[PATCH v4 2/2] selftests/mm: add tests for UFFDIO_MOVE of a uffd-protected swap entry

[Donggeun Yoo <donggeunyoo.kernel@gmail.com>]

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

Assisted-by: LLM
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
---
 tools/testing/selftests/mm/uffd-unit-tests.c | 84 ++++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index ef9b3956bdcfd..97484c82f24e1 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -2037,6 +2037,75 @@ 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 or RWP-protected area
+ * must not carry the uffd bit into a destination registered for missing
+ * faults only: 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_test_common(uffd_global_test_opts_t *gopts,
+				       bool rwp)
+{
+	unsigned long page_size = gopts->page_size;
+	struct uffdio_move move = {
+		.dst = (unsigned long)gopts->area_dst,
+		.src = (unsigned long)gopts->area_src,
+		.len = page_size,
+	};
+	int pagemap_fd = pagemap_open();
+
+	if (rwp) {
+		if (uffd_register_rwp(gopts->uffd, gopts->area_src, page_size))
+			err("register src failure");
+		rwprotect_range(gopts->uffd, (unsigned long)gopts->area_src,
+				page_size, true);
+	} else {
+		if (uffd_register(gopts->uffd, gopts->area_src, page_size,
+				  false, true, false))
+			err("register src failure");
+		wp_range(gopts->uffd, (unsigned long)gopts->area_src,
+			 page_size, true);
+	}
+	if (uffd_register(gopts->uffd, gopts->area_dst, page_size,
+			  true, false, false))
+		err("register dst failure");
+
+	if (madvise(gopts->area_src, page_size, MADV_PAGEOUT))
+		err("MADV_PAGEOUT");
+	if (!pagemap_is_swapped(pagemap_fd, gopts->area_src)) {
+		uffd_test_skip("MADV_PAGEOUT did not swap the page; is swap enabled?");
+		goto out;
+	}
+
+	if (ioctl(gopts->uffd, UFFDIO_MOVE, &move)) {
+		uffd_test_fail("UFFDIO_MOVE failed: %s", strerror(errno));
+		goto out;
+	}
+
+	if (pagemap_get_entry(pagemap_fd, gopts->area_dst) & PM_UFFD_WP)
+		uffd_test_fail("uffd bit moved into an area registered for missing faults only");
+	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 void uffd_move_swap_wp_test(uffd_global_test_opts_t *gopts,
+				   uffd_test_args_t *targs)
+{
+	uffd_move_swap_test_common(gopts, false);
+}
+
+static void uffd_move_swap_rwp_test(uffd_global_test_opts_t *gopts,
+				    uffd_test_args_t *targs)
+{
+	uffd_move_swap_test_common(gopts, true);
+}
+
 static bool
 uffdio_verify_results(const char *name, int ret, int error, long result)
 {
@@ -2359,6 +2428,21 @@ 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 = "move-swap-rwp",
+		.uffd_fn = uffd_move_swap_rwp_test,
+		.mem_targets = MEM_ANON,
+		.uffd_feature_required = UFFD_FEATURE_MOVE | UFFD_FEATURE_RWP,
+		.test_case_ops = &uffd_move_test_case_ops,
+	},
 	{
 		.name = "wp-fork",
 		.uffd_fn = uffd_wp_fork_test,
-- 
2.53.0