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