摘要:
The creation of address spaces that need not map in their address range all of the routines of the operating system basic control program (BCP) is provided. The BCP, though, will have easy access to (addressability of) the home address space, i.e. to the virtually mapped and addressable control blocks therein. Addressability can be switched from a previously dispatched address space to the home address space. The dispatcher becomes capable of addressing the home address space when predetermined bits in a program status word are set. Once the home address space becomes addressable, the BCP is now capable of easily accessing control blocks in the home address space without the need to modify CPU status or pointers to any other address spaces. If pointers to any other address space are modified, current address translation in the home address space would not be affected. Providing access to the home address space increases performance and reduces complexity.
摘要:
The embodiment provides selective supervisory disablement of fetch protection for a special storage subarea (such as for the first half of the first 4KB block) while fetch protection is enabled for an area containing the subarea by a single storage protect key. That is, the fetch protect for the subarea (normally provided in the fetch protect for the entire area) by the area's protect key is overriden by the selective subarea disablement control, so that accesses to the subarea are not fetch protected by the storage key. The override protection control is secured by its enablement via a field position in a control register only accessible to supervisory programming. Thus, while fetch protection is set on for a predefined 4KB block, the fetch protect override controls can disable the fetch protection for a portion of the block's real addresses (e.g. addresses 0-2047).