Re: [PATCH v10 1/2] drm/i915/selftests: Prevent userspace mapping invalidation

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

On Fri May 8, 2026 at 10:02 AM CEST, Krzysztof Karas wrote:
> Migration testing in i915 assumes current task's address space
> to allocate new userspace mapping and uses it without
> registering real user for that address space in mm_struct.
> On single NUMA node setups PCI probe executes in the same
> context as userspace process calling the test (i915_selftest
> from IGT), but when multiple nodes are available, the PCI code
> puts probe into a kernel workqueue. This switches execution to
> a kworker, which does not have its own address space in
> userspace and must borrow such memory from another process, so
> "current->active_mm" is unknown at the start of the test.
>
> It was observed that mm->mm_users would occasionally be 0
> or drop to 0 during the test due to short delay between
> scheduling and executing work in forked process, which reaped
> userspace mappings, further leading to failures upon reading
> from userland memory.
>
> Prevent this by adding a PID parameter to a trusted task, so its
> mm struct may be used if needed.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14204
> Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>

-- 
Best regards,
Sebastian