Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

Leon Romanovsky
2026-01-21T19:45:18Z

On Wed, Jan 21, 2026 at 12:01:40PM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 21, 2026 at 04:28:17PM +0100, Christian König wrote:
> > On 1/21/26 14:31, Jason Gunthorpe wrote:
> > > On Wed, Jan 21, 2026 at 10:20:51AM +0100, Christian König wrote:
> > >> On 1/20/26 15:07, Leon Romanovsky wrote:
> > >>> From: Leon Romanovsky <leonro@nvidia.com>
> > >>>
> > >>> dma-buf invalidation is performed asynchronously by hardware, so VFIO must
> > >>> wait until all affected objects have been fully invalidated.
> > >>>
> > >>> Fixes: 5d74781ebc86 ("vfio/pci: Add dma-buf export support for MMIO regions")
> > >>> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> > >>
> > >> Reviewed-by: Christian König <christian.koenig@amd.com>
> > >>
> > >> Please also keep in mind that the while this wait for all fences for
> > >> correctness you also need to keep the mapping valid until
> > >> dma_buf_unmap_attachment() was called.
> > >
> > > Can you elaborate on this more?
> > >
> > > I think what we want for dma_buf_attach_revocable() is the strong
> > > guarentee that the importer stops doing all access to the memory once
> > > this sequence is completed and the exporter can rely on it. I don't
> > > think this works any other way.
> > >
> > > This is already true for dynamic move capable importers, right?
> >
> > Not quite, no.
>
> :(
>
> It is kind of shocking to hear these APIs work like this with such a
> loose lifetime definition. Leon can you include some of these detail
> in the new comments?

If we can clarify what needs to be addressed for v5, I will proceed.
At the moment, it's still unclear what is missing in v4.

Thanks