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[Xen-devel] feature suggestion: DMAR table emulation for Xen

To: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] feature suggestion: DMAR table emulation for Xen
From: Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 13 May 2010 16:14:00 +0200
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As many people on this list realize, lots of machines that have VT-d in
hardware, effectively does not support VT-d because of broken BIOSes
that usually do not expose DMAR ACPI table at all (or do it with some

So, the idea is to implement dmar emulation for Xen. E.g. if we pass
certain boot option, e.g. emulate_chipset4_dmar, then Xen would read
DMAR table from the image hardcoded into the Xen hypervisor.

We could provide images for series 4 and 5 chipsets. I think there are
no differences in how DMAR table looks between various specific chipsets
from the same family (e.g. Q45 would be probably using the very same
DMAR as PM45). Can somebody from Intel confirm this?

Implementing such a feature would make it possible to use Xen w/ IOMMU
support on many newer machines that otherwise do not support it.


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