Re: [PATCH v7 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf

[Christian König]

On 11/17/25 18:16, Jason Gunthorpe wrote:
> On Mon, Nov 17, 2025 at 08:36:20AM -0700, Alex Williamson wrote:
>> On Tue, 11 Nov 2025 09:54:22 +0100
>> Christian König <christian.koenig@xxxxxxx> wrote:
>>
>>> On 11/10/25 21:42, Alex Williamson wrote:
>>>> On Thu,  6 Nov 2025 16:16:45 +0200
>>>> Leon Romanovsky <leon@xxxxxxxxxx> wrote:
>>>>   
>>>>> Changelog:
>>>>> v7:
>>>>>  * Dropped restore_revoke flag and added vfio_pci_dma_buf_move
>>>>>    to reverse loop.
>>>>>  * Fixed spelling errors in documentation patch.
>>>>>  * Rebased on top of v6.18-rc3.
>>>>>  * Added include to stddef.h to vfio.h, to keep uapi header file independent.  
>>>>
>>>> I think we're winding down on review comments.  It'd be great to get
>>>> p2pdma and dma-buf acks on this series.  Otherwise it's been posted
>>>> enough that we'll assume no objections.  Thanks,  
>>>
>>> Already have it on my TODO list to take a closer look, but no idea when that will be.
>>>
>>> This patch set is on place 4 or 5 on a rather long list of stuff to review/finish.
>>
>> Hi Christian,
>>
>> Gentle nudge.  Leon posted v8[1] last week, which is not drawing any
>> new comments.  Do you foresee having time for review that I should
>> still hold off merging for v6.19 a bit longer?  Thanks,
> 
> I really want this merged this cycle, along with the iommufd part,
> which means it needs to go into your tree by very early next week on a
> shared branch so I can do the iommufd part on top.
> 
> It is the last blocking kernel piece to conclude the viommu support
> roll out into qemu for iommufd which quite a lot of people have been
> working on for years now.
> 
> IMHO there is nothing profound in the dmabuf patch, it was written by
> the expert in the new DMA API operation, and doesn't form any
> troublesome API contracts. It is also the same basic code as from the
> v1 in July just moved into dmabuf .c files instead of vfio .c files at
> Christoph's request.

As long as it is only an internal API between iommu and vfio which also respects the standard DMA-buf semantics to either pin buffers or provide a move_notify interface then feel free to go ahead with it.

Skimming over it my only concern is patch #6 which adds the helper to the common DMA-buf code and that in turn would need an in-deep review which I currently don't have time for.

So if we could keep those inside the VFIO driver for now I think that should be good to go.

Regards,
Christian.


> My hope is DRM folks will pick up the baton and continue to improve
> this to move other drivers away from dma_map_resource(). Simona told
> me people have wanted DMA API improvements for ages, now we have them,
> now is the time!
> 
> Any remarks after the fact can be addressed incrementally.
> 
> If there are no concrete technical remarks please take it. 6 months is
> long enough to wait for feedback.
> 
> Thanks,
> Jason