Re: [PATCH] drm/i915: Add OACONTROL to the command parser register whitelist.

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Mar 26, 2014 at 09:03:58AM -0700, Volkin, Bradley D wrote:
> On Tue, Mar 25, 2014 at 11:21:23PM -0700, Daniel Vetter wrote:
> > On Tue, Mar 25, 2014 at 10:52:03PM -0700, Kenneth Graunke wrote:
> > > Mesa needs to be able to write OACONTROL in order to expose the
> > > Observability Architecture's performance counters via OpenGL.
> > > 
> > > Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
> > 
> > Thanks a lot for quickly tracking this down. Now when we've talked about
> > OA a little while ago we concluded that mesa should clear OACONTROL again
> > before the batch ends to make sure that userspace can't unduly observe
> > other processes. So I think it'd be worth to keep track of this with a
> > flag (set when OACONTROL is != 0 and reset when the batch loads 0). Also
> > we need to make sure that userspace sets the right OACONTROL modes (not
> > the one which streams into a global gtt buffer essentially). So some
> > additional work required.
> 
> Ok, I'll look into this. And apologies for not catching it myself.
> 
> If we have to do additional checks on fields within the registers then I
> suppose we'll need to limit those registers to MI_LOAD_REGISTER_IMM. That
> might require separate whitelists for MI_LOAD_REGISTER_IMM/MEM. Not the end
> of the world, but certainly some additional complexity.
> 
> For the resetting check, are there other registers in the current list that
> should have this tracking? If so, is 0 the reset value in all cases?
> 
> Let me know if there is anything in the works that would require additional
> registers or different uses of any registers.

Afaik there's no other register we want to reset again. I think all other
register we might want to clear are already part of hw contexts, so no
chance to leak stuff (e.g. the streamout registers and a end-of-pipe
counters). Ken might know of something I've missed.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch