amdgpu/TTM oopses since merging swiotlb_dma_ops into the dma_direct code

[Christian König]

Am 10.01.19 um 14:57 schrieb Christoph Hellwig:
> On Thu, Jan 10, 2019 at 10:59:02AM +0100, Michel Dänzer wrote:
>> Hi Christoph,
>>
>>
>> https://bugs.freedesktop.org/109234 (please ignore comments #6-#9) was
>> bisected to your commit 55897af63091 "dma-direct: merge swiotlb_dma_ops
>> into the dma_direct code". Any ideas?
>  From the trace it looks like we git the case where swiotlb tries
> to copy back data from a bounce buffer, but hits a dangling or NULL
> pointer.  So a couple questions for the submitter:
>
>   - does the system have more than 4GB memory and thus use swiotlb?
>     (check /proc/meminfo, and if something SWIOTLB appears in dmesg)
>   - does the device this happens on have a DMA mask smaller than
>     the available memory, that is should swiotlb be used here to start
>     with?

Rather unlikely. The device is an AMD GPU, so we can address memory up 
to 1TB.

Christian.

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