The SMMU provides address translation for an I/O device to identify more than its actual addressing capability. In absence of memory isolation, I/O devices may be able to corrupt system memory. The SMMU provides device isolation to prevent DMA attacks. To offer isolation and memory protection, it restricts device access for DMA-capable I/O to a pre-assigned physical space.
As an example, consider the AXI interfaces from programmable logic to the PS that passes through the SMMU in the PS. When enabled, the SMMU also offers protection from DMA masters in the PL restricted access to the PS memory region; this is protection in the context of a symmetric multiprocessing system running an OS. The OS on an APU can isolate the DMA from interfering with other devices under the APU. In a similar way, the SMMU can also be enabled to restrict DMA units or other PS masters from accessing the PS memory region.