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Transparent Recovery of Solid Storage Key Errors in a Paging System

IP.com Disclosure Number: IPCOM000081168D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Doggett, RH: AUTHOR [+4]

Abstract

Storage protection is achieved by associating a storage key code with each page of storage, and providing a protection key code in the current Program Status Word (PSW) accompanying the request for storage access. For each storage access, the storage key for the associated page is fetched and checked to insure that it is valid (i.e., it has correct parity or valid checking block code). If valid, the storage key is compared with the protection key associated with the executing program. If the keys are equal, storage access is granted and processing continues; if not, access is not permitted, the instruction is terminated, a program interruption occurs and a program exception indication is placed in the interruption code of the old PSW.

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Transparent Recovery of Solid Storage Key Errors in a Paging System

Storage protection is achieved by associating a storage key code with each page of storage, and providing a protection key code in the current Program Status Word (PSW) accompanying the request for storage access. For each storage access, the storage key for the associated page is fetched and checked to insure that it is valid (i.e., it has correct parity or valid checking block code). If valid, the storage key is compared with the protection key associated with the executing program. If the keys are equal, storage access is granted and processing continues; if not, access is not permitted, the instruction is terminated, a program interruption occurs and a program exception indication is placed in the interruption code of the old PSW. If the storage key is not valid, a machine check interruption occurs to invoke a supervisory program which executes with a protection key code of zero.

When it is ascertained that a storage key error has occurred, an attempt is made to refresh the failing storage key code with a Set Storage Key instruction. If this attempt succeeds, the storage key error is considered "intermittent" and processing continues. If, however, this attempt fails (i.e., another machine check interruption occurs when the Set Storage Key instruction is executed), the storage key error is considered "solid".

Solid storage key errors may be corrected if the page with the failing key does not c...