> So CPU internal states or protection are in theory irrelevant. Go look up what IOMMU means. We're not talking about a feature inside an individual CPU core,

> So CPU internal states or protection are in theory irrelevant. Go look up what IOMMU means. We're not talking about a feature inside an individual CPU core, but in the PCIe Root Complex that implements DMA capabilities in the first place; it's the thing that sits between peripheral devices and the DRAM controller. That functionality is on the CPU die these days.