The system memory management unit (SMMU) provides isolation to I/O and DMA capable devices by virtualizing their address space.. 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 can 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.
To understand more about SMMU features and functionality, see this link to the “System Memory Management Unit” section of the Zynq UltraScale+ Device Technical Reference Manual (UG1085).