http://www.kerneltraffic.org/kernel-traffic/kt20031201_243.html

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Nuno Silva mentioned:

The good people at Cambridge made a (very nice) VMM that exploits ring0/1/3 to let one machine run various kernels independently (the kernels need to be ported to the xen arch).

Xen itself executes in ring0 and the "guest" operating systems execute in ring1. User code runs in ring3, as usual. They have linux running under xen ;)

The project's home page is at http://www.cl.cam.ac.uk/Research/SRG/netos/xen/ and one paper describing the whole thing is here: http://www.cl.cam.ac.uk/netos/papers/2003-xensosp.pdf

And Linus replied:

This is what I alluded to [in a previous comment] - saying that if you move the driver down to ring1, then you should move _everything_ down to ring1 and just leave a microkernel at ring0.

Now, I'm not big on microkernels, but a pure virtual machine abstraction is at least not the distateful academic mental masturbation that we saw in the 80's.

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