linux-kernel - Re: [PATCH v4 3/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

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Message-ID: <20181205144308.GA28409@infradead.org>
Date:   Wed, 5 Dec 2018 06:43:08 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Levin Alexander <Alexander.Levin@...rosoft.com>,
        Huaisheng Ye <yehs1@...ovo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tomasz Figa <tfiga@...gle.com>, yingjoe.chen@...iatek.com,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4 3/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory,
 and improve debugging

On Wed, Dec 05, 2018 at 02:40:06PM +0000, Robin Murphy wrote:
> 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.

Well, arm32 can't address more than 32-bits in the linear kernel
mapping, so GFP_KERNEL should be perfectly fine there if the limit
really is 32-bits and not 31 or smaller because someone stole a bit
or two somewhere.