Re: [PATCH v4 1/5] PCI/P2PDMA: Don't enforce ACS check for device functions of Intel GPUs

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Sep 25, 2025 at 03:11:50PM +0200, Thomas Hellström wrote:
> On Thu, 2025-09-25 at 13:28 +0200, Christian König wrote:
> > On 25.09.25 12:51, Thomas Hellström wrote:
> > > > > In that case I strongly suggest to add a private DMA-buf
> > > > > interface
> > > > > for the DMA-
> > > > > bufs exported by vfio-pci which returns which BAR and offset
> > > > > the
> > > > > DMA-buf
> > > > > represents.
> > > 
> > > @Christian, Is what you're referring to here the "dma_buf private
> > > interconnect" we've been discussing previously, now only between
> > > vfio-
> > > pci and any interested importers instead of private to a known
> > > exporter
> > > and importer?
> > > 
> > > If so I have a POC I can post as an RFC on a way to negotiate such
> > > an
> > > interconnect.
> > 
> > I was just about to write something up as well, but feel free to go
> > ahead if you already have something.
> 
> Just posted a POC. It might be that you have better ideas, though.

I think is also needs an API that is not based on scatterlist. Please
lets not push a private interconnect address through the scatterlist
dma_addr_t!

Assuming that you imagine we'd define some global well known
interconnect

'struct blah pci_bar_interconnect {..}'

And if that is negotiated then the non-scatterlist communication would
give the (struct pci_dev *, bar index, bar offset) list?

I think this could solve the kvm/iommufd problems at least!

Jason