Re: [9fans] Intel Vanderpool VM extensions

[Martin C.Atkins <martin_ml@parvat.com>]

On Thu, 10 Mar 2005 22:55:05 +0000 Derek Fawcus <dfawcus@cisco.com> wrote:
>..
> > <http://www.intel.com/cd/ids/developer/asmo-na/eng/197666.htm>.
>..
> Interesting... I'd not heard of this.  SoI had a quick glance...
>
> Does this stuff make the x86 completely virtualisable without
> jumping through the hoops that vmware / qemu have to follow?

I don't know. Looks complicated, doesn't it? It was a lack of vision
that they didn't make the architecture virtualizable, right from the
start (when the 386 was defined, or even earlier), like PowerPC. Does
PowerPC (for example) need special instructions? Ugh! I though it was
enough if the 'right' instructions did the 'right' things. This is all
very...., very Intelly, isn't it?

BTW: [Is ARM natively virtualizable? I can't remember, but I suspect not]

As I understand it, the hoops that Vmware has to go through are
somewhat different from those that qemu uses. Vmware 'interprets'
code in pages containing non-virtualizable instructions, and lets the
rest execute natively, while qemu just 'interprets' everything. Hence
qemu can run x86 operating systems on non-x86 processors (and
vice-versa), but Vmware should be faster (especially for application
code). Of course, both use similar JIT-like techniques to make the
'interpretation' go as fast as possible.

However, this means that yes, Vanderpool would/should (assuming
they've got it "right" :-) make vmware 'trivial' (like MOL
(maconlinux) is, on the Mac), but no, it will not help qemu at all,
since the JIT interpretation of code is central to qemu's approach.

[Although there is no reason, in principle, why qemu couldn't also
"give up on" interpretation in the 'right' circumstances (x86 on x86,
user-mode pages, etc), a direction that I believe bochs is following,
thus blurring the differences further. It would probably need a
kernel module 'helper' to do this, though.]

That's my understanding, anyway. Please correct/clarify...

Martin

--
Martin C. Atkins			martin_ml@parvat.com
Parvat Infotech Private Limited		http://www.parvat.com{/,/martin}