A CPU that supports VMX or SVM provides 4 host rings and 4 guest rings. They are used as follows: host/ring0=NOVA microhypervisor, host/ring3=NOVA user-level environment, guest/ring0=Linux kernel, guest/ring3=Linux apps.
Interesting that it requires SVM/VMX. Seeing as there are good performance reasons for Linux VirtIO and other cooperative para-virtualization schemes I'm wondering what the reasoning is for making a new hypervisor that doesn't support such a feature. I notice the NOVA page is lacking in an FAQ - could someone here educate me? Is this just a "you want performance? Use our ABI!" deal?
Cheers, Thomas