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Re: [Xen-devel] [RFC][PATCH] Emulate instructions in vm86 mode

To: Bastian Blank <bastian@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC][PATCH] Emulate instructions in vm86 mode
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 08 Sep 2006 22:11:11 +0100
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On 8/9/06 21:58, "Bastian Blank" <bastian@xxxxxxxxxxxx> wrote:

>> Hmm, the code write 0 for this values to the exception frame in VM86
>> mode, lets check if this is the problem.
> It seems that this is the problem.
> The following patch always bounces traps in vm86 mode to the guest
> kernel and don't longer clears the segment register values in the
> exception frame.
> Signed-off-by: Bastian Blank <waldi@xxxxxxxxxx>

That is only on the 'failsafe' stackframe path. It is okay to write zero
values there because we already wrote the real values lower down on the
stack frame (at labels FLT7 to FLT10). In fact you probably shouldn't end up
taking the 'failsafe' path anyway, so the code you remove wouldn't normally
be executed at all unless something in the guest is buggy.

 -- Keir

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