[PATCH v3 0/3] support kselftest on nommu platform

[PATCH v3 0/3] support kselftest on nommu platform

[Hajime Tazaki]

This patchset adds an ability to execute kselftest on nommu platforms.

Currently there are several issues if we wish to run kselftests on nommu
targets:

- it cannot compile/build test binaries because the current files mainly
  assume to build with glibc,
- some of the tests are not able to run on nommu targets as there are no
  fork(2) syscall.

The first issue can be avoided if we can build static PIE binaries (if
targets support it), but in our case (build on ubuntu/glibc and run on
alpine/musl-libc), it fails to invoke due to lack of the GNU ifunc
mechanism.  Thus, we need to cross-compile with musl toolchain, which
needs to be solved the first issue.

The second issue is the lack of fork(2) syscall on those platforms.
Especially the test harness helper (kselftest_harness.h) uses the
syscall, which cannot be simply with vfork(2).  `timeout` command used
in `runner.sh` never works for nommu platform as it uses fork(2).

nommu component in the mm subsystem has several known issues and having
test cases should help this situation, thus this patchset is very first
step toward enriching test environment which has not been well tested
for a while.  The test cases is implemented based on the document
(Documentation/admin-guide/mm/nommu-mmap.rst).

Initial shape for this patches is implemented as an opt-in TARGET, not
built/invoked automatically if users don't specify this nommu target.

- v2:
https://lore.kernel.org/linux-mm/20260825015945.141739-1-thehajime@gmail.com/
- rfc:
https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/

Hajime Tazaki (3):
  selftests: kselftest: avoid cd - in runner
  selftests: run tests on nommu architecture
  selftests/nommu: add nommu mmap and mremap behavior tests

 Documentation/dev-tools/kselftest.rst         |  14 +
 tools/testing/selftests/kselftest/runner.sh   |   9 +-
 tools/testing/selftests/nommu/Makefile        |   8 +
 tools/testing/selftests/nommu/local.mk        |   7 +
 .../testing/selftests/nommu/nommu_mmap_test.c | 258 +++++++++++++
 .../selftests/nommu/nommu_mremap_test.c       | 362 ++++++++++++++++++
 6 files changed, 656 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/nommu/Makefile
 create mode 100644 tools/testing/selftests/nommu/local.mk
 create mode 100644 tools/testing/selftests/nommu/nommu_mmap_test.c
 create mode 100644 tools/testing/selftests/nommu/nommu_mremap_test.c


base-commit: e8d0f6a1b2a447d02845984fa6288787543cb03c
-- 
2.43.0

[PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[Hajime Tazaki]

The kselftest runner currently uses `cd -` to restore its working
directory after running a test.

This is not supported by the minimal BusyBox hush shell used by some
NOMMU targets. Store the original directory explicitly and restore it
with a quoted path instead.

This also avoids printing the directory change performed by `cd -` and
handles paths containing whitespace correctly.

Cc: Shuah Khan <shuah@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Cc: "Ricardo B. Marliere" <rbm@suse.com>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-um@lists.infradead.org
Cc: linux-mm@kvack.org
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
---
 tools/testing/selftests/kselftest/runner.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
index 311811dc55a0..8fc1018d6fec 100644
--- a/tools/testing/selftests/kselftest/runner.sh
+++ b/tools/testing/selftests/kselftest/runner.sh
@@ -130,6 +130,7 @@ run_one()
 				return $KSFT_FAIL
 			fi
 		fi
+		OLDDIR=$(pwd)
 		cd `dirname $TEST` > /dev/null
 		(((( tap_timeout "$cmd" 2>&1; echo $? >&3) |
 			tap_prefix >&4) 3>&1) |
@@ -147,7 +148,7 @@ run_one()
 		*)
 			ktap_test_fail "$TEST_HDR_MSG # exit=$rc";;
 		esac
-		cd - >/dev/null
+		cd "$OLDDIR" >/dev/null
 	fi
 
 	return $rc
-- 
2.43.0

[PATCH v3 2/3] selftests: run tests on nommu architecture

[Hajime Tazaki]

Architectures lacks MMU doesn't support fork(2) syscall and only
vfork(2) is available with limitations.  Thus, we cannot run kselftest
on nommu architecture as is.

This commit addresses this issue with the following changes:

- on test run stage, avoid calling timeout command when NOMMU=1 variable
  added to environmental variable, since timeout command uses fork
  syscall which nommu platform doesn't support.
- describe the difference of nommu tests in the document.

So command line to build/execute tests for nommu should be like below:

 $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu
 $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
 $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p \
   -c nommu

Cc: Shuah Khan <shuah@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Cc: "Ricardo B. Marliere" <rbm@suse.com>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-um@lists.infradead.org
Cc: linux-mm@kvack.org
Cc: linux-doc@vger.kernel.org
Closes: https://sashiko.dev/#/patchset/20260813063401.1786548-1-thehajime%40gmail.com
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

--

v2 => v3
- remove unnecessary modification
- new target is moved from TARGETS=mm/nommu to TARGETS=nommu
- rename CONFIG_NOMMU to NOMMU to avoid confusion to kernel config

rfc => v2
- reformat ktap header, reported by Sashiko review
- https://lore.kernel.org/linux-mm/20260825015945.141739-2-thehajime@gmail.com/

rfc: https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/
---
 Documentation/dev-tools/kselftest.rst       | 14 ++++++++++++++
 tools/testing/selftests/kselftest/runner.sh |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst
index 64c0ec7428a2..c35b819947b7 100644
--- a/Documentation/dev-tools/kselftest.rst
+++ b/Documentation/dev-tools/kselftest.rst
@@ -230,6 +230,20 @@ section::
 
