Re: [PATCH v3] selftests/mm: Add UFFDIO_MOVE huge zeropage PMD regression test

[Mike Rapoport <rppt@kernel.org>]

On Wed, Mar 18, 2026 at 12:18:11PM +0800, Chris Down wrote:
> The existing uffd-unit-tests move-pmd coverage exercises PMD-sized
> UFFDIO_MOVE on anonymous THPs, but it does not force the huge zeropage
> PMD path in move_pages_huge_pmd().
> 
> Add a dedicated anonymous UFFDIO_MOVE PMD test that exercises this
> relatively comprehensively.
> 
> Signed-off-by: Chris Down <chris@chrisdown.name>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  tools/testing/selftests/mm/uffd-unit-tests.c | 100 +++++++++++++++++++
>  tools/testing/selftests/mm/vm_util.c         |  12 +++
>  tools/testing/selftests/mm/vm_util.h         |   1 +
>  3 files changed, 113 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 6f5e404a446c..9cc4cbab9a23 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -1227,6 +1227,99 @@ static void uffd_move_pmd_test(uffd_global_test_opts_t *gopts, uffd_test_args_t
>  			      uffd_move_pmd_handle_fault);
>  }
>  
> +static void uffd_move_pmd_huge_zeropage_test(uffd_global_test_opts_t *gopts,
> +					     uffd_test_args_t *targs)
> +{
> +	unsigned long pmd_size = read_pmd_pagesize();
> +	unsigned long pmd_pages;
> +	unsigned long bytes = gopts->nr_pages * gopts->page_size;
> +	char *orig_area_src = gopts->area_src, *orig_area_dst = gopts->area_dst;
> +	char *aligned_src, *aligned_dst;
> +	unsigned long src_offs, dst_offs, max_offs;
> +	pthread_t uffd_mon;
> +	struct uffd_args args = { 0 };
> +	char c = '\0';
> +	int pagemap_fd;
> +
> +	if (pmd_size <= gopts->page_size) {
> +		uffd_test_skip("huge page size is 0, feature missing?");
> +		return;
> +	}
> +	if (!detect_huge_zeropage()) {
> +		uffd_test_skip("transparent huge zeropage disabled");
> +		return;
> +	}
> +
> +	pmd_pages = pmd_size / gopts->page_size;
> +	if (bytes < pmd_size) {
> +		uffd_test_skip("not enough pages for one PMD-sized move");
> +		return;
> +	}
> +
> +	aligned_src = ALIGN_UP(orig_area_src, pmd_size);
> +	aligned_dst = ALIGN_UP(orig_area_dst, pmd_size);
> +	src_offs = (aligned_src - orig_area_src) / gopts->page_size;
> +	dst_offs = (aligned_dst - orig_area_dst) / gopts->page_size;
> +	max_offs = src_offs > dst_offs ? src_offs : dst_offs;
> +	if (max_offs + pmd_pages > gopts->nr_pages) {
> +		uffd_test_skip("could not find aligned PMD-sized src/dst window");
> +		return;
> +	}
> +
> +	if (madvise(orig_area_dst, bytes, MADV_HUGEPAGE))
> +		err("madvise(MADV_HUGEPAGE) failure");
> +	if (madvise(orig_area_src, bytes, MADV_DONTFORK))
> +		err("madvise(MADV_DONTFORK) failure");
> +	if (madvise(aligned_src, pmd_size, MADV_DONTNEED))
> +		err("madvise(MADV_DONTNEED) failure");
> +
> +	/* Fault in a PMD-sized huge zeropage mapping in the source. */
> +	force_read_pages(aligned_src, pmd_pages, gopts->page_size);
> +
> +	pagemap_fd = pagemap_open();
> +	if (!pagemap_is_huge_zero(pagemap_fd, aligned_src)) {
> +		close(pagemap_fd);
> +		uffd_test_skip("could not fault in the huge zeropage");
> +		return;
> +	}
> +	gopts->area_src = aligned_src;
> +	gopts->area_dst = aligned_dst;
> +
> +	if (uffd_register(gopts->uffd, gopts->area_dst, pmd_size, true, false, false))
> +		err("register failure");
