netdev - Re: [PATCH net-next v6] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

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Date:   Mon, 15 Nov 2021 10:53:12 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Guillaume Tucker <guillaume.tucker@...labora.com>,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxarm@...neuler.org,
        hawk@...nel.org, akpm@...ux-foundation.org, peterz@...radead.org,
        will@...nel.org, jhubbard@...dia.com, yuzhao@...gle.com,
        mcroce@...rosoft.com, fenghua.yu@...el.com, feng.tang@...el.com,
        jgg@...pe.ca, aarcange@...hat.com, guro@...com,
        "kernelci@...ups.io" <kernelci@...ups.io>
Subject: Re: [PATCH net-next v6] page_pool: disable dma mapping support for
 32-bit arch with 64-bit DMA

On Mon, Nov 15, 2021 at 08:48:30PM +0200, Ilias Apalodimas wrote:
> page_pool (the API in question), apart from allocating memory can manage
> the mappings for you.  However while doing so it stores some parts (incl
> the dma addr) in struct page.  The code in there could be simplified if 
> we skipped support of the 'mapping' feature for 32-bit architectures with 
> 64-bit DMA.  We thought no driver was using the mapping feature (on 32bits)
> and cleaned up that part, but apparently we missed 
> '32-bit -- LPAE -- page pool manages DMA mappings'

It is a very common configuration on various architectures, so I fear
you'll have to support it and undo the cleanup.