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Re: [Qemu-devel] Re: xen is not working with qemu0.7/kqemu

From: Mark Williamson
Subject: Re: [Qemu-devel] Re: xen is not working with qemu0.7/kqemu
Date: Fri, 17 Jun 2005 15:23:15 +0100
User-agent: KMail/1.7.1

> >but of course, it will also kill the good performance
> >xen could have with a windows support (which already
> >worked, but is very unlikely to work in the future, as
> >it requires M$ to adapt their OS to the xen architecture)
> >
> >best,
> >Herbert
> Won't it be possible to adapt kqemu/qvm86/qemu to make it aware of the
> Xen architecture (i-e, "porting Qemu to xen") Please note that this is
> a purely rethorical question, as I don't know what it really involves.

Porting kqemu / qvm86 to run under Linux/Xen would seem to be the best way to 
run Windows under Xen right now.  Win4Lin also runs under Linux/Xen.

> On the other hand, Mark Williamson, one of the Xen dev pointed on Xen
> devel ML on a very interesting document from Microsoft
> (http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-08878
> It seems that MS will follow an approach similar to Xen for their
> future virtualization technology (maybe because MS research was
> involved in Xen's first steps)
> We can dream and hope that it will be possible to adapt Xen to run MS
> VM  (though I believe MS will do whatever is possible to make this
> impossible).

I think we'd be pleased to see MS adopt a sufficiently permissive license for 
their VMM interface specs to allow that to happen.

With VT (Intel) or Pacifica (AMD) hardware support, it'll be possible to run 
unmodified Windows under Xen, as you can under QEmu on vanilla x86.  The 
device emulation for this is actually supplied by QEmu-derived code.  Equally 
well, kqemu / qvm86 could also be adapted to leverage VT / Pacifica where 
available to allow native execution of (almost) all guest OS code under QEmu.  
I'd like to see both ;-)

Interestingly, the plan is for the MS hypervisor to *require* VT / Pacifica, 
to run virtual machines even with their paravirtualisation APIs.  This gives 
QEmu and Xen a bit of an edge for some users, although by their projected 
release date (seems to be in the 2007 - 2009 period) such hardware will be 
rather more common.


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