On 9/25/26 06:29, Donggeun Yoo wrote:
> 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.
>
> Assisted-by: LLM
> Signed-off-by: Donggeun Yoo <[email protected]>
> ---
> 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 ef9b3956bdcfd..ae8b718f0a278 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))
Side note: this binary encoding of features is horrible.
> + 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);
> + }
Is this loop really required? I thought the page should just be unmapped from
the page table. It might still be in the swapcache and under writeback, but
that's irrelevant.
> + 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,
> + },
Do we also want to check wrp? I'd assume it suffers from the same problem (did
not check carefully though)
--
Cheers,
David
