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Re: [Xen-devel] [Patch] cpu synchronization while doing MTRR register up

To: Nitin A Kamble <nitin.a.kamble@xxxxxxxxx>
Subject: Re: [Xen-devel] [Patch] cpu synchronization while doing MTRR register update
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Wed, 5 Aug 2009 09:29:30 +0100
Cc: "asit.k.mallick@xxxxxxxxx" <asit.k.mallick@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, "suresh.b.siddha@xxxxxxxxx" <suresh.b.siddha@xxxxxxxxx>
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At 19:26 +0100 on 04 Aug (1249413981), Nitin A Kamble wrote:
> Processors starting with westmere are caching VMCS data for better VMX
> performance. These processors also has Hyper-threading support. With
> hyper-threading, when one thread's cache is disabled, it also disables
> cache for the sibling threads. And MTRR register updating procedure
> involves cache disabling. So if cpus are not synchronized, updating MTRR
> registers on a thread, results in the VMCS data from sibling threads
> becoming inaccessible, and it causes system failure.

What's the observed failure here?  Hang/crash on resume from S3?  Or
something more common?



Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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