[Intel-gfx] [PATCH v3] drm/i915/userptr: Disallow wrapping GTT into a userptr

[Chris Wilson]

On Wed, Mar 08, 2017 at 01:46:35PM +0000, Chris Wilson wrote:
> On Wed, Mar 08, 2017 at 01:28:31PM +0000, Tvrtko Ursulin wrote:
> > Okay risking more embarrassing misses, but is this not a false
> > negative? Userptr created from an equal or smaller than the GTT
> > mapping would not trigger this return false for some reason?
> 
> I was thinking about the case where the vma is far to the right of addr,
> where it started past end. However, that is now protected by checking
> vm_start > addr for the first vma. I didn't want a false positive, but
> yeah this should now be a false negative for a single GTT vma spanning
> the userptr. Weird that gem_userptr_blits didn't catch that case :|

Ah, added the boundary tests to gem_userptr_blits/invalid-gtt-mapping
and by printk confirmed hitting the bug you pointed out. However, the
igt still passes because we defer to the worker and that generates the
EFAULT. Catching it as a real error is proving difficult, needs Michal's
machinery on top of the overlap of neighbouring vma.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre