From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750942AbWGBWFN (ORCPT ); Sun, 2 Jul 2006 18:05:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750987AbWGBWFN (ORCPT ); Sun, 2 Jul 2006 18:05:13 -0400 Received: from mail-in-06.arcor-online.net ([151.189.21.46]:37339 "EHLO mail-in-01.arcor-online.net") by vger.kernel.org with ESMTP id S1750942AbWGBWFL (ORCPT ); Sun, 2 Jul 2006 18:05:11 -0400 Date: Mon, 3 Jul 2006 00:04:49 +0200 (CEST) From: Bodo Eggert <7eggert@gmx.de> To: Alan Cox cc: 7eggert@gmx.de, Arjan van de Ven , Ulrich Drepper , Pavel Machek , Jason Baron , akpm@osdl.org, linux-kernel@vger.kernel.org Subject: Re: make PROT_WRITE imply PROT_READ In-Reply-To: <1151834171.14346.2.camel@localhost.localdomain> Message-ID: References: <6qIEW-1Tx-23@gated-at.bofh.it> <6qIEW-1Tx-21@gated-at.bofh.it> <6qUwd-2Aq-9@gated-at.bofh.it> <6qUwd-2Aq-7@gated-at.bofh.it> <6qUFV-2N8-13@gated-at.bofh.it> <6qUFY-2N8-33@gated-at.bofh.it> <6rlmT-8op-37@gated-at.bofh.it> <6siwJ-3dC-5@gated-at.bofh.it> <6sLoY-4GV-31@gated-at.bofh.it> <6sZUS-V5-19@gated-at.bofh.it> <6tib4-2wA-3@gated-at.bofh.it> <6tmHL-Oq-5@gated-at.bofh.it> <6tpZ7-5Tj-13@gated-at.bofh.it> <1151834171.14346.2.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-be10.7eggert.dyndns.org-MailScanner-Information: See www.mailscanner.info for information X-be10.7eggert.dyndns.org-MailScanner: Found to be clean X-be10.7eggert.dyndns.org-MailScanner-From: 7eggert@web.de Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2 Jul 2006, Alan Cox wrote: > Ar Sad, 2006-07-01 am 15:19 +0200, ysgrifennodd Bodo Eggert: > > > unpredictably depending on the precise ordering of events on a clean > > > page. > > > > You asked for a fault, and as long as the hardware supports it, you'll > > get one (and you're supposed to). If the hardware doesn't support read > > faults on mapped pages, you may not get all the read faults you want. The > > proposed patch makes the situation worse by disabeling the _requested_ > > failures even in situations where it can be done. > > The later patch as posted has no effect on such platforms I'm talking about the affected platforms. > because it > does not touch anything but the architecture code. Without that its > random what happens because the CPU cannot enforce write only but the > fault handler tries to. That means if you fault reading because the page > is not present you may get a fault while if you access a page which is > present you won't get a fault. IMO it's the best we can get, even if the results are ... > That gets quite random and has bizarre effects. OTOH, there is not much difference between randomly wrong and consistently wrong, so I shall be happy either way (as if it would even matter). -- 'Calm down -- it's only ones and zeros.'