Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755193AbaDKSo5 (ORCPT ); Fri, 11 Apr 2014 14:44:57 -0400 Received: from arkanian.console-pimps.org ([212.110.184.194]:46949 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754798AbaDKSoz (ORCPT ); Fri, 11 Apr 2014 14:44:55 -0400 Date: Fri, 11 Apr 2014 19:44:33 +0100 From: Matt Fleming To: "H. Peter Anvin" Cc: Thomas =?iso-8859-1?Q?B=E4chler?= , 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: <20140411184433.GA15344@console-pimps.org> References: <1397239154-30121-1-git-send-email-thomas@archlinux.org> <53482E61.8050606@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <53482E61.8050606@zytor.com> 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 Fri, 11 Apr, at 11:03:13AM, H. Peter Anvin wrote: > On 04/11/2014 10:59 AM, Thomas B?chler wrote: > > EFI stub support is only missing for a 64 bit kernel on 32-bit firmware, > > on 64-bit kernels, EFI stub works as usual. > > --- > > > > Matt, I don't know if this help was intentionally discouraging, > > however, out of curiosity, I tested this with ovmf, and the > > kernel boots fine on 64-bit firmware bit with EFI stub, and on > > 32-bit firmware using efilinux. > > > > Documenting this properly is important for distribution kernels. > > We would want to support this on Arch, but not if it means > > introducing a regression for EFI stub users. > > > > arch/x86/Kconfig | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 5b8ec0f..2bbbbb9 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -1529,8 +1529,8 @@ config EFI_MIXED > > mode. > > > > Note that it is not possible to boot a mixed-mode enabled > > - kernel via the EFI boot stub - a bootloader that supports > > - the EFI handover protocol must be used. > > + kernel via the EFI boot stub on 32-bit firmware - a bootloader > > + that supports the EFI handover protocol must be used. > > > > If unsure, say N. > > > > 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. -- 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/