[PATCH v6 06/13] nvme-pci: implement dma-buf backed requests

[Pavel Begunkov]

On 9/23/26 05:55, Christoph Hellwig wrote:
> On Tue, Sep 22, 2026 at 02:37:08PM +0100, Pavel Begunkov wrote:
>>> Sashiko had a few comments, which I think are correct - if we use
>>> dma_map_sg to map the data, we need to use the sync_sg APIs to
>>> transfer ownership.  That only matters on non-coherent architectures
>>> with MMU, but we need to get it right.
>>
>> I've seen that and fixed everything locally that should be fixed,
>> apart from the sync. I wonder what we can do about that? I can
>> somehow replace it with the sg variant for now, but sync'ing the
>> entire possibly multi-GB mapping for, let's say, a 512B I/O, sounds
>> not wise.
> 
> If we'd want to fix this for real we'd need to add an offset to the
> sync by sg methods.  Or move away from scatterlists in dma-buf, given
> that they are a horrible API.  All of these are bigger projects,
> though.  So for now I think you'd want to do the sync all, and have
> the people who run high-performance io_uring code on non-coherent
> platforms suffer.
> 
>> And I can think of another place that does mix sync_single
>> with sgs.
> 
> Which one?

All the recent networking zero-copy / dma-buf apis.

-- 
Pavel Begunkov