[no subject]

later,
chris

---------- Forwarded message ----------
Date: Tue, 24 Feb 2004 09:50:02 -0600
From: richard.brunner at amd.com
To: linux-kernel at vger.kernel.org
Subject: RE: IOMMUs was Re: Intel vs AMD x86-64


> -----Original Message-----
&gt; From: Andi Kleen [<a  rel="nofollow" href="mailto:ak";>mailto:ak</a> at suse.de] 

 
&gt; On Opteron the IOMMU code (ab)uses the built in AGPv3 GART in 
&gt; the CPU, which 
&gt; was originally intended for AGP. AMD converted it to be able 
&gt; to remap PCI especially for Linux, which I think deserves applause.
&gt; 
&gt; It works surprisingly well even though it was not designed as 
&gt; a real IOMMU. Of course one of the main advantages of a real 
&gt; IOMMU - preventing arbitary memory corruption from broken 
&gt; devices - is lost because the remapping table is just a hole 
&gt; in the memory. I'm 
&gt; secretly hoping that when there is more support for Linux at 
&gt; chipset vendors they will someday add a bit to isolate all 
&gt; traffic that doesn't go through the GART from the main 
&gt; memory. This way you could get a much more reliable system 
&gt; that can tolerate broken PCI devices at a moderate 
&gt; performance penalty.

Andi is being modest. It was he and Andrea Arcangeli who convinced 
me we had a problem. We found a way to trick the AGP
GART hardware into helping, and then they turned it into a 
&quot;real&quot; solution and helped us work the warts out of the BIOS 
to enable it.

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