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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 91DF3C433DF for ; Thu, 4 Jun 2020 14:05:24 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1361A207DF for ; Thu, 4 Jun 2020 14:05:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1361A207DF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49d6xC0jC9zDqYY for ; 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Thu, 4 Jun 2020 15:59:38 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 30FE18B8C6; Thu, 4 Jun 2020 15:59:40 +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 7rmDmWjkLUfq; Thu, 4 Jun 2020 15:59:40 +0200 (CEST) Received: from pc16570vm.idsi0.si.c-s.fr (po15451.idsi0.si.c-s.fr [10.25.210.22]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B7C278B8C4; Thu, 4 Jun 2020 15:59:39 +0200 (CEST) Subject: Re: linux-next: build failure on powerpc 8xx with 16k pages To: Will Deacon References: <20200604111723.GA1267@willie-the-truck> From: Christophe Leroy Message-ID: <96fdc23c-ca08-6b6a-ebdd-23cedfada77d@csgroup.eu> Date: Thu, 4 Jun 2020 13:55:45 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200604111723.GA1267@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stephen Rothwell , peterz@infradead.org, Linux Kernel Mailing List , Linux Next Mailing List , Andrew Morton , PowerPC , Thomas Gleixner Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 06/04/2020 11:17 AM, Will Deacon wrote: > Hi, [+Peter] > > On Thu, Jun 04, 2020 at 10:48:03AM +0000, Christophe Leroy wrote: >> Using mpc885_ads_defconfig with CONFIG_PPC_16K_PAGES instead of >> CONFIG_PPC_4K_PAGES, getting the following build failure: >> >> CC mm/gup.o >> In file included from ./include/linux/kernel.h:11:0, >> from mm/gup.c:2: >> In function 'gup_hugepte.constprop', >> inlined from 'gup_huge_pd.isra.78' at mm/gup.c:2465:8: >> ./include/linux/compiler.h:392:38: error: call to '__compiletime_assert_257' >> declared with attribute error: Unsupported access size for >> {READ,WRITE}_ONCE(). >> _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> ^ >> ./include/linux/compiler.h:373:4: note: in definition of macro >> '__compiletime_assert' >> prefix ## suffix(); \ >> ^ >> ./include/linux/compiler.h:392:2: note: in expansion of macro >> '_compiletime_assert' >> _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> ^ >> ./include/linux/compiler.h:405:2: note: in expansion of macro >> 'compiletime_assert' >> compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ >> ^ >> ./include/linux/compiler.h:291:2: note: in expansion of macro >> 'compiletime_assert_rwonce_type' >> compiletime_assert_rwonce_type(x); \ >> ^ >> mm/gup.c:2428:8: note: in expansion of macro 'READ_ONCE' >> pte = READ_ONCE(*ptep); >> ^ >> In function 'gup_get_pte', >> inlined from 'gup_pte_range' at mm/gup.c:2228:9, >> inlined from 'gup_pmd_range' at mm/gup.c:2613:15, >> inlined from 'gup_pud_range' at mm/gup.c:2641:15, >> inlined from 'gup_p4d_range' at mm/gup.c:2666:15, >> inlined from 'gup_pgd_range' at mm/gup.c:2694:15, >> inlined from 'internal_get_user_pages_fast' at mm/gup.c:2785:3: > > At first glance, this looks like a real bug in the 16k page code -- you're > loading the pte non-atomically on the fast GUP path and so you're prone to > tearing, which probably isn't what you want. For a short-term hack, I'd > suggest having CONFIG_HAVE_FAST_GUP depend on !CONFIG_PPC_16K_PAGES, but if > you want to support this them you'll need to rework your pte_t so that it > can be loaded atomically. What do you mean by *rework* pte_t ? pte are 32 bits words in size and are spread every 4 words in memory. Therefore pte_t has to be 128 bits because unlike huge_pte handling which always use huge_pte_offset() in loops, many many places in the kernel do pte++, so we need the pte type to be the size of the interval from one pte to the next one. Christophe