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[Xen-devel] Re: [patch 14/26] Xen-paravirt_ops: add common patching mach

To: Ingo Molnar <mingo@xxxxxxx>
Subject: [Xen-devel] Re: [patch 14/26] Xen-paravirt_ops: add common patching machinery
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Date: Sat, 17 Mar 2007 20:15:36 +1100
Cc: Zachary Amsden <zach@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Anthony Liguori <anthony@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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On Fri, 2007-03-16 at 10:20 +0100, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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@xxxxxxx>

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.


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