linux-kernel - Re: [PATCH v6 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

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Message-ID: <20181210153524.GB24554@edgewater-inn.cambridge.arm.com>
Date:   Mon, 10 Dec 2018 15:35:24 +0000
From:   Will Deacon <will.deacon@....com>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Robin Murphy <robin.murphy@....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,
        hch@...radead.org, Matthew Wilcox <willy@...radead.org>,
        hsinyi@...omium.org, stable@...r.kernel.org
Subject: Re: [PATCH v6 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory,
 and improve debugging

On Mon, Dec 10, 2018 at 09:15:03AM +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.
> 
> For level 1/2 pages, ensure GFP_DMA32 is used if CONFIG_ZONE_DMA32
> is defined (e.g. on arm64 platforms).
> 
> For level 2 pages, allocate a slab cache in SLAB_CACHE_DMA32. Note
> that we do not explicitly pass GFP_DMA[32] to kmem_cache_zalloc,
> as this is not strictly necessary, and would cause a warning
> in mm/sl*b.c, as we did not update GFP_SLAB_BUG_MASK.
> 
> Also, print an error when the physical address does not fit in
> 32-bit, to make debugging easier in the future.
> 
> Cc: stable@...r.kernel.org
> Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32")
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> ---

Acked-by: Will Deacon <will.deacon@....com>

Will