+ selftests-mm-fix-soft-dirty-kselftest-supported-check.patch added to mm-unstable branch

+ selftests-mm-fix-soft-dirty-kselftest-supported-check.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: fix soft-dirty kselftest supported check
has been added to the -mm mm-unstable branch.  Its filename is
     selftests-mm-fix-soft-dirty-kselftest-supported-check.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-fix-soft-dirty-kselftest-supported-check.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Audra Mitchell <audra@redhat.com>
Subject: selftests/mm: fix soft-dirty kselftest supported check
Date: Fri, 20 Mar 2026 14:39:15 -0400

On architectures with separate user address space, such as s390 or those
without an MMU, the soft-dirty kselftest may fail when checking to see if
the feature is supported.

  # --------------------
  # running ./soft-dirty
  # --------------------
  # TAP version 13
  # 1..15
  # Bail out! PAGEMAP_SCAN succeeded unexpectedly
  # # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
  # [FAIL]
  not ok 1 soft-dirty # exit=1
  # SUMMARY: PASS=0 SKIP=0 FAIL=1

The soft-dirty test will initate an ioctl with the PAGEMAP_SCAN flag with
an invalid address for the page_region.  This is done intentionally to
have the ioctl return with an expected EFAULT and with the correct
categories returned.

However, on architectures with separate user address space, such as s390
or those without an MMU, the call to __access_ok (used to validate the
variables provided with the ioctl) will always return true and we will not
fail as expected.

        if (IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) ||
            !IS_ENABLED(CONFIG_MMU))
                return true;

Let's simplify the check for PAGEMAP_SCAN and provide a valid page_region
address so that we get a non-errno return if it is supported.

Link: https://lkml.kernel.org/r/20260320184010.759461-2-audra@redhat.com
Fixes: 600bca580579 ("selftests/mm: check that PAGEMAP_SCAN returns correct categories")
Signed-off-by: Audra Mitchell <audra@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/vm_util.c |   24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

--- a/tools/testing/selftests/mm/vm_util.c~selftests-mm-fix-soft-dirty-kselftest-supported-check
+++ a/tools/testing/selftests/mm/vm_util.c
@@ -67,20 +67,26 @@ static uint64_t pagemap_scan_get_categor
 }
 
 /* `start` is any valid address. */
-static bool pagemap_scan_supported(int fd, char *start)
+static bool pagemap_scan_supported(int fd)
 {
+	const size_t pagesize = getpagesize();
 	static int supported = -1;
-	int ret;
+	struct page_region r;
+	void *test_area;
 
 	if (supported != -1)
 		return supported;
 
-	/* Provide an invalid address in order to trigger EFAULT. */
-	ret = __pagemap_scan_get_categories(fd, start, (struct page_region *) ~0UL);
-	if (ret == 0)
-		ksft_exit_fail_msg("PAGEMAP_SCAN succeeded unexpectedly\n");
-
-	supported = errno == EFAULT;
+	test_area = mmap(0, pagesize, PROT_READ | PROT_WRITE,
+			MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+	if (test_area == MAP_FAILED) {
+		ksft_print_msg("WARN: mmap() failed: %s\n", strerror(errno));
+		supported = 0;
+	} else {
+		supported = __pagemap_scan_get_categories(fd, test_area, &r) >= 0;
+		ksft_print_msg("errno: %d\n", errno);
+		munmap(test_area, pagesize);
+	}
 
 	return supported;
 }
@@ -90,7 +96,7 @@ static bool page_entry_is(int fd, char *
 {
 	bool m = pagemap_get_entry(fd, start) & pagemap_flags;
 
-	if (pagemap_scan_supported(fd, start)) {
+	if (pagemap_scan_supported(fd)) {
 		bool s = pagemap_scan_get_categories(fd, start) & pagescan_flags;
 
 		if (m == s)
_

Patches currently in -mm which might be from audra@redhat.com are

selftests-mm-fix-soft-dirty-kselftest-supported-check.patch