On Fri, Dec 13, 2019 at 11:33:59AM -0800, Gurchetan Singh wrote:
> I'm just going to put Chia's review comment here since it sums
> the issue rather nicely:
>
> "(1) Semantically, a dma-buf is in DMA domain. CPU access from the
> importer must be surrounded by {begin,end}_cpu_access. This gives the
> exporter a chance to move the buffer to the CPU domain temporarily.
>
> (2) When the exporter itself has other means to do CPU access, it is
> only reasonable for the exporter to move the buffer to the CPU domain
> before access, and to the DMA domain after access. The exporter can
> potentially reuse {begin,end}_cpu_access for that purpose.
>
> Because of (1), udmabuf does need to implement the
> {begin,end}_cpu_access hooks. But "begin" should mean
> dma_sync_sg_for_cpu and "end" should mean dma_sync_sg_for_device.
>
> Because of (2), if userspace wants to continuing accessing through the
> memfd mapping, it should call udmabuf's {begin,end}_cpu_access to
> avoid cache issues."
>
> Reported-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> Suggested-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> Fixes: 284562e1f34 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")
Needs 12 hash digits.
Also your signed-off is missing ...
cheers,
Gerd
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