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

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Message-ID: <4B4F4507.2000108@redhat.com>
Date:	Thu, 14 Jan 2010 11:23:35 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jump	patching
 without stop_machine

Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:
>> On Tue, 2010-01-12 at 11:26 -0500, Jason Baron wrote:
>>
>>> +/**
>>> + * text_poke_fixup() -- cross-modifying kernel text with fixup address.
>>> + * @addr:	Modifying address.
>>> + * @opcode:	New instruction.
>>> + * @len:	length of modifying bytes.
>>> + * @fixup:	Fixup address.
>>> + *
>>> + * Note: You must backup replaced instructions before calling this,
>>> + * if you need to recover it.
>>> + * Note: Must be called under text_mutex.
>>> + */
>>> +void *__kprobes text_poke_fixup(void *addr, const void *opcode, size_t len,
>>> +				void *fixup)
>>> +{
>>> +	static const unsigned char int3_insn = BREAKPOINT_INSTRUCTION;
>>> +	static const int int3_size = sizeof(int3_insn);
>>> +
>>> +	/* Replacing 1 byte can be done atomically. */
>>> +	if (unlikely(len <= 1))
>>> +		return text_poke(addr, opcode, len);
>>
>> This part bothers me. The text_poke just writes over the text directly
>> (using a separate mapping). But if that memory is in the pipeline of
>> another CPU, I think this could cause a GPF.
> 
> It looks like we are thinking along the same lines.
> 
> I'm under the impression that I pointed out this exact same issue in the
> previous round of review a few weeks ago. Does this submission reflect
> the up-to-date state of this patch ?

No, the latest patch just skips step 3 if len == 1.
(Jason, could you update your repository?)
I thought I sent it the end of the last year ... :)

http://lkml.org/lkml/2009/12/18/312

Thank you,

-- 
Masami Hiramatsu

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

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

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