Re: [PATCH RFC 03/26] dma-buf: Add dma_buf_mapping_attach()

["Christian König" <christian.koenig@amd.com>]

On 10/16/26 22:26, Karl Mehltretter wrote:
> On Tue, Feb 17, 2026 at 08:11:34PM -0400, Jason Gunthorpe wrote:
>> +	match_args.attach = attach;
>> +	if (dmabuf->ops->match_mapping) {
>> +		ret = dmabuf->ops->match_mapping(&match_args);
>> +	}
>> +
>>  	attach->dmabuf = dmabuf;
>>  	attach->importer_ops = importer_ops;
>>  	attach->importer_priv = importer_priv;
> 
> I may misunderstand the intended contract. match_mapping() runs while the
> attachment is still zeroed and without dmabuf->resv held.
> 
> Patch 11's amdgpu callback needs importer_ops and importer_priv, so its XGMI
> match cannot work here. Patch 12's VFIO callback asserts dmabuf->resv and
> reads priv->vdev, which cleanup changes under that lock.
> 
> Should the core initialize the attachment and hold dmabuf->resv for
> match_mapping(), or should callbacks avoid attachment and lock-protected
> state?

Right. This completely misplaced.

The matching can't be done at attachment time, but rather needs to be done before creating a mapping while holding the resv lock so that the matching decision can't change.

Regards,
Christian.

> 
> Thanks,
> Karl