Re: [PATCH 3/4] x86 paravirt_ops: implementation of paravirt_ops

From: Rusty Russell
Date: Mon Aug 07 2006 - 02:11:38 EST

On Mon, 2006-08-07 at 07:39 +0200, Andi Kleen wrote:
> On Monday 07 August 2006 06:47, Rusty Russell wrote:
> > This patch does the dumbest possible replacement of paravirtualized
> > instructions: calls through a "paravirt_ops" structure. Currently
> > these are function implementations of native hardware: hypervisors
> > will override the ops structure with their own variants.
> You should call it HAL - that would make it clearer what it is.

People get visions of grandeur when HAL is mentioned: they think it'll
abstract everything. I really only want to do the minimum needed for
the hypervisors we have on the table today.

Maybe one day it will abstract everything, then we can call it a HAL.
But I won't be doing that work 8)

> I think I would prefer to patch always. Is there a particular
> reason you can't do that?

We could patch all the indirect calls into direct calls, but I don't
think it's worth bothering: most simply don't matter.

The implementation ensures that someone can get boot on a new hypervisor
by populating the ops struct. Later they can go back and implement the
patching stuff.

> It would be better to merge this with the existing LOCK prefix patching
> or perhaps the normal alternative() patcher (is there any particular
> reason you can't use it?)
> Three alternative patching mechanisms just seems to be too many

Each backend wants a different patch, so alternative() doesn't cut it.
We could look at generalizing alternative() I guess, but it works fine
so I didn't want to touch it.

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