Data processing apparatus having a real memory region with a corresponding fixed memory protection key value and method for allocating memories therefor

摘要

A region comprising a plurality of real pages in a part of a real storage unit is provided with a first key storage unit having a plurality of key storage entries each corresponding to one of the plurality of real pages, while a second region comprising a plurality of real pages in the second part of the real storage unit is provided with a second key storage unit having a single key storage entry. When a real address designated by an instruction to be executed belongs to the first region, an entry corresponding to this address is accessed by a storage protection control circuit. When this address belongs to the second region, the second key storage unit is accessed irrespective of the address. Further, a key within the accessed key information is compared with a key on a program status word (PSW) allocated to a program to determine whether the execution of the instruction is permitted.