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

To: <dan.magenheimer@xxxxxxxxxx>, "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Integrate kqemu emulation into xen hypervisor possible?
From: "Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>
Date: Tue, 1 Apr 2008 14:19:14 -0400
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Thread-topic: [Xen-devel] Integrate kqemu emulation into xen hypervisor possible?
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.

You can do that today by running a qemu user-space daemon in a
PVM (or HVM). Not very fast, but for debugging that's probably
a good thing.

> 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.

Or in Philosophy class on the discussion of existence or a
demonstration of deus ex machina.

> On the other hand, kqemu isn't really needed for that, just full
> emulation of the VT instruction set, correct?

Yup, not really needed and can be done now with just the
user-space qemu.

> 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 :-)

Well in theory, if the Xen development team added back the
parts of qemu that provided translative emulation and an
option to use those parts, then yes, one in theory would
be able to emulate different architectures as well.

I'm mainly interested in full virtualization without hardware
support though...


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