 .. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress
 
+Build and test on nommu target
+==============================
+
+If you (cross-)build kselftests for nommu targets, or run tests on nommu targets, use
+``NOMMU=1`` as a make variable/environment setting to tell build system to do the additional
+checks.  These nommu targets may differ in several ways, such as not supporting fork(2) or
+using musl or another libc.  Set this variable to apply the necessary build and test adjustments.
+
+::
+
+  $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu  # <= build-only
+  $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
+  $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p -c nommu
+
 Contributing new tests
 ======================
 
diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
index 8fc1018d6fec..95b5ebb8bbb9 100644
--- a/tools/testing/selftests/kselftest/runner.sh
+++ b/tools/testing/selftests/kselftest/runner.sh
@@ -38,8 +38,12 @@ tap_prefix()
 
 tap_timeout()
 {
+	# nommu doesn't support timeout command (missing fork(2))
+	if [ "$NOMMU" = "1" ] ; then
+		echo "timeout isn't supported for NOMMU"
+		$1
 	# Make sure tests will time out if utility is available.
-	if [ -x /usr/bin/timeout ] ; then
+	elif [ -x /usr/bin/timeout ] ; then
 		/usr/bin/timeout --foreground "$kselftest_timeout" \
 			/usr/bin/timeout "$kselftest_timeout" $1
 	else
-- 
2.43.0

[PATCH v3 3/3] selftests/nommu: add nommu mmap and mremap behavior tests

[Hajime Tazaki]

Introduce a kselftest utility to validate memory mapping capabilities
under nommu kernels, aligned with
Documentation/admin-guide/mm/nommu-mmap.rst.

The test implements basic checks into a generic architecture-agnostic
test matrix applicable across nommu targets. It evaluates:

1. MAP_FIXED allocation rejections.
2. Standard MAP_PRIVATE and MAP_ANONYMOUS allocation resilience.
3. Regular file mappings via standard filesystem storage.
4. Block device subsystem mappings (gracefully skipping if node is
   missing).
5. Shared vs Private backing discrepancies under nommu conditions.
6. mremap limits, ensuring non-expandable restrictions behave properly.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Liam R. Howlett" <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-um@lists.infradead.org
Closes: https://sashiko.dev/#/patchset/20260825015945.141739-1-thehajime@gmail.com
Assisted-by: Gemini:Pro [AI_Reviewer] [Sashiko_Linter]
Assisted-by: cubic.dev:unspecified
Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

--

v2 => v3
- remove unnecessary modifications
- address Sashiko review

rfc => v2
- prepare a different TARGETS for tests (mm/nommu)
- drop shrink fix tests
- drop mmap /dev/zero tests
- https://lore.kernel.org/linux-mm/20260825015945.141739-3-thehajime@gmail.com/

rfc:
- https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/
---
 tools/testing/selftests/nommu/Makefile        |   8 +
 tools/testing/selftests/nommu/local.mk        |   7 +
 .../testing/selftests/nommu/nommu_mmap_test.c | 258 +++++++++++++
 .../selftests/nommu/nommu_mremap_test.c       | 362 ++++++++++++++++++
 4 files changed, 635 insertions(+)
 create mode 100644 tools/testing/selftests/nommu/Makefile
 create mode 100644 tools/testing/selftests/nommu/local.mk
 create mode 100644 tools/testing/selftests/nommu/nommu_mmap_test.c
 create mode 100644 tools/testing/selftests/nommu/nommu_mremap_test.c

