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xen-devel
Re: [Xen-devel] Real-mode bug with AMD, gPXE, and 32-bit rep movs
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To: |
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] Real-mode bug with AMD, gPXE, and 32-bit rep movs |
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From: |
Tim Deegan <Tim.Deegan@xxxxxxxxxx> |
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Date: |
Thu, 26 Mar 2009 14:54:46 +0000 |
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Cc: |
George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Christoph Egger <Christoph.Egger@xxxxxxx>, "Huang2, Wei" <Wei.Huang2@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx> |
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Thu, 26 Mar 2009 07:55:16 -0700 |
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At 14:43 +0000 on 26 Mar (1238078627), Keir Fraser wrote:
> Your assertion that it causes GP on Intel is weird. We should be running in
> the emulator already since for the movs to 0x200000 to work we must be
> running in big real mode (i.e., one of the segment registers has a limit
> greater than 0xffff) and so we cannot be emulating that by running the guest
> in vm86 mode.
We do use vm86 mode for big-real-mode; we just clip the segment limits
to 16 bits and carry on, since almost all instructions don't use the big
segments. Then when we take a fault for the A32 REP MOVS with the
>16-bit offset we go into the emulator and it does the right thing.
Cheers,
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]
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