Re: IOMMUs was Re: Intel vs AMD x86-64

[Mike Fedyk]

On Tue, Feb 24, 2004 at 09:50:02AM -0600, richard.brunner@xxxxxxx wrote:
> 
> > -----Original Message-----
> > From: Andi Kleen [mailto:ak@xxxxxxx] 
> 
>  
> > On Opteron the IOMMU code (ab)uses the built in AGPv3 GART in 
> > the CPU, which 
> > was originally intended for AGP. AMD converted it to be able 
> > to remap PCI especially for Linux, which I think deserves applause.
> > 
> > It works surprisingly well even though it was not designed as 
> > a real IOMMU. Of course one of the main advantages of a real 
> > IOMMU - preventing arbitary memory corruption from broken 
> > devices - is lost because the remapping table is just a hole 
> > in the memory. I'm 
> > secretly hoping that when there is more support for Linux at 
> > chipset vendors they will someday add a bit to isolate all 
> > traffic that doesn't go through the GART from the main 
> > memory. This way you could get a much more reliable system 
> > that can tolerate broken PCI devices at a moderate 
> > 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 
> "real" solution and helped us work the warts out of the BIOS 
> to enable it.

Yowza!  Open source helping to make better processors.  :-D
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