diff --git a/tools/testing/selftests/nommu/Makefile b/tools/testing/selftests/nommu/Makefile
new file mode 100644
index 000000000000..8e7cd7315c53
--- /dev/null
+++ b/tools/testing/selftests/nommu/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for nommu selftests
+
+TEST_GEN_PROGS += nommu_mmap_test
+TEST_GEN_PROGS += nommu_mremap_test
+
+include ../lib.mk
+include local.mk
diff --git a/tools/testing/selftests/nommu/local.mk b/tools/testing/selftests/nommu/local.mk
new file mode 100644
index 000000000000..0bd1300f00f4
--- /dev/null
+++ b/tools/testing/selftests/nommu/local.mk
@@ -0,0 +1,7 @@
+# detect if users request NOMMU build or not
+# User can set NOMMU to 1 to build/test for NOMMU platforms
+NOMMU ?= 0
+ifeq ($(NOMMU),1)
+CFLAGS += -DNOMMU
+export NOMMU
+endif
diff --git a/tools/testing/selftests/nommu/nommu_mmap_test.c b/tools/testing/selftests/nommu/nommu_mmap_test.c
new file mode 100644
index 000000000000..8d396638da56
--- /dev/null
+++ b/tools/testing/selftests/nommu/nommu_mmap_test.c
@@ -0,0 +1,258 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <limits.h>
+#include "kselftest.h"
+
+#include <sys/vfs.h>
+#ifndef RAMFS_MAGIC
+#define RAMFS_MAGIC 0x858458f6
+#endif
+
+static size_t ps;
+
+struct test_case_t {
+	const char *name;
+	const char *pathname;
+	int open_flags;
+	int mmap_prot;
+	int mmap_flags;
+	int exp_err;
+	int (*resolve_exp_err)(const char *path);
+};
+
+static int get_shm_expected_error(const char *path)
+{
+	struct statfs fs;
+
+	if (statfs(path, &fs) == 0) {
+		if (fs.f_type == RAMFS_MAGIC)
+			return 0; /* ramfs succeed with contiguous memory */
+	}
+	 /* hostfs, etc returns ENODEV due to lack of contiguous allocation */
+	return ENODEV;
+}
+
+static struct test_case_t test_cases[] = {
+	{
+		.name = "anonymous private allocation",
+		.pathname = NULL,
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ | PROT_WRITE,
+		.mmap_flags = MAP_ANONYMOUS | MAP_PRIVATE,
+		.exp_err = 0,
+		.resolve_exp_err = NULL,
+	},
+	{
+		.name = "non-anonymous private file mapping (rw-)",
+		.pathname = "/tmp/ksft.nommu-reg-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ | PROT_WRITE,
+		.mmap_flags = MAP_PRIVATE,
+		.exp_err = 0,
+		.resolve_exp_err = NULL,
+	},
+	{
+		.name = "non-anonymous private file mapping (r--)",
+		.pathname = "/tmp/ksft.nommu-reg-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_PRIVATE,
+		.exp_err = 0,
+		.resolve_exp_err = NULL,
+	},
+	{
+		.name = "non-anonymous shared file mapping (rw-)",
+		.pathname = "/tmp/ksft.nommu-shm-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ | PROT_WRITE,
+		.mmap_flags = MAP_SHARED,
+		.exp_err = 0,
+#ifdef NOMMU
+		.resolve_exp_err = get_shm_expected_error,
+#else
+		.resolve_exp_err = NULL,
+#endif
+	},
+	{
+		.name = "non-anonymous shared file mapping (r--)",
+		.pathname = "/tmp/ksft.nommu-shm-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_SHARED,
+		.exp_err = 0,
+#ifdef NOMMU
+		.resolve_exp_err = get_shm_expected_error,
+#else
+		.resolve_exp_err = 0,
+#endif
+	},
+};
+
+static int run_mapping_matrix_test(struct test_case_t *tcase)
+{
+	int fd;
+	void *ptr;
+	char path_buf[PATH_MAX];
+	const char *path = tcase->pathname;
+	int rc = KSFT_PASS;
+	int expected_error;
+
+	ksft_print_msg("[RUN] Testing: %s\n", tcase->name);
+
+	if (tcase->pathname == NULL) {
+		fd = -1;
+	} else if (strstr(tcase->pathname, "XXXXXX")) {
+		strncpy(path_buf, tcase->pathname, sizeof(path_buf) - 1);
+		path_buf[sizeof(path_buf) - 1] = '\0';
+		fd = mkstemp(path_buf);
+		if (fd < 0) {
+			ksft_test_result_skip("Failed to setup temp node: %s\n",
+					      tcase->pathname);
+			return KSFT_SKIP;
+		}
+		if (ftruncate(fd, ps) != 0) {
+			ksft_test_result_fail("ftruncate failed for: %s\n",
+					      tcase->pathname);
+			close(fd);
+			unlink(path_buf);
+			return KSFT_FAIL;
+		}
+		path = path_buf;
+	} else {
+		fd = open(tcase->pathname, tcase->open_flags, 0600);
+		if (fd < 0) {
+			ksft_test_result_skip("Device node not accessible: %s\n",
+				       tcase->pathname);
+			return KSFT_SKIP;
+		}
+	}
+
+	expected_error = tcase->exp_err;
+	if (tcase->resolve_exp_err && fd >= 0)
+		expected_error = tcase->resolve_exp_err(path);
+
+	ptr = mmap(NULL, ps, tcase->mmap_prot, tcase->mmap_flags, fd, 0);
+
+	if (expected_error != 0) {
+		if (ptr != MAP_FAILED) {
+			ksft_test_result_fail("%s: mmap unexpectedly succeeded (exp error %d)\n",
+					      tcase->name, expected_error);
+			munmap(ptr, ps);
+			rc = KSFT_FAIL;
+			goto cleanup;
+		}
+		if (errno != expected_error) {
+			ksft_test_result_fail("%s: mmap failed with %d (%s), but expected %d\n",
+					      tcase->name, errno, strerror(errno), expected_error);
+			rc = KSFT_FAIL;
+			goto cleanup;
+		}
+		ksft_test_result_pass("%s: Correctly rejected with expected error %s(%d)\n",
+				      tcase->name, strerror(expected_error), expected_error);
+		rc = KSFT_PASS;
+		goto cleanup;
+	}
+
+	if (ptr == MAP_FAILED) {
+		ksft_test_result_fail("%s: mmap failed unexpectedly: %s\n",
+				      tcase->name, strerror(errno));
+		rc = KSFT_FAIL;
+		goto cleanup;
+	}
+
+	ksft_test_result_pass("%s: mmap validation successfully passed\n", tcase->name);
+	munmap(ptr, ps);
+
+cleanup:
+	if (fd >= 0) {
+		close(fd);
+		if (tcase->pathname && strstr(tcase->pathname, "XXXXXX"))
+			unlink(path_buf);
+	}
+	return rc;
+}
+
+static int test_map_fixed(void)
+{
+	void *fixed_addr;
