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

To: "Mark Williamson" <mark.williamson@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Integrate kqemu emulation into xen hypervisor possible?
From: "Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>
Date: Wed, 2 Apr 2008 10:09:24 -0400
Cc: "Magenheimer, "Magenheimer@maw48, Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Integrate kqemu emulation into xen hypervisor possible?
Mark Williamson wrote:
> > > > 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.
> IIRC, kqemu has a load of x86-specific code setting up shadow pagetables, 
> etc.  
> My expectation would be that this would want a fair bit of fixing up in order 
> to work properly under Xen (if it can work at all under the constraints of 
> PV...?).
> In a way, it seems a shame not to leverage the shadow PT support that's in 
> the 
> hypervisor already.  It's probably less work to integrate kqemu into XenLinux 
> though, and it has fewer security implications (I don't think kqemu is 
> recommended for secure sandboxing, so you probably wouldn't want it in the 
> hypervisor!).  It'd be nice if it were possible to use it in domUs too...

Cursory glance at the code tells me that it's current implementation
will not play well at all between dom0 and the hypervisor.

It may just be that the technology behind the functional idea of kqemu
would need to be re-worked to expressly support Xen.

A project that will in the end mean that kqemu-xen will end up being
a separately maintained branch of kqemu, since as it will be Xen
specific it will be less likely to be adopted by Qemu, as it is a
separate kernel module it will be less likely to be adopted by Xen,
and since it isn't KVM related it is less likely to be merged into
the kernel. :-(

So whoever follows this route should be prepared to be the maintainer
of a separate project for a long time.

Of course I could be wrong, and if it works well, either Qemu or Xen
may adopt it...

All I know is I personnally don't have the time to learn the memory
management aspects necessary to make it a reality.


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