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 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 356A7C433B4 for ; Wed, 14 Apr 2021 21:58:27 +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 87B9F61179 for ; Wed, 14 Apr 2021 21:58:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87B9F61179 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 4FLGZ90S00z3c0k for ; Thu, 15 Apr 2021 07:58:25 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.85.151; 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 [185.58.85.151]) (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 4FLGYm2k9Bz2xZM for ; Thu, 15 Apr 2021 07:58:04 +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-mtapsc-4-PsdLgvNoPOivxmwyvxbtWw-1; Wed, 14 Apr 2021 22:56:40 +0100 X-MC-Unique: PsdLgvNoPOivxmwyvxbtWw-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; Wed, 14 Apr 2021 22:56:39 +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; Wed, 14 Apr 2021 22:56:39 +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: AQHXMXYmwdfrgigLI0exh4xFUSZq9Kq0jZ3g Date: Wed, 14 Apr 2021 21:56:39 +0000 Message-ID: References: <20210410205246.507048-1-willy@infradead.org> <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> In-Reply-To: <20210414213556.GY2531743@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: 14 April 2021 22:36 >=20 > On Wed, Apr 14, 2021 at 09:13:22PM +0200, Jesper Dangaard Brouer wrote: > > (If others want to reproduce). First I could not reproduce on ARM32. > > Then I found out that enabling CONFIG_XEN on ARCH=3Darm was needed to > > cause the issue by enabling CONFIG_ARCH_DMA_ADDR_T_64BIT. >=20 > hmmm ... you should be able to provoke it by enabling ARM_LPAE, > which selects PHYS_ADDR_T_64BIT, and >=20 > config ARCH_DMA_ADDR_T_64BIT > def_bool 64BIT || PHYS_ADDR_T_64BIT >=20 > > struct page { > > long unsigned int flags; /* 0 4= */ > > > > /* XXX 4 bytes hole, try to pack */ > > > > union { > > struct { > > struct list_head lru; /* 8 8= */ > > struct address_space * mapping; /* 16 4= */ > > long unsigned int index; /* 20 4= */ > > long unsigned int private; /* 24 4= */ > > }; /* 8 20= */ > > struct { > > dma_addr_t dma_addr Adding __packed here will remove the 4 byte hole before the union and the compiler seems clever enough to know that anything following a 'long' must also be 'long' aligned. So you don't get anything horrid like byte accesses. On 64bit dma_addr will remain 64bit aligned. On arm32 dma_addr will be 32bit aligned - but forcing two 32bit access won't make any difference. So definitely the only simple fix. =09David > > ; /* 8 8= */ > > }; /* 8 8= */ > [...] > > } __attribute__((__aligned__(8))); /* 8 24= */ > > union { > > atomic_t _mapcount; /* 32 4= */ > > unsigned int page_type; /* 32 4= */ > > unsigned int active; /* 32 4= */ > > int units; /* 32 4= */ > > }; /* 32 4= */ > > atomic_t _refcount; /* 36 4= */ > > > > /* size: 40, cachelines: 1, members: 4 */ > > /* sum members: 36, holes: 1, sum holes: 4 */ > > /* forced alignments: 1, forced holes: 1, sum forced holes: 4 *= / > > /* last cacheline: 40 bytes */ > > } __attribute__((__aligned__(8))); >=20 > If you also enable CONFIG_MEMCG or enough options to make > LAST_CPUPID_NOT_IN_PAGE_FLAGS true, you'll end up with another 4-byte > hole at the end. - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)