[PATCH v2 0/6] selftests/liveupdate: add memfd tests

[PATCH v2 0/6] selftests/liveupdate: add memfd tests

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Hi,

This series adds some tests for memfd preservation across a live update.
Currently memfd is only tested indirectly via luo_kexec_simple or
luo_multi_session. Add a dedicated test suite for it.

Patches 1 and 2 are preparatory, adding base framework and helpers, and
the other patches each add a test. Some of the code is taken from the
libluo patches [0] I sent a while ago.

[0] https://lore.kernel.org/linux-mm/20250723144649.1696299-33-pasha.tatashin@soleen.com/

Changes in v2:
- Drop LIVEUPDATE_DEV since it isn't used.
- Split luo_fd and stage declaration on separate lines.
- Split all 2-stage tests into helper function for each test.
- Fix wording and argument order when LUO_DEVICE fails to open.
- Rename verify_fd_content() to verify_fd_content_read().
- Advance buffer pointer in {read,write}_size().
- Add a check to make sure current working directory is not on a tmpfs
  mount. If so, skip the tests since saved data files will be lost.
- Rename RANDOM_DATA_FILE and RANDOM_DATA_FILE_FALLOCATE to
  MEMFD_DATA_FS_COPY and FALLOCATE_DATA_FS_COPY respectively. Also
  update the file names to reflect this naming convention.
- Collect R-bys.

Regards,
Pratyush Yadav

Pratyush Yadav (Google) (6):
  selftests/liveupdate: add framework for memfd tests
  selftests/liveupdate: add helper functions for memfd tests
  selftests/liveupdate: add test for memfd content preservation
  selftests/liveupdate: add test for zero-size memfd preservation
  selftests/liveupdate: add test for operations on a preserved memfd
  selftests/liveupdate: add fallocate test for memfd

 tools/testing/selftests/liveupdate/Makefile   |   2 +
 .../testing/selftests/liveupdate/luo_memfd.c  | 355 ++++++++++++++++++
 .../selftests/liveupdate/luo_test_utils.c     | 189 +++++++++-
 .../selftests/liveupdate/luo_test_utils.h     |  10 +
 4 files changed, 555 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/liveupdate/luo_memfd.c


base-commit: 98ddd87f9704ef2fc837ec2ca38877c364d8dada
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 1/6] selftests/liveupdate: add framework for memfd tests

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Currently memfd preservation using LUO is only tested indirectly via the
luo_multi_session or luo_kexec_simple tests. Their main purpose is to
test other live update functionality.

Add a framework for writing memfd tests. The framework hooks into the
kselftest harness, but adds some things on top to make it suitable for
live update.

The LUO FD (/dev/liveupdate) can only be opened by one process at a
time. Each test runs in its own process. This means the LUO FD must be
owned by the main process and shared to children. main() opens the LUO
FD and shares it to child runners using a global variable.

Live update tests run in two stages. One before kexec and one after.
Detect the stage using a special state session. If the session is
present, it means the test is in post-kexec state.

Additionally, take in an optional --stage argument that lets callers
specify expected stage. This is useful as a safety net to catch LUO core
failures. If LUO core fails to preserve the state session properly, this
option can help detect this and fail early. Since the option is not
recognized by the kselftest harness, remove it from argv before calling
test_harness_run().

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 tools/testing/selftests/liveupdate/Makefile   |  1 +
 .../testing/selftests/liveupdate/luo_memfd.c  | 78 +++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 tools/testing/selftests/liveupdate/luo_memfd.c

diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
index 080754787ede..051daae55eec 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -6,6 +6,7 @@ TEST_GEN_PROGS += liveupdate
 
 TEST_GEN_PROGS_EXTENDED += luo_kexec_simple
 TEST_GEN_PROGS_EXTENDED += luo_multi_session
+TEST_GEN_PROGS_EXTENDED += luo_memfd
 
