[Intel-gfx] [PATCH] drm/i915: Differentiate between aliasing-ppgtt and ggtt pinning

[Andi Shyti]

Hi Chris,

> > On Thu, Mar 26, 2020 at 02:27:27PM +0000, Chris Wilson wrote:
> > > Userptr causes lockdep to complain when we are using the aliasing-ppgtt
> > > (and ggtt, but for that it is rightfully so to complain about) in that
> > > when we revoke the userptr we take a mutex which we also use to revoke
> > > the mmaps. However, we only revoke mmaps for GGTT bindings and we never
> > > allow userptr to create a GGTT binding so the warning should be false
> > > and is simply caused by our conflation of the aliasing-ppgtt with the
> > > ggtt. So lets try treating the binding into the aliasing-ppgtt as a
> > > separate lockclass from the ggtt. The downside is that we are
> > > deliberately suppressing lockdep;s ability to warn us of cycles.
> >                                 ^^^^
> > typo
> > 
> > > 
> > > Closes: https://gitlab.freedesktop.org/drm/intel/issues/478
> > 
> > I'm not a big fan of links in commit messages, I think they would
> > be forbidden by law, but I'm not being picky on that.
> 
> I'm lazy, I take clickable links.
> 
> > I don't know, thogh, why your S-o-b is missing.
> 
> I felt uncomfortable with this hack, but it passes CI (but it may be
> suppressing too much -- I think the code is safe at the moment, but we
> may lose our sensitivity to future bugs).

We can only hope in CI critical cases are covered well enough...
in the worst case we can always revert it.

Andi