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=-2.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PDS_BAD_THREAD_QP_64, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 010FBC433ED for ; Thu, 15 Apr 2021 21:12:29 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 024E061073 for ; Thu, 15 Apr 2021 21:12:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 024E061073 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4FLsVf3PGXz3btZ for ; Fri, 16 Apr 2021 07:12:26 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.86.151; helo=eu-smtp-delivery-151.mimecast.com; envelope-from=david.laight@aculab.com; receiver=) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4FLsVH1S0Kz30NN for ; Fri, 16 Apr 2021 07:12:04 +1000 (AEST) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-157-edG-rOXuODirktZxzgM_1A-1; Thu, 15 Apr 2021 22:11:57 +0100 X-MC-Unique: edG-rOXuODirktZxzgM_1A-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 15 Apr 2021 22:11:56 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Thu, 15 Apr 2021 22:11:56 +0100 From: David Laight To: 'Matthew Wilcox' , Jesper Dangaard Brouer Subject: RE: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Thread-Topic: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Thread-Index: AQHXMXYmwdfrgigLI0exh4xFUSZq9Kq0jZ3ggAFYFFmAAC15oA== Date: Thu, 15 Apr 2021 21:11:56 +0000 Message-ID: <5179a01a462f43d6951a65de2a299070@AcuMS.aculab.com> References: <20210410205246.507048-2-willy@infradead.org> <20210411114307.5087f958@carbon> <20210411103318.GC2531743@casper.infradead.org> <20210412011532.GG2531743@casper.infradead.org> <20210414101044.19da09df@carbon> <20210414115052.GS2531743@casper.infradead.org> <20210414211322.3799afd4@carbon> <20210414213556.GY2531743@casper.infradead.org> <20210415200832.32796445@carbon> <20210415182155.GD2531743@casper.infradead.org> In-Reply-To: <20210415182155.GD2531743@casper.infradead.org> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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: Arnd Bergmann , Grygorii Strashko , "netdev@vger.kernel.org" , Ilias Apalodimas , "linux-mips@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Matteo Croce , "linuxppc-dev@lists.ozlabs.org" , Christoph Hellwig , "linux-arm-kernel@lists.infradead.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Matthew Wilcox > Sent: 15 April 2021 19:22 >=20 > On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote: > > +static inline > > +dma_addr_t page_pool_dma_addr_read(dma_addr_t dma_addr) > > +{ > > +=09/* Workaround for storing 64-bit DMA-addr on 32-bit machines in str= uct > > +=09 * page. The page->dma_addr share area with page->compound_head wh= ich > > +=09 * use bit zero to mark compound pages. This is okay, as DMA-addr a= re > > +=09 * aligned pointers which have bit zero cleared. > > +=09 * > > +=09 * In the 32-bit case, page->compound_head is 32-bit. Thus, when > > +=09 * dma_addr_t is 64-bit it will be located in top 32-bit. Solve by > > +=09 * swapping dma_addr 32-bit segments. > > +=09 */ > > +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT >=20 > #if defined(CONFIG_ARCH_DMA_ADDR_T_64BIT) && defined(__BIG_ENDIAN) > otherwise you'll create the problem on ARM that you're avoiding on PPC ..= . >=20 > I think you want to delete the word '_read' from this function name becau= se > you're using it for both read and write. I think I'd use explicit dma_addr_hi and dma_addr_lo and separate read/write functions just to make absolutely sure nothing picks up the swapped value. Isn't it possible to move the field down one long? This might require an explicit zero - but this is not a common code path - the extra write will be noise. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)