Re: [PATCH v5 8/9] vfio/pci: Enable peer-to-peer DMA transactions by default

Jason Gunthorpe
2025-10-22T11:39:04Z

On Wed, Oct 22, 2025 at 12:08:48AM -0700, Christoph Hellwig wrote:
> On Mon, Oct 20, 2025 at 10:08:55AM -0300, Jason Gunthorpe wrote:
> > Sure, but this should be handled by the P2P subsystem and PCI quirks,
> > IMHO. It isn't VFIOs job.. If people complain about broken HW then it
> > is easy to add those things.
>
> I think it is. You now open up behavior generally that previously
> had specific drivers in charge.

It has always been available in VFIO. This series is fixing it up to
not have the lifetime bugs.

> > IDK where Intel GPU lands on this, but VFIO has always supported P2P
>
> How?

It uses follow_pfnmap_start()/etc to fish the MMIO PFNs out of a VMA and
stick them into the iommu.

Jason