linux-kernel - Re: [RFC PATCH] x86: stop machine text poke should issue sync core

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Date:	Wed, 02 Mar 2011 22:10:34 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] x86: stop machine text poke should issue sync core

On 02/28/2011 07:24 AM, Mathieu Desnoyers wrote:
> 
> Index: linux-2.6-lttng/arch/x86/kernel/alternative.c
> ===================================================================
> --- linux-2.6-lttng.orig/arch/x86/kernel/alternative.c
> +++ linux-2.6-lttng/arch/x86/kernel/alternative.c
> @@ -612,6 +612,12 @@ static int __kprobes stop_machine_text_p
>  
>  	flush_icache_range((unsigned long)tpp->addr,
>  			   (unsigned long)tpp->addr + tpp->len);
> +	/*
> +	 * Intel Archiecture Software Developer's Manual section 7.1.3 specifies
> +	 * that a core serializing instruction such as "cpuid" should be
> +	 * executed on _each_ core before the new instruction is made visible.
> +	 */
> +	sync_core();
>  	return 0;
>  }
>  

Isn't this executed from an IPI handler, which will return with IRET (a
serializing instruction) anyway?

	-hpa
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