Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031280AbWKUSga (ORCPT ); Tue, 21 Nov 2006 13:36:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031282AbWKUSga (ORCPT ); Tue, 21 Nov 2006 13:36:30 -0500 Received: from terminus.zytor.com ([192.83.249.54]:9955 "EHLO terminus.zytor.com") by vger.kernel.org with ESMTP id S1031280AbWKUSg3 (ORCPT ); Tue, 21 Nov 2006 13:36:29 -0500 Message-ID: <45634704.8020407@zytor.com> Date: Tue, 21 Nov 2006 10:35:48 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 1.5.0.8 (X11/20061107) MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Avi Kivity , Arnd Bergmann , kvm-devel@lists.sourceforge.net, akpm@osdl.org, linux-kernel@vger.kernel.org Subject: Re: [kvm-devel] [PATCH] KVM: Avoid using vmx instruction directly References: <20061109110852.A6B712500F7@cleopatra.q> <200611091429.42040.arnd@arndb.de> <45532EE3.4000104@qumranet.com> <200611091542.31101.arnd@arndb.de> <455340B8.2080206@qumranet.com> <4553BC18.6090207@goop.org> In-Reply-To: <4553BC18.6090207@goop.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1033 Lines: 25 Jeremy Fitzhardinge wrote: > Avi Kivity wrote: >>> Or gcc >>> might move the assignment of phys_addr to after the inline assembly. >>> >> "asm volatile" prevents that (and I'm not 100% sure it's necessary). > > No, it won't necessarily. "asm volatile" simply forces gcc to emit the > assembler, even if it thinks its output doesn't get used. It makes no > ordering guarantees with respect to other code (or even other "asm > volatiles"). The "memory" clobbers should fix the ordering of the asms > though. > I think you're wrong about that; in particular, I'm pretty sure "asm volatiles" are ordered among themselves. What the "volatile" means is "this has side effects you (the compiler) don't understand", and gcc can't assume that it can reorder such side effects. -hpa - 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/