On 1/15/21 4:56 PM, Chris Wilson wrote:
Quoting Jinoh Kang (2021-01-15 16:23:31)
If GUP-ineligible pages are passed to a GEM userptr object, -EFAULT is returned only when the object is actually bound.
The xf86-video-intel userspace driver cannot differentiate this condition, and marks the GPU as wedged.
The idea was to call gem_set_domain on the object to validate the pages after creation. I only did that for read-only... I did however make mesa use set-domain for validation.
Thanks for the info!
As a question how are you getting to call userptr on something that wasn't passed by SHM ipc?
Basically XShmAttachFd, which is not exposed on libX11.
This not only disables graphics acceleration but may also cripple other functions such as VT switch.
That should be a non-sequitur; certainly VT switch works without ever using the GPU.
Not that VT switch doesn't work; rather, there's some heavy graphic artifacts such as blank rectangles or part of window going completely transparent. I suppose that's another issue.
Solve this by "prefaulting" user pages on GEM object creation, testing whether all pages are eligible for get_user_pages() in the process. On failure, return -EFAULT so that userspace can fallback to software blitting.
See https://patchwork.freedesktop.org/series/33449/ for adding PROBE | POPULATE flags.
But we can just use set-domain.
So this patch was unnecessary. Thanks for the pointer as to how to patch the userspace.
-Chris