From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3353FC433E2 for ; Tue, 8 Sep 2020 05:22:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02EF821897 for ; Tue, 8 Sep 2020 05:22:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728629AbgIHFWw (ORCPT ); Tue, 8 Sep 2020 01:22:52 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:65048 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726387AbgIHFWu (ORCPT ); Tue, 8 Sep 2020 01:22:50 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4Bltny2bk8z9tyfS; Tue, 8 Sep 2020 07:22:46 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id zhKYZbflWiU8; Tue, 8 Sep 2020 07:22:46 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4Bltny1W9Lz9tyfR; Tue, 8 Sep 2020 07:22:46 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 073A98B793; Tue, 8 Sep 2020 07:22:47 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 5cxa6T4RQxxI; Tue, 8 Sep 2020 07:22:46 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BACC88B768; Tue, 8 Sep 2020 07:22:44 +0200 (CEST) Subject: Re: [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding To: Mike Rapoport , Gerald Schaefer Cc: Peter Zijlstra , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Christian Borntraeger , Richard Weinberger , linux-x86 , Russell King , Jason Gunthorpe , Ingo Molnar , Catalin Marinas , Andrey Ryabinin , Heiko Carstens , Arnd Bergmann , John Hubbard , Jeff Dike , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , linux-power , LKML , Andrew Morton , Linus Torvalds References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> <20200907201256.GC1976319@kernel.org> From: Christophe Leroy Message-ID: <9bde9857-fdfd-e384-ea27-a14e5a06f1e6@csgroup.eu> Date: Tue, 8 Sep 2020 07:22:39 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200907201256.GC1976319@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 07/09/2020 à 22:12, Mike Rapoport a écrit : > On Mon, Sep 07, 2020 at 08:00:55PM +0200, Gerald Schaefer wrote: >> This is v2 of an RFC previously discussed here: >> https://lore.kernel.org/lkml/20200828140314.8556-1-gerald.schaefer@linux.ibm.com/ >> >> Patch 1 is a fix for a regression in gup_fast on s390, after our conversion >> to common gup_fast code. It will introduce special helper functions >> pXd_addr_end_folded(), which have to be used in places where pagetable walk >> is done w/o lock and with READ_ONCE, so currently only in gup_fast. >> >> Patch 2 is an attempt to make that more generic, i.e. change pXd_addr_end() >> themselves by adding an extra pXd value parameter. That was suggested by >> Jason during v1 discussion, because he is already thinking of some other >> places where he might want to switch to the READ_ONCE logic for pagetable >> walks. In general, that would be the cleanest / safest solution, but there >> is some impact on other architectures and common code, hence the new and >> greatly enlarged recipient list. >> >> Patch 3 is a "nice to have" add-on, which makes pXd_addr_end() inline >> functions instead of #defines, so that we get some type checking for the >> new pXd value parameter. >> >> Not sure about Fixes/stable tags for the generic solution. Only patch 1 >> fixes a real bug on s390, and has Fixes/stable tags. Patches 2 + 3 might >> still be nice to have in stable, to ease future backports, but I guess >> "nice to have" does not really qualify for stable backports. > > I also think that adding pXd parameter to pXd_addr_end() is a cleaner > way and with this patch 1 is not really required. I would even merge > patches 2 and 3 into a single patch and use only it as the fix. Why not merging patches 2 and 3, but I would keep patch 1 separate but after the generic changes, so that we first do the generic changes, then we do the specific S390 use of it. Christophe