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Date:   Mon, 28 Aug 2023 08:38:10 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Alexander Duyck <alexander.duyck@gmail.com>
Cc:     Yunsheng Lin <linyunsheng@huawei.com>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Mina Almasry <almasrymina@google.com>, davem@davemloft.net,
        pabeni@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Lorenzo Bianconi <lorenzo@kernel.org>,
        Liang Chen <liangchen.linux@gmail.com>,
        Alexander Lobakin <aleksander.lobakin@intel.com>,
        Saeed Mahameed <saeedm@nvidia.com>,
        Leon Romanovsky <leon@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>
Subject: Re: [PATCH net-next v7 1/6] page_pool: frag API support for 32-bit
 arch with 64-bit DMA
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On Mon, 28 Aug 2023 07:50:33 -0700 Alexander Duyck wrote:
> Actually we could keep it pretty simple. We just have to create a
> #define using DMA_BIT_MASK for the size of the page pool DMA. We could
> name it something like PP_DMA_BIT_MASK. The drivers would just have to
> use that to define their bit mask when they call
> dma_set_mask_and_coherent. In that case the DMA API would switch to
> bounce buffers automatically in cases where the page DMA address would
> be out of bounds.
> 
> The other tweak we could look at doing would be to just look at the
> dma_get_required_mask and add a warning and/or fail to load page pool
> on systems where the page pool would not be able to process that when
> ANDed with the device dma mask.
> 
> With those two changes the setup should be rock solid in terms of any
> risks of the DMA address being out of bounds, and with minimal
> performance impact as we would have verified all possibilities before
> we even get into the hot path.

Sounds like a plan!