Message-ID: <694fca1d-1584-45d9-9e50-5c219b9c7c94@lucifer.local>
Date: Mon, 30 Jun 2025 14:51:04 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: wang lian <lianux.mm@...il.com>
Cc: david@...hat.com, linux-mm@...ck.org, akpm@...ux-foundation.org,
        Liam.Howlett@...cle.com, brauner@...nel.org, gkwang@...x-info.com,
        jannh@...gle.com, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, p1ucky0923@...il.com,
        ryncsn@...il.com, shuah@...nel.org, sj@...nel.org, vbabka@...e.cz,
        zijing.zhang@...ton.me
Subject: Re: [PATCH] selftests/mm: Add process_madvise() tests

On Sat, Jun 28, 2025 at 07:39:45PM +0800, wang lian wrote:
> This patch adds tests for the process_madvise(), focusing on
> verifying behavior under various conditions including valid
> usage and error cases.

Hi sorry to be a pain, but I'm not sure this will get picked up properly like this.

Please resend this _not in reply to anything_ and with the subject:

[PATCH v2] selftests/mm: add process_madvise() tests

Note we do not capitalise the first letter in the subject line.

>
> Changelog v2:
> - Drop MADV_DONTNEED tests based on feedback
> - Focus solely on process_madvise() syscall
> - Improve error handling and structure
> - Add future-proof flag test
> - Style and comment cleanups
>

^ This is good but please put changelogs under the --- below, otherwise they end
up as part of the commit msg which isn't appropriate.

Once you do that we can review in reply to the new email.

Thanks!

