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Re: [Xen-devel] [PATCH 0/14] Nested Virtualization: Overview

On Tuesday 17 August 2010 08:04:20 Dong, Eddie wrote:
> Hi, Chris:
> Christoph Egger wrote:
> > Hi!
> >
> > This patch series brings Nested Virtualization to Xen.
> > This is the third patch series. Improvements to the
> > previous patch submission:
> >
> > - implement HVM-on-HVM (instead of SVM-on-HVM)
> Given that we don't have consensus on cross architecture nested
> virtualization support, I am doubting why this is urgent for now.

The reason to be "urgent" is not the time. This is the best way from
the software engineering side.

> I would prefer we make SVM-on-SVM and VMX-on-VMX work first. After that,
> if you prove SVM-on-VMX has real performance gain (which I doubt), we can
> see how to make a much generic effort to accomodate both natively nested
> virtualization and cross architecture nested virtualization.

Tim and Keir made clear they don't want to have two implementations after
I submitted my patch series the *first* time.

> Drawing a picture which doesn't have a real usage with massive common code
> change is a kind of too much load for us now. Xen hvm_function table is a
> good example. Intel enabled VMX at very beginning of Xen HVM support, and
> SVM comes later on with a lot of code reuse from VMX side. Then the
> community and both side work together to make an API wrapper to reuse
> common code better and accomodate both architecture. I think we have to go
> similar path to make it work first.

Tim remembers on this and said in this mail

"With HVM it has turned out to be quite a lot, but it's taken years of
reshuffling to pull code out into common HVM routines (and we're not there

If I understand Tim correctly, the way you suggest is a "no".
(Added Tim on CC)


> > - move cpuid handling into tools (per Keir's request)
> >
> > There might still be some nuances to fiddle with to make it
> > fit for VMX. Feedback from Intel is appreciated, therefore.
> Thx, Eddie

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