Re: [PATCH v3 3/7] dma-buf: Document RDMA non-ODP invalidate_mapping() special case

Jason Gunthorpe
2026-01-21T13:59:50Z

On Wed, Jan 21, 2026 at 02:52:53PM +0100, Christian König wrote:
> On 1/21/26 14:18, Jason Gunthorpe wrote:
> > On Wed, Jan 21, 2026 at 10:17:16AM +0100, Christian König wrote:
> >> The whole idea is to make invalidate_mappings truly optional.
> >
> > But it's not really optional! It's absence means we are ignoring UAF
> > security issues when the exporters do their move_notify() and nothing
> > happens.
>
> No that is unproblematic.
>
> See the invalidate_mappings callback just tells the importer that
> the mapping in question can't be relied on any more.
>
> But the mapping is truly freed only by the importer calling
> dma_buf_unmap_attachment().
>
> In other words the invalidate_mappings give the signal to the
> importer to disable all operations and the
> dma_buf_unmap_attachment() is the signal from the importer that the
> housekeeping structures can be freed and the underlying address
> space or backing object re-used.

I see

Can we document this please, I haven't seen this scheme described
anyhwere.

And let's clarify what I said in my other email that this new revoke
semantic is not just a signal to maybe someday unmap but a hard
barrier that it must be done once the fences complete, similar to
non-pinned importers.

The cover letter should be clarified with this understanding too.

Jason