 TEST_FILES += do_kexec.sh
 
diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
new file mode 100644
index 000000000000..47d2c3163b62
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_memfd.c
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (c) 2026, Google LLC.
+ * Pratyush Yadav (Google) <pratyush@kernel.org>
+ */
+
+/*
+ * Selftests for memfd preservation via LUO.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include <linux/liveupdate.h>
+
+#include "../kselftest.h"
+#include "../kselftest_harness.h"
+
+#include "luo_test_utils.h"
+
+#define STATE_SESSION_NAME "luo-state"
+#define STATE_MEMFD_TOKEN 1
+
+static int luo_fd = -1;
+static int stage;
+
+int main(int argc, char *argv[])
+{
+	int expected_stage = 0;
+	int session;
+
+	/*
+	 * The test takes an optional --stage argument. This lets callers
+	 * provide the expected stage, and if that doesn't match the test errors
+	 * out.
+	 *
+	 * Look for the stage. Since test_harness_run() doesn't recognize it,
+	 * once found, remove it from argv.
+	 */
+	for (int i = 1; i < argc; i++) {
+		if (strcmp(argv[i], "--stage") == 0) {
+			if (i + 1 < argc) {
+				expected_stage = atoi(argv[i + 1]);
+				memmove(&argv[i], &argv[i + 2], (argc - i - 1) * sizeof(char *));
+				argc -= 2;
+				i--;
+			} else {
+				ksft_exit_fail_msg("Option --stage requires an argument\n");
+			}
+		}
+	}
+
+	luo_fd = luo_open_device();
+	if (luo_fd < 0)
+		ksft_exit_skip("Failed to open %s (%s) device. Is LUO enabled?\n",
+			       LUO_DEVICE, strerror(errno));
+
+	session = luo_retrieve_session(luo_fd, STATE_SESSION_NAME);
+	if (session == -ENOENT)
+		stage = 1;
+	else if (session >= 0)
+		stage = 2;
+	else
+		ksft_exit_fail_perror("Failed to check for state session");
+
+	if (expected_stage && expected_stage != stage)
+		ksft_exit_fail_msg("Stage mismatch: expected %d, got %d\n",
+				   expected_stage, stage);
+
+	if (stage == 1)
+		create_state_file(luo_fd, STATE_SESSION_NAME, STATE_MEMFD_TOKEN, 2);
+
+	test_harness_run(argc, argv);
+}
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 2/6] selftests/liveupdate: add helper functions for memfd tests

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Add some helper functions that will be used by memfd tests. This moves
some of the complexity out of the test itself, which results in better
test readability and less code duplication.

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 .../selftests/liveupdate/luo_test_utils.c     | 189 +++++++++++++++++-
 .../selftests/liveupdate/luo_test_utils.h     |  10 +
 2 files changed, 198 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.c b/tools/testing/selftests/liveupdate/luo_test_utils.c
index 3c8721c505df..585add102ac2 100644
--- a/tools/testing/selftests/liveupdate/luo_test_utils.c
+++ b/tools/testing/selftests/liveupdate/luo_test_utils.c
@@ -1,8 +1,12 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 /*
- * Copyright (c) 2025, Google LLC.
+ * Copyright (c) 2025-2026, Google LLC.
  * Pasha Tatashin <pasha.tatashin@soleen.com>
+ * Pratyush Yadav (Google) <pratyush@kernel.org>
+ *
+ * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
+ * Pratyush Yadav <ptyadav@amazon.de>
  */
 
 #define _GNU_SOURCE
@@ -20,9 +24,192 @@
 #include <sys/stat.h>
 #include <errno.h>
 #include <stdarg.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
 
 #include "luo_test_utils.h"
 
