Message-ID: <48A4B132.80501@zytor.com>
Date: Thu, 14 Aug 2008 15:26:58 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       Harvey Harrison <harvey.harrison@gmail.com>,
       Andi Kleen <andi@firstfloor.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
       Steven Rostedt <srostedt@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       David Miller <davem@davemloft.net>, Roland McGrath <roland@redhat.com>,
       Ulrich Drepper <drepper@redhat.com>,
       Rusty Russell <rusty@rustcorp.com.au>,
       Gregory Haskins <ghaskins@novell.com>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       "Luis Claudio R. Goncalves" <lclaudio@uudg.org>,
       Clark Williams <williams@redhat.com>,
       Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with	preemptible
 kernel and CPU hotplug
References: <48A3A806.8060509@goop.org> <20080814151805.GA29507@Krystal> <48A459B1.2070601@zytor.com> <20080814165802.GC517@Krystal> <48A465F2.8000701@goop.org> <20080814173021.GA4697@Krystal> <48A46EC2.1010301@goop.org> <48A47B83.3090408@zytor.com> <20080814185338.GB7896@Krystal> <48A487A6.9060501@goop.org> <20080814203122.GC7896@Krystal> <48A4A7B4.3060008@goop.org>
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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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