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Re: [Xen-devel] [PATCH 10/14] Nested Virtualization: svm specific implem

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 10/14] Nested Virtualization: svm specific implementation
From: Christoph Egger <Christoph.Egger@xxxxxxx>
Date: Wed, 18 Aug 2010 09:48:32 +0200
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On Tuesday 17 August 2010 18:57:55 Tim Deegan wrote:
> At 16:49 +0100 on 17 Aug (1282063795), Christoph Egger wrote:
> > > Can you explain why we shouldn't sync the vTPR and the vlapic state
> > > when the guest is in nested mode?
> >
> > When the vcpu is in guest mode then
> > v->arch.hvm_svm.vmcb->vintr.fields.tpr represents the tpr of the l2
> > guest. The l2 guest is not allowed to touch the l1 guest's vTPR.
> Hmmm.  I'm not sure I understand exactly what the hardware vTPR should
> contain when the L2 is running; I'll have to think back about exactly
> what the sync of vtpr <-> vlapic means and whether the L2 guest can
> cause surprising things to happen by setting the vTPR.

The l2 guest can confuse the l1 guest. E.g. Booting Windows 7
as l1 guest and the XP mode as l2 guest won't work when done
incorrectly. The l1 guest handles the vtpr and vlapic for the l2 guest
and noone else.


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