+int cwd_is_tmpfs(void)
+{
+	struct statfs buf;
+
+	if (statfs(".", &buf) < 0)
+		return -errno;
+
+	return buf.f_type == TMPFS_MAGIC;
+}
+
+/* Read exactly specified size from fd. Any less results in error. */
+int read_size(int fd, char *buffer, size_t size)
+{
+	size_t remain = size;
+	ssize_t bytes_read;
+
+	while (remain) {
+		bytes_read = read(fd, buffer, remain);
+		if (bytes_read == 0)
+			return -ENODATA;
+		if (bytes_read < 0)
+			return -errno;
+
+		remain -= bytes_read;
+		buffer += bytes_read;
+	}
+
+	return 0;
+}
+
+/* Write exactly specified size from fd. Any less results in error. */
+int write_size(int fd, const char *buffer, size_t size)
+{
+	size_t remain = size;
+	ssize_t written;
+
+	while (remain) {
+		written = write(fd, buffer, remain);
+		if (written == 0)
+			return -EIO;
+		if (written < 0)
+			return -errno;
+
+		remain -= written;
+		buffer += written;
+	}
+
+	return 0;
+}
+
+int generate_random_data(char *buffer, size_t size)
+{
+	int fd, ret;
+
+	fd = open("/dev/urandom", O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = read_size(fd, buffer, size);
+	close(fd);
+	return ret;
+}
+
+int save_test_data(const char *filename, const char *buffer, size_t size)
+{
+	int fd, ret;
+
+	fd = open(filename, O_RDWR | O_CREAT, 0666);
+	if (fd < 0)
+		return -errno;
+
+	ret = write_size(fd, buffer, size);
+	fsync(fd);
+	close(fd);
+	return ret;
+}
+
+int load_test_data(const char *filename, char *buffer, size_t size)
+{
+	int fd, ret;
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = read_size(fd, buffer, size);
+	close(fd);
+	return ret;
+}
+
+/* Create and initialize a memfd with random data. */
+int create_random_memfd(const char *memfd_name, char *buffer, size_t size)
+{
+	int fd;
+	int ret;
+
+	fd = memfd_create(memfd_name, 0);
+	if (fd < 0)
+		return -errno;
+
+	ret = generate_random_data(buffer, size);
+	if (ret < 0) {
+		close(fd);
+		return ret;
+	}
+
+	if (write_size(fd, buffer, size) < 0) {
+		close(fd);
+		return -errno;
+	}
+
+	/* Reset file position to beginning */
+	if (lseek(fd, 0, SEEK_SET) < 0) {
+		close(fd);
+		return -errno;
+	}
+
+	return fd;
+}
+
+/*
+ * Make sure fd contains expected data up to size. Returns 0 on success, 1 on
+ * data mismatch, -errno on error.
+ */
+int verify_fd_content_read(int fd, const char *expected_data, size_t size)
+{
+	char *buffer;
+	int ret;
+
+	buffer = malloc(size);
+	if (!buffer)
+		return -ENOMEM;
+
+	/* Reset file position to beginning */
+	if (lseek(fd, 0, SEEK_SET) < 0) {
+		ret = -errno;
+		goto out;
+	}
+
+	ret = read_size(fd, buffer, size);
+	if (ret < 0)
+		goto out;
+
+	if (memcmp(buffer, expected_data, size) != 0) {
+		ret = 1;
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	free(buffer);
+	return ret;
+}
+
+/*
+ * Verify fd content using mmap. Returns 0 on success, 1 on data mismatch,
+ * -errno on error.
+ */
+int verify_fd_content_mmap(int fd, const char *expected_data, size_t size)
+{
+	char *mapped_mem;
+	int ret;
+
+	mapped_mem = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+	if (mapped_mem == MAP_FAILED)
+		return -errno;
+
+	/* ret = memcmp(mapped_mem, expected_data, size) ? 1 : 0; */
+	ret = 0;
+	for (size_t i = 0; i < size; i++) {
+		if (mapped_mem[i] != expected_data[i]) {
+			ret = 1;
+			break;
+		}
+	}
+
+	munmap(mapped_mem, size);
+	return ret;
+}
+
 int luo_open_device(void)
 {
 	return open(LUO_DEVICE, O_RDWR);
diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.h b/tools/testing/selftests/liveupdate/luo_test_utils.h
index 90099bf49577..a69dce2649b0 100644
--- a/tools/testing/selftests/liveupdate/luo_test_utils.h
+++ b/tools/testing/selftests/liveupdate/luo_test_utils.h
@@ -35,6 +35,16 @@ void restore_and_read_stage(int state_session_fd, int token, int *stage);
 
 void daemonize_and_wait(void);
 