> Signed-off-by: wang lian<lianux.mm@...il.com>
> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Suggested-by: David Hildenbrand <david@...hat.com>
> ---
>  tools/testing/selftests/mm/.gitignore     |   1 +
>  tools/testing/selftests/mm/Makefile       |   1 +
>  tools/testing/selftests/mm/process_madv.c | 414 ++++++++++++++++++++++
>  tools/testing/selftests/mm/run_vmtests.sh |   5 +
>  4 files changed, 421 insertions(+)
>  create mode 100644 tools/testing/selftests/mm/process_madv.c
>
> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
> index 911f39d634be..a8c3be02188c 100644
> --- a/tools/testing/selftests/mm/.gitignore
> +++ b/tools/testing/selftests/mm/.gitignore
> @@ -42,6 +42,7 @@ memfd_secret
>  hugetlb_dio
>  pkey_sighandler_tests_32
>  pkey_sighandler_tests_64
> +process_madv
>  soft-dirty
>  split_huge_page_test
>  ksm_tests
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 2352252f3914..725612e09582 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -86,6 +86,7 @@ TEST_GEN_FILES += mseal_test
>  TEST_GEN_FILES += on-fault-limit
>  TEST_GEN_FILES += pagemap_ioctl
>  TEST_GEN_FILES += pfnmap
> +TEST_GEN_FILES += process_madv
>  TEST_GEN_FILES += thuge-gen
>  TEST_GEN_FILES += transhuge-stress
>  TEST_GEN_FILES += uffd-stress
> diff --git a/tools/testing/selftests/mm/process_madv.c b/tools/testing/selftests/mm/process_madv.c
> new file mode 100644
> index 000000000000..73999c8e3570
> --- /dev/null
> +++ b/tools/testing/selftests/mm/process_madv.c
> @@ -0,0 +1,414 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +#define _GNU_SOURCE
> +#include "../kselftest_harness.h"
> +#include <errno.h>
> +#include <setjmp.h>
> +#include <signal.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mman.h>
> +#include <sys/syscall.h>
> +#include <unistd.h>
> +#include <sched.h>
> +#include <sys/pidfd.h>
> +#include "vm_util.h"
> +
> +#include "../pidfd/pidfd.h"
> +
> +/*
> + * Ignore the checkpatch warning, as per the C99 standard, section 7.14.1.1:
> + *
> + * "If the signal occurs other than as the result of calling the abort or raise
> + *  function, the behavior is undefined if the signal handler refers to any
> + *  object with static storage duration other than by assigning a value to an
> + *  object declared as volatile sig_atomic_t"
> + */
> +static volatile sig_atomic_t signal_jump_set;
> +static sigjmp_buf signal_jmp_buf;
> +
> +/*
> + * Ignore the checkpatch warning, we must read from x but don't want to do
> + * anything with it in order to trigger a read page fault. We therefore must use
> + * volatile to stop the compiler from optimising this away.
> + */
> +#define FORCE_READ(x) (*(volatile typeof(x) *)x)
> +
> +static void handle_fatal(int c)
> +{
> +	if (!signal_jump_set)
> +		return;
> +
> +	siglongjmp(signal_jmp_buf, c);
> +}
> +
> +FIXTURE(process_madvise)
> +{
> +	int pidfd;
> +	int flag;
> +};
> +
> +static void setup_sighandler(void)
> +{
> +	struct sigaction act = {
> +		.sa_handler = &handle_fatal,
> +		.sa_flags = SA_NODEFER,
> +	};
> +
> +	sigemptyset(&act.sa_mask);
> +	if (sigaction(SIGSEGV, &act, NULL))
> +		ksft_exit_fail_perror("sigaction");
> +}
> +
> +static void teardown_sighandler(void)
> +{
> +	struct sigaction act = {
> +		.sa_handler = SIG_DFL,
> +		.sa_flags = SA_NODEFER,
> +	};
> +
> +	sigemptyset(&act.sa_mask);
> +	sigaction(SIGSEGV, &act, NULL);
> +}
> +
> +FIXTURE_SETUP(process_madvise)
> +{
> +	self->pidfd = PIDFD_SELF;
> +	self->flag = 0;
> +	setup_sighandler();
> +};
> +
> +FIXTURE_TEARDOWN_PARENT(process_madvise)
> +{
> +	teardown_sighandler();
> +}
> +
> +static ssize_t sys_process_madvise(int pidfd, const struct iovec *iovec,
> +				   size_t vlen, int advice, unsigned int flags)
> +{
> +	return syscall(__NR_process_madvise, pidfd, iovec, vlen, advice, flags);
> +}
> +
> +/*
> + * Enable our signal catcher and try to read/write the specified buffer. The
> + * return value indicates whether the read/write succeeds without a fatal
> + * signal.
> + */
> +static bool try_access_buf(char *ptr, bool write)
> +{
> +	bool failed;
> +
> +	/* Tell signal handler to jump back here on fatal signal. */
> +	signal_jump_set = true;
> +	/* If a fatal signal arose, we will jump back here and failed is set. */
> +	failed = sigsetjmp(signal_jmp_buf, 0) != 0;
> +
> +	if (!failed) {
> +		if (write)
> +			*ptr = 'x';
> +		else
> +			FORCE_READ(ptr);
> +	}
> +
> +	signal_jump_set = false;
> +	return !failed;
> +}
> +
> +/* Try and read from a buffer, return true if no fatal signal. */
> +static bool try_read_buf(char *ptr)
> +{
