linux-kernel - Re: [RFC][PATCH] x86: make text

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Message-ID: <49AC2FDF.9070700@redhat.com>
Date:	Mon, 02 Mar 2009 14:13:35 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC][PATCH] x86: make text_poke() atomic

Arjan van de Ven wrote:
> On Mon, 2 Mar 2009 13:36:17 -0500
> Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
>> * Arjan van de Ven (arjan@...radead.org) wrote:
>>>> Use map_vm_area() instead of vmap() in text_poke() for avoiding
>>>> page allocation and delayed unmapping, and call
>>>> vunmap_page_range() and local_flush_tlb() directly because this
>>>> mapping is temporary and local.
>>>>
>>>> At the result of above change, text_poke() becomes atomic and can
>>>> be called from stop_machine() etc.
>>> .... but text_poke() realistically needs to call stop_machine()
>>> since you can't poke live code.... so that makes me wonder how
>>> useful this is...
>> Hi Arjan,
>>
>> Stop machine is not required when inserting a breakpoint. 
> 
> that is your assumption; when I spoke with CPU architects they
> cringed ;(

Is that true even if modifying just one-byte (like int3 insertion)
and we don't care synchronous write(that means code modification
effects on other processors after a while)?

Thank you,

-- 
Masami Hiramatsu

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

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

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