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 08:06:00 -0700
Message-ID: <20140326150600.GA4519@bwidawsk.net>
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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>
List-Id: intel-gfx@lists.freedesktop.org

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.

> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
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-- 
Ben Widawsky, Intel Open Source Technology Center