> +	return try_access_buf(ptr, false);
> +}
> +
> +TEST_F(process_madvise, basic)
> +{
> +	const unsigned long pagesize = (unsigned long)sysconf(_SC_PAGESIZE);
> +	const int madvise_pages = 4;
> +	char *map;
> +	ssize_t ret;
> +	struct iovec vec[madvise_pages];
> +
> +	/*
> +	 * Create a single large mapping. We will pick pages from this
> +	 * mapping to advise on. This ensures we test non-contiguous iovecs.
> +	 */
> +	map = mmap(NULL, pagesize * 10, PROT_READ | PROT_WRITE,
> +		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +	ASSERT_NE(map, MAP_FAILED);
> +
> +	/* Fill the entire region with a known pattern. */
> +	memset(map, 'A', pagesize * 10);
> +
> +	/*
> +	 * Setup the iovec to point to 4 non-contiguous pages
> +	 * within the mapping.
> +	 */
> +	vec[0].iov_base = &map[0 * pagesize];
> +	vec[0].iov_len = pagesize;
> +	vec[1].iov_base = &map[3 * pagesize];
> +	vec[1].iov_len = pagesize;
> +	vec[2].iov_base = &map[5 * pagesize];
> +	vec[2].iov_len = pagesize;
> +	vec[3].iov_base = &map[8 * pagesize];
> +	vec[3].iov_len = pagesize;
> +
> +	ret = sys_process_madvise(PIDFD_SELF, vec, madvise_pages, MADV_DONTNEED,
> +				  0);
> +	if (ret == -1 && errno == EPERM)
> +		ksft_exit_skip(
> +			"process_madvise() unsupported or permission denied, try running as root.\n");
> +	else if (errno == EINVAL)
> +		ksft_exit_skip(
> +			"process_madvise() unsupported or parameter invalid, please check arguments.\n");
> +
> +	/* The call should succeed and report the total bytes processed. */
> +	ASSERT_EQ(ret, madvise_pages * pagesize);
> +
> +	/* Check that advised pages are now zero. */
> +	for (int i = 0; i < madvise_pages; i++) {
> +		char *advised_page = (char *)vec[i].iov_base;
> +
> +		/* Access should be successful (kernel provides a new page). */
> +		ASSERT_TRUE(try_read_buf(advised_page));
> +		/* Content must be 0, not 'A'. */
> +		ASSERT_EQ(*advised_page, 0);
> +	}
> +
> +	/* Check that an un-advised page in between is still 'A'. */
> +	char *unadvised_page = &map[1 * pagesize];
> +
> +	ASSERT_TRUE(try_read_buf(unadvised_page));
> +	ASSERT_EQ(*unadvised_page, 'A');
> +
> +	/* Cleanup. */
> +	ASSERT_EQ(munmap(map, pagesize * 10), 0);
> +}
> +
> +static long get_smaps_anon_huge_pages(pid_t pid, void *addr)
> +{
> +	char smaps_path[64];
> +	char *line = NULL;
> +	unsigned long start, end;
> +	long anon_huge_kb;
> +	size_t len;
> +	FILE *f;
> +	bool in_vma;
> +
> +	in_vma = false;
> +	sprintf(smaps_path, "/proc/%d/smaps", pid);
> +	f = fopen(smaps_path, "r");
> +	if (!f)
> +		return -1;
> +
> +	while (getline(&line, &len, f) != -1) {
> +		/* Check if the line describes a VMA range */
> +		if (sscanf(line, "%lx-%lx", &start, &end) == 2) {
> +			if ((unsigned long)addr >= start &&
> +			    (unsigned long)addr < end)
> +				in_vma = true;
> +			else
> +				in_vma = false;
> +			continue;
> +		}
> +
> +		/* If we are in the correct VMA, look for the AnonHugePages field */
> +		if (in_vma &&
> +		    sscanf(line, "AnonHugePages: %ld kB", &anon_huge_kb) == 1)
> +			break;
> +	}
> +
> +	free(line);
> +	fclose(f);
> +
> +	return (anon_huge_kb > 0) ? (anon_huge_kb * 1024) : 0;
> +}
> +
> +/**
> + * TEST_F(process_madvise, remote_collapse)
> + *
> + * This test deterministically validates process_madvise() with MADV_COLLAPSE
> + * on a remote process, other advices are difficult to verify reliably.
> + *
> + * The test verifies that a memory region in a child process, initially
> + * backed by small pages, can be collapsed into a Transparent Huge Page by a
> + * request from the parent. The result is verified by parsing the child's
> + * /proc/<pid>/smaps file.
> + */
> +TEST_F(process_madvise, remote_collapse)
> +{
> +	const unsigned long pagesize = (unsigned long)sysconf(_SC_PAGESIZE);
> +	pid_t child_pid;
> +	int pidfd;
> +	long huge_page_size;
> +	int pipe_info[2];
> +	ssize_t ret;
> +	struct iovec vec;
> +
> +	struct child_info {
> +		pid_t pid;
> +		void *map_addr;
> +	} info;
> +
> +	huge_page_size = default_huge_page_size();
> +	if (huge_page_size <= 0)
> +		ksft_exit_skip("Could not determine a valid huge page size.\n");
> +
> +	ASSERT_EQ(pipe(pipe_info), 0);
> +
> +	child_pid = fork();
> +	ASSERT_NE(child_pid, -1);
> +
> +	if (child_pid == 0) {
> +		char *map;
> +		size_t map_size = 2 * huge_page_size;
> +
> +		close(pipe_info[0]);
> +
> +		map = mmap(NULL, map_size, PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +		ASSERT_NE(map, MAP_FAILED);
> +
> +		/* Fault in as small pages */
> +		for (size_t i = 0; i < map_size; i += pagesize)
> +			map[i] = 'A';
> +
