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Date:   Sun, 14 Apr 2019 23:30:58 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Tom Murphy <tmurphy@arista.com>
Cc:     iommu@lists.linux-foundation.org, Heiko Stuebner <heiko@sntech.de>,
        Will Deacon <will.deacon@arm.com>,
        David Brown <david.brown@linaro.org>,
        linux-samsung-soc@vger.kernel.org, dima@arista.com,
        Krzysztof Kozlowski <krzk@kernel.org>,
        linux-rockchip@lists.infradead.org, Kukjin Kim <kgene@kernel.org>,
        Andy Gross <andy.gross@linaro.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        linux-arm-msm@vger.kernel.org, linux-mediatek@lists.infradead.org,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        murphyt7@tcd.ie, Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 1/9] iommu/dma-iommu: Add iommu_map_atomic
Message-ID: <20190415063058.GA1377@infradead.org>
References: <20190411184741.27540-1-tmurphy@arista.com>
 <20190411184741.27540-2-tmurphy@arista.com>
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On Thu, Apr 11, 2019 at 07:47:30PM +0100, Tom Murphy via iommu wrote:
> The iommu ops .map function (or the iommu_map function which calls it)
> was always supposed to be sleepable (according to Joerg's comment in
> this thread: https://lore.kernel.org/patchwork/patch/977520/ ) and so
> should probably have had a "might_sleep()" since it was written. However
> currently the dma-iommu api can call iommu_map in an atomic context,
> which it shouldn't do. This doesn't cause any problems because any iommu
> driver which uses the dma-iommu api uses gfp_atomic in it's iommu_ops
> .map function. But doing this wastes the memory allocators atomic pools.
> 
> Add a new function iommu_map_atomic, use it in the dma-iommu api and add
> “might_sleep()” to the iommu_map function.
> 
> After this change all drivers which use the dma-iommu api need to
> implement the new iommu ops .map_atomic function. For the moment just
> reuse the driver's iommus ops .map function for .map_atomic.

Instead of duplicating the callchain shouldn't we just pass down a flag
to indicate if the context can sleep or not?  Especially as all the
existing arm drivers already implement the atomic behavior, which is
a majority of struct iommu_ops based iommu drivers.