From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263633AbTEJDOI (ORCPT ); Fri, 9 May 2003 23:14:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263637AbTEJDOI (ORCPT ); Fri, 9 May 2003 23:14:08 -0400 Received: from neon-gw-l3.transmeta.com ([63.209.4.196]:27911 "EHLO neon-gw.transmeta.com") by vger.kernel.org with ESMTP id S263633AbTEJDOH (ORCPT ); Fri, 9 May 2003 23:14:07 -0400 To: linux-kernel@vger.kernel.org From: "H. Peter Anvin" Subject: Re: [PATCH] i386 uaccess to fixmap pages Date: 9 May 2003 20:26:40 -0700 Organization: Transmeta Corporation, Santa Clara CA Message-ID: References: <20030509124042.GB25569@mail.jlokier.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Disclaimer: Not speaking for Transmeta in any way, shape, or form. Copyright: Copyright 2003 H. Peter Anvin - All Rights Reserved Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Followup to: By author: Linus Torvalds In newsgroup: linux.dev.kernel > > It actually does have some cost in that form, namely the fact that the > kernel 1:1 mapping needs to be 4MB-aligned in order to take advantage of > large-pte support. So we'd have to move the kernel to something like > 0xc0400000 (and preferably higher, to make sure there is a nice hole in > between - say 0xc1000000), which in turn has a cost of verifying that > nothing assumes the current lay-out (we've had the 1/2/3GB TASK_SIZE > patches floating around, but they've never had "odd sizes"). > > There's another cost, which is that right now we share the pgd with the > kernel fixmaps, and this would mean that we'd have a new one. That's just > a single page, though. > > But it might "just work", and it would be interesting to see what the > patch would look like. Hint hint. > Another option would be to put it in the "user" part of the address space at 0xbffff000 (and move the %esp base value.) That would have the nice side benefit that stuff like UML or whatever who wanted to map something over the vsyscall could do so. Downside: each process needs a PTE for this. -hpa -- at work, in private! "Unix gives you enough rope to shoot yourself in the foot." Architectures needed: ia64 m68k mips64 ppc ppc64 s390 s390x sh v850 x86-64