Browse Prior Art Database

Cross Memory Connections Manager

IP.com Disclosure Number: IPCOM000120321D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 7 page(s) / 337K

Publishing Venue

IBM

Related People

Clark, C: AUTHOR [+4]

Abstract

Within MVS there exists cross memory resources which are used in the authorization process which govern one address space's ability to access another address space's private storage. These resources are either assigned to the address space at its creation or assigned when the resource is explicitly requested by a program running within the address space. Two of these resources are the address space identifier (ASID) and the extended authorization index (EAX).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 18% of the total text.

Cross Memory Connections Manager

      Within MVS there exists cross memory resources which are
used in the authorization process which govern one address space's
ability to access another address space's private storage.  These
resources are either assigned to the address space at its creation or
assigned when the resource is explicitly requested by a program
running within the address space.  Two of these resources are the
address space identifier (ASID) and the extended authorization index
(EAX).

      The ASID of an address space is a key used by the machine to
select the set of virtual addresses which define the addressable
space owned by the address space.  The ASID is also referred to as
the ASN (address space number).  The ASID is used by the PC, PT, PR,
LASP and SSAR instructions when performing ASN translation.  Of these
instructions, explicit authorization checks are performed by the
machine for LASP, PT and SSAR only.  The MVS series responsible to
set up program call linkage tables performs the required
authorization checks before the PC can be issued.

      The ASID of an address space is assigned at the time the
address space is created.  There exists a fixed number of ASIDs which
can be used to identify address spaces.  In an environment where no
cross memory linkages are constructed, the ASID used to identify an
address space is reassigned to a subsequent occurrence of an address
space after the first address space terminates.  In fact, ASIDs must
be reassigned to eliminate the need for an IPL when the finite number
of ASIDs are exhausted.  Therefore, ASIDs must be reclaimed by the
operating system when the associated address space terminates, and
then reallocated to support a subsequent address space creation
request.

      However, when one address space has given another address space
explicit permission to access its data, the ASID of the "accessed"
address space cannot be reallocated when it terminates.  After a
program in one address space establishes addressability to the
storage of another address space (via PC instruction), MVS will
reestablish this cross memory environment at each dispatch of the
program until the "accessing" program explicitly gives up
addressability (via the PT or PR instruction).  After the PC linkage
tables are constructed, there are no further authorization checks
performed when re-establishing primary addressability to the target
address space.  No checking of the primary address space
authorization tables is performed at time of dispatch. In fact, there
is no bit defined in the authority table which governs the
establishment of a primary address space. If the ASID of the
terminated cross memory service address space is reallocated to a
subsequent occurrence of an address space, the latent addressing
binds established to the prior address space could cause the new
address space to be accessed without its permission.

      Within MVS, the ASIDs which define...