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

[Chris Down <chris@chrisdown.name>]

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>
---
 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