[walterbell]

On the iMac Pro, will PCI devices be able to DMA into both the Intel and ARM CPUs? Is there a single IOMMU which will arbitrate DMA for both CPUs?

[jnwatson]

The IOMMU functionality is built into the Platform Controller Hub, which is between the baseboard management controller (the ARM) and the main processor.

Theoretically it would be possible to prevent DMA between the two, but it is highly doubtful Apple would program it that way.