[Xen-users] branch tracing and MSR usage

To:	xen-users@xxxxxxxxxxxxxxxxxxx
Subject:	[Xen-users] branch tracing and MSR usage
From:	"Ryan Gardner" <ryan@xxxxxxxxxx>
Date:	Fri, 19 Oct 2007 11:04:20 -0400
Delivery-date:	Fri, 19 Oct 2007 08:05:10 -0700
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Hi,

I'm a student working on a research project using xen, and part of
what we are doing requires the ability to use the branch tracing
facilities of the processor.  I.e. we need to be able to write to the
IA32_DEBUGCTL MSR and read from the Last Branch Record (LBR) stack
(the second of which it appears we can do).

We saw a thread discussing this:
http://lists.xensource.com/archives/html/xen-devel/2007-08/msg00198.html
.  However, it doesn't appear that the method was ever finalized, and
we were unable to find a patch.  Does such a patch exist, or is there
simple way we can read and write to the necessary MSRs in our VM?  Can
we just hack the xen code to set the correct bits in the VMCS MSR
bitmaps?  If so, where are those bitmaps set in the code?

Thanks a lot.

Ryan

(Sorry if this hit the list twice.  The one I sent yesterday didn't
appear to go through.)

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[Xen-users] branch tracing and MSR usage