Re: ABI coupling to hypervisors via CONFIG_PARAVIRT
From: Linus Torvalds
Date: Fri Mar 09 2007 - 17:29:01 EST
On Fri, 9 Mar 2007, Ingo Molnar wrote:
>
> hm. So your point is that VMI is in essence a Turing machine (a
> near-complete one)? No matter what redesign we do on the Linux side, the
> VMI paravirt_ops will always be able to adopt to it?
No, I don't think it's turing-complete ;)
But since it tries to basically come fairly close to emulating the
hardware we already use, any higher-level abstraction we do (which
obviously has to work on real hardware too!) is likely to be translatable
into the "pseudo-hardware" thing that is the VMI interfaces.
> but ... maybe because VMI is so lowlevel and covers /all/ of x86 today,
> it will always be able to emulate whatever different concept we can come
> up with? Do we really know this absolutely sure?
"For sure"? Absolutely not. But since any new interfaces we come up with
for doing timers etc had better work perfectly fine on an old hardware
platform too, we can't exactly require any interfaces that do things that
a bog-standard old dual-PPro didn't do 10 years ago, can we?
So assumign that the VMI interface is roughly as powerful (by virtue of
basically emulating it) as the old single-ioapic/single-lapic systems we
used to use, I don't think it should ever be a real problem. Hmm?
Linus
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