[Xen-devel] IOMMU Domain for Dom0

[Alex Merritt <merritt.alex@xxxxxxxxx>]

Hello,

I'm looking to enable the NVIDIA CUDA driver/runtime stack to work in
Dom0 on Xen. I've contacted NVIDIA through various capacities and have
gotten replies essentially saying they cannot provide assistance, and
have been following the nvnews.com forums. However, now that I have
IOMMU-capable processors (with VT-d) and a version of Xen which can
successfully program this hardware, I am interested to determine if it
is possible to program the IOMMU *for* Dom0 (i.e. the target is Dom0,
not an HVM/pvops guest).

I have successfully been able to launch an HVM guest, passing a few
GPUs through. Installing an unmodified developer driver from NVIDIA
works using the standard method (no SYSSRC=/-OUT= or anything) and
CUDA applications execute as expected. Can this be done for Dom0,
achieving the same result without requiring any involvement from
NVIDIA or modifications to the driver?

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. My goal with this email is to get feedback
on two fronts: 1) is there a limitation due to the architecture,
meaning that as Dom0 is pvops it cannot use VT-d, or is it a
implementation addition to Xen that would be needed? 2) If the latter
is true (programming needed), how much effort (code/time) would
you/anyone estimate it would take to enable this to work, and could
you provide some starting pointers for me to do so? I am untrained
when it comes to the Xen sourcecode.

I'm using Xen 4.1.1 and pv-ops linux (not upstream) 2.6.32.40 on an
Intel X5660 with a Tylersburg chipset. My host OS is Fedora 13, but
that needn't be static.

I originally asked this on xen-users, but was informed this mailing
list would be better suited:
http://lists.xensource.com/archives/html/xen-users/2011-06/msg00451.html

Many thanks in advance!
Alex

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