[PATCH 2/2] selftests/mm: verify droppable mappings cannot be locked

Anthony Yznaga
2026-04-02T00:34:33Z

For configs that support MAP_DROPPABLE verify that a mapping created
with MAP_DROPPABLE cannot be locked via mlock(), and that it will not
be locked if it's created after mlockall(MCL_FUTURE).

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
tools/testing/selftests/mm/mlock2-tests.c | 91 ++++++++++++++++++++---
1 file changed, 82 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/mm/mlock2-tests.c b/tools/testing/selftests/mm/mlock2-tests.c
index b474f2b20def..2750a3d6e8e4 100644
--- a/tools/testing/selftests/mm/mlock2-tests.c
+++ b/tools/testing/selftests/mm/mlock2-tests.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <sys/mman.h>
+#include <linux/mman.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
@@ -163,14 +164,17 @@ static int lock_check(unsigned long addr)
return (vma_rss == vma_size);
}

-static int unlock_lock_check(char *map)
+static int unlock_lock_check(char *map, bool mlock_supported)
{
- if (is_vmflag_set((unsigned long)map, LOCKED)) {
+ if (!is_vmflag_set((unsigned long)map, LOCKED))
+ return 0;
+
+ if (mlock_supported)
ksft_print_msg("VMA flag %s is present on page 1 after unlock\n", LOCKED);
- return 1;
- }
+ else
+ ksft_print_msg("VMA flag %s is present on an unsupported VMA\n", LOCKED);

- return 0;
+ return 1;
}

static void test_mlock_lock(void)
@@ -196,7 +200,7 @@ static void test_mlock_lock(void)
ksft_exit_fail_msg("munlock(): %s\n", strerror(errno));
}

- ksft_test_result(!unlock_lock_check(map), "%s: Unlocked\n", __func__);
+ ksft_test_result(!unlock_lock_check(map, true), "%s: Unlocked\n", __func__);
munmap(map, 2 * page_size);
}

@@ -296,7 +300,7 @@ static void test_munlockall0(void)
ksft_exit_fail_msg("munlockall(): %s\n", strerror(errno));
}

- ksft_test_result(!unlock_lock_check(map), "%s: No locked memory\n", __func__);
+ ksft_test_result(!unlock_lock_check(map, true), "%s: No locked memory\n", __func__);
munmap(map, 2 * page_size);
}

@@ -336,7 +340,74 @@ static void test_munlockall1(void)
ksft_exit_fail_msg("munlockall() %s\n", strerror(errno));
}

- ksft_test_result(!unlock_lock_check(map), "%s: No locked memory\n", __func__);
+ ksft_test_result(!unlock_lock_check(map, true), "%s: No locked memory\n", __func__);
+ munmap(map, 2 * page_size);
+}
+
+/*
+ * Droppable memory should not be lockable.
+ */
+static void test_mlock_droppable(void)
+{
+ char *map;
+ unsigned long page_size = getpagesize();
+
+ /*
+ * Ensure MCL_FUTURE is not set.
+ */
+ if (mlockall(MCL_CURRENT))
+ ksft_exit_fail_msg("mlockall(MCL_CURRENT): %s\n", strerror(errno));
+ if (munlockall())
+ ksft_exit_fail_msg("munlockall() %s\n", strerror(errno));
+
+ map = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
+ if (map == MAP_FAILED) {
+ if (errno == EOPNOTSUPP) {
+ ksft_test_result_skip("%s: MAP_DROPPABLE not supported\n", __func__);
+ return;
+ }
+ ksft_exit_fail_msg("mmap error: %s\n", strerror(errno));
+ }
+
+ if (mlock2_(map, 2 * page_size, 0)) {
+ munmap(map, 2 * page_size);
+ ksft_exit_fail_msg("mlock2(0): %s\n", strerror(errno));
+ }
+
+ ksft_test_result(!unlock_lock_check(map, false), "%s: droppable memory not locked\n",
+ __func__);
+
+ munmap(map, 2 * page_size);
+}
+
+static void test_mlockall_future_droppable(void)
+{
+ char *map;
+ unsigned long page_size = getpagesize();
+
+ if (mlockall(MCL_CURRENT | MCL_FUTURE))
+ ksft_exit_fail_msg("mlockall(MCL_CURRENT | MCL_FUTURE): %s\n", strerror(errno));
+
+ map = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
+
+ if (map == MAP_FAILED) {
+ if (errno == EOPNOTSUPP) {
+ ksft_test_result_skip("%s: MAP_DROPPABLE not supported\n", __func__);
+ return;
+ }
+ ksft_exit_fail_msg("mmap error: %s\n", strerror(errno));
+ }
+
+ ksft_test_result(!unlock_lock_check(map, false), "%s: droppable memory not locked\n",
+ __func__);
+
+ if (munlockall()) {
+ munmap(map, 2 * page_size);
+ ksft_exit_fail_msg("munlockall() %s\n", strerror(errno));
+ }
+
munmap(map, 2 * page_size);
}

@@ -442,7 +513,7 @@ int main(int argc, char **argv)

munmap(map, size);

- ksft_set_plan(13);
+ ksft_set_plan(15);

test_mlock_lock();
test_mlock_onfault();
@@ -451,6 +522,8 @@ int main(int argc, char **argv)
test_lock_onfault_of_present();
test_vma_management(true);
test_mlockall();
+ test_mlock_droppable();
+ test_mlockall_future_droppable();

ksft_finished();
}
--
2.47.3