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RE: [Xen-users] Question about stability 32bit chroot and xen 2.0.7

To: "Robin van Leeuwen" <robin.van.leeuwen@xxxxxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] Question about stability 32bit chroot and xen 2.0.7
From: "Petersson, Mats" <mats.petersson@xxxxxxx>
Date: Fri, 2 Sep 2005 11:12:15 +0200
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Thread-topic: [Xen-users] Question about stability 32bit chroot and xen 2.0.7
> But i want it the other way around. I want to run a stable 64 
> bit server
> (debian-amd64 stable) with a stable xen (2.0.7) but, 2.0.7 
> doesn't support 64 bit's. Is there a way i still can use 
> 2.0.7 AND make use of debian-amd64-stable.

There is no way you can run a 64-bit OS on top of a 32-bit hypervisor,
stable, unstable or otherwise. The reason, primarily, is that the
hypervisor has to understand entire processor architecture, and AMD64
has 8 more gp registers than the 32-bit x86 architecture. These
registers are not accessible in 32-bit mode, so you would end up with
unsaved registers. Since some of these registers are of the type that
doesn't automatically get saved by the OS or C calling convention (ABI),
they absolutely need to be saved and restored with Xen's context
switches. 

So you need a Xen hypervisor that understands 64-bit processors, or you
have to run a 32-bit OS. 

[Aside from that, amd64 also uses 4 level page tables in combination
with PAE mode, none of which I believe are supported in 2.0.x].

> 
> There is another catch (maybe an advantage) I have to 
> recompile it myself to change some kernel-config settings and 
> recompile at least the kernels.
> 
> Can this be done?

No. 

--
Mats
> 
> kind regards,
> 
> Robin van Leeuwen
> 
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
> 


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