			      uffd_move_pmd_handle_fault);
 }
 
+/*
+ * Moving a swapped-out page out of a write-protected area must not carry the
+ * uffd-wp bit into a destination that is not write-protect registered: such a
+ * bit is never cleared afterwards, so pagemap keeps reporting the page as
+ * uffd-tracked.
+ *
+ * Needs a swap device; skipped if MADV_PAGEOUT cannot evict the page.
+ */
+static void uffd_move_swap_wp_test(uffd_global_test_opts_t *gopts,
+				   uffd_test_args_t *targs)
+{
+	unsigned long page_size = gopts->page_size;
+	struct uffdio_move move = { };
+	int pagemap_fd, i;
+
+	if (uffd_register(gopts->uffd, gopts->area_src, page_size,
+			  false, true, false))
+		err("register src failure");
+	if (uffd_register(gopts->uffd, gopts->area_dst, page_size,
+			  true, false, false))
+		err("register dst failure");
+
+	wp_range(gopts->uffd, (unsigned long)gopts->area_src, page_size, true);
+
+	pagemap_fd = pagemap_open();
+	for (i = 0; i < 100; i++) {
+		if (madvise(gopts->area_src, page_size, MADV_PAGEOUT))
+			err("MADV_PAGEOUT");
+		if (pagemap_is_swapped(pagemap_fd, gopts->area_src))
+			break;
+		usleep(10000);
+	}
+	if (!pagemap_is_swapped(pagemap_fd, gopts->area_src)) {
+		uffd_test_skip("MADV_PAGEOUT did not swap the page; is swap enabled?");
+		goto out;
+	}
+
+	move.dst = (unsigned long)gopts->area_dst;
+	move.src = (unsigned long)gopts->area_src;
+	move.len = page_size;
+	if (ioctl(gopts->uffd, UFFDIO_MOVE, &move))
+		err("UFFDIO_MOVE");
+
+	if (pagemap_get_entry(pagemap_fd, gopts->area_dst) & PM_UFFD_WP)
+		uffd_test_fail("uffd-wp bit moved into an area that is not write-protected");
+	else
+		uffd_test_pass();
+out:
+	close(pagemap_fd);
+	uffd_unregister(gopts->uffd, gopts->area_src, page_size);
+	uffd_unregister(gopts->uffd, gopts->area_dst, page_size);
+}
+
 static bool
 uffdio_verify_results(const char *name, int ret, int error, long result)
 {
@@ -2359,6 +2412,14 @@ uffd_test_case_t uffd_tests[] = {
 		.uffd_feature_required = UFFD_FEATURE_MOVE,
 		.test_case_ops = &uffd_move_test_pmd_case_ops,
 	},
+	{
+		.name = "move-swap-wp",
+		.uffd_fn = uffd_move_swap_wp_test,
+		.mem_targets = MEM_ANON,
+		.uffd_feature_required = UFFD_FEATURE_MOVE |
+		UFFD_FEATURE_PAGEFAULT_FLAG_WP,
+		.test_case_ops = &uffd_move_test_case_ops,
+	},
 	{
 		.name = "wp-fork",
 		.uffd_fn = uffd_wp_fork_test,
-- 
2.53.0