Preface
This publication summarizes the assists for
Virtual-Machine Facility/370 (VM/370) and gives
a detailed description of the virtual-machine assist
and the shadow-table,..bypass assist.
This publication is intended for system
programmers. The reader should be familiar with
the general machine functions of System/370, as
described in IBM System! 370 Principles of Operation, GA22-7000, and with the VM!370 system. The reader may also wish to refer to IBM
Virtual Machine Facility! 370: System Logic and
Problem Determination Guide, SY20-0885, and to
IBM Virtual Machine Facility! 370: Data Areas
and Control Block Logic, SY20-0884. First Edition (May 1980)
Changes are periodically made to the information herein; before using this
pUblication in connection with the operation of IBM equipment, refer to the
IBM System/360 Bibliography, GC20-0360, IBM System/3 70 and 4300 Processors Bibliography, GC2D-000l, for editions that are applicable and
current.
It is possible that this material may contain reference to, or information
about, IBM products (machines and programs), programming, or services
that are not announced in your country. Such references or information
must not be construed to mean that IBM intends to announce such IBM
products, programming, or services in your country.
Publications are not stocked at the address given below; requests for IBM
publications should be made to your IBM representative or to the IBM
branch office serving your locality.
A form for reader's comments is provided at the back of this publication. If
the form has been removed, comments may be addressed to IBM Corpora­
tion, Product Publications, Department B98, PO Box 390, Poughkeepsie, NY, U.S.A. 12602. IBM may use or distribute any of the information you supply
in any way it believes appropriate without incurring any obligation whatever. You may, of course, continue to use the information you supply.
© Copyright International Business Machines Corporation 1980

Contents
Chapter 1. Assists for VM/370 2 Control of VM/370 Assists 3
Interaction of VM/370 Assists 5
Interaction of VM/370 Assists with Other Facilities 5
Control Mode 5 Program-Event Recording 5
Dynamic Address Translation 6
Low-Address Protection 6
Multiple Processors 6 DOS/OS Compatibility Facility 6
General Conventions 6
Control-Block Alignment 6 Virtual PSW 6
Updating Swap-Table Entries 6
Addressing Conditions 6
Method of Detailed Description 7
Chapter 2. Virtual-Machine Assist 9 INSERT PSW KEY 9 INSERT STORAGE KEY 10 LOAD PSW 12 LOAD REAL ADDRESS ] 3 RESET REFERENCE BIT -- 15 SET PSW KEY FROM ADDRESS 17 SET STORAGE KEY 18- SET SYSTEM MASK 19 STORE CONTROL 20 StORETHENAND-SYSTEM MASK 21 STORE THEN OR SYSTEM MASK 22 SUPERVISOR CALL 23
Shadow-Table Validation 24 Chapter 3. VM-Common-Segment Modification of VMA 29 Chapter 4. ShadowaTableaBypass Assist 31
Relation of Shadow-Table-Bypass Assist to Other Assists 31
INVALIDATE PAGE TABLE ENTRY LOAD CONTROL 33 LOAD REAL ADDRESS 34 PURGE TLB 35 STORE THEN AND SYSTEM MASK STORE THEN OR SYSTEM MASK TEST PROTECTION 38 Page-Fault Reflection 39
32
36
37
Appendix. Deviations for Virtual-Machine-Assist
Functions 43
Index 45 I I i I I iii