The XMPU is configurable either one time or using secure transactions to the APB programming interface. At boot time, the XMPU is configured and its configuration can be locked. If an XMPU register set is locked, the XMPU can only be reconfigured after the next power-on reset (POR). If the configuration is not locked, the XMPU can be reconfigured any number of times by trusted software (using a secure transaction).
Recommended: AMD recommends only configuring each XMPU one time. When an XMPU is programmed, all of its settings must be programmed to ensure that only the allowed transactions go through.