linux-kernel - Re: [PATCH -tip v10 0/9] kprobes: Kprobes jump optimization support

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Date:	Wed, 24 Feb 2010 08:41:13 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip v10 0/9] kprobes: Kprobes jump optimization support

Masami Hiramatsu wrote:
> Steven Rostedt wrote:
>> On Thu, 2010-02-18 at 17:12 -0500, Masami Hiramatsu wrote:
>>
>>> This version of patch series uses text_poke_smp() which
>>> update kernel text by stop_machine(). That is 'officially'
>>> supported on Intel's processors. text_poke_smp() can't
>>> be used for modifying NMI code,
>>
>> But it can be made to use with NMI code. If you look at what I did to
>> allow ftrace to modify NMI code, it may be able to do the same thing.
> 
> Yeah, I know. But basically, kprobes doesn't support probing NMI.
> Maybe, it's possibly the next step. :)

I mean that it may be overkill for this series, because the kprobes
itself doesn't support NMI. So I think it should be done by another
series (for simplify patches).


BTW, now there are two candidates for NMI supported text_poke()
on x86. AFAIK, those have following issues/features.

- text_poke_fixup()
  - Send IPI twice instead of kstop_machine.
  - Need a detour buffer if replacing code is not a jump.
  - Unofficial method for x86.

- generic ftrace_modify_code
  - Use kstop_machine and wait an NMI.
  - Temporarily clear the kernel text read-only flag entirely 
    (can we use text_poke instead?)

Thank you,

-- 
Masami Hiramatsu
e-mail: mhiramat@...hat.com
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