Re: [Xen-devel] Integrate kqemu emulation into xen hypervisor possible?

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Tue, Apr 01, 2008 at 10:50:36AM -0600, Dan Magenheimer wrote:
> > Ross S. W. Walker, le Tue 01 Apr 2008 11:41:24 -0400, a écrit :
> > > Samuel Thibault wrote:
> > > > Ross S. W. Walker, le Tue 01 Apr 2008 11:19:35 -0400, a écrit :
> > > > > I was wondering if now that the kqemu source has been 
> > GPL'd if it was
> > > > > possible if it's functionality could be incorporated 
> > into the Xen
> > > > > hypervisor to provide full virtualization on hardware 
> > that doesn't
> > > > > support it?
> > > >
> > > > What would be the benefit, compared to just running qemu in
> > > > user space?
> > 
> > Oooh, oops, you are talking about *k*qemu, not qemu, sorry, ok, I see.
> > Well, a first step would be to make kqemu work with Xen's dom0 Linux.
> > Then, adding the feature in the Hypervisor may make sense indeed, but
> > I'm not sure you'd get much bigger performance than with just the dom0
> > support.
> 
> If I'm not misunderstanding, an interesting side effect of this
> would be recursive virtual machines, e.g. Xen could run Xen running
> an hvm.
> 
> Who cares about such a thing in the real world, you ask?
> Probably not particularly useful in production, but it
> would be useful in education and debugging.
> 
> On the other hand, kqemu isn't really needed for that, just full
> emulation of the VT instruction set, correct?

Indeed that is correct - atlhough I've not tried it out, upstream QEMU does
already emulate the SVM instructions which should allow Xen / KVM to do
fullyvirt.

> What kqemu-in-xen *could* be used for would be running x86 VMs on
> a non-x86 architecture! (Insert shameless plug for googling
> MagiXen here :-)

No it can't - AFAIK kqemu is for matched host-guest arch only. Only plain
emulated QEMU can do mixed host-guest archiecture, and it cannot take
advantage of kqemu when doing this emulation.

Dan.
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