linux-kernel - Re: [PATCH v2 1/8] x86: speed up int3-based patching using less paranoid write

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Message-ID: <1384253072.1296.21.camel@pathway.suse.cz>
Date:	Tue, 12 Nov 2013 11:44:32 +0100
From:	Petr Mladek <pmladek@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v2 1/8] x86: speed up int3-based patching using less
 paranoid write

Steven Rostedt píše v Pá 08. 11. 2013 v 07:43 -0500:
> On Fri, 08 Nov 2013 21:04:26 +0900
> Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
> 
> > (2013/11/08 18:12), Petr Mladek wrote:
> > > This change is inspired by the int3-based patching code used in
> > > ftrace. See the commit fd4363fff3d9 (x86: Introduce int3
> > > (breakpoint)-based instruction patching).
> > > 
> > > When trying to use text_poke_bp in ftrace, the result was slower than
> > > the original implementation.
> > > 
> > > It turned out that one difference was in text_poke vs. ftrace_write.
> > > text_poke did many extra operations to make sure that the change
> > > was atomic.
> > 
> > AFAIK, the main reason why text_poke is used is avoiding
> > RODATA protection (by alias mapping).
> 
> That is correct, and the reason ftrace didn't do that is because it
> would be quite expensive to map 22,000 addresses for each change.

I see. I am going to prepare v3 with the following changes:

	+ use text_poke in text_poke_bp back again because it is not
          effective to make the pages rw only for a single address;
          the alias mapping is faster here

	+ use the faster text_poke_part only in text_poke_bp_iter;
          the caller of this function will be responsible for
          making the code rw

	+ I will rework the error handling as suggested in the other
          mails; I will try to add some also for text_poke.

Thanks a lot for hints.

Best Regards,
Petr

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