Re: [PATCH v5 09/14] PCI: portdrv: Suppress kernel DMA ownership auto-claiming

[Jason Gunthorpe]

On Tue, Jan 04, 2022 at 11:06:31AM -0600, Bjorn Helgaas wrote:

> > The existing vfio framework allows the portdrv driver to be bound
> > to the bridge while its downstream devices are assigned to user space.
> 
> I.e., the existing VFIO framework allows a switch to be in the same
> IOMMU group as the devices below it, even though the switch has a
> kernel driver and the other devices may have userspace drivers?

Yes, this patch exists to maintain current VFIO behavior which has this
same check.

I belive the basis for VFIO doing this is that the these devices
cannot do DMA, so don't care about the DMA API or the group->domain,
and do not expose MMIO memory so do not care about the P2P attack.

A comment in the code to this effect would be good, IMHO.

Jason