RE: [Xen-users] PCI Passthrough to VMX Guest

["M.A. Williamson" <maw48@xxxxxxxxx>]

> One of the problems with this is that the OS/Driver that supports the
> nVidia (or other graphics adapter) will need to actually know it's
> physical addresses in memory - something that it doesn't, because the
> HVM solution may well tell the OS that it's got 512MB of memory from 0
> to 512M, but it's ACTUALLY living at 512M to 1G. So when the graphics
> driver says "You have a bitmap at 128MB", it should actually say "You
> have a bitmap at 640MB". Until there's an IOMMU implementation, there's
> nothing we can do about this. 
OK, good point! Although IIRC, you guys have a solution for this on the way 
;-)
> So even if you COULD assign your PCI device to the DomU, it still
> wouldn't do the right thing... :-(
>
> So until then, there's a bit of a problem implementing any complex
> hardware support in a virtual machine. There may be ways to solve this,
> but they are non-trivial (and most like specific to the particular
> hardware...). 
I guess in principle we could port the PCI frontend to run in an unmodified 
guest... (?) It could then perform IOMMU functionality in software by 
hooking the right places in the DMA API (and arranging bounce buffering if 
necessary).
It's not entirely clear to me that this would be worth it, though.

Cheers,
Mark

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