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Re: [Xen-devel] Xen inside Xen with VMX?

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Xen inside Xen with VMX?
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 31 Jan 2008 17:53:12 +0000
Cc: Morten Hansen <paradigm__82@xxxxxxxxxxx>
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You can run Xen within an HVM domain but you won't be able to run HVM domains 
inside that.  The HVM environment does not provide emulated VMX / SVM support 
at the moment.

> If it's not possible I guess
> VT etc. doesn't really offer true emulation since the guest would be able
> to detect the emulation by noticing that it wasn't itself able to become a
> hypervisor.

Well, there are plenty of existing machines out there that don't support HVM - 
and even one ones that theoretically do it may be disabled in the BIOS.  So 
you can't tell just from that aspect of the CPU behaviour that you're running 
in a VM.

There are more obvious Xen/Qemu-specific interfaces that can tell the guest 
straightforwardly that it's in a VM, though.

Cheers,
Mark

-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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