[Intel-gfx] [PATCH] drm/i915: Check for get_pages instead of shmem (filp)

[Kristian Høgsberg]

On Fri, Feb 5, 2016 at 5:48 PM, Ben Widawsky
<benjamin.widawsky at intel.com> wrote:
> This behavior of checking for a shmem backed GEM object was introduced here:
> commit 4c914c0c7c787b8f730128a8cdcca9c50b0784ab
> Author: Brad Volkin <bradley.d.volkin at intel.com>
> Date:   Tue Feb 18 10:15:45 2014 -0800
>
>     drm/i915: Refactor shmem pread setup
>
> It is possible for an object to not be a shmem backed GEM object (for example
> userptr objects). An example of how we hit this failure can be found through
> copy_batch() in the command parser because we allocate a userptr object for the
> batch which contains privileged instructions. Userptr calls
> drm_gem_private_object_init() which explicitly sets the filp to none.
>
> It is equally feasible to simply remove the check altogether. You'll probably
> oops with get_pages somewhere, but that's okay IMO because this condition
> should be a driver bug, and not trigger-able by userspace. On this note, the
> function name could probably benefit from a change, but whatever.
>
> NOTE: I manually retyped this from a test machine. So I haven't even compiled
> this exact patch.
>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Kristian Høgsberg <krh at bitplanet.net>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Signed-off-by: Ben Widawsky <benjamin.widawsky at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 66b1705..a198928 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -489,7 +489,7 @@ int i915_gem_obj_prepare_shmem_read(struct drm_i915_gem_object *obj,
>
>         *needs_clflush = 0;
>
> -       if (!obj->base.filp)
> +       if (!obj->ops->get_pages)

Do we want to do what Chris did in
a2a4f916c2f344d4e596c875dd1e66764afec8b8 (on drm-intel-fixes):

+       if (WARN_ON((obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE) == 0))

?

>                 return -EINVAL;
>
>         if (!(obj->base.read_domains & I915_GEM_DOMAIN_CPU)) {
> --
> 2.7.0
>