From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753990Ab3AWHw0 (ORCPT ); Wed, 23 Jan 2013 02:52:26 -0500 Received: from arkanian.console-pimps.org ([212.110.184.194]:49884 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753685Ab3AWHwY (ORCPT ); Wed, 23 Jan 2013 02:52:24 -0500 Message-ID: <1358927532.2496.24.camel@mfleming-mobl1.ger.corp.intel.com> Subject: Re: [PATCH 1/2] efi: Make 'efi_enabled' a function to query EFI facilities From: Matt Fleming To: Ben Hutchings Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, Tim Gardner , Matthew Garrett , Olof Johansson , Tony Luck , Steve Langasek , Colin Ian King , David Airlie , Corentin Chary , Dave Jiang , Peter Jones , Konrad Rzeszutek Wilk , "Rafael J. Wysocki" , stable@vger.kernel.org Date: Wed, 23 Jan 2013 07:52:12 +0000 In-Reply-To: <1358914581.3151.6.camel@deadeye.wl.decadent.org.uk> References: <1358800838-10459-1-git-send-email-matt@console-pimps.org> <1358800838-10459-2-git-send-email-matt@console-pimps.org> <50FDA81B.9090602@zytor.com> <1358802778.2496.11.camel@mfleming-mobl1.ger.corp.intel.com> <1358914581.3151.6.camel@deadeye.wl.decadent.org.uk> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4 (3.4.4-2.fc17) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-01-23 at 04:16 +0000, Ben Hutchings wrote: > On Mon, 2013-01-21 at 21:12 +0000, Matt Fleming wrote: > [...] > > From 92e73f936e40a8c6562e47425d434a4e62d2b8e2 Mon Sep 17 00:00:00 2001 > > From: Matt Fleming > > Date: Wed, 14 Nov 2012 09:42:35 +0000 > > Subject: [PATCH] efi: Make 'efi_enabled' a function to query EFI facilities > > > > Originally 'efi_enabled' indicated whether a kernel was booted from > > EFI firmware. Over time its semantics have changed, and it now > > indicates whether or not we are booted on an EFI machine with > > bit-native firmware, e.g. 64-bit kernel with 64-bit firmware. > > > > The immediate motivation for this patch is the bug report at, > > > > https://bugs.launchpad.net/ubuntu-cdimage/+bug/1040557 > > > > which details how running a platform driver on an EFI machine that is > > designed to run under BIOS can cause the machine to become > > bricked. Also, the following report, > > > > https://bugzilla.kernel.org/show_bug.cgi?id=47121 > > > > details how running said driver can also cause Machine Check > > Exceptions. Drivers need a new means of detecting whether they're > > running on an EFI machine, as sadly the expression, > > > > if (!efi_enabled) > > > > hasn't been a sufficient condition for quite some time. > [...] > > This patch maps the old efi_enabled flag to efi_enabled(EFI_BOOT). Your > second patch adds a test for efi_enabled(EFI_BOOT) to the samsung-laptop > driver. So the samsung-laptop driver could be fixed by adding a check > for the old flag; it doesn't depend on the addition of new flags at all. > The changes elsewhere may well be important, but the cited motivation > here just doesn't make sense. If we instead check for the old flag then the samsung-laptop driver would run if booting a 32-bit kernel with 64-bit EFI firmware, or vice versa, because efi_enabled == 0 in that case. It's not sufficient to just check the old flag, the samsung-laptop driver really can't be allowed to run at all if booting from EFI, and the old flag doesn't provide us with that guarantee. -- Matt Fleming, Intel Open Source Technology Center