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

To: Christoph Egger <Christoph.Egger@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH 0/14] Nested Virtualization: Overview
From: "Dong, Eddie" <eddie.dong@xxxxxxxxx>
Date: Tue, 17 Aug 2010 14:04:20 +0800
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Thread-topic: [Xen-devel] [PATCH 0/14] Nested Virtualization: Overview
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. 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. 

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.

> - 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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