linux-kernel - Re: [PATCH 06/19] dma-iommu: fix and refactor iommu_dma

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Date:   Mon, 11 Feb 2019 17:03:25 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/19] dma-iommu: fix and refactor iommu_dma_mmap

On Tue, Feb 05, 2019 at 03:02:23PM +0000, Robin Murphy wrote:
> On 14/01/2019 09:41, Christoph Hellwig wrote:
>> The current iommu_dma_mmap code does not properly handle memory from the
>> page allocator that hasn't been remapped, which can happen in the rare
>> case of allocations for a coherent device that aren't allowed to block.
>>
>> Fix this by replacing iommu_dma_mmap with a slightly tweaked copy of
>> dma_common_mmap with special handling for the remapped array of
>> pages allocated from __iommu_dma_alloc.
>
> If there's an actual bugfix here, can we make that before all of the other 
> code movement? If it's at all related to other reports of weird mmap 
> behaviour it might warrant backporting, and either way I'm finding it 
> needlessly tough to follow what's going on in this patch :(

The bug fix is to handle non-vmalloc pages.  I'll see if I can do
a smaller and more bandaid-y fix first.