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SubjectRe: [RFC, PATCH 0/24] VMI i386 Linux virtualization interface proposal
Chuck Ebbert wrote:
> In-Reply-To: <20060315102522.GA5926@infradead.org>
>
> On Wed, 15 Mar 2006 10:25:22 +0000, Christoph Hellwig wrote:
>
> I'd like to see a test harness implementation that has no actual
> hypervisor functionality and just implements the VMI calls natively.
> This could be used to test the interface and would provide a nice
> starting point for those who want to write a VMI hypervisor.
>

I was going to make one yesterday. But Fry's electronics stopped
carrying flashable blank PCI cards. :) Anyone know of a vendor?

It is possible to do in a software layer, although it really is a lot
easier to have the BIOS take care of all the fuss of finding a place in
low memory for you to live, setting up the various memory maps and
everything else for you.

There is enormous benefit to having such a layer - you have a very power
test harness, not just to make sure VMI works, but even more
importantly, to inspect and verify the native kernel operation as well.
You have a plethora of imporant hooks into the system, which feed you
knowledge you can not otherwise gain about which page tables have been
made active, when you take IRQs, where the kernel stack lives.

All of this is ripe for a debug harness that can verify the kernel
doesn't overflow the kernel stack, doesn't write to active page table
entries without proper accessors and subsequent invalidations, and obeys
the rules that are required for correctness when running under a
hypervisor. You probably even want to do hypervisor like things - such
as write protecting the kernel page tables so that you can be confident
there are no stray raw PTE accesses.

We actually found one (harmless on native) in i386, which was enabling
NX bit.

Zach
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