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

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Message-ID: <20100114164215.GA2823@redhat.com>
Date:	Thu, 14 Jan 2010 11:42:15 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>,
	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

On Thu, Jan 14, 2010 at 11:23:35AM -0500, Masami Hiramatsu 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,
> 

sorry about that...i've updated to the latest.

thanks,

-Jason
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