+int cwd_is_tmpfs(void);
+int read_size(int fd, char *buffer, size_t size);
+int write_size(int fd, const char *buffer, size_t size);
+int generate_random_data(char *buffer, size_t size);
+int save_test_data(const char *filename, const char *buffer, size_t size);
+int load_test_data(const char *filename, char *buffer, size_t size);
+int create_random_memfd(const char *memfd_name, char *buffer, size_t size);
+int verify_fd_content_read(int fd, const char *expected_data, size_t size);
+int verify_fd_content_mmap(int fd, const char *expected_data, size_t size);
+
 typedef void (*luo_test_stage1_fn)(int luo_fd);
 typedef void (*luo_test_stage2_fn)(int luo_fd, int state_session_fd);
 
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 3/6] selftests/liveupdate: add test for memfd content preservation

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Add a selftest that makes sure the contents of a memfd are correctly
preserved across a live update. In stage 1, create a memfd and fill it
with random data, and preserve it. Save the random data to the file
system. This will be used by stage 2 to verify the contents are correct.

In stage 2, retrieve the memfd and compare its contents with the
contents saved on the file system.

Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 tools/testing/selftests/liveupdate/Makefile   |  1 +
 .../testing/selftests/liveupdate/luo_memfd.c  | 80 +++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
index 051daae55eec..8e2eb6500c07 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -13,6 +13,7 @@ TEST_FILES += do_kexec.sh
 include ../lib.mk
 
 CFLAGS += $(KHDR_INCLUDES)
+CFLAGS += -I$(top_srcdir)/tools/include
 CFLAGS += -Wall -O2 -Wno-unused-function
 CFLAGS += -MD
 
diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
index 47d2c3163b62..70eb96950f04 100644
--- a/tools/testing/selftests/liveupdate/luo_memfd.c
+++ b/tools/testing/selftests/liveupdate/luo_memfd.c
@@ -3,6 +3,9 @@
 /*
  * Copyright (c) 2026, Google LLC.
  * Pratyush Yadav (Google) <pratyush@kernel.org>
+ *
+ * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
+ * Pratyush Yadav <ptyadav@amazon.de>
  */
 
 /*
@@ -11,11 +14,14 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <unistd.h>
 
 #include <linux/liveupdate.h>
+#include <linux/sizes.h>
 
 #include "../kselftest.h"
 #include "../kselftest_harness.h"
@@ -25,9 +31,83 @@
 #define STATE_SESSION_NAME "luo-state"
 #define STATE_MEMFD_TOKEN 1
 
+#define MEMFD_DATA_SESSION_NAME "memfd_data_session"
+#define MEMFD_DATA_TOKEN 1
+#define MEMFD_DATA_BUFFER_SIZE SZ_1M
+#define MEMFD_DATA_FS_COPY "memfd_data_fs_copy.bin"
+
 static int luo_fd = -1;
 static int stage;
 
