linux-kernel - Re: [PATCH] [5/12] x86_64: Make patching more robust, fix paravirt issue

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Message-ID: <20070821112330.GD32640@bingen.suse.de>
Date:	Tue, 21 Aug 2007 13:23:30 +0200
From:	Andi Kleen <ak@...e.de>
To:	Glauber de Oliveira Costa <glommer@...il.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	patches@...-64.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] [5/12] x86_64: Make patching more robust, fix paravirt issue

On Tue, Aug 21, 2007 at 04:30:10AM -0300, Glauber de Oliveira Costa wrote:
> On 8/20/07, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> > Chris Wright wrote:
> > > That did get backed out (at least the part that broke paravirt patching)
> > > in 602033ed5907a59ce86f709082a35be047743a86.  Linus' tree should be
> > > working fine right now with d34fda4a84c18402640a1a2342d6e6d9829e6db7
> > > committed, and can be further refined with the patch below that's just
> > > waiting on some further testing.
> > >
> >
> > I don't think this is necessary.  It isn't worth complicating the
> > interface to avoid the memcpy.
> >
> >     J
> Damn,
> 
> I can't believe I've just lost a night tracking the issue, without
> seeing the discussion here ;-)
> I came out to this very same conclusion, and was about to send a patch
> that fixes it, by doing a memcpy before starting the instruction
> replacement.
> 
> (I wouldn't say anything, as this is solved, but my night have to get
> some value, after all! ;-)
> 
> So I'm with Jeremy. We don't lose too much by putting a memcpy there,
> this code is not exactly critical. It also seems cleaner, and less
> error prone. I have a patch ready here, but I think by this time, you
> guys have too ;-)

x86-64 also has a __inline_memcpy that is guaranteed inlined. It was
originally for such cases when memcpy didn't work. Could be added to i386
too if there is need

-Andi
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