Re: [RFC PATCH] iommu/arm-smmu-v3: Allow nested attach for PCI bridges without vDEVICE

[Jason Gunthorpe]

On Mon, Aug 17, 2026 at 09:29:10AM +0000, Dmitry Malkin wrote:
> > Don't use it that way?
> 
> Why not? We use pci=config_acs to configure ACS at kernel startup
> and enable direct PCIe peer-to-peer traffic between GPUs and
> NICs. All affected devices are assigned to the same VM and IOMMU
> domain, which also reduces the memory footprint by reducing the
> number of page tables and lowers IOTLB pressure.

This kind of situation is very challenging to setup in the VM, and at
this point you may as well include the switch to the VM too.

Then you don't have issues here.

Jason