+	void *ptr;
+
+	ksft_print_msg("[RUN] Testing MAP_FIXED behavior\n");
+
+	fixed_addr = mmap(NULL, ps, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (fixed_addr == MAP_FAILED) {
+		ksft_test_result_skip("Unable to reserve test address: %s\n",
+				strerror(errno));
+		return KSFT_SKIP;
+	}
+
+	if (munmap(fixed_addr, ps)) {
+		ksft_test_result_fail("Unable to release test address: %s\n",
+				strerror(errno));
+		return KSFT_FAIL;
+	}
+
+	ptr = mmap(fixed_addr, ps, PROT_READ | PROT_WRITE,
+		MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+#ifdef NOMMU
+	if (ptr == MAP_FAILED && (errno == ENODEV || errno == EINVAL)) {
+		ksft_test_result_pass("MAP_FIXED correctly rejected under nommu\n");
+		return KSFT_PASS;
+	}
+	if (ptr != MAP_FAILED) {
+		ksft_test_result_fail("MAP_FIXED unexpectedly allowed under nommu\n");
+		munmap(ptr, ps);
+		return KSFT_FAIL;
+	}
+	ksft_test_result_fail("MAP_FIXED failed under NOMMU: %s\n",
+			      strerror(errno));
+	return KSFT_FAIL;
+#else
+	if (ptr != MAP_FAILED) {
+		ksft_test_result_pass("MAP_FIXED successfully allocated under MMU\n");
+		munmap(ptr, ps);
+		return KSFT_PASS;
+	}
+	ksft_test_result_fail("MAP_FIXED failed allocation under MMU\n");
+	return KSFT_FAIL;
+#endif
+}
+
+int main(int argc, char **argv)
+{
+	int result = KSFT_PASS;
+	int i, rc;
+
+	ps = sysconf(_SC_PAGESIZE);
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(test_cases) + 1);
+
+#ifdef NOMMU
+	ksft_print_msg("Running strict MMAP test criteria under nommu architecture\n");
+#else
+	ksft_print_msg("Running MMAP test criteria under MMU architecture\n");
+#endif
+
+	if (test_map_fixed() == KSFT_FAIL)
+		result = KSFT_FAIL;
+
+	for (i = 0; i < (int)ARRAY_SIZE(test_cases); i++) {
+		rc = run_mapping_matrix_test(&test_cases[i]);
+		if (rc == KSFT_FAIL)
+			result = KSFT_FAIL;
+	}
+
+	if (result == KSFT_PASS)
+		ksft_finished();
+
+	ksft_exit_fail();
+}
diff --git a/tools/testing/selftests/nommu/nommu_mremap_test.c b/tools/testing/selftests/nommu/nommu_mremap_test.c
new file mode 100644
index 000000000000..2aaca59085fb
--- /dev/null
+++ b/tools/testing/selftests/nommu/nommu_mremap_test.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <limits.h>
+#include "kselftest.h"
+
+#include <sys/vfs.h>
+#ifndef RAMFS_MAGIC
+#define RAMFS_MAGIC 0x858458f6
+#endif
+
+static size_t ps;
+
+static long get_fs_type(const char *path)
+{
+	struct statfs fs;
+
+	if (statfs(path, &fs) == 0)
+		return fs.f_type;
+
+	return 0;
+}
+
+static void munmap_shrink_test(void)
+{
+	void *addr;
+	int ret;
+
+	/* munmap shrink test */
+	for (int i = 0; i < 4; i++) {
+		addr = mmap(NULL, ps * 4, PROT_READ | PROT_WRITE,
+			    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+		if (addr == MAP_FAILED) {
+			ksft_test_result_fail("mmap failed: %s(%d)\n", strerror(errno), errno);
+			return;
+		}
+		ret = munmap((char *)addr + ps * i, ps);
+		if (ret != 0) {
+			ksft_test_result_fail("memory %p isn't unmapped at %p\n",
+					addr, (char *)addr + ps * i);
+			return;
+		}
+
+		if (i == 0) {
+			if (munmap(addr +  ps, ps * 3))
+				goto error;
+		} else if (i == 1) {
+			if (munmap(addr, ps) || munmap(addr + (ps * 2), ps * 2))
+				goto error;
+		} else if (i == 2) {
+			if (munmap(addr, ps * 2) || munmap(addr + (ps * 3), ps))
+				goto error;
+		} else if (i == 3) {
+			if (munmap(addr, ps * 3))
+				goto error;
+		}
+	}
+
+	ksft_test_result_pass("%s success\n", __func__);
+	return;
+error:
+	for (int j = 0; j < 4; j++)
+		munmap((char *)addr + j * ps, ps);
+	ksft_test_result_fail("%s clean up failures\n", __func__);
+}
+
+static size_t page_align(size_t len)
+{
+	return (len + ps - 1) / ps * ps;
+}
+
+static void mremap_shrink_test(void)
+{
+	void *addr, *addr2;
+	size_t current_len;
+	size_t old_len, new_len;
+	struct param {
+		size_t old;
+		size_t new;
+	} params[] = {
+		/* should not happen any shrink */
+		{ .old = ps * 4 - 1, .new = ps * 4 - 2 },
+		/* should not happen any shrink */
+		{ .old = ps * 4 - 1, .new = ps * 4 },
+		{ .old = ps * 4, .new = ps * 2 },
+		/* should not happen any shrink */
+		{ .old = ps * 2, .new = ps * 2 - 2 },
+		{ .old = ps * 2 - 2, .new = ps * 1 },
+	};
+
+	/* mremap shrink test */
+	current_len = page_align(ps * 4 - 1);
+	addr = mmap(NULL, ps * 4 - 1, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (addr == MAP_FAILED) {
+		ksft_test_result_fail("mmap failed: %s(%d)\n", strerror(errno), errno);
+		return;
+	}
+
+	for (int i = 0; i < ARRAY_SIZE(params); i++) {
+		old_len = params[i].old;
+		new_len = params[i].new;
+		current_len = page_align(new_len);
+		addr2 = mremap(addr, old_len, new_len, MREMAP_MAYMOVE);
+		if (addr2 == MAP_FAILED) {
+			ksft_test_result_fail("memory %p isn't remapped at %p\n", addr, addr2);
+			munmap(addr, page_align(old_len));
+			return;
+		}
+
+		addr = addr2;
+	}
+
+	if (munmap(addr, current_len)) {
+		ksft_test_result_fail("%s cleanup failed: %s\n",
+				      __func__, strerror(errno));
+		return;
+	}
+	ksft_test_result_pass("%s success\n", __func__);
+}
+
+static int get_shared_writable_file_expected_error(const char *path)
+{
+	if (get_fs_type(path) == RAMFS_MAGIC)
+		return EPERM; /* ramfs failed */
+
+	return 0;
+}
+
+struct mremap_case_t {
+	const char *name;
+	const char *pathname;
+	int open_flags;
+	int mmap_prot;
+	int mmap_flags;
+	int exp_err;
+	int (*resolve_exp_err)(const char *path);
+	unsigned int old_pages;
+	unsigned int new_pages;
+};
+
+static struct mremap_case_t mremap_cases[] = {
+	{
+		.name = "anonymous shrink (r--)",
+		.pathname = NULL,
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_ANONYMOUS | MAP_PRIVATE,
+		.exp_err = 0,
+		.resolve_exp_err = 0,
+	},
+	{
+		.name = "shared file shrink (r--)",
+		.pathname = "/tmp/ksft.nommu-remap-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_SHARED,
+		.exp_err = 0,
+#ifdef NOMMU
+		.resolve_exp_err = get_shared_writable_file_expected_error,
+#else
+		.resolve_exp_err = 0,
+#endif
+	},
+	{
+		.name = "private file unchanged length (r-)",
+		.pathname = "/tmp/ksft.nommu-remap-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_PRIVATE,
+#ifdef NOMMU
+		.exp_err = EPERM,
+#else
+		.exp_err = 0,
+#endif
+		.resolve_exp_err = 0,
+		.old_pages = 4,
+		.new_pages = 4,
+	},
+	{
+		.name = "private file unchanged length (rw-)",
+		.pathname = "/tmp/ksft.nommu-remap-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ | PROT_WRITE,
+		.mmap_flags = MAP_PRIVATE,
+		.exp_err = 0,
+		.resolve_exp_err = 0,
+		.old_pages = 4,
+		.new_pages = 4,
+	},
+	{
+		.name = "private file growth (r-)",
+		.pathname = "/tmp/ksft.nommu-remap-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ,
+		.mmap_flags = MAP_PRIVATE,
+#ifdef NOMMU
+		.exp_err = EPERM,
+#else
+		.exp_err = 0,
+#endif
+		.resolve_exp_err = 0,
+		.old_pages = 4,
+		.new_pages = 8,
+	},
+	{
+		.name = "private file growth (rw-)",
+		.pathname = "/tmp/ksft.nommu-remap-XXXXXX",
+		.open_flags = O_CREAT | O_RDWR | O_EXCL,
+		.mmap_prot = PROT_READ | PROT_WRITE,
+		.mmap_flags = MAP_PRIVATE,
+#ifdef NOMMU
+		.exp_err = ENOMEM,
+#else
+		.exp_err = 0,
+#endif
+		.resolve_exp_err = 0,
+		.old_pages = 4,
+		.new_pages = 8,
+	},
+};
+
+static int run_mremap_test(struct mremap_case_t *tcase)
+{
+	int fd = -1;
+	void *addr, *addr2;
+	char pb[PATH_MAX];
+	const char *path = tcase->pathname;
+	int rc = KSFT_PASS;
+	int expected_error;
+	unsigned int old_pages = tcase->old_pages ?: 4;
+	unsigned int new_pages = tcase->new_pages ?: 2;
+	unsigned int file_pages = old_pages > new_pages ?
+				  old_pages : new_pages;
+
+	ksft_print_msg("[RUN] Testing mremap: %s\n", tcase->name);
+
+	if (tcase->pathname && strstr(tcase->pathname, "XXXXXX")) {
+		strncpy(pb, tcase->pathname, sizeof(pb) - 1);
+		pb[sizeof(pb) - 1] = '\0';
+		fd = mkstemp(pb);
+		if (fd < 0) {
+			ksft_test_result_skip("Failed to setup file backing\n");
+			return KSFT_SKIP;
+		}
+		if (ftruncate(fd, ps * file_pages) != 0) {
+			ksft_test_result_fail("Failed to setup file backing\n");
+			close(fd);
+			unlink(pb);
+			return KSFT_FAIL;
+		}
+
+#ifdef NOMMU
+		if ((tcase->mmap_flags & MAP_SHARED) && get_fs_type(pb) != RAMFS_MAGIC) {
+			ksft_test_result_skip("Skip the test under non-ramfs filesystem (%s)\n",
+					      pb);
+			close(fd);
+			unlink(pb);
+			return KSFT_SKIP;
+		}
+#endif
+		path = pb;
+	} else if (tcase->pathname) {
+		fd = open(tcase->pathname, tcase->open_flags, 0600);
+		if (fd < 0) {
+			ksft_test_result_skip("Backing node not accessible\n");
+			return KSFT_SKIP;
+		}
+
+#ifdef NOMMU
+		if ((tcase->mmap_flags & MAP_SHARED) &&
+		    get_fs_type(tcase->pathname) != RAMFS_MAGIC) {
+			ksft_test_result_skip("Skip the test under non-ramfs filesystem (%s)\n",
+					      tcase->pathname);
+			close(fd);
+			return KSFT_SKIP;
+		}
+#endif
+	}
+
+	addr = mmap(NULL, ps * old_pages, tcase->mmap_prot,
+		    tcase->mmap_flags, fd, 0);
+	if (addr == MAP_FAILED) {
+		ksft_print_msg("mmap mapping failed %s(%d)\n", strerror(errno), errno);
+		rc = KSFT_FAIL;
+		goto out;
+	}
+
+	expected_error = tcase->exp_err;
+	if (tcase->resolve_exp_err && fd >= 0)
+		expected_error = tcase->resolve_exp_err(path);
+
+	addr2 = mremap(addr, ps * old_pages, ps * new_pages,
+		       MREMAP_MAYMOVE);
+
+	if (expected_error != 0) {
+		if (addr2 != MAP_FAILED) {
+			ksft_print_msg("Expected error %d, but mremap unexpectedly succeeded\n",
+				       expected_error);
+			rc = KSFT_FAIL;
+		} else if (errno != expected_error) {
+			ksft_print_msg("Expected error %d, got %s(%d)\n",
+				       expected_error, strerror(errno), errno);
+			rc = KSFT_FAIL;
+		} else {
+			ksft_print_msg("%s/%s: Handled expected error path (errno=%d)\n",
+				       __func__, tcase->name, expected_error);
+		}
+	} else if (addr2 == MAP_FAILED) {
+		ksft_print_msg("mremap shrink failed unexpectedly: %s\n",
+			       strerror(errno));
+		rc = KSFT_FAIL;
+	} else {
+		ksft_print_msg("%s/%s step successful\n", __func__, tcase->name);
+	}
+
+	/* clean up */
+	if (munmap(addr2 == MAP_FAILED ? addr : addr2,
+		   addr2 == MAP_FAILED ? ps * old_pages : ps * new_pages)) {
+		ksft_print_msg("munmap failed: %s\n", strerror(errno));
+		rc = KSFT_FAIL;
+	}
+
+out:
+	if (fd >= 0) {
+		close(fd);
+		if (tcase->pathname && strstr(tcase->pathname, "XXXXXX"))
+			unlink(pb);
+	}
+
+	ksft_test_result_report(rc, "%s:%s\n", __func__, tcase->name);
+	return rc;
+}
+
+int main(int argc, char **argv)
+{
+	int res = KSFT_PASS;
+	int i;
+
+	ps = sysconf(_SC_PAGESIZE);
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(mremap_cases) + 2);
+
+	munmap_shrink_test();
+	mremap_shrink_test();
+
+	for (i = 0; i < (int)ARRAY_SIZE(mremap_cases); i++) {
+		if (run_mremap_test(&mremap_cases[i]) == KSFT_FAIL)
+			res = KSFT_FAIL;
+	}
+
+	if (res == KSFT_PASS)
+		ksft_finished();
+
+	ksft_exit_fail();
+}
-- 
2.43.0

Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Johannes Berg]

On Sat, 2026-09-26 at 10:08 +0900, Hajime Tazaki wrote:
> Architectures lacks MMU doesn't support fork(2) syscall and only

nit: Architectures lacking MMU don't support the fork(2) syscall ...

Not sure where this should be merged? I guess selftests would make most
sense, but you can't actually test it out before the UML nommu changes,
so that doesn't work too well right now?

johannes

Re: [PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[David Hildenbrand (Arm)]

On 9/26/26 03:08, Hajime Tazaki wrote:
> The kselftest runner currently uses `cd -` to restore its working
> directory after running a test.
> 
> This is not supported by the minimal BusyBox hush shell used by some
> NOMMU targets. Store the original directory explicitly and restore it
> with a quoted path instead.
> 
> This also avoids printing the directory change performed by `cd -` and
> handles paths containing whitespace correctly.
> 
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Will Drewry <wad@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Brendan Jackman <brendan.jackman@linux.dev>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: "Ricardo B. Marliere" <rbm@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: linux-mm@kvack.org
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Lorenzo Stoakes (ARM)]

On Mon, Sep 28, 2026 at 09:44:49AM +0200, Johannes Berg wrote:
> On Sat, 2026-09-26 at 10:08 +0900, Hajime Tazaki wrote:
> > Architectures lacks MMU doesn't support fork(2) syscall and only
>
> nit: Architectures lacking MMU don't support the fork(2) syscall ...
>
> Not sure where this should be merged? I guess selftests would make most
> sense, but you can't actually test it out before the UML nommu changes,
> so that doesn't work too well right now?

I seem to recall Hajime saying he tested this on an actual nommu
device/virtualised equivalent so nommu UML isn't strictly necessary (though very
nice to have!)

I think I saw something fly by that implied it might be coming in 7.4 is that
so? :)

>
> johannes

--
Cheers, Lorenzo

Re: [PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[Lorenzo Stoakes (ARM)]

On Sat, Sep 26, 2026 at 10:08:17AM +0900, Hajime Tazaki wrote:
> The kselftest runner currently uses `cd -` to restore its working
> directory after running a test.
>
> This is not supported by the minimal BusyBox hush shell used by some
> NOMMU targets. Store the original directory explicitly and restore it
> with a quoted path instead.
>
> This also avoids printing the directory change performed by `cd -` and
> handles paths containing whitespace correctly.
>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Will Drewry <wad@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Brendan Jackman <brendan.jackman@linux.dev>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: "Ricardo B. Marliere" <rbm@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: linux-mm@kvack.org
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

Looks fine to me so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  tools/testing/selftests/kselftest/runner.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
> index 311811dc55a0..8fc1018d6fec 100644
> --- a/tools/testing/selftests/kselftest/runner.sh
> +++ b/tools/testing/selftests/kselftest/runner.sh
> @@ -130,6 +130,7 @@ run_one()
>  				return $KSFT_FAIL
>  			fi
>  		fi
> +		OLDDIR=$(pwd)
>  		cd `dirname $TEST` > /dev/null
>  		(((( tap_timeout "$cmd" 2>&1; echo $? >&3) |
>  			tap_prefix >&4) 3>&1) |
> @@ -147,7 +148,7 @@ run_one()
>  		*)
>  			ktap_test_fail "$TEST_HDR_MSG # exit=$rc";;
>  		esac
> -		cd - >/dev/null
> +		cd "$OLDDIR" >/dev/null
>  	fi
>
>  	return $rc
> --
> 2.43.0
>

--
Cheers, Lorenzo

Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Lorenzo Stoakes (ARM)]

On Sat, Sep 26, 2026 at 10:08:18AM +0900, Hajime Tazaki wrote:
> Architectures lacks MMU doesn't support fork(2) syscall and only
> vfork(2) is available with limitations.  Thus, we cannot run kselftest
> on nommu architecture as is.
>
> This commit addresses this issue with the following changes:
>
> - on test run stage, avoid calling timeout command when NOMMU=1 variable
>   added to environmental variable, since timeout command uses fork
>   syscall which nommu platform doesn't support.
> - describe the difference of nommu tests in the document.
>
> So command line to build/execute tests for nommu should be like below:
>
>  $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu
>  $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
>  $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p \
>    -c nommu
>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Will Drewry <wad@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Brendan Jackman <brendan.jackman@linux.dev>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: "Ricardo B. Marliere" <rbm@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: linux-mm@kvack.org
> Cc: linux-doc@vger.kernel.org
> Closes: https://sashiko.dev/#/patchset/20260813063401.1786548-1-thehajime%40gmail.com
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

