Re: [RFC v3 1/2] drm/i915/selftests: Add userspace PID parameter

[Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>]

Hi Krzysztof,

On Fri, 2026-04-03 at 09:00 +0000, Krzysztof Karas wrote:
> Currently, memory management tests using VMAs for object mapping
> are not guaranteed to execute in completely safe environment of
> user process in kernel context.
> 
> Since these tests may execute in kworker, for example on
> multi-cell NUMA systems, their process would not get its own
> userspace memory, so it'd borrow mm_struct from a process
> previously handled by the scheduler (current->active_mm).
> The test does not control the lifetime of that process and its
> address space, so on occasion it could borrow memory that is
> being cleaned up or that would be cleaned up during test
> execution.
> 
> Add a new parameter to i915 to let users running these tests
> pass a PID of trusted userspace process to ensure the mappings
> will always be utilized in a stable and predictable environment.
> 
> Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>

I would still prefer this combined with a part of next patch that uses the 
user provided PID for acquiring a missing current->mm, and the other part,
the one that skips selected test cases if current->mm is missing, split 
into a separate patch.  That way, both would be self-contained and could 
be reverted independently if needed.  But anyway,

Reviewed-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>


> ---
>  drivers/gpu/drm/i915/i915_selftest.h           | 1 +
>  drivers/gpu/drm/i915/selftests/i915_selftest.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_selftest.h b/drivers/gpu/drm/i915/i915_selftest.h
> index 72922028f4ba..e29ca298e7eb 100644
> --- a/drivers/gpu/drm/i915/i915_selftest.h
> +++ b/drivers/gpu/drm/i915/i915_selftest.h
> @@ -35,6 +35,7 @@ struct i915_selftest {
>  	unsigned long timeout_jiffies;
>  	unsigned int timeout_ms;
>  	unsigned int random_seed;
> +	unsigned int userspace_pid;
>  	char *filter;
>  	int mock;
>  	int live;
> diff --git a/drivers/gpu/drm/i915/selftests/i915_selftest.c b/drivers/gpu/drm/i915/selftests/i915_selftest.c
> index 8460f0a70d04..a1ccfde7380a 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_selftest.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_selftest.c
> @@ -507,6 +507,8 @@ void igt_hexdump(const void *buf, size_t len)
>  module_param_named(st_random_seed, i915_selftest.random_seed, uint, 0400);
>  module_param_named(st_timeout, i915_selftest.timeout_ms, uint, 0400);
>  module_param_named(st_filter, i915_selftest.filter, charp, 0400);
> +module_param_named(st_userspace_pid, i915_selftest.userspace_pid, uint, 0400);
> +MODULE_PARM_DESC(st_userspace_pid, "For usage in tests that map userspace memory and require address space with controllable lifetime.");
>  
>  module_param_named_unsafe(mock_selftests, i915_selftest.mock, int, 0400);
>  MODULE_PARM_DESC(mock_selftests, "Run selftests before loading, using mock hardware (0:disabled [default], 1:run tests then load driver, -1:run tests then leave dummy module)");