Re: [PATCH v3 2/2] selftests/mm: add tests for UFFDIO_MOVE of a uffd-protected swap entry

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/26/26 14:41, Donggeun Yoo wrote:
> Move a swapped-out page out of a write-protected or RWP-protected area into
> a destination registered for missing faults only, and read pagemap bit 57
> at the destination.  The destination was never protected, so the bit must
> be clear.
> 
> Assisted-by: LLM
> Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
> ---
>  tools/testing/selftests/mm/uffd-unit-tests.c | 84 ++++++++++++++++++++
>  1 file changed, 84 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index ef9b3956bdcfd..580178630eded 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -2037,6 +2037,75 @@ static void uffd_move_pmd_split_test(uffd_global_test_opts_t *gopts, uffd_test_a
>  			      uffd_move_pmd_handle_fault);
>  }
>  
> +/*
> + * Moving a swapped-out page out of a write-protected or RWP-protected area
> + * must not carry the uffd bit into a destination registered for missing
> + * faults only: such a bit is never cleared afterwards, so pagemap keeps
> + * reporting the page as uffd-tracked.
> + *
> + * Needs a swap device; skipped if MADV_PAGEOUT cannot evict the page.
> + */
> +static void uffd_move_swap_test_common(uffd_global_test_opts_t *gopts,
> +				       bool rwp)
> +{
> +	unsigned long page_size = gopts->page_size;
> +	struct uffdio_move move = { };
> +	int pagemap_fd;
> +
> +	if (rwp) {
> +		if (uffd_register_rwp(gopts->uffd, gopts->area_src, page_size))
> +			err("register src failure");
> +	} else if (uffd_register(gopts->uffd, gopts->area_src, page_size,
> +				 false, true, false)) {
> +		err("register src failure");
> +	}

Why not combine it with the protection?


	if (rwp) {
		if (uffd_register_rwp(gopts->uffd, gopts->area_src, page_size))
			err("register src failure");
		rwprotect_range(gopts->uffd, (unsigned long)gopts->area_src,
				page_size, true);
	} else {
		if (uffd_register(gopts->uffd, gopts->area_src, page_size,
				 false, true, false))
			err("register src failure");
		wp_range(gopts->uffd, (unsigned long)gopts->area_src,
			 page_size, true);
	}


> +	if (uffd_register(gopts->uffd, gopts->area_dst, page_size,
> +			  true, false, false))
> +		err("register dst failure");
> +
> +	if (rwp)
> +		rwprotect_range(gopts->uffd, (unsigned long)gopts->area_src,
> +				page_size, true);
> +	else
> +		wp_range(gopts->uffd, (unsigned long)gopts->area_src,
> +			 page_size, true);
> +
> +	pagemap_fd = pagemap_open();

Why not do that at the very top?

	int pagemap_fd = pagemap_open();

> +	if (madvise(gopts->area_src, page_size, MADV_PAGEOUT))
> +		err("MADV_PAGEOUT");
> +	if (!pagemap_is_swapped(pagemap_fd, gopts->area_src)) {
> +		uffd_test_skip("MADV_PAGEOUT did not swap the page; is swap enabled?");
> +		goto out;
> +	}
> +
> +	move.dst = (unsigned long)gopts->area_dst;
> +	move.src = (unsigned long)gopts->area_src;
> +	move.len = page_size;

You can set that all already when initializing aboce

struct uffdio_move move = {
	.dst = (unsigned long)gopts->area_dst,
	[...]
};

> +	if (ioctl(gopts->uffd, UFFDIO_MOVE, &move))
> +		err("UFFDIO_MOVE");
BTW, why do we fail the entire test here instead of only this test case?

-- 
Cheers,

David