> +		/* Send info and pause */
> +		info.pid = getpid();
> +		info.map_addr = map;
> +		ret = write(pipe_info[1], &info, sizeof(info));
> +		ASSERT_EQ(ret, sizeof(info));
> +		close(pipe_info[1]);
> +
> +		pause();
> +		exit(0);
> +	}
> +
> +	close(pipe_info[1]);
> +
> +	/* Receive child info */
> +	ret = read(pipe_info[0], &info, sizeof(info));
> +	if (ret <= 0) {
> +		waitpid(child_pid, NULL, 0);
> +		ksft_exit_skip("Failed to read child info from pipe.\n");
> +	}
> +	ASSERT_EQ(ret, sizeof(info));
> +	close(pipe_info[0]);
> +	child_pid = info.pid;
> +
> +	pidfd = pidfd_open(child_pid, 0);
> +	ASSERT_GE(pidfd, 0);
> +
> +	/* Baseline Check from Parent's perspective */
> +	ASSERT_EQ(get_smaps_anon_huge_pages(child_pid, info.map_addr), 0);
> +
> +	vec.iov_base = info.map_addr;
> +	vec.iov_len = huge_page_size;
> +	ret = sys_process_madvise(pidfd, &vec, 1, MADV_COLLAPSE, 0);
> +	if (ret == -1) {
> +		if (errno == EINVAL)
> +			ksft_exit_skip(
> +				"PROCESS_MADV_ADVISE is not supported.\n");
> +		else if (errno == EPERM)
> +			ksft_exit_skip(
> +				"No process_madvise() permissions, try running as root.\n");
> +		goto cleanup;
> +	}
> +	ASSERT_EQ(ret, huge_page_size);
> +
> +	ASSERT_EQ(get_smaps_anon_huge_pages(child_pid, info.map_addr),
> +		  huge_page_size);
> +
> +	ksft_test_result_pass(
> +		"MADV_COLLAPSE successfully verified via smaps.\n");
> +
> +cleanup:
> +	/* Cleanup */
> +	kill(child_pid, SIGKILL);
> +	waitpid(child_pid, NULL, 0);
> +	if (pidfd >= 0)
> +		close(pidfd);
> +}
> +
> +/*
> + * Test process_madvise() with various invalid pidfds to ensure correct error
> + * handling. This includes negative fds, non-pidfd fds, and pidfds for
> + * processes that no longer exist.
> + */
> +TEST_F(process_madvise, invalid_pidfd)
> +{
> +	struct iovec vec;
> +	pid_t child_pid;
> +	ssize_t ret;
> +	int pidfd;
> +
> +	vec.iov_base = (void *)0x1234;
> +	vec.iov_len = 4096;
> +
> +	/* Using an invalid fd number (-1) should fail with EBADF. */
> +	ret = sys_process_madvise(-1, &vec, 1, MADV_DONTNEED, 0);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EBADF);
> +
> +	/*
> +	 * Using a valid fd that is not a pidfd (e.g. stdin) should fail
> +	 * with EBADF.
> +	 */
> +	ret = sys_process_madvise(STDIN_FILENO, &vec, 1, MADV_DONTNEED, 0);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EBADF);
> +
> +	/*
> +	 * Using a pidfd for a process that has already exited should fail
> +	 * with ESRCH.
> +	 */
> +	child_pid = fork();
> +	ASSERT_NE(child_pid, -1);
> +
> +	if (child_pid == 0)
> +		exit(0);
> +
> +	pidfd = pidfd_open(child_pid, 0);
> +	ASSERT_GE(pidfd, 0);
> +
> +	/* Wait for the child to ensure it has terminated. */
> +	waitpid(child_pid, NULL, 0);
> +
> +	ret = sys_process_madvise(pidfd, &vec, 1, MADV_DONTNEED, 0);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, ESRCH);
> +	close(pidfd);
> +}
> +
> +/*
> + * Test process_madvise() with an invalid flag value. Now we only support flag=0
> + * future we will use it support sync so reserve this test.
> + */
> +TEST_F(process_madvise, flag)
> +{
> +	const unsigned long pagesize = (unsigned long)sysconf(_SC_PAGESIZE);
> +	unsigned int invalid_flag;
> +	struct iovec vec;
> +	char *map;
> +	ssize_t ret;
> +
> +	map = mmap(NULL, pagesize, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1,
> +		   0);
> +	ASSERT_NE(map, MAP_FAILED);
> +
> +	vec.iov_base = map;
> +	vec.iov_len = pagesize;
> +
> +	invalid_flag = 0x80000000;
> +
> +	ret = sys_process_madvise(PIDFD_SELF, &vec, 1, MADV_DONTNEED,
> +				  invalid_flag);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +
> +	/* Cleanup. */
> +	ASSERT_EQ(munmap(map, pagesize), 0);
> +}
> +
> +TEST_HARNESS_MAIN
> \ No newline at end of file
> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
> index f96d43153fc0..5c28ebcf1ea9 100755
> --- a/tools/testing/selftests/mm/run_vmtests.sh
> +++ b/tools/testing/selftests/mm/run_vmtests.sh
> @@ -61,6 +61,8 @@ separated by spaces:
>  	ksm tests that require >=2 NUMA nodes
>  - pkey
>  	memory protection key tests
> +- process_madvise
> +	test process_madvise
>  - soft_dirty
>  	test soft dirty page bit semantics
>  - pagemap
> @@ -424,6 +426,9 @@ CATEGORY="hmm" run_test bash ./test_hmm.sh smoke
>  # MADV_GUARD_INSTALL and MADV_GUARD_REMOVE tests
>  CATEGORY="madv_guard" run_test ./guard-regions
>
> +# PROCESS_MADVISE TEST
> +CATEGORY="process_madv" run_test ./process_madv
> +
>  # MADV_DONTNEED and PROCESS_DONTNEED tests
>  CATEGORY="madv_dontneed" run_test ./madv_dontneed
>
> --
> 2.43.0
>

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