Re: [PATCH v5 6/8] dma-buf: Add dma_buf_attach_revocable()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Jan 30, 2026 at 09:43:22AM +0100, Christian König wrote:
> On 1/24/26 20:14, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> > 
> > Some exporters need a flow to synchronously revoke access to the DMA-buf
> > by importers. Once revoke is completed the importer is not permitted to
> > touch the memory otherwise they may get IOMMU faults, AERs, or worse.
> 
> That approach is seriously not going to fly.
> 
> You can use the invalidate_mappings approach to trigger the importer
> to give back the mapping, but when the mapping is really given back
> is still completely on the importer side.

Yes, and that is what this is all doing, there is the wait for the
importer's unmap to happen in the sequence.

> In other words you can't do the shot down revoke semantics you are
> trying to establish here.

All this is doing is saying if dma_buf_attach_revocable() == true then
the importer will call unmap within bounded time after
dma_buf_invalidate_mappings().

That's it. If the importing driver doesn't want to do that then it
should make dma_buf_attach_revocable()=false.

VFIO/etc only want to interwork with importers that can do this.

Jason