[Intel-gfx] [PATCH] drm/i915/gtt: Setup guards in scratch page

[Chris Wilson]

Quoting Mika Kuoppala (2018-08-22 14:27:14)
> There have been cases where GPU engine has managed to run past
> execbuffer ending due to reasons unknown at that time:
> coherency problems, page table setup errors, hw glitches.

You are trading an obvious error for a subtle one; if userspace got its
batch wrong and doesn't die, the output will likely be wrong instead.

mesa/src/intel/tools/intel_sanitize_gpu for how userspace could do this
detection itself. You can intercept the execbuf, place a canary after
the batch and report if the canary gets written.
-Chris