From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Widawsky <ben@bwidawsk.net>
Subject: Re: [PATCH] drm/i915: Prevent context obj from being
 corrupted
Date: Wed, 26 Mar 2014 08:07:58 -0700
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To: Daniel Vetter <daniel@ffwll.ch>
Cc: Ben Widawsky <benjamin.widawsky@linux.intel.com>, Intel GFX <intel-gfx@lists.freedesktop.org>
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On Wed, Mar 26, 2014 at 08:06:00AM -0700, Ben Widawsky wrote:
> On Wed, Mar 26, 2014 at 08:04:38AM +0100, Daniel Vetter wrote:
> > On Wed, Mar 26, 2014 at 07:24:16AM +0100, Daniel Vetter wrote:
> > > On Tue, Mar 25, 2014 at 07:01:50PM -0700, Ben Widawsky wrote:
> > > > While the context is not being used, we can make the PTEs invalid, so
> > > > nothing can accidentally corrupt it. Systems tend to have a lot of
> > > > trouble when the context gets corrupted.
> > > > 
> > > > NOTE: This is a slightly different patch than what I posted to Bugzilla.
> > > > 
> > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=75724
> > > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > > 
> > > We could stop the aliasing ppgtt binder from always binding into the
> > > ppgtt. Which is the bug I'm signed up to fix, and which probably curbs 99%
> > > of all potential corruption. The last 1% is the kernel getting his
> > > kmapping wrong ...
> > 
> > Actually your patch doesn't accomplish much, since MI_UPDATE_GTT only
> > updates the global gtt, not the aliasing ppgtt. Which means that userspace
> > batches can still happily stomp all over your precious context objects.
> > See comment #5 in that bug report:
> > 
> > https://bugs.freedesktop.org/show_bug.cgi?id=75724#c5
> > 
> > Cheers, Daniel
> 
> Quoting you from comment #5:
> "ctx objects should only be bound in the global gtt with aliasing
> ppgtt."
> 
> The bug was not present with full PPGTT.
> 

Oh, I see the confusion. I don't necessarily think it's userspace that's
corrupting this. I just want to prove it's *not* being corrupted.

-- 
Ben Widawsky, Intel Open Source Technology Center