+static void memfd_data_stage_1(struct __test_metadata *_metadata)
+{
+	int fd, session;
+	char *buffer;
+	struct liveupdate_session_preserve_fd preserve_arg = { .size = sizeof(preserve_arg) };
+
+	buffer = malloc(MEMFD_DATA_BUFFER_SIZE);
+	ASSERT_NE(buffer, NULL);
+
+	session = luo_create_session(luo_fd, MEMFD_DATA_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	fd = create_random_memfd("memfd_data", buffer, MEMFD_DATA_BUFFER_SIZE);
+	ASSERT_GE(fd, 0);
+
+	ASSERT_EQ(save_test_data(MEMFD_DATA_FS_COPY, buffer, MEMFD_DATA_BUFFER_SIZE), 0);
+
+	preserve_arg.fd = fd;
+	preserve_arg.token = MEMFD_DATA_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_PRESERVE_FD, &preserve_arg), 0);
+
+	daemonize_and_wait();
+}
+
+static void memfd_data_stage_2(struct __test_metadata *_metadata)
+{
+	int fd, session;
+	char *buffer;
+	struct liveupdate_session_retrieve_fd retrieve_arg = { .size = sizeof(retrieve_arg) };
+
+	buffer = malloc(MEMFD_DATA_BUFFER_SIZE);
+	ASSERT_NE(buffer, NULL);
+
+	session = luo_retrieve_session(luo_fd, MEMFD_DATA_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	ASSERT_EQ(load_test_data(MEMFD_DATA_FS_COPY, buffer, MEMFD_DATA_BUFFER_SIZE), 0);
+
+	retrieve_arg.token = MEMFD_DATA_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_RETRIEVE_FD, &retrieve_arg), 0);
+	fd = retrieve_arg.fd;
+	ASSERT_GE(fd, 0);
+
+	ASSERT_EQ(verify_fd_content_read(fd, buffer, MEMFD_DATA_BUFFER_SIZE), 0);
+
+	ASSERT_EQ(luo_session_finish(session), 0);
+}
+
+/*
+ * Test that a memfd with its data is preserved across live update.
+ */
+TEST(memfd_data)
+{
+	if (cwd_is_tmpfs())
+		SKIP(return, "test saves data to rootfs, cannot run on tmpfs");
+
+	switch (stage) {
+	case 1:
+		memfd_data_stage_1(_metadata);
+		break;
+	case 2:
+		memfd_data_stage_2(_metadata);
+		break;
+	default:
+		TH_LOG("Unknown stage %d\n", stage);
+		ASSERT_FALSE(true);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	int expected_stage = 0;
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 4/6] selftests/liveupdate: add test for zero-size memfd preservation

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

A zero-size memfd is a special case of memfd preservation. It takes a
different path from normal both during preservation and during restore.
In the serialization structure, the number of folios is zero and the
vmalloc array with folios is empty. The restore logic should check for
this and make sure to not touch the invalid array.

Add a test to make sure this path works as expected. In stage 1, the
test creates and preserves a memfd without any data. In stage 2, the
test retrieves the memfd and makes sure it is still without data.

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 .../testing/selftests/liveupdate/luo_memfd.c  | 57 +++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
index 70eb96950f04..3ba0709f2c61 100644
--- a/tools/testing/selftests/liveupdate/luo_memfd.c
+++ b/tools/testing/selftests/liveupdate/luo_memfd.c
@@ -36,6 +36,9 @@
 #define MEMFD_DATA_BUFFER_SIZE SZ_1M
 #define MEMFD_DATA_FS_COPY "memfd_data_fs_copy.bin"
 
+#define ZERO_SESSION_NAME "zero_session"
+#define ZERO_MEMFD_TOKEN 1
+
 static int luo_fd = -1;
 static int stage;
 
@@ -108,6 +111,60 @@ TEST(memfd_data)
 	}
 }
 
+static void zero_memfd_stage_1(struct __test_metadata *_metadata)
+{
+	int zero_fd, session;
+	struct liveupdate_session_preserve_fd preserve_arg = { .size = sizeof(preserve_arg) };
+
+	session = luo_create_session(luo_fd, ZERO_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	zero_fd = memfd_create("zero_memfd", 0);
+	ASSERT_GE(zero_fd, 0);
+
+	preserve_arg.fd = zero_fd;
+	preserve_arg.token = ZERO_MEMFD_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_PRESERVE_FD, &preserve_arg), 0);
+
+	daemonize_and_wait();
+}
+
+static void zero_memfd_stage_2(struct __test_metadata *_metadata)
+{
+	int zero_fd, session;
+	struct liveupdate_session_retrieve_fd retrieve_arg = { .size = sizeof(retrieve_arg) };
+
+	session = luo_retrieve_session(luo_fd, ZERO_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	retrieve_arg.token = ZERO_MEMFD_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_RETRIEVE_FD, &retrieve_arg), 0);
+	zero_fd = retrieve_arg.fd;
+	ASSERT_GE(zero_fd, 0);
+
+	ASSERT_EQ(lseek(zero_fd, 0, SEEK_END), 0);
+
+	ASSERT_EQ(luo_session_finish(session), 0);
+}
+
+/*
+ * Test that a zero-sized memfd is preserved across live update.
+ */
+TEST(zero_memfd)
+{
+	switch (stage) {
+	case 1:
+		zero_memfd_stage_1(_metadata);
+		break;
+	case 2:
+		zero_memfd_stage_2(_metadata);
+		break;
+	default:
+		TH_LOG("Unknown stage %d\n", stage);
+		ASSERT_FALSE(true);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	int expected_stage = 0;
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 5/6] selftests/liveupdate: add test for operations on a preserved memfd

