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

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

Joanna,

RMRR memory ranges specified memory ranges that might be used for BIOS 
initiated DMA's for USB and integrated graphics devices.  These ranges are set 
by the BIOS.

Do they stay the same across different platforms?

Allen

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Joanna Rutkowska
Sent: Thursday, May 13, 2010 7:14 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] feature suggestion: DMAR table emulation for Xen

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 bugs?).

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.

joanna.


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