linux-kernel - Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

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Message-ID: <48A4B132.80501@zytor.com>
Date:	Thu, 14 Aug 2008 15:26:58 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with	preemptible
 kernel and CPU hotplug

Jeremy Fitzhardinge wrote:
> Mathieu Desnoyers wrote:
>> I'm just worried about this comment from Harvey Harrison :
>>
>> arch/x86/mm/fault.c : is_prefetch()
>>
>>                          * Values 0x26,0x2E,0x36,0x3E are valid x86 
>> prefixes.
>>                          * In X86_64 long mode, the CPU will signal 
>> invalid
>>                          * opcode if some of these prefixes are 
>> present so
>>                          * X86_64 will never get here anyway
>>   
> 
> I would say that comment is wrong.  But we'd never put a lock prefix on 
> a prefetch, so you won't be added a ds prefix either.
> 

Locking prefetches is definitely wrong :)

I don't know if the comment is correct; I've certainly never heard of 
that myself.

	-hpa
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