[PATCH v4 0/3] fix MAP_DROPPABLE not supported errno

[PATCH v4 0/3] fix MAP_DROPPABLE not supported errno

[Anthony Yznaga]

Mark Brown reported seeing a regression in -next on 32 bit arm with the
mlock selftests. Before exiting and marking the tests failed, the following
message was logged after an attempt to create a MAP_DROPPABLE mapping:

Bail out! mmap error: Unknown error 524

It turns out error 524 is ENOTSUPP which is an error that userspace is not
supposed to see, but it indicates in this instance that MAP_DROPPABLE is
not supported.

The first patch changes the errno returned to EOPNOTSUPP. The second patch
is a second version of a prior patch to introduce selftests to verify
locking behavior with droppable mappings with the additional change to skip
the tests when MAP_DROPPABLE is not supported. The third patch fixes the
MAP_DROPPABLE selftest so that it is run by the framework and skips if
MAP_DROPPABLE is not supported.

v4:
- Removed unnecessary #ifdef MAP_DROPPABLE from patch 2 (DavidH)
- Changed the tests to also skip if mmap() returns EINVAL
- Added a third patch to fix the MAP_DROPPABLE selftest

v3:
- Added acked-by's and reviewed-by's to patch 1
- Addressed sashiko AI reviewbot questions:
  - Call munlockall() if test_mlockall_future_droppable() returns early
  - Skip the tests if they are compiled for an older kernel without
    MAP_DROPPABLE.

v2:
- Remove unnecessary mlock() call from selftest (DavidH)
- Change tests to not exit on failure (DavidH)

Anthony Yznaga (3):
  mm: fix mmap errno value when MAP_DROPPABLE is not supported
  selftests/mm: verify droppable mappings cannot be locked
  selftests/mm: run the MAP_DROPPABLE selftest

 mm/mmap.c                                 |  2 +-
 tools/testing/selftests/mm/droppable.c    |  9 ++-
 tools/testing/selftests/mm/mlock2-tests.c | 84 ++++++++++++++++++++---
 tools/testing/selftests/mm/run_vmtests.sh |  1 +
 4 files changed, 85 insertions(+), 11 deletions(-)

-- 
2.47.3

[PATCH v4 1/3] mm: fix mmap errno value when MAP_DROPPABLE is not supported

[Anthony Yznaga]

On configs where MAP_DROPPABLE is not supported (currently any 32-bit
config except for PPC32), mmap fails with errno set to ENOTSUPP.
However, ENOTSUPP is not a standard error value that userspace knows
about. The acceptable userspace-visible errno to use is EOPNOTSUPP.
checkpatch.pl has a warning to this effect.

Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
Cc: <stable@vger.kernel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reported-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 mm/mmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 5754d1c36462..2311ae7c2ff4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -504,7 +504,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 			break;
 		case MAP_DROPPABLE:
 			if (VM_DROPPABLE == VM_NONE)
-				return -ENOTSUPP;
+				return -EOPNOTSUPP;
 			/*
 			 * A locked or stack area makes no sense to be droppable.
 			 *
-- 
2.47.3

[PATCH v4 2/3] selftests/mm: verify droppable mappings cannot be locked

[Anthony Yznaga]

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>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
---
 tools/testing/selftests/mm/mlock2-tests.c | 84 ++++++++++++++++++++---
 1 file changed, 75 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/mm/mlock2-tests.c b/tools/testing/selftests/mm/mlock2-tests.c
index b474f2b20def..e16e288cc7c1 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 +340,67 @@ 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 (munlockall()) {
+		ksft_test_result_fail("munlockall() %s\n", strerror(errno));
+		return;
+	}
+
+	map = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
+	if (map == MAP_FAILED) {
+		if ((errno == EOPNOTSUPP) || (errno == EINVAL))
+			ksft_test_result_skip("%s: MAP_DROPPABLE not supported\n", __func__);
+		else
+			ksft_test_result_fail("mmap error: %s\n", strerror(errno));
+		return;
+	}
+
+	if (mlock2_(map, 2 * page_size, 0))
+		ksft_test_result_fail("mlock2(0): %s\n", strerror(errno));
+	else
+		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_test_result_fail("mlockall(MCL_CURRENT | MCL_FUTURE): %s\n", strerror(errno));
+		return;
+	}
+
+	map = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
+
+	if (map == MAP_FAILED) {
+		if ((errno == EOPNOTSUPP) || (errno == EINVAL))
+			ksft_test_result_skip("%s: MAP_DROPPABLE not supported\n", __func__);
+		else
+			ksft_test_result_fail("mmap error: %s\n", strerror(errno));
+		munlockall();
+		return;
+	}
+
+	ksft_test_result(!unlock_lock_check(map, false), "%s: droppable memory not locked\n",
+			__func__);
+
+	munlockall();
 	munmap(map, 2 * page_size);
 }
 
@@ -442,7 +506,7 @@ 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 +515,8 @@ 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

[PATCH v4 3/3] selftests/mm: run the MAP_DROPPABLE selftest

[Anthony Yznaga]

The test was not being run by the selftest framework so it was never
noticed that it would fail with an assertion failure on configs without
support for MAP_DROPPABLE. Update the test so that it is skipped instead
when MAP_DROPPABLE is not supported, and add it to the mmap category so
that the test is run by the framework.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 tools/testing/selftests/mm/droppable.c    | 9 ++++++++-
 tools/testing/selftests/mm/run_vmtests.sh | 1 +
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/droppable.c b/tools/testing/selftests/mm/droppable.c
index 44940f75c461..30c8be37fcb9 100644
--- a/tools/testing/selftests/mm/droppable.c
+++ b/tools/testing/selftests/mm/droppable.c
@@ -26,7 +26,14 @@ int main(int argc, char *argv[])
 	ksft_set_plan(1);
 
 	alloc = mmap(0, alloc_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
-	assert(alloc != MAP_FAILED);
+	if (alloc == MAP_FAILED) {
+		if ((errno == EOPNOTSUPP) || (errno == EINVAL)) {
+			ksft_test_result_skip("MAP_DROPPABLE not supported\n");
+			exit(KSFT_SKIP);
+		}
+		ksft_test_result_fail("mmap error: %s\n", strerror(errno));
+		exit(KSFT_FAIL);
+	}
 	memset(alloc, 'A', alloc_size);
 	for (size_t i = 0; i < alloc_size; i += page_size)
 		assert(*(uint8_t *)(alloc + i));
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index d8468451b3a3..e1e355d50e65 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -382,6 +382,7 @@ else
 fi
 
 CATEGORY="mmap" run_test ./map_populate
+CATEGORY="mmap" run_test ./droppable
 
 CATEGORY="mlock" run_test ./mlock-random-test
 
-- 
2.47.3