From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932817Ab1JDQbN (ORCPT ); Tue, 4 Oct 2011 12:31:13 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34592 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932466Ab1JDQbJ (ORCPT ); Tue, 4 Oct 2011 12:31:09 -0400 Message-ID: <4E8B3489.60902@zytor.com> Date: Tue, 04 Oct 2011 09:30:01 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2 MIME-Version: 1.0 To: Jason Baron CC: Jeremy Fitzhardinge , Steven Rostedt , "David S. Miller" , David Daney , Michael Ellerman , Jan Glauber , the arch/x86 maintainers , Xen Devel , Linux Kernel Mailing List , Jeremy Fitzhardinge , peterz@infradead.org Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out References: <477dead9647029012f93c651f2892ed0e86b89e7.1317506051.git.jeremy.fitzhardinge@citrix.com> <20111003150205.GB2462@redhat.com> <4E89E28C.7010700@goop.org> <20111004141011.GA2520@redhat.com> In-Reply-To: <20111004141011.GA2520@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/2011 07:10 AM, Jason Baron wrote: > > 1) The jmp +0, is a 'safe' no-op that I know is going to initially > boot for all x86. I'm not sure if there is a 5-byte nop that works on > all x86 variants - but by using jmp +0, we make it much easier to debug > cases where we may be using broken no-ops. > There are *plenty*. jmp+0 is about as pessimal as you can get. The current recommendation when you don't know the CPU you're running at is: 3E 8D 74 26 00 (GENERIC_NOP5_ATOMIC) ... on 32 bits and ... 0F 1F 44 00 00 (P6_NOP5_ATOMIC) ... on 64 bits. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.