Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753322AbaDNJeZ (ORCPT ); Mon, 14 Apr 2014 05:34:25 -0400 Received: from arkanian.console-pimps.org ([212.110.184.194]:46528 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752562AbaDNJeB (ORCPT ); Mon, 14 Apr 2014 05:34:01 -0400 Date: Mon, 14 Apr 2014 10:33:32 +0100 From: Matt Fleming To: Thomas =?iso-8859-1?Q?B=E4chler?= Cc: Ingo Molnar , "H. Peter Anvin" , Matt Fleming , Thomas Gleixner , Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] efi: Clarify Kconfig help for EFI_MIXED Message-ID: <20140414093332.GA10956@console-pimps.org> References: <1397239154-30121-1-git-send-email-thomas@archlinux.org> <53482E61.8050606@zytor.com> <20140411184433.GA15344@console-pimps.org> <20140414071534.GA19501@gmail.com> <534B9C12.4050708@archlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <534B9C12.4050708@archlinux.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 14 Apr, at 10:28:02AM, Thomas B?chler wrote: > Am 14.04.2014 09:15, schrieb Ingo Molnar: > >>> Right, it is really that it is not possible to boot a mixed-mode kernel > >>> on its non-native firmware using the stub, since the stub itself can > >>> only be one way or the other. > >> > >> Yeah, my help text was a bit... unhelpful. > >> > >> CONFIG_EFI_MIXED does not introduce a regression of any sort, you can > >> enable it without worrying about that. > >> > >> All the boot configurations that used to work will continue to work. > >> > >> What I meant to say was that it isn't possible to use the EFI mixed > >> *feature* (booting a 64-bit kernel with 32-bit firmware) with the > >> EFI boot stub - so you can build support into your kernel but > >> there's no way to make the CPU actually execute those code paths. > > > > Same goes for booting a 32-bit kernel on 64-bit firmware, right? > > > > It seems that isn't implemented: > > config EFI_MIXED > bool "EFI mixed-mode support" > depends on EFI_STUB && X86_64 > Correct, since that would require translating 64-bit pointers from the firmware into 32-bit pointers for the kernel, which isn't as straight forward as the 32-bit firmware / 64-bit kernel case, i.e. ensure all allocations are < 4GB and truncate 64-bit pointers when they're passed to the firmware. That and the fact that no one has said "We really need support". -- Matt Fleming, Intel Open Source Technology Center -- 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/