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 5BCA8C2BBD0 for ; Tue, 8 Sep 2020 04:43:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9148821D1B for ; Tue, 8 Sep 2020 04:43:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9148821D1B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B624E6B0002; Tue, 8 Sep 2020 00:43:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AEB5B6B0037; Tue, 8 Sep 2020 00:43:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 98EF96B0055; Tue, 8 Sep 2020 00:43:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0073.hostedemail.com [216.40.44.73]) by kanga.kvack.org (Postfix) with ESMTP id 74DE86B0002 for ; Tue, 8 Sep 2020 00:43:00 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 2D39F181AC9CB for ; Tue, 8 Sep 2020 04:43:00 +0000 (UTC) X-FDA: 77238649320.08.nail45_540413c270d2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 03BF51819E76B for ; Tue, 8 Sep 2020 04:42:59 +0000 (UTC) X-HE-Tag: nail45_540413c270d2 X-Filterd-Recvd-Size: 4919 Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Tue, 8 Sep 2020 04:42:59 +0000 (UTC) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4Blsw04dynz9v07M; Tue, 8 Sep 2020 06:42:56 +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 1zRgiYU2XgXP; Tue, 8 Sep 2020 06:42:56 +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 4Blsw02Lphz9v07L; Tue, 8 Sep 2020 06:42:56 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0E1EE8B775; Tue, 8 Sep 2020 06:42:57 +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 IWq5rXD7F6WV; Tue, 8 Sep 2020 06:42:56 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id D80618B768; Tue, 8 Sep 2020 06:42:54 +0200 (CEST) Subject: Re: [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding To: Gerald Schaefer , Jason Gunthorpe , John Hubbard Cc: Peter Zijlstra , Dave Hansen , linux-mm , Paul Mackerras , linux-sparc , Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-arch , linux-s390 , Vasily Gorbik , Richard Weinberger , linux-x86 , Russell King , Christian Borntraeger , Ingo Molnar , Catalin Marinas , Andrey Ryabinin , Heiko Carstens , Arnd Bergmann , Jeff Dike , linux-um , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , linux-arm , linux-power , LKML , Andrew Morton , Linus Torvalds , Mike Rapoport References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> From: Christophe Leroy Message-ID: <9f9acde7-c400-53b0-38ec-ad3e48de5371@csgroup.eu> Date: Tue, 8 Sep 2020 06:42:50 +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: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr X-Rspamd-Queue-Id: 03BF51819E76B X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 07/09/2020 =C3=A0 20:00, Gerald Schaefer a =C3=A9crit=C2=A0: > This is v2 of an RFC previously discussed here: > https://lore.kernel.org/lkml/20200828140314.8556-1-gerald.schaefer@linu= x.ibm.com/ >=20 > Patch 1 is a fix for a regression in gup_fast on s390, after our conver= sion > 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. >=20 > Patch 2 is an attempt to make that more generic, i.e. change pXd_addr_e= nd() > themselves by adding an extra pXd value parameter. That was suggested b= y > Jason during v1 discussion, because he is already thinking of some othe= r > places where he might want to switch to the READ_ONCE logic for pagetab= le > walks. In general, that would be the cleanest / safest solution, but th= ere > is some impact on other architectures and common code, hence the new an= d > greatly enlarged recipient list. >=20 > 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 th= e > new pXd value parameter. >=20 > 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 migh= t > still be nice to have in stable, to ease future backports, but I guess > "nice to have" does not really qualify for stable backports. If one day you have to backport a fix that requires patch 2 and/or 3,=20 just mark it "depends-on:" and the patches will go in stable at the=20 relevant time. Christophe