> +
> +	args.gopts = gopts;
> +	args.handle_fault = uffd_move_pmd_handle_fault;
> +	if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
> +		err("uffd_poll_thread create");
> +
> +	/*
> +	 * One fault on dst should trigger a single PMD-sized UFFDIO_MOVE from
> +	 * the huge zeropage PMD we populated in the source.
> +	 */
> +	force_read_pages(gopts->area_dst, pmd_pages, gopts->page_size);
> +
> +	if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c))
> +		err("pipe write");
> +	if (pthread_join(uffd_mon, NULL))
> +		err("join() failed");
> +
> +	if (args.missing_faults != 1 || args.minor_faults != 0) {
> +		uffd_test_fail("stats check error");
> +	} else if (!pagemap_is_huge_zero(pagemap_fd, gopts->area_dst)) {
> +		uffd_test_fail("moved destination is not a huge zeropage PMD");
> +	} else if (!check_huge_anon(gopts->area_dst, 0, pmd_size)) {
> +		/* vm_normal_page_pmd() must continue to treat the moved PMD as special. */
> +		uffd_test_fail("moved huge zeropage PMD counted as AnonHugePages");
> +	} else {
> +		uffd_test_pass();
> +	}
> +
> +	gopts->area_src = orig_area_src;
> +	gopts->area_dst = orig_area_dst;
> +	close(pagemap_fd);
> +}
> +
>  static void uffd_move_pmd_split_test(uffd_global_test_opts_t *gopts, uffd_test_args_t *targs)
>  {
>  	if (madvise(gopts->area_dst, gopts->nr_pages * gopts->page_size, MADV_NOHUGEPAGE))
> @@ -1550,6 +1643,13 @@ uffd_test_case_t uffd_tests[] = {
>  		.uffd_feature_required = UFFD_FEATURE_MOVE,
>  		.test_case_ops = &uffd_move_test_pmd_case_ops,
>  	},
> +	{
> +		.name = "move-pmd-huge-zeropage",
> +		.uffd_fn = uffd_move_pmd_huge_zeropage_test,
> +		.mem_targets = MEM_ANON,
> +		.uffd_feature_required = UFFD_FEATURE_MOVE,
> +		.test_case_ops = &uffd_move_test_pmd_case_ops,
> +	},
>  	{
>  		.name = "move-pmd-split",
>  		.uffd_fn = uffd_move_pmd_split_test,
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index a6d4ff7dfdc0..55cc4cc058a2 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -120,6 +120,18 @@ bool pagemap_is_populated(int fd, char *start)
>  				PAGE_IS_PRESENT | PAGE_IS_SWAPPED);
>  }
>  
> +bool pagemap_is_huge_zero(int fd, char *start)
> +{
> +	uint64_t categories;
> +
> +	if (!pagemap_scan_supported(fd, start))
> +		return false;
> +
> +	categories = pagemap_scan_get_categories(fd, start);
> +	return (categories & (PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE)) ==
> +		(PAGE_IS_PRESENT | PAGE_IS_PFNZERO | PAGE_IS_HUGE);
> +}
> +
>  unsigned long pagemap_get_pfn(int fd, char *start)
>  {
>  	uint64_t entry = pagemap_get_entry(fd, start);
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index e9c4e24769c1..e0b6ae1b12f5 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -85,6 +85,7 @@ uint64_t pagemap_get_entry(int fd, char *start);
>  bool pagemap_is_softdirty(int fd, char *start);
>  bool pagemap_is_swapped(int fd, char *start);
>  bool pagemap_is_populated(int fd, char *start);
> +bool pagemap_is_huge_zero(int fd, char *start);
>  unsigned long pagemap_get_pfn(int fd, char *start);
>  void clear_softdirty(void);
>  bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
> 
> base-commit: f0caa1d49cc07b30a7e2f104d3853ec6dc1c3cad
> -- 
> 2.53.0
> 

-- 
Sincerely yours,
Mike.