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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 C8572C04EBF for ; Wed, 5 Dec 2018 14:40:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8BE3B20850 for ; Wed, 5 Dec 2018 14:40:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8BE3B20850 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727790AbeLEOkN (ORCPT ); Wed, 5 Dec 2018 09:40:13 -0500 Received: from foss.arm.com ([217.140.101.70]:55752 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726918AbeLEOkN (ORCPT ); Wed, 5 Dec 2018 09:40:13 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6FD2380D; Wed, 5 Dec 2018 06:40:12 -0800 (PST) Received: from [10.1.196.75] (e110467-lin.cambridge.arm.com [10.1.196.75]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8E4E63F59C; Wed, 5 Dec 2018 06:40:08 -0800 (PST) Subject: Re: [PATCH v4 3/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging To: Christoph Hellwig , Nicolas Boichat Cc: Will Deacon , Joerg Roedel , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Michal Hocko , Mel Gorman , Levin Alexander , Huaisheng Ye , Mike Rapoport , linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Yong Wu , Matthias Brugger , Tomasz Figa , yingjoe.chen@mediatek.com, Matthew Wilcox References: <20181205054828.183476-1-drinkcat@chromium.org> <20181205054828.183476-4-drinkcat@chromium.org> <20181205135406.GA29031@infradead.org> From: Robin Murphy Message-ID: <1d211576-9153-cca1-5cd0-8c9881bd3fa4@arm.com> Date: Wed, 5 Dec 2018 14:40:06 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181205135406.GA29031@infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/12/2018 13:54, Christoph Hellwig wrote: > On Wed, Dec 05, 2018 at 01:48:28PM +0800, Nicolas Boichat wrote: >> IOMMUs using ARMv7 short-descriptor format require page tables >> (level 1 and 2) to be allocated within the first 4GB of RAM, even >> on 64-bit systems. > >> +#ifdef CONFIG_ZONE_DMA32 >> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32 >> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA32 >> +#else >> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA >> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA >> +#endif > > How does using GFP_DMA make sense based on the above? If the system > has more than 32-bits worth of RAM it should be using GFP_DMA32, else > GFP_KERNEL, not GFP_DMA for an arch defined small addressability pool. 32-bit Arm doesn't have ZONE_DMA32, but has (or at least had at the time) a 2GB ZONE_DMA. Whether we actually need that or not depends on how this all interacts with LPAE and highmem, but I'm not sure of those details off-hand. Robin.