Re: [PATCH v4 5/5] selftests/mm: add UFFDIO_MOVE ioctl test

[Peter Xu <peterx@redhat.com>]

On Fri, Oct 27, 2023 at 05:38:15PM -0700, Suren Baghdasaryan wrote:
> Add tests for new UFFDIO_MOVE ioctl which uses uffd to move source
> into destination buffer while checking the contents of both after
> the move. After the operation the content of the destination buffer
> should match the original source buffer's content while the source
> buffer should be zeroed. Separate tests are designed for PMD aligned and
> unaligned cases because they utilize different code paths in the kernel.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  tools/testing/selftests/mm/uffd-common.c     |  24 ++++
>  tools/testing/selftests/mm/uffd-common.h     |   1 +
>  tools/testing/selftests/mm/uffd-unit-tests.c | 141 +++++++++++++++++++
>  3 files changed, 166 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
> index 69e6653ad255..98957fd788d8 100644
> --- a/tools/testing/selftests/mm/uffd-common.c
> +++ b/tools/testing/selftests/mm/uffd-common.c
> @@ -643,6 +643,30 @@ int copy_page(int ufd, unsigned long offset, bool wp)
>  	return __copy_page(ufd, offset, false, wp);
>  }
>  
> +int move_page(int ufd, unsigned long offset)
> +{
> +	struct uffdio_move uffdio_move;
> +
> +	if (offset >= nr_pages * page_size)
> +		err("unexpected offset %lu\n", offset);
> +	uffdio_move.dst = (unsigned long) area_dst + offset;
> +	uffdio_move.src = (unsigned long) area_src + offset;
> +	uffdio_move.len = page_size;
> +	uffdio_move.mode = UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
> +	uffdio_move.move = 0;
> +	if (ioctl(ufd, UFFDIO_MOVE, &uffdio_move)) {
> +		/* real retval in uffdio_move.move */
> +		if (uffdio_move.move != -EEXIST)
> +			err("UFFDIO_MOVE error: %"PRId64,
> +			    (int64_t)uffdio_move.move);
> +		wake_range(ufd, uffdio_move.dst, page_size);
> +	} else if (uffdio_move.move != page_size) {
> +		err("UFFDIO_MOVE error: %"PRId64, (int64_t)uffdio_move.move);
> +	} else
> +		return 1;
> +	return 0;
> +}
> +
>  int uffd_open_dev(unsigned int flags)
>  {
>  	int fd, uffd;
> diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h
> index 19930fd6682b..c9526b2cb6b3 100644
> --- a/tools/testing/selftests/mm/uffd-common.h
> +++ b/tools/testing/selftests/mm/uffd-common.h
> @@ -121,6 +121,7 @@ void wp_range(int ufd, __u64 start, __u64 len, bool wp);
>  void uffd_handle_page_fault(struct uffd_msg *msg, struct uffd_args *args);
>  int __copy_page(int ufd, unsigned long offset, bool retry, bool wp);
>  int copy_page(int ufd, unsigned long offset, bool wp);
> +int move_page(int ufd, unsigned long offset);
>  void *uffd_poll_thread(void *arg);
>  
>  int uffd_open_dev(unsigned int flags);
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index debc423bdbf4..89e9529ce941 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -1064,6 +1064,133 @@ static void uffd_poison_test(uffd_test_args_t *targs)
>  	uffd_test_pass();
>  }
>  
> +static void uffd_move_handle_fault(
> +	struct uffd_msg *msg, struct uffd_args *args)
> +{
> +	unsigned long offset;
> +
> +	if (msg->event != UFFD_EVENT_PAGEFAULT)
> +		err("unexpected msg event %u", msg->event);
> +
> +	if (msg->arg.pagefault.flags &
> +	    (UFFD_PAGEFAULT_FLAG_WP | UFFD_PAGEFAULT_FLAG_MINOR | UFFD_PAGEFAULT_FLAG_WRITE))
> +		err("unexpected fault type %llu", msg->arg.pagefault.flags);
> +
> +	offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
> +	offset &= ~(page_size-1);
> +
> +	if (move_page(uffd, offset))
> +		args->missing_faults++;
> +}
> +
> +static void uffd_move_test(uffd_test_args_t *targs)
> +{
> +	unsigned long nr;
> +	pthread_t uffd_mon;
> +	char c;
> +	unsigned long long count;
> +	struct uffd_args args = { 0 };
> +
> +	/* Prevent source pages from being mapped more than once */
> +	if (madvise(area_src, nr_pages * page_size, MADV_DONTFORK))
> +		err("madvise(MADV_DONTFORK) failure");
> +
> +	if (uffd_register(uffd, area_dst, nr_pages * page_size,
> +			  true, false, false))
> +		err("register failure");
> +
> +	args.handle_fault = uffd_move_handle_fault;
> +	if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
> +		err("uffd_poll_thread create");
> +
> +	/*
> +	 * Read each of the pages back using the UFFD-registered mapping. We
> +	 * expect that the first time we touch a page, it will result in a missing
> +	 * fault. uffd_poll_thread will resolve the fault by moving source
> +	 * page to destination.
> +	 */
> +	for (nr = 0; nr < nr_pages; nr++) {
> +		/* Check area_src content */
> +		count = *area_count(area_src, nr);
> +		if (count != count_verify[nr])
> +			err("nr %lu source memory invalid %llu %llu\n",
> +			    nr, count, count_verify[nr]);
> +
> +		/* Faulting into area_dst should move the page */
> +		count = *area_count(area_dst, nr);
> +		if (count != count_verify[nr])
> +			err("nr %lu memory corruption %llu %llu\n",
> +			    nr, count, count_verify[nr]);
> +
> +		/* Re-check area_src content which should be empty */
> +		count = *area_count(area_src, nr);
> +		if (count != 0)
> +			err("nr %lu move failed %llu %llu\n",
> +			    nr, count, count_verify[nr]);
> +	}
> +
> +	if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
> +		err("pipe write");
> +	if (pthread_join(uffd_mon, NULL))
> +		err("join() failed");
> +
> +	if (args.missing_faults != nr_pages || args.minor_faults != 0)
> +		uffd_test_fail("stats check error");
> +	else
> +		uffd_test_pass();
> +}
> +
> +static int prevent_hugepages(void)
> +{
> +	/* This should be done before source area is populated */
> +	if (madvise(area_src, nr_pages * page_size, MADV_NOHUGEPAGE)) {
> +		/* Ignore if CONFIG_TRANSPARENT_HUGEPAGE=n */
> +		if (errno != EINVAL)
> +			return -errno;
> +	}
> +	return 0;
> +}
> +
> +struct uffd_test_case_ops uffd_move_test_case_ops = {
> +	.post_alloc = prevent_hugepages,
> +};
> +
> +#define ALIGN_UP(x, align_to) \
> +	(__typeof__(x))((((unsigned long)(x)) + ((align_to)-1)) & ~((align_to)-1))
> +
> +static char *orig_area_src, *orig_area_dst;
> +static int pmd_align_areas(void)
> +{
> +	orig_area_src = area_src;
> +	orig_area_dst = area_dst;
> +	area_src = ALIGN_UP(area_src, page_size);
> +	area_dst = ALIGN_UP(area_dst, page_size);
> +	nr_pages--;
> +
> +	return 0;
> +}
> +
> +static void pmd_restore_areas(void)
> +{
> +	area_src = orig_area_src;
> +	area_dst = orig_area_dst;
> +	nr_pages++;
> +}

