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Re: [Xen-devel] Real-mode bug with AMD, gPXE, and 32-bit rep movs

To: Christoph Egger <Christoph.Egger@xxxxxxx>
Subject: Re: [Xen-devel] Real-mode bug with AMD, gPXE, and 32-bit rep movs
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Thu, 26 Mar 2009 16:31:27 +0000
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, "Huang2, Wei" <Wei.Huang2@xxxxxxx>
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At 16:24 +0000 on 26 Mar (1238084646), Christoph Egger wrote:
> I think it's #2. Look at the #GP causes in APM 
> Volume 2 for MOVSx: the only one in real mode is if the address 
> exceeded a data segment limit.  And the comment from Deegan about 
> clipping segment limits to 16 bits makes me think that the clipping is 
> happening on AMD machines and it shouldn't be.

That particular clipping happens in vmx.c so I certainly hope it doesn't
get called on AMD machines. :)  But yes, it's likely that some
big-real-mode segment state has got lost somewhere.

Tim.

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

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