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RE: [Xen-devel] linux' X86_MSR config option

To: "Jan Beulich" <jbeulich@xxxxxxxxxx>, "Keir Fraser" <keir@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] linux' X86_MSR config option
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Wed, 30 May 2007 13:01:08 +0200
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Thread-topic: [Xen-devel] linux' X86_MSR config option

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Jan Beulich
> Sent: 30 May 2007 11:03
> To: Keir Fraser
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] linux' X86_MSR config option
> >>> Keir Fraser <keir@xxxxxxxxxxxxx> 30.05.07 11:53 >>>
> >On 30/5/07 10:52, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> >
> >> .. is out of sync on i386 and x86-64 - should it be 
> allowed on i386, or should
> >> it be suppressed on x86-64? Since Xen fails ill accesses, 
> I would assume
> >> enabling it on i386 is fine.
> >
> >Is this the MSRs-from-userland option? Should be safe to enable.
> Yes.
> >But probably fairly pointless?
> Not so for debugging purposes - I asked because I just now 
> needed it to read
> a BIOS-initialized MSR, and it's quite handy if you don't 
> have to reboot into a
> native kernel to do just this.

I'm looking at something similar: A tool that can say if SVM is
enabled/available or not, to be run in Dom0 or before installing Xen.
The same method (directly or indirectly) could also be used by
high-level tools to determine if it's viable to install/create HVM
virtual machines. 

This would certainly be "read only" accesses, as there's nothing much
that can be done if SVM is disabled by BIOS. 

> Jan
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