Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754268Ab0ARQAA (ORCPT ); Mon, 18 Jan 2010 11:00:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754138Ab0ARP77 (ORCPT ); Mon, 18 Jan 2010 10:59:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753793Ab0ARP76 (ORCPT ); Mon, 18 Jan 2010 10:59:58 -0500 Message-ID: <4B548562.6030008@redhat.com> Date: Mon, 18 Jan 2010 10:59:30 -0500 From: Masami Hiramatsu User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-3.fc11 Thunderbird/3.0 MIME-Version: 1.0 To: Arjan van de Ven CC: Mathieu Desnoyers , "H. Peter Anvin" , rostedt@goodmis.org, Jason Baron , linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de, andi@firstfloor.org, roland@redhat.com, rth@redhat.com Subject: Re: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jump patching without stop_machine References: <1263483139.28171.3857.camel@gandalf.stny.rr.com> <4B4F3A1A.2030906@zytor.com> <20100117185539.GF9008@Krystal> <20100117111608.35a98ee2@infradead.org> In-Reply-To: <20100117111608.35a98ee2@infradead.org> X-Enigmail-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1580 Lines: 49 Arjan van de Ven wrote: > On Sun, 17 Jan 2010 13:55:39 -0500 > Mathieu Desnoyers wrote: > >> * H. Peter Anvin (hpa@zytor.com) wrote: >>> On 01/14/2010 07:32 AM, Steven Rostedt wrote: >>>>> + >>>>> + /* Replacing 1 byte can be done atomically. */ >>>>> + if (unlikely(len <= 1)) >>>>> + return text_poke(addr, opcode, len); >>>> >>>> This part bothers me. The text_poke just writes over the text >>>> directly (using a separate mapping). But if that memory is in the >>>> pipeline of another CPU, I think this could cause a GPF. >>>> >>> >>> Could you clarify why you think that? >> >> Basically, what Steven and I were concerned about in this particular >> patch version is the fact that this code took a "shortcut" for >> single-byte text modification, thus bypassing the int3-bypass scheme >> altogether. > > single byte instruction updates are likely 100x safer than any scheme > of multi-byte instruction scheme that I have seen, other than a full > stop_machine(). > > That does not mean it is safe, it just means it's an order of > complexity less to analyze ;-) Yeah, so in the latest patch, I updated it to use int3 even if len == 1. :-) Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.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/