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RE: [Xen-devel] running {MS/free}-DOS under XEN

To: "Tomas Kovacik" <Tomas.Kovacik@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] running {MS/free}-DOS under XEN
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Thu, 10 May 2007 17:25:51 +0200
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Thread-topic: [Xen-devel] running {MS/free}-DOS under XEN

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Tomas Kovacik
> Sent: 10 May 2007 10:00
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] running {MS/free}-DOS under XEN
> Hi there.
> I was looking around for a log time but I did not find any 
> user who would be able to run MS-DOS or freeDOS under Xen. I 
> use vmlinuz-2.6.20-1.2316.fc5xen kernel and when I try to 
> boot MS-DOS 7.1 it freezes with message shown in attachement 
> 1. Also freeDOS freezes with message as in attachement2.
> I tried to install these two systems from the same iso image 
> under qemu and it went OK so it seems that XEN there is some 
> issue with XEN and DOS running together.

Which version of Xen is this ("xm info" will give you version numbers),
and is it an AMD or Intel processor you're using?

I have recently (and succcessfully) run MS-DOS 6.22c on an AMD-V capable
processor with xen-unstable, changeset circa 14800. I expect this will
work on the latest xen-3.1-testing version as well. Whether it works on
older versions, I'll let you figure out. 

On Intel processors, there is a potential problemm in that these
processors don't support native real-mode in virtualized mode. This
means that the guest has to trick around with "vm86-mode", which causes
problems particularly with dos-extenders that switch from real mode to
protected mode and back again [the real problem here is maintaining the
extended segment values that may have been set during the excursion to
protected mode - if there is no segment values "expected to survive" the
transition, it should work just fine to switch between modes on Intel
processors too]. 

> could somebody help me to run some version od DOS under XEN? 
> thank you very much.

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