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Re: [Xen-users] Re: IOMMU capable hardware

  • To: "Igor Chubin" <igor@xxxxxxx>
  • From: "David Stone" <unclestoner@xxxxxxxxx>
  • Date: Sun, 16 Dec 2007 12:04:02 -0500
  • Cc: Mark Williamson <mark.williamson@xxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Joop Boonen <joop_boonen@xxxxxx>
  • Delivery-date: Sun, 16 Dec 2007 09:04:35 -0800
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Hi, I have been doing some significant experimentation with Intel's
IOMMU (VT-d) so I can answer your questions.

 * Yes, real IOMMUs (at least Intel's VT-d) are available on the
market today, both as loose motherboards and in OEM systems.  For
details see /docs/misc/vtd.txt in the Xen source.  To repeat what is
in that file:
  1) For VT-d enabling work on Xen, we have been using development
  systems using following Intel motherboards:
      - DQ35MP
      - DQ35JO
  2) As far as we know, following OEM systems also has vt-d enabled.
  Feel free to add others as they become available.
    - HP Compaq:  DC7800
This is very recent...I think the motherboards only became generally
available this spring.  Anyway I ordered a Dell Optiplex 755 and it
does indeed have VT-d and it works with Xen.
  * I'm not sure about AMD's IOMMU...my impression is that it is
currently not generally available, and/or there is less support in
  * If your motherboard/chipset supports VT-d, you will see it in the
BIOS configuration (it will probably be turned off by default).
Again, unless you motherboard is very new or acquired in a
non-standard way, it will _not_ have VT-d.
  * Support in Xen was introduced by Intel in 3.2, which is just now
getting ready to release.  On 3.2 (unstable) I've been able to get a
PCI NIC to pass through, but not a PCI Express graphics card (that
story is on another thread).  There _does_ seem to be testing of a PCI
Express NIC so I guess PCI Express is in general supported.
  * You are correct that open-source PV drivers for Windows DomUs are
just now under development and of course are being developed on a
per-device type basis.  IOMMU allows you to pass through an arbitrary
PCI device so you need neither PV drivers nor qemu emulation.  This
will presumaby perform well as you suggest, and more importantly it
allows you to use device types that qemu doesn't emulate!


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