linux-kernel - Re: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jump patching without stop

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Message-ID: <4B54A68E.4050409@redhat.com>
Date:	Mon, 18 Jan 2010 13:21:02 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>, rostedt@...dmis.org,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, tglx@...utronix.de, andi@...stfloor.org,
	roland@...hat.com, rth@...hat.com
Subject: Re: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jump	patching
 without stop_machine

Mathieu Desnoyers wrote:
> * Arjan van de Ven (arjan@...radead.org) wrote:
>> On Mon, 18 Jan 2010 10:59:30 -0500
>> Masami Hiramatsu <mhiramat@...hat.com> wrote:
>>
>>> Yeah, so in the latest patch, I updated it to use int3 even if
>>> len == 1. :-)
>>>
>>
>>
>> int3 is not making a difference for your case; there is no guarantee
>> that the other processor even sees the "int3 inbetween state" at all;
>> if it's not safe without int3 then it won't be safe with int3 either.
> 
> What Masami means is that he updated his patch to use the int3+IPI
> broadcast scheme.

Right.

> 
> Therefore, the CPUs not seeing the int3 inbetween state will be forced
> to issue a serializing instruction while the int3 is in place anyway.

By the way, in kprobes, we just use a text_poke() to put int3.
I assume that we'd better send IPI afterward, wouldn't it?

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

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

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