Re: [PATCH v2 2/4] dma-buf: Document revoke semantics

[Leon Romanovsky <leon@kernel.org>]

On Sun, Jan 18, 2026 at 03:29:02PM +0100, Thomas Hellström wrote:
> On Sun, 2026-01-18 at 14:08 +0200, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> > 
> > Document a DMA-buf revoke mechanism that allows an exporter to
> > explicitly
> > invalidate ("kill") a shared buffer after it has been handed out to
> > importers. Once revoked, all further CPU and device access is
> > blocked, and
> > importers consistently observe failure.
> 
> See previous comment WRT this.
> 
> > 
> > This requires both importers and exporters to honor the revoke
> > contract.
> > 
> > For importers, this means implementing .invalidate_mappings() and
> > calling
> > dma_buf_pin() after the DMA‑buf is attached to verify the exporter’s
> > support
> > for revocation.
> 
> Why would the importer want to verify the exporter's support for
> revocation? If the exporter doesn't support it, the only consequence
> would be that invalidate_mappings() would never be called, and that
> dma_buf_pin() is a NOP. Besides, dma_buf_pin() would not return an
> error if the exporter doesn't implement the pin() callback?

The idea is that both should do revoke and there is a need to indicate
that this exporter has some expectations from the importers. One of them
is that invalidate_mappings exists.

Thanks

> 
> Or perhaps I missed a prereq patch?
> 
> Thanks,
> Thomas
> 
>