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

To: Christoph Egger <Christoph.Egger@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH 10/14] Nested Virtualization: svm specific implementation
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Wed, 18 Aug 2010 11:45:11 +0100
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At 08:48 +0100 on 18 Aug (1282121312), Christoph Egger wrote:
> 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.

What cases will cause it to break?  I had just convinced myself that
your patch was correct but now you've got me worried again. :)



Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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