Re: [Xen-devel] Fwd: [PATCH 0/18] Nested Virtualization: Overview

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 17/04/2010 12:43, "Joerg Roedel" <joro@xxxxxxxxxx> wrote:

>> 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. :)
> 
> Well, it would make sense for Intel too virtualize SVM because it
> doesn't has the performance issues with lots and lots of emulated
> vmread/vmwrite instructions that cause vmexits in the nested case. The
> bigger problem with SVM on VMX is that it could never be complete
> because afaik VMX has fewer intercepts than SVM.

I don't think either VMX-on-SVM or SVM-on-VMX should be an aim. I mean, we'd
have to completely emulate the underlying Intel processor, say, as AMD, to
ensure SVM code paths get taken in the guest kernel/hypervisor. It's not
really on.

 -- Keir



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