Re: [PATCH v6] drm/i915/selftests: Keep mock file open during unfaultable migrate with fill

[Sebastian Brzezinka <sebastian.brzezinka@intel.com>]

Hi Krzysztof,

On Wed Jan 14, 2026 at 5:04 PM CET, Krzysztof Karas wrote:
> igt_mmap_migrate() tests migration with various parameters.
> In one of the cases, where FILL and UNFAULTABLE flags are set,
> during first stages of this test, a mock file is opened in
> igt_mmap_offset(), which results in allocating GEM objects for
> page table structures and scratch in GPU mappable memory.
>
> Then, also in igt_mmap_offset(), the file is closed (fput) and
> the cleanup of these objects is scheduled on a delayed worqueue,
> which is designed to execute after unspecified amount of time.
>
> Next, the test calls igt_fill_mappable() to fill mappable GPU
> memory. At this point, three scenarios are possible
> (N = max size of GPU memory for this test in MiB):
>  1) the objects allocated for the mock file get cleaned up after
>     crucial part of the test is over, so the memory is full with
>     the 1 MiB they occupy and N - 1 MiB added by
>     igt_fill_mappable(), so the migration fails properly;
>  2) the object cleanup fires before igt_fill_mappable()
>     completes, so the whole memory is populated with N MiB from
>     igt_fill_mappable(), so migration fails as well;
>  3) the object cleanup is performed right after fill is done,
>     so only N - 1 MiB are in the mappable portion of GPU memory,
>     allowing the migration to succeed - we'd expect no space
>     left to perform migration, but an object was able to fit in
>     the remaining 1 MiB, which caused get_user() to succeed, so
>     a page fault did not fail.
>
> The test incorrectly assumes that the GPU mappable memory state
> is unchanging during the test. Amend this by keeping the mock
> file open until migration and page fault checking is complete.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13929
> Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Looks good to me.
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>

-- 
Best regards,
Sebastian