FIT Pointer Rules

The physical location of FIT in firmware address space must satisfy the following requirements:

1. The entire FIT table must reside within the firmware address range of (4 GB to 16 MB) to (4 GB-40h). If the FIT is located outside this region, the processor will invoke a legacy boot process and a root of trust will not be established using FIT.
2. FIT must also reside within the firmware address region that is accessible by the hardware upon CPU reset. Any initialization done by system service processors present on the platform prior to invocation of CPU reset is permitted.
3. With introduction of Boot Guard Technology, FIT table is no longer optional element of architecture. CPU behavior, if FIT table is absent or invalid depends on platform provisioning and will range from immediate unbreakable shutdown and up to fallback to time-limited legacy boot followed by a platform reset, when timeout expires.
4. If FIT table is used by a platform, and Top Swap is used as a method of platform recovery, the need to keep top and swap blocks updated can be avoided, if FIT resides outside of boot and recovery areas. It has to be noted, such that flash layout is suitable only for platform not employing Boot Guard, which has own rules of Top Swap implementation.