From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934650AbbI2Kle (ORCPT ); Tue, 29 Sep 2015 06:41:34 -0400 Received: from mail-io0-f174.google.com ([209.85.223.174]:35100 "EHLO mail-io0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933788AbbI2KlY (ORCPT ); Tue, 29 Sep 2015 06:41:24 -0400 MIME-Version: 1.0 In-Reply-To: <20150929091230.GA2023@gmail.com> References: <1443218539-7610-1-git-send-email-matt@codeblueprint.co.uk> <1443218539-7610-2-git-send-email-matt@codeblueprint.co.uk> <20150926055643.GA25877@gmail.com> <20150926134329.GA3144@codeblueprint.co.uk> <20150927070355.GB26125@gmail.com> <20150928082245.GA28796@gmail.com> <20150929091230.GA2023@gmail.com> Date: Tue, 29 Sep 2015 12:41:23 +0200 Message-ID: Subject: Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime From: Ard Biesheuvel To: Ingo Molnar Cc: Matt Fleming , Thomas Gleixner , "H. Peter Anvin" , Matt Fleming , "linux-kernel@vger.kernel.org" , "linux-efi@vger.kernel.org" , "Lee, Chun-Yi" , Borislav Petkov , Leif Lindholm , Peter Jones , James Bottomley , Matthew Garrett , Dave Young , "stable@vger.kernel.org" , Linus Torvalds , Borislav Petkov , Andy Lutomirski , Denys Vlasenko , Brian Gerst , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29 September 2015 at 11:12, Ingo Molnar wrote: > > * Ard Biesheuvel wrote: > >> > except that I don't think >> > the condition on 64-bit makes any sense: >> > >> > + if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) { >> > >> > I can see us being nervous wrt. backported patches, but is there any strong reason >> > to not follow this up with a third (non-backported) patch that changes this to: >> > >> > + if (!efi_enabled(EFI_OLD_MEMMAP)) { >> > >> > for v4.4? >> > >> >> The 32-bit side essentially implements the old memmap only, which is the the >> bottom-up version. So old memmap will be implied by 32-bit but not set in the >> EFI flags, resulting in the reverse enumeration being used with the bottom-up >> mapping logic. The net result of that is that we create the same problem for >> 32-bit that we are trying to solve for 64-bit, i.e., the regions will end up in >> reverse order in the VA mapping. >> >> To deobfuscate this particular conditional, we could set EFI_OLD_MEMMAP >> unconditionally on 32-bit x86. Or we could reshuffle variables and conditionals >> in various other way. > > Setting EFI_OLD_MEMMAP would be fine, if doing that has no bad side effects. > >> [...] I am not convinced that the overall end result will be any better though. > > That's not true, we change an obscure, implicit dependency on 32-bit detail to an > explicit EFI_OLD_MEMMAP flag that shows exactly what's happening. That's a clear > improvement. > OK, fair enough. I agree that setting the flag for 32-bit would be semantically correct. I will leave it to Matt to comment whether it is reasonable in terms of changes to other parts of the code. Thanks, Ard.