From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 Subject: Re: [RFC PATCH v2 0/3] mm/gup: fix gup_fast with dynamic page table folding 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 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-s390-owner@vger.kernel.org List-ID: 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 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