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Once a memfd is preserved, certain operations are not allowed to
succeed since they might make the state of the memfd inconsistent with
the serialized state. Among these operations are truncating or growing
the memfd. Writes and reads to already existing memfd should succeed.

Add a test that makes sure a preserved memfd does not allow growing or
shrinking, but does allow reads and writes to existing memory to go
thorough.

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 .../testing/selftests/liveupdate/luo_memfd.c  | 57 +++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
index 3ba0709f2c61..a1e9f34da006 100644
--- a/tools/testing/selftests/liveupdate/luo_memfd.c
+++ b/tools/testing/selftests/liveupdate/luo_memfd.c
@@ -39,6 +39,10 @@
 #define ZERO_SESSION_NAME "zero_session"
 #define ZERO_MEMFD_TOKEN 1
 
+#define PRESERVED_SESSION_NAME "preserved_session"
+#define PRESERVED_MEMFD_TOKEN 1
+#define PRESERVED_BUFFER_SIZE SZ_1M
+
 static int luo_fd = -1;
 static int stage;
 
@@ -165,6 +169,59 @@ TEST(zero_memfd)
 	}
 }
 
+/*
+ * Test that preserved memfd can't grow or shrink, but reads and writes still
+ * work.
+ */
+TEST(preserved_ops)
+{
+	char write_buffer[128] = {'A'};
+	int fd, session;
+	char *buffer;
+	struct liveupdate_session_preserve_fd preserve_arg = { .size = sizeof(preserve_arg) };
+
+	if (stage != 1)
+		SKIP(return, "test only expected to run on stage 1");
+
+	buffer = malloc(PRESERVED_BUFFER_SIZE);
+	ASSERT_NE(buffer, NULL);
+
+	session = luo_create_session(luo_fd, PRESERVED_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	fd = create_random_memfd("preserved_memfd", buffer, PRESERVED_BUFFER_SIZE);
+	ASSERT_GE(fd, 0);
+
+	preserve_arg.fd = fd;
+	preserve_arg.token = PRESERVED_MEMFD_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_PRESERVE_FD, &preserve_arg), 0);
+
+	/*
+	 * Write to the preserved memfd (within existing size). This should
+	 * work.
+	 */
+	ASSERT_GE(lseek(fd, 0, SEEK_SET), 0);
+	/* Write buffer is smaller than total file size. */
+	ASSERT_EQ(write_size(fd, write_buffer, sizeof(write_buffer)), 0);
+	ASSERT_EQ(verify_fd_content_read(fd, write_buffer, sizeof(write_buffer)), 0);
+
+	/* Try to grow the file using write(). */
+
+	/* First, seek to one byte behind initial size. */
+	ASSERT_GE(lseek(fd, PRESERVED_BUFFER_SIZE - 1, SEEK_SET), 0);
+
+	/*
+	 * Then, write some data that should increase the file size. This should
+	 * fail.
+	 */
+	ASSERT_LT(write_size(fd, write_buffer, sizeof(write_buffer)), 0);
+	ASSERT_EQ(lseek(fd, 0, SEEK_END), PRESERVED_BUFFER_SIZE);
+
+	/* Try to shrink the file using truncate. This should also fail. */
+	ASSERT_LT(ftruncate(fd, PRESERVED_BUFFER_SIZE / 2), 0);
+	ASSERT_EQ(lseek(fd, 0, SEEK_END), PRESERVED_BUFFER_SIZE);
+}
+
 int main(int argc, char *argv[])
 {
 	int expected_stage = 0;
-- 
2.53.0.1213.gd9a14994de-goog

[PATCH v2 6/6] selftests/liveupdate: add fallocate test for memfd

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

When memory is added to a memfd via fallocate(), it does not get zeroed
immediately. This is tracked by the absence of the uptodate folio flag.
Initially, memfd preservation simply saved the folio flags at preserve
time. This led to a bug, where all writes to un-initialized fallocated
memory after preserve were lost after live update. This is fixed by
commit 50d7b4332f27 ("mm: memfd_luo: always make all folios uptodate").

