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=-5.3 required=3.0 tests=BAYES_00, 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 BF8B7C433B4 for ; Mon, 19 Apr 2021 06:34:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 00C7761165 for ; Mon, 19 Apr 2021 06:34:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00C7761165 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4C9A26B0036; Mon, 19 Apr 2021 02:34:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4797D6B006E; Mon, 19 Apr 2021 02:34:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 341516B0070; Mon, 19 Apr 2021 02:34:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 17FAE6B0036 for ; Mon, 19 Apr 2021 02:34:46 -0400 (EDT) Received: from smtpin37.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id C6471180AD830 for ; Mon, 19 Apr 2021 06:34:45 +0000 (UTC) X-FDA: 78048153330.37.3989082 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf11.hostedemail.com (Postfix) with ESMTP id F3CEA2000261 for ; Mon, 19 Apr 2021 06:34:32 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A92C068B05; Mon, 19 Apr 2021 08:34:41 +0200 (CEST) Date: Mon, 19 Apr 2021 08:34:41 +0200 From: Christoph Hellwig To: Matthew Wilcox Cc: Jesper Dangaard Brouer , David Laight , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , Ilias Apalodimas , Matteo Croce , Grygorii Strashko , Arnd Bergmann , Christoph Hellwig Subject: Re: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems Message-ID: <20210419063441.GA18787@lst.de> References: <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> <20210416152755.GL2531743@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210416152755.GL2531743@casper.infradead.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: F3CEA2000261 X-Stat-Signature: yc7zzidzwhwfhxkbto6f97ebct6onf5h Received-SPF: none (lst.de>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=verein.lst.de; client-ip=213.95.11.211 X-HE-DKIM-Result: none/none X-HE-Tag: 1618814072-908307 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: On Fri, Apr 16, 2021 at 04:27:55PM +0100, Matthew Wilcox wrote: > On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote: > > See below patch. Where I swap32 the dma address to satisfy > > page->compound having bit zero cleared. (It is the simplest fix I could > > come up with). > > I think this is slightly simpler, and as a bonus code that assumes the > old layout won't compile. So, why do we even do this crappy overlay of a dma address? This just all seems like a giant hack. Random subsystems should not just steal a few struct page fields as that just turns into the desasters like the one we've seen here or probably something worse next time.