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Re: [Xen-devel] deleting mtrrs in dom0

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] deleting mtrrs in dom0
From: Kurt Garloff <kurt@xxxxxxxxxx>
Date: Sun, 27 Mar 2005 01:03:55 +0100
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Hi Keir,

On Thu, Mar 24, 2005 at 06:26:44PM +0000, Keir Fraser wrote:
> It's been hacked just enough to get X working, but the /proc semantics 
> haven't been given much thought. The problem is that reading /proc/mtrr 
> tells you what the real physical MTRRs contain, but these registers 
> weren't initialised by domain0 but by Xen, during SMP bootstrap. So 
> when you attempt to delete them you will probably find error messages 
> in /var/log/messages saying 'reg1 has count=0'.

I thought the MTRRs have been set by the BIOS, not Xen.

The MTRRs are not set to my satisfaction, that's why I'd like to change

> There are a few possible fixes, one being to let domain0 get staright 
> at the MTRRs after it has booted, but this needs great care -- 
> the registers have to be carefully synchronised across all physical 
> CPUs to avoid memory deadlocks.
Obviously, Linux has code to do that -- under Xen it unfortunately
only sees a subset of the CPUs, though.

Kurt Garloff                   <kurt@xxxxxxxxxx>             [Koeln, DE]
Physics:Plasma modeling <garloff@xxxxxxxxxxxxxxxxxxx> [TU Eindhoven, NL]
Linux: SUSE Labs (Director)    <garloff@xxxxxxx>            [Novell Inc]

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