From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752895Ab2ARVuF (ORCPT ); Wed, 18 Jan 2012 16:50:05 -0500 Received: from terminus.zytor.com ([198.137.202.10]:32985 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752735Ab2ARVuD (ORCPT ); Wed, 18 Jan 2012 16:50:03 -0500 Message-ID: <4F173DD5.9000308@zytor.com> Date: Wed, 18 Jan 2012 13:47:01 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 MIME-Version: 1.0 To: Linus Torvalds CC: Indan Zupancic , Andi Kleen , Jamie Lokier , Andrew Lutomirski , Oleg Nesterov , Will Drewry , linux-kernel@vger.kernel.org, keescook@chromium.org, john.johansen@canonical.com, serge.hallyn@canonical.com, coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com, djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org, jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com, penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu, akpm@linux-foundation.org, khilman@ti.com, borislav.petkov@amd.com, amwang@redhat.com, ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de, dhowells@redhat.com, daniel.lezcano@free.fr, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, olofj@chromium.org, mhalcrow@google.com, dlaor@redhat.com, Roland McGrath Subject: Re: Compat 32-bit syscall entry from 64-bit task!? References: <20120116183730.GB21112@redhat.com> <49017bd7edab7010cd9ac767e39d99e4.squirrel@webmail.greenhost.nl> <20120118015013.GR11715@one.firstfloor.org> <20120118020453.GL7180@jl-vm1.vm.bytemark.co.uk> <20120118022217.GS11715@one.firstfloor.org> <4F1731C1.4050007@zytor.com> <4F1733DF.7040905@zytor.com> <4F1739F1.2070902@zytor.com> In-Reply-To: X-Enigmail-Version: 1.3.4 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 01/18/2012 01:42 PM, Linus Torvalds wrote: > On Wed, Jan 18, 2012 at 1:30 PM, H. Peter Anvin wrote: >> >> I would have assumed it would be a new register set (which could be >> expanded in the future if we have additional system information to provide.) > > Well, I really don't think we want to expose much. In fact, I'd argue > we should expose as little as humanly possible. > > Which at this point is literally just a single bit (and effectively > another bit to say "we support the new feature"). > > So... > I actually think we need to also have a bit for some of the 32-bit entry point differences, since the registers have different meanings for them. We have kluges in place for them, but those kluges cause their own problems when registers are modified. So that means at least four states (SYSCALL64, SYSENTER, SYSCALL32, INT 80) plus the presence bit. Furthermore, three out of those states apply even to pure 32-bit kernels. -hpa