>
> --
>
> v2 => v3
> - remove unnecessary modification
> - new target is moved from TARGETS=mm/nommu to TARGETS=nommu
> - rename CONFIG_NOMMU to NOMMU to avoid confusion to kernel config
>
> rfc => v2
> - reformat ktap header, reported by Sashiko review
> - https://lore.kernel.org/linux-mm/20260825015945.141739-2-thehajime@gmail.com/
>
> rfc: https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/
> ---
>  Documentation/dev-tools/kselftest.rst       | 14 ++++++++++++++
>  tools/testing/selftests/kselftest/runner.sh |  6 +++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst
> index 64c0ec7428a2..c35b819947b7 100644
> --- a/Documentation/dev-tools/kselftest.rst
> +++ b/Documentation/dev-tools/kselftest.rst
> @@ -230,6 +230,20 @@ section::
>
>  .. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress
>
> +Build and test on nommu target
> +==============================
> +
> +If you (cross-)build kselftests for nommu targets, or run tests on nommu targets, use
> +``NOMMU=1`` as a make variable/environment setting to tell build system to do the additional
> +checks.  These nommu targets may differ in several ways, such as not supporting fork(2) or
> +using musl or another libc.  Set this variable to apply the necessary build and test adjustments.
> +
> +::
> +
> +  $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu  # <= build-only
> +  $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
> +  $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p -c nommu
> +
>  Contributing new tests
>  ======================
>
> diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
> index 8fc1018d6fec..95b5ebb8bbb9 100644
> --- a/tools/testing/selftests/kselftest/runner.sh
> +++ b/tools/testing/selftests/kselftest/runner.sh
> @@ -38,8 +38,12 @@ tap_prefix()
>
>  tap_timeout()
>  {
> +	# nommu doesn't support timeout command (missing fork(2))
> +	if [ "$NOMMU" = "1" ] ; then
> +		echo "timeout isn't supported for NOMMU"
> +		$1
>  	# Make sure tests will time out if utility is available.
> -	if [ -x /usr/bin/timeout ] ; then
> +	elif [ -x /usr/bin/timeout ] ; then
>  		/usr/bin/timeout --foreground "$kselftest_timeout" \
>  			/usr/bin/timeout "$kselftest_timeout" $1
>  	else
> --
> 2.43.0
>

--
Cheers, Lorenzo

Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Johannes Berg]

On Mon, 2026-09-28 at 12:00 +0100, Lorenzo Stoakes (ARM) wrote:
> > Not sure where this should be merged? I guess selftests would make most
> > sense, but you can't actually test it out before the UML nommu changes,
> > so that doesn't work too well right now?
> 
> I seem to recall Hajime saying he tested this on an actual nommu
> device/virtualised equivalent so nommu UML isn't strictly necessary (though very
> nice to have!)

Oh, I don't recall, but I guess that's plausibe.

> I think I saw something fly by that implied it might be coming in 7.4 is that
> so? :)

I did end up merging just about everything that was pending for
uml/next, so if we don't forget to send a pull request in the merge
window, or something equally catastrophic happens, yes ;-)

Sorry for the delay. The onslaught of LLMs means priority is elsewhere,
sadly.

johannes

Re: [PATCH v3 3/3] selftests/nommu: add nommu mmap and mremap behavior tests

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 1103 bytes --]

On Sat, Sep 26, 2026 at 10:08:19AM +0900, Hajime Tazaki wrote:
> Introduce a kselftest utility to validate memory mapping capabilities
> under nommu kernels, aligned with
> Documentation/admin-guide/mm/nommu-mmap.rst.

> +static int run_mapping_matrix_test(struct test_case_t *tcase)
> +{
> +	int fd;
> +	void *ptr;
> +	char path_buf[PATH_MAX];
> +	const char *path = tcase->pathname;
> +	int rc = KSFT_PASS;
> +	int expected_error;
> +
> +	ksft_print_msg("[RUN] Testing: %s\n", tcase->name);

> +		if (fd < 0) {
> +			ksft_test_result_skip("Failed to setup temp node: %s\n",
> +					      tcase->pathname);

Your test reports should use a consistant string when reporting the
result for a given test, that way tooling can tie results together
between different runs.  Report the diagnostic information with a
separate print.

> +	if (result == KSFT_PASS)
> +		ksft_finished();
> +
> +	ksft_exit_fail();
> +}

Just unconditionally call ksft_finshed(), it will check the counts of
reported tests and exit with an appropriate error code - you don't need
to manually collate the results in your test code.

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Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Lorenzo Stoakes (ARM)]

On Mon, Sep 28, 2026 at 02:32:50PM +0200, Johannes Berg wrote:
> On Mon, 2026-09-28 at 12:00 +0100, Lorenzo Stoakes (ARM) wrote:
> > > Not sure where this should be merged? I guess selftests would make most
> > > sense, but you can't actually test it out before the UML nommu changes,
> > > so that doesn't work too well right now?
> >
> > I seem to recall Hajime saying he tested this on an actual nommu
> > device/virtualised equivalent so nommu UML isn't strictly necessary (though very
> > nice to have!)
>
> Oh, I don't recall, but I guess that's plausibe.
>
> > I think I saw something fly by that implied it might be coming in 7.4 is that
> > so? :)
>
> I did end up merging just about everything that was pending for
> uml/next, so if we don't forget to send a pull request in the merge
> window, or something equally catastrophic happens, yes ;-)

Awesome, thanks! :)

>
> Sorry for the delay. The onslaught of LLMs means priority is elsewhere,
> sadly.

Yeah understood, onslaught has reached all areas of the kernel it seems...

>
> johannes

--
Cheers, Lorenzo

Re: [PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[Pedro Falcato]

On Sat, Sep 26, 2026 at 10:08:17AM +0900, Hajime Tazaki wrote:
> The kselftest runner currently uses `cd -` to restore its working
> directory after running a test.
> 
> This is not supported by the minimal BusyBox hush shell used by some
> NOMMU targets. Store the original directory explicitly and restore it
> with a quoted path instead.
> 
> This also avoids printing the directory change performed by `cd -` and
> handles paths containing whitespace correctly.
> 
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Will Drewry <wad@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Brendan Jackman <brendan.jackman@linux.dev>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: "Ricardo B. Marliere" <rbm@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: linux-mm@kvack.org
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

NACK.

https://pubs.opengroup.org/onlinepubs/009695099/utilities/cd.html

-
When a hyphen is used as the operand, this shall be equivalent to the command:
cd "$OLDPWD" && pwd

which changes to the previous working directory and then writes its name.


If you're running selftests on !POSIX compliant shells, that's a
you-issue. Fix the shell, or use something decent.


-- 
Pedro

Re: [PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[Pedro Falcato]

On Mon, Sep 28, 2026 at 06:27:42PM +0100, Pedro Falcato wrote:
> On Sat, Sep 26, 2026 at 10:08:17AM +0900, Hajime Tazaki wrote:
> > The kselftest runner currently uses `cd -` to restore its working
> > directory after running a test.
> > 
> > This is not supported by the minimal BusyBox hush shell used by some
> > NOMMU targets. Store the original directory explicitly and restore it
> > with a quoted path instead.
> > 
> > This also avoids printing the directory change performed by `cd -` and
> > handles paths containing whitespace correctly.
> > 
> > Cc: Shuah Khan <shuah@kernel.org>
> > Cc: Kees Cook <kees@kernel.org>
> > Cc: Andy Lutomirski <luto@amacapital.net>
> > Cc: Will Drewry <wad@chromium.org>
> > Cc: Mark Brown <broonie@kernel.org>
> > Cc: Brendan Jackman <brendan.jackman@linux.dev>
> > Cc: Hangbin Liu <liuhangbin@gmail.com>
> > Cc: "Ricardo B. Marliere" <rbm@suse.com>
> > Cc: linux-kselftest@vger.kernel.org
> > Cc: linux-um@lists.infradead.org
> > Cc: linux-mm@kvack.org
> > Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
> 
> NACK.
> 
> https://pubs.opengroup.org/onlinepubs/009695099/utilities/cd.html
> 
> -
> When a hyphen is used as the operand, this shall be equivalent to the command:
> cd "$OLDPWD" && pwd
> 
> which changes to the previous working directory and then writes its name.
> 
> 
> If you're running selftests on !POSIX compliant shells, that's a
> you-issue. Fix the shell, or use something decent.

... I realize I was a bit too aggressive but seriously, lets not support
broken software, please?

-- 
Pedro

Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

[Hajime Tazaki]

On Mon, 28 Sep 2026 16:44:49 +0900,
Johannes Berg wrote:
> 
> On Sat, 2026-09-26 at 10:08 +0900, Hajime Tazaki wrote:
> > Architectures lacks MMU doesn't support fork(2) syscall and only
> 
> nit: Architectures lacking MMU don't support the fork(2) syscall ...

ah, thanks.  will fix this line.

> Not sure where this should be merged? I guess selftests would make most
> sense, but you can't actually test it out before the UML nommu changes,
> so that doesn't work too well right now?

I think this can be used for other NOMMU architecture (riscv, arm,
m68k) if those are properly build so, it isn't intended for UML only
tests.


-- Hajime

Re: [PATCH v3 1/3] selftests: kselftest: avoid cd - in runner

[Hajime Tazaki]

On Tue, 29 Sep 2026 03:16:48 +0900,
Pedro Falcato wrote:
> 
> On Mon, Sep 28, 2026 at 06:27:42PM +0100, Pedro Falcato wrote:
> > On Sat, Sep 26, 2026 at 10:08:17AM +0900, Hajime Tazaki wrote:
> > > The kselftest runner currently uses `cd -` to restore its working
> > > directory after running a test.
> > > 
> > > This is not supported by the minimal BusyBox hush shell used by some
> > > NOMMU targets. Store the original directory explicitly and restore it
> > > with a quoted path instead.
> > > 
> > > This also avoids printing the directory change performed by `cd -` and
> > > handles paths containing whitespace correctly.
> > > 
> > > Cc: Shuah Khan <shuah@kernel.org>
> > > Cc: Kees Cook <kees@kernel.org>
> > > Cc: Andy Lutomirski <luto@amacapital.net>
> > > Cc: Will Drewry <wad@chromium.org>
> > > Cc: Mark Brown <broonie@kernel.org>
> > > Cc: Brendan Jackman <brendan.jackman@linux.dev>
> > > Cc: Hangbin Liu <liuhangbin@gmail.com>
> > > Cc: "Ricardo B. Marliere" <rbm@suse.com>
> > > Cc: linux-kselftest@vger.kernel.org
> > > Cc: linux-um@lists.infradead.org
> > > Cc: linux-mm@kvack.org
> > > Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
> > 
> > NACK.
> > 
> > https://pubs.opengroup.org/onlinepubs/009695099/utilities/cd.html
> > 
> > -
> > When a hyphen is used as the operand, this shall be equivalent to the command:
> > cd "$OLDPWD" && pwd
> > 
> > which changes to the previous working directory and then writes its name.
> > 
> > 
> > If you're running selftests on !POSIX compliant shells, that's a
> > you-issue. Fix the shell, or use something decent.
> 
> ... I realize I was a bit too aggressive but seriously, lets not support
> broken software, please?

thanks for the comments.

no, your comment makes 100% sense to me.
under fork-less environment, we have less options but I agree that
this should be addressed in a shell implementation.

I will try to fix a busybox shell and drop this patch from next spin.

-- Hajime

Re: [PATCH v3 3/3] selftests/nommu: add nommu mmap and mremap behavior tests

[Hajime Tazaki]

On Mon, 28 Sep 2026 21:34:15 +0900,
Mark Brown wrote:

> > +	ksft_print_msg("[RUN] Testing: %s\n", tcase->name);
> 
> > +		if (fd < 0) {
> > +			ksft_test_result_skip("Failed to setup temp node: %s\n",
> > +					      tcase->pathname);
> 
> Your test reports should use a consistant string when reporting the
> result for a given test, that way tooling can tie results together
> between different runs.  Report the diagnostic information with a
> separate print.
> 
> > +	if (result == KSFT_PASS)
> > +		ksft_finished();
> > +
> > +	ksft_exit_fail();
> > +}
> 
> Just unconditionally call ksft_finshed(), it will check the counts of
> reported tests and exit with an appropriate error code - you don't need
> to manually collate the results in your test code.

thanks for the comments, and I understand all of them.   I will revise
those in next spin.

-- Hajime