Add a test that fallocates some memory in a memfd, preserves it, writes
to it. Then in stage 2 it verifies the written content is still present.

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 .../testing/selftests/liveupdate/luo_memfd.c  | 83 +++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
index a1e9f34da006..bc6ab063363f 100644
--- a/tools/testing/selftests/liveupdate/luo_memfd.c
+++ b/tools/testing/selftests/liveupdate/luo_memfd.c
@@ -43,6 +43,11 @@
 #define PRESERVED_MEMFD_TOKEN 1
 #define PRESERVED_BUFFER_SIZE SZ_1M
 
+#define FALLOCATE_SESSION_NAME "fallocate_session"
+#define FALLOCATE_MEMFD_TOKEN 1
+#define FALLOCATE_BUFFER_SIZE SZ_1M
+#define FALLOCATE_DATA_FS_COPY "fallocate_data_fs_copy.bin"
+
 static int luo_fd = -1;
 static int stage;
 
@@ -222,6 +227,84 @@ TEST(preserved_ops)
 	ASSERT_EQ(lseek(fd, 0, SEEK_END), PRESERVED_BUFFER_SIZE);
 }
 
+static void fallocate_memfd_stage_1(struct __test_metadata *_metadata)
+{
+	int fd, session;
+	char *buffer;
+	struct liveupdate_session_preserve_fd preserve_arg = { .size = sizeof(preserve_arg) };
+
+	buffer = malloc(FALLOCATE_BUFFER_SIZE);
+	ASSERT_NE(buffer, NULL);
+
+	session = luo_create_session(luo_fd, FALLOCATE_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	fd = memfd_create("fallocate_memfd", 0);
+	ASSERT_GE(fd, 0);
+
+	/* Fallocate memory but do not write to it yet */
+	ASSERT_EQ(fallocate(fd, 0, 0, FALLOCATE_BUFFER_SIZE), 0);
+
+	preserve_arg.fd = fd;
+	preserve_arg.token = FALLOCATE_MEMFD_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_PRESERVE_FD, &preserve_arg), 0);
+
+	/* Now write to it after preserving */
+	ASSERT_GE(generate_random_data(buffer, FALLOCATE_BUFFER_SIZE), 0);
+	ASSERT_EQ(save_test_data(FALLOCATE_DATA_FS_COPY, buffer, FALLOCATE_BUFFER_SIZE), 0);
+
+	ASSERT_GE(lseek(fd, 0, SEEK_SET), 0);
+	ASSERT_EQ(write_size(fd, buffer, FALLOCATE_BUFFER_SIZE), 0);
+
+	daemonize_and_wait();
+}
+
+static void fallocate_memfd_stage_2(struct __test_metadata *_metadata)
+{
+	int fd, session;
+	char *buffer;
+	struct liveupdate_session_retrieve_fd retrieve_arg = { .size = sizeof(retrieve_arg) };
+
+	buffer = malloc(FALLOCATE_BUFFER_SIZE);
+	ASSERT_NE(buffer, NULL);
+
+	session = luo_retrieve_session(luo_fd, FALLOCATE_SESSION_NAME);
+	ASSERT_GE(session, 0);
+
+	ASSERT_EQ(load_test_data(FALLOCATE_DATA_FS_COPY, buffer, FALLOCATE_BUFFER_SIZE), 0);
+
+	retrieve_arg.token = FALLOCATE_MEMFD_TOKEN;
+	ASSERT_GE(ioctl(session, LIVEUPDATE_SESSION_RETRIEVE_FD, &retrieve_arg), 0);
+	fd = retrieve_arg.fd;
+	ASSERT_GE(fd, 0);
+
+	ASSERT_EQ(verify_fd_content_read(fd, buffer, FALLOCATE_BUFFER_SIZE), 0);
+
+	ASSERT_EQ(luo_session_finish(session), 0);
+}
+
+/*
+ * Test that an fallocated memfd is preserved across live update and can be
+ * written to after being preserved.
+ */
+TEST(fallocate_memfd)
+{
+	if (cwd_is_tmpfs())
+		SKIP(return, "test saves data to rootfs, cannot run on tmpfs");
+
+	switch (stage) {
+	case 1:
+		fallocate_memfd_stage_1(_metadata);
+		break;
+	case 2:
+		fallocate_memfd_stage_2(_metadata);
+		break;
+	default:
+		TH_LOG("Unknown stage %d\n", stage);
+		ASSERT_FALSE(true);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	int expected_stage = 0;
-- 
2.53.0.1213.gd9a14994de-goog

