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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 52AB4C43460 for ; Wed, 14 Apr 2021 11:51:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E168C611F2 for ; Wed, 14 Apr 2021 11:51:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E168C611F2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 19EEF6B007B; Wed, 14 Apr 2021 07:51:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1764A6B007D; Wed, 14 Apr 2021 07:51:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 017876B007E; Wed, 14 Apr 2021 07:51:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0042.hostedemail.com [216.40.44.42]) by kanga.kvack.org (Postfix) with ESMTP id D6ADF6B007B for ; Wed, 14 Apr 2021 07:51:43 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 8EF8DA8CB for ; Wed, 14 Apr 2021 11:51:43 +0000 (UTC) X-FDA: 78030808086.24.FC971D0 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf10.hostedemail.com (Postfix) with ESMTP id 6A59F40002C4 for ; Wed, 14 Apr 2021 11:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=6j2YFPpldChGlEhTkgAYG/8AUFiAqXWlLNjztkCHHPQ=; b=J5BS1O4q7ajQjzXd/LDJSC/n5W nLaatbwhpGPw27uZHO96g6+/tyMJhvL6qzIDuTqVYDpLZWsiE1eH4gs+RGnwjwtZofj11rAp/QNXo 5zG9CPBgECBICOpGLmaKDiNFg88n/0HpOy3h47nUCcA+napEcZ6cGJeegmGXvIMAF1IlI0QKv3yBn t6pmOrCaFDoZvjKu2kkCNcN34EEDw6FAeKgqXUk9Y5TV1rcrTtUeqHGfKDG51wcCgKv9JHy4zWIOT ccnhwj9yHyFetqx/J/jBsogxkFb+x3kADp7eIqy6wSJt5ccTYHYk9f87uwXMNh3c7s66KKsbIgnZx RoTlxVDw==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lWe2m-0073tL-Rj; Wed, 14 Apr 2021 11:51:01 +0000 Date: Wed, 14 Apr 2021 12:50:52 +0100 From: Matthew Wilcox To: Jesper Dangaard Brouer Cc: 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: <20210414115052.GS2531743@casper.infradead.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210414101044.19da09df@carbon> X-Stat-Signature: 9ppecyzf4hf8pqu4fbmw4k6jiche76wo X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6A59F40002C4 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618401097-728204 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 Wed, Apr 14, 2021 at 10:10:44AM +0200, Jesper Dangaard Brouer wrote: > Yes, indeed! - And very frustrating. It's keeping me up at night. > I'm dreaming about 32 vs 64 bit data structures. My fitbit stats tell > me that I don't sleep well with these kind of dreams ;-) Then you're going to love this ... even with the latest patch, there's still a problem. Because dma_addr_t is still 64-bit aligned _as a type_, that forces the union to be 64-bit aligned (as we already knew and worked around), but what I'd forgotten is that forces the entirety of struct page to be 64-bit aligned. Which means ... /* size: 40, cachelines: 1, members: 4 */ /* padding: 4 */ /* forced alignments: 1 */ /* last cacheline: 40 bytes */ } __attribute__((__aligned__(8))); .. that we still have a hole! It's just moved from being at offset 4 to being at offset 36. > That said, I think we need to have a quicker fix for the immediate > issue with 64-bit bit dma_addr on 32-bit arch and the misalignment hole > it leaves[3] in struct page. In[3] you mention ppc32, does it only > happens on certain 32-bit archs? AFAICT it happens on mips32, ppc32, arm32 and arc. It doesn't happen on x86-32 because dma_addr_t is 32-bit aligned. Doing this fixes it: +++ b/include/linux/types.h @@ -140,7 +140,7 @@ typedef u64 blkcnt_t; * so they don't care about the size of the actual bus addresses. */ #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT -typedef u64 dma_addr_t; +typedef u64 __attribute__((aligned(sizeof(void *)))) dma_addr_t; #else typedef u32 dma_addr_t; #endif > I'm seriously considering removing page_pool's support for doing/keeping > DMA-mappings on 32-bit arch's. AFAIK only a single driver use this. ... if you're going to do that, then we don't need to do this.