linux-kernel - Re: [patch 14/26] Xen-paravirt_ops: add common patching machinery

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Date:	Sat, 17 Mar 2007 20:15:36 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, Chris Wright <chrisw@...s-sol.org>,
	Zachary Amsden <zach@...are.com>,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [patch 14/26] Xen-paravirt_ops: add common patching machinery

On Fri, 2007-03-16 at 10:20 +0100, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > Implement the actual patching machinery.  paravirt_patch_default() 
> > contains the logic to automatically patch a callsite based on a few 
> > simple rules:
> > 
> >  - if the paravirt_op function is paravirt_nop, then patch nops
> >  - if the paravirt_op function is a jmp target, then jmp to it
> >  - if the paravirt_op function is callable and doesn't clobber too much
> >     for the callsite, call it directly
> > 
> > paravirt_patch_default is suitable as a default implementation of 
> > paravirt_ops.patch, will remove most of the expensive indirect calls 
> > in favour of either a direct call or a pile of nops.
> 
> Acked-by: Ingo Molnar <mingo@...e.hu>

I like this one too, but note that it needs a twist when we change to
use direct calls to wrappers for the Great paravirt_ops Unexporting.

Rusty.


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