[ANNOUNCE] NOVA Microhypervisor 0.1 prerelease

Udo A. Steinberg udo at hypervisor.org
Mon Mar 8 21:34:26 CET 2010

On Mon, 8 Mar 2010 11:31:52 -0800 Thomas DuBuisson (TD) wrote:

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

If you want to paravirtualize I/O, then you can do so in NOVA without even
modifying the hypervisor. All you need is extend the device emulation in
the user-level VMM so that it comprehends whatever VirtIO interface is used
by your favorite guest OS.

However, NOVA does not support paravirtualized guest operating systems that
use ring compression or ring deprivileging to be able to run in user mode on
top of something else (e.g., L4Linux) -- which is presumably what Marcel
inquired about.

I don't get the part about the ABI. An unmodified guest operating system
does not care about the hypervisor ABI at all.


	- Udo
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