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xen-devel
RE: [Xen-devel] Fwd: [PATCH 0/18] Nested Virtualization: Overview
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To: |
Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Christoph Egger <Christoph.Egger@xxxxxxx> |
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Subject: |
RE: [Xen-devel] Fwd: [PATCH 0/18] Nested Virtualization: Overview |
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From: |
"Dong, Eddie" <eddie.dong@xxxxxxxxx> |
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Date: |
Tue, 20 Apr 2010 10:07:37 +0800 |
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"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "He, Qing" <qing.he@xxxxxxxxx> |
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[Xen-devel] Fwd: [PATCH 0/18] Nested Virtualization: Overview |
Keir Fraser wrote:
> On 16/04/2010 11:27, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:
>
>>> Please read the XenNestedHVM.pdf paper, particularly the section
>>> "Software Architecture". This describes how this is made to be
>>> generic and what needs to be done to adapt to Intel.
>>
>> Your PDFs suggest that even on Intel CPUs, the nested hypervisor
>> should always see SVM, not VMX. You shouldn't be surprised or
>> offended if that isn't popular with Intel. :)
>
> I don't see any good argument for it either. I.e., I don't think we
> care about migrating between AMD and Intel hosts with nestedhvm
> enabled, which I think would be the only argument for it. I know we
> added support for cross-emulating SYSENTER and SYSCALL, but that's
> needed for cross-migration of any 64-bit guest running compat-mode
> apps (i.e., really need to make cross-migration possible at all). I'm
> sceptical enough of the utility of cross-vendor migration *at all*,
> let alone supporting in tandem with advanced features also of dubious
> utility (at least in enterprise space), like nestedhvm.
>
Although SVM on VMX is possible in theory, I doutb on the feasibility given
that there are many semantics difference between VMCB & VMCS, which will
eventually have to be emulated with extra complexity.
Qing will post his natural VMX on VMX patch this week, base on his Xen summit
talk on http://www.xen.org/files/xensummit_intel09/xensummit-nested-virt.pdf :)
We can have next level of discussion/comparation then.
BTW, If somebody has implemented SVM on VMX solution already, we can have
performance comparation between 2 approaches to assist the discussion.
Thx, Eddie
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