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[Xen-users] IOMMU Domain for Dom0

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Alex Merritt <merritt.alex@xxxxxxxxx>
  • Date: Mon, 20 Jun 2011 22:17:56 -0600
  • Delivery-date: Mon, 20 Jun 2011 21:19:52 -0700
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>


I've been experimenting with VT-d supported PCI-passthrough in Xen for
HVM guests, and was wondering if it is possible to create an IOMMU
domain for Dom0 as well. I'm not sure if I'm asking the question
correctly, but to avoid changing a bare-metal driver for an I/O device
to translate system memory addresses used by a DMA engine, would I
instead be able to allow the IOMMU to transparently translate
addresses just like for guest VMs, but within Dom0? Some searching and
reading of the wiki pages on xen.org tells me the answer is "no". But
I cannot determine if this is purely because the implementation within
the VMM doesn't exist, or because it is that Dom0 is para-virtualized
and thus cannot use VT-d without VT-x. I'm suspecting it is not the
latter, as the VTdHowTo wiki page hints PV guests may use VT-d and the
Intel manual for VT-d describes OS developers may take advantage of
this extension.

My immediate interest is more to see if it "can be done" via a hack or
something, not necessarily whether it would make sense for Xen to
support this in the future.

I'm using Xen 4.1.1 and pv-ops linux (not upstream) on an
Intel X5660 with a Tylersburg chipset.


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