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To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        "Tvrtko Ursulin" <tursulin@ursulin.net>,
        Intel-gfx@lists.freedesktop.org
From: Chris Wilson <chris@chris-wilson.co.uk>
In-Reply-To: <005d683d-9f72-cb01-152f-4ccef0bbfd8b@linux.intel.com>
Cc: linux-kernel@vger.kernel.org
References: <20170731185512.20010-5-tvrtko.ursulin@linux.intel.com>
 <20170905102403.18463-1-tvrtko.ursulin@linux.intel.com>
 <150469489418.28581.10979037821117823587@mail.alporthouse.com>
 <005d683d-9f72-cb01-152f-4ccef0bbfd8b@linux.intel.com>
Message-ID: <150470157212.5486.15223573670024117741@mail.alporthouse.com>
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Subject: Re: [Intel-gfx] [PATCH v2 5/5] tools/testing/scatterlist: Test new
 __sg_alloc_table_from_pages
Date: Wed, 06 Sep 2017 13:39:32 +0100
Sender: linux-kernel-owner@vger.kernel.org
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Quoting Tvrtko Ursulin (2017-09-06 13:10:57)
> 
> On 06/09/2017 11:48, Chris Wilson wrote:
> > All ascending. Interesting challenge for 3,2,1,0; it can be coalesced,
> > we just don't. I wonder if we are missing some like that. But for the
> 
> Hm, how do you think descending pages could be coalesced? By 
> re-arranging the pages? But that would break everything, do I don't get it.

Wishful thinking; I wasn't considering the order inside the object, just
their physical addresses.
> 
> > moment, 0, 2, 1, would be a good addition to the above set.
> > 
> > Is there any value in checking overflows in this interface?
> 
> Overflows as in size > num_pages * PAGE_SIZE as passed in to 
> __sg_alloc_table_from_pages ? It is not checked in the implementation at 
> the moment and it looks it is harmless.

Just thinking aloud if there was a way to get a mult/add overflow. That
we do page size coalescing, the only avenue is from a buggy max_seg.

Going back to the makefile, perhaps add the magic for ubsan as well?
-fsanitize=address -fsanitize=undefined
-Chris