Re: [PATCH v2 0/6] selftests/liveupdate: add memfd tests

[Andrew Morton]

On Fri,  3 Apr 2026 19:40:06 +0000 Pratyush Yadav <pratyush@kernel.org> wrote:

> This series adds some tests for memfd preservation across a live update.
> Currently memfd is only tested indirectly via luo_kexec_simple or
> luo_multi_session. Add a dedicated test suite for it.
> 
> Patches 1 and 2 are preparatory, adding base framework and helpers, and
> the other patches each add a test. Some of the code is taken from the
> libluo patches [0] I sent a while ago.

Look like a nice series and it comes well-reviewed.  Maybe my "we're
all full" policy-making should have a selftests escape clause...

I see that the malignant gaze of Sauron's eye fell upon your work:
	https://sashiko.dev/#/patchset/20260403194014.3704180-1-pratyush@kernel.org

Re: [PATCH v2 0/6] selftests/liveupdate: add memfd tests

[Pasha Tatashin]

On Fri, Apr 3, 2026 at 6:08 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri,  3 Apr 2026 19:40:06 +0000 Pratyush Yadav <pratyush@kernel.org> wrote:
>
> > This series adds some tests for memfd preservation across a live update.
> > Currently memfd is only tested indirectly via luo_kexec_simple or
> > luo_multi_session. Add a dedicated test suite for it.
> >
> > Patches 1 and 2 are preparatory, adding base framework and helpers, and
> > the other patches each add a test. Some of the code is taken from the
> > libluo patches [0] I sent a while ago.
>
> Look like a nice series and it comes well-reviewed.  Maybe my "we're
> all full" policy-making should have a selftests escape clause...

LOL. I noticed Sashiko is uncharacteristically lenient toward
selftests; I guess it sees a use for them as well.
>
> I see that the malignant gaze of Sauron's eye fell upon your work:
>         https://sashiko.dev/#/patchset/20260403194014.3704180-1-pratyush@kernel.org

Re: [PATCH v2 0/6] selftests/liveupdate: add memfd tests

[Pratyush Yadav]

On Fri, Apr 03 2026, Andrew Morton wrote:

> On Fri,  3 Apr 2026 19:40:06 +0000 Pratyush Yadav <pratyush@kernel.org> wrote:
>
>> This series adds some tests for memfd preservation across a live update.
>> Currently memfd is only tested indirectly via luo_kexec_simple or
>> luo_multi_session. Add a dedicated test suite for it.
>> 
>> Patches 1 and 2 are preparatory, adding base framework and helpers, and
>> the other patches each add a test. Some of the code is taken from the
>> libluo patches [0] I sent a while ago.
>
> Look like a nice series and it comes well-reviewed.  Maybe my "we're
> all full" policy-making should have a selftests escape clause...
>
> I see that the malignant gaze of Sauron's eye fell upon your work:
> 	https://sashiko.dev/#/patchset/20260403194014.3704180-1-pratyush@kernel.org

Nothing escapes His Eye...

It does raise some good points for patch 2. I'll send a v3 shortly. It
would be great if this series can go in with this merge window. Since
these are only minor bugfixes and no fundamental changes, I'll keep the
R-by.

-- 
Regards,
Pratyush Yadav