Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757765Ab1COOSX (ORCPT ); Tue, 15 Mar 2011 10:18:23 -0400 Received: from mail.openrapids.net ([64.15.138.104]:41058 "EHLO blackscsi.openrapids.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755888Ab1COOSW (ORCPT ); Tue, 15 Mar 2011 10:18:22 -0400 Date: Tue, 15 Mar 2011 10:18:17 -0400 From: Mathieu Desnoyers To: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Cc: Masami Hiramatsu , Peter Zijlstra , Arjan van de Ven , Steven Rostedt , Andrew Morton , Andi Kleen , Frederic Weisbecker , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: stop machine text poke should issue sync core (v2) Message-ID: <20110315141817.GA27124@Krystal> References: <20110303160137.GB1590@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110303160137.GB1590@Krystal> X-Editor: vi X-Info: http://www.efficios.com X-Operating-System: Linux/2.6.26-2-686 (i686) X-Uptime: 10:16:12 up 111 days, 19:19, 5 users, load average: 0.03, 0.02, 0.00 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3608 Lines: 89 * Mathieu Desnoyers (mathieu.desnoyers@efficios.com) wrote: > 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. Hi, Is anyone willing to merge this fix into the x86 tree ? Thanks, Mathieu > > Failure to do so can lead to unspecified behavior (Intel XMC erratas include > General Protection Fault in the list), so we should avoid this at all cost. > > This problem can affect modified code executed by interrupt handlers after > interrupt are re-enabled at the end of stop_machine, because no core serializing > instruction is executed between the code modification and the moment interrupts > are reenabled. > > Because stop_machine_text_poke performs the text modification from the first CPU > decrementing stop_machine_first, modified code executed in thread context is > also affected by this problem. To explain why, we have to split the CPUs in two > categories: the CPU that initiates the text modification (calls text_poke_smp) > and all the others. The scheduler, executed on all other CPUs after > stop_machine, issues an "iret" core serializing instruction, and therefore > handles core serialization for all these CPUs. However, the text modification > initiator can continue its execution on the same thread and access the modified > text without any scheduler call. Given that the CPU that initiates the code > modification is not guaranteed to be the one actually performing the code > modification, it falls into the XMC errata. > > Q: Isn't this executed from an IPI handler, which will return with IRET (a > serializing instruction) anyway? > A: No, now stop_machine uses per-cpu workqueue, so that handler will be > executed from worker threads. There is no iret anymore. > > Signed-off-by: Mathieu Desnoyers > Reviewed-by: Masami Hiramatsu > CC: Thomas Gleixner > CC: Ingo Molnar > CC: "H. Peter Anvin" > CC: Arjan van de Ven > CC: Peter Zijlstra > CC: Steven Rostedt > CC: Andrew Morton > CC: Andi Kleen > CC: Frederic Weisbecker > --- > arch/x86/kernel/alternative.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > Index: linux-tip/arch/x86/kernel/alternative.c > =================================================================== > --- linux-tip.orig/arch/x86/kernel/alternative.c > +++ linux-tip/arch/x86/kernel/alternative.c > @@ -620,7 +620,12 @@ static int __kprobes stop_machine_text_p > flush_icache_range((unsigned long)p->addr, > (unsigned long)p->addr + p->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; > } > > > -- > Mathieu Desnoyers > Operating System Efficiency R&D Consultant > EfficiOS Inc. > http://www.efficios.com -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/