Browse Prior Art Database

Modifying a Page in Real Storage Using Virtual Addresses

IP.com Disclosure Number: IPCOM000120754D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 56K

Publishing Venue

IBM

Related People

Myers, JJ: AUTHOR [+4]

Abstract

This article describes the use of new privileged instructions which access (and modify) a page in real storage using virtual addresses before the page (which incurred a page fault) is validated.

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This is the abbreviated version, containing approximately 57% of the total text.

Modifying a Page in Real Storage Using Virtual Addresses

      This article describes the use of new privileged
instructions which access (and modify) a page in real storage using
virtual addresses before the page (which incurred a page fault) is
validated.

      The new instructions are capable of accessing the invalidated
page because of the new bit in the page table called the limited
access bit.  The limited access bit defines a new state of a page,
and works in conjunction with the (page) invalid bit (which, if set,
indicates that the virtual address assigned to the frame is invalid).
When the invalid bit is set and the limited access bit is set and a
real frame is assigned, then the privileged instructions can load/
store into the (invalid) page using the virtual addresses.  (The
instructions will not cause entries into the Dynamic Lookaside Table
(DLAT).)  The instructions are privileged and function identically to
the ICM and STCM instructions except that the pages that the
operation addresses must be marked invalid and for limited access.

      Use of the invention could be by an operating system fetch in
the relocation of a program's address constants. (Relocation is done
by intercepting page faults to program text pages and performing the
necessary modifications before the pages appear in the user's virtual
storage.)  Relocation must occur before the pages appear in the
user's virtual storage.  The invention allows fetch to perform a
relocation...