Please stop using more global variables.. uffd tests are even less
maintainable.

Maybe you can consider add a flag for uffd_test_ctx_init()?  For allocating
either small/thp/default?

> +
> +static int adjust_page_size(void)
> +{
> +	page_size = default_huge_page_size();

This is hacky too, currently page_size is the real page_size backing the
memory.

To make thp test simple, maybe just add one more test to MOVE a large chunk
to replace the thp test, which may contain a few thps?  It also doesn't
need to be fault based.

> +	nr_pages = UFFD_TEST_MEM_SIZE / page_size;
> +
> +	return 0;
> +}
> +
> +struct uffd_test_case_ops uffd_move_pmd_test_case_ops = {
> +	.pre_alloc = adjust_page_size,
> +	.post_alloc = pmd_align_areas,
> +	.pre_release = pmd_restore_areas,
> +};
> +
>  /*
>   * Test the returned uffdio_register.ioctls with different register modes.
>   * Note that _UFFDIO_ZEROPAGE is tested separately in the zeropage test.
> @@ -1141,6 +1268,20 @@ uffd_test_case_t uffd_tests[] = {
>  		.mem_targets = MEM_ALL,
>  		.uffd_feature_required = 0,
>  	},
> +	{
> +		.name = "move",
> +		.uffd_fn = uffd_move_test,
> +		.mem_targets = MEM_ANON,
> +		.uffd_feature_required = UFFD_FEATURE_MOVE,
> +		.test_case_ops = &uffd_move_test_case_ops,
> +	},
> +	{
> +		.name = "move-pmd",
> +		.uffd_fn = uffd_move_test,
> +		.mem_targets = MEM_ANON,
> +		.uffd_feature_required = UFFD_FEATURE_MOVE,
> +		.test_case_ops = &uffd_move_pmd_test_case_ops,
> +	},
>  	{
>  		.name = "wp-fork",
>  		.uffd_fn = uffd_wp_fork_test,
> -- 
> 2.42.0.820.g83a721a137-goog
> 

-- 
Peter Xu