[Xen-devel] PCI Passthrough using GART on AMD CPUs?

[Jeff Williams <alcander@xxxxxx>]

Hey everyone,

I realize that people asking about PCI passthrough has been thoroughly beaten to
death many a time, however I couldn't find the answer to these questions
anywhere (and I'd really like to know :P) so please just bare with me.

I know the GART built into AMD chipsets can act as a "mini IOMMU" and do DMA
translation but not protection/isolation. However, last I checked PCI
passthrough only worked on Xen 3.2 (unstable) if a VT-d supporting chipset was
detected.

So what I wanted to know:

1) If PCI passthrough can be done using GART, then is this being worked on? Also
can PCI hotplug work as with VT-d?
2) Are there any technological limitations which prevent the GART from being
used with PCI passthrough or is this just not coded?
2) If it is not coded, is it a matter of someone not wanting to do this or is it
a matter of such a patch never being merged into mainline because of potential
stability issues due to lack of isolation?

I would like to know since AMD's real IOMMU won't be in chipsets until 2010 and
you can't get features like SLI on Intel's chipsets. If I can use the GART on a
Phenom say, then I can get a nVidia SLI board and have the benefits of the more
advanced features already present in the Phenom like RVI.

What do you guys think? I really appreciate your work - keep it up!

Jeff


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