linux-kernel - Re: [PATCH 5.2 073/131] dma-direct: correct the physical addr in dma_direct_sync_sg_for

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Message-ID: <9dd82745-1673-afc3-5eb4-8b79ddb5824b@arm.com>
Date:   Tue, 6 Aug 2019 13:57:56 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Fugang Duan <fugang.duan@....com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 5.2 073/131] dma-direct: correct the physical addr in
 dma_direct_sync_sg_for_cpu/device

On 06/08/2019 13:41, Sasha Levin wrote:
> On Mon, Aug 05, 2019 at 03:02:40PM +0200, Greg Kroah-Hartman wrote:
>> [ Upstream commit 449fa54d6815be8c2c1f68fa9dbbae9384a7c03e ]
>>
>> dma_map_sg() may use swiotlb buffer when the kernel command line includes
>> "swiotlb=force" or the dma_addr is out of dev->dma_mask range.  After
>> DMA complete the memory moving from device to memory, then user call
>> dma_sync_sg_for_cpu() to sync with DMA buffer, and copy the original
>> virtual buffer to other space.
>>
>> So dma_direct_sync_sg_for_cpu() should use swiotlb physical addr, not
>> the original physical addr from sg_phys(sg).
>>
>> dma_direct_sync_sg_for_device() also has the same issue, correct it as
>> well.
>>
>> Fixes: 55897af63091("dma-direct: merge swiotlb_dma_ops into the 
>> dma_direct code")
>> Signed-off-by: Fugang Duan <fugang.duan@....com>
>> Reviewed-by: Robin Murphy <robin.murphy@....com>
>> Signed-off-by: Christoph Hellwig <hch@....de>
>> Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> I'm going to drop this one. There's a fix to it upstream, but the fix
> also seems to want 0036bc73ccbe ("drm/msm: stop abusing dma_map/unmap for
> cache") which we're not taking, so I'm just going to drop this one as
> well.

Given that the two commits touch entirely separate files I'm not sure 
what the imagined dependency could be :/

0036bc73ccbe is indeed not a fix (frankly I'm not convinced it's even a 
valid change at all) but even conceptually it bears no relation 
whatsoever to the genuine bug fixed by 449fa54d6815.

Robin.

> 
> If someone wants it in the stable trees, please send a tested backport.
> 
> -- 
> Thanks,
> Sasha