Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752772AbaDNHPl (ORCPT ); Mon, 14 Apr 2014 03:15:41 -0400 Received: from mail-ee0-f44.google.com ([74.125.83.44]:40064 "EHLO mail-ee0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752534AbaDNHPk (ORCPT ); Mon, 14 Apr 2014 03:15:40 -0400 Date: Mon, 14 Apr 2014 09:15:35 +0200 From: Ingo Molnar To: Matt Fleming Cc: "H. Peter Anvin" , 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: <20140414071534.GA19501@gmail.com> References: <1397239154-30121-1-git-send-email-thomas@archlinux.org> <53482E61.8050606@zytor.com> <20140411184433.GA15344@console-pimps.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20140411184433.GA15344@console-pimps.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 * Matt Fleming wrote: > 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. Same goes for booting a 32-bit kernel on 64-bit firmware, right? Thanks, Ingo -- 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/