Zone protection is used to override the access protection specified in a TLB entry. Zones are an arbitrary grouping of virtual pages with common access protection. Zones can contain any number of pages specifying any combination of page sizes. There is no requirement for a zone to contain adjacent pages.
The zone-protection register (ZPR) is a 32-bit register used to specify the type of protection override applied to each of 16 possible zones. The protection override for a zone is encoded in the ZPR as a 2-bit field.
The 4-bit zone-select field in a TLB entry (TLBLO[ZSEL]) selects one of the 16 zone fields from the ZPR (Z0–Z15). For example, zone Z5 is selected when ZSEL = 0101.
Changing a zone field in the ZPR applies a protection override across all pages in that zone. Without the ZPR, protection changes require individual alterations to each page translation entry within the zone.
Unimplemented zones (when C_MMU_ZONES < 16) are treated as
if they contained 11.