4. EXCEPTIONS › 4.3 Detailed Exception Descriptions › 00310: Low Core Protection Not In Use

00310: Low Core Protection Not In Use

FILE              TSO System Activity
SAS FILE NAME     DETAIL.TSOTSO01
SOURCE LOCATION   sharedprefix.MICS.SOURCE(DYTSOEXC)

SEVERITY          Critical      (SEVERITY='C')
MANAGEMENT AREA   Availability  (MGMTAREA='AVAILABILITY')

PURPOSE      Indicates possible MVS reliability exposure.

RATIONALE    In SE-1, a new low core protection mechanism was
             introduced to supplement storage key protection.
             By setting bit 3 of control register 0, MVS can
             disallow stores under CPU program control which
             use a LOGICAL address less than 512 (decimal).
             CA MICS will never note this exception for
             pre-SE systems.

             MVS does turn this protection off and then on
             again when certain low core fields must be
             changed, but TSO/MON should never see it.  It
             should be done very quickly while the CPU is
             disabled for interrupts.

             However, this protection is not airtight.  The
             I/O Supervisor (IOS) does NOT turn it off and on
             when it goes to set the Channel Address Word
             (CAW) in preparation for issuing SIO/SIOF.
             Rather, the system segment/page tables are set
             to map addresses FFF000-FFFFFF to real addresses
             000000-000FFF (which are in turn converted to
             "absolute" addresses by PREFIXing).

DEFINITION   This exception is noted when the data element
             TSOXLCPN (Intvls When Low Core Protection Not in
             Use) is found with a nonzero value and the
             parameters specified for this system in
             prefix.MICS.PARMS(SYSID) indicate the MVS level
             as SE1 or above.  Consult the CA MICS Data
             Dictionary for more information about the
             TSOXLCPN data element.

EXCEPTION    The SAS statements identifying the exception
STATEMENTS   situation and describing the condition are
             stored in the source member named in SOURCE
             LOCATION and are described below:

_SYSID;      * BRING IN PARMS(SYSID) DEFINITIONS;
************************************************************;
*
** 00310
** LOW CORE PROTECTION NOT IN USE
*;
IF TSOXLCPN > 0 AND SCP ^ = 'MVS'
 THEN DO;
  EXCCODE='00310'; SEVERITY='C'; MGMTAREA='AVAILABILITY';
  EXCDESC1='LOW CORE PROTECTION NOT IN USE';
  EXCDESC2=' ENDTS=' || PUT(ENDTS,DATETIME19.2);
  LINK HIT;
END;

THRESHOLD     None required.  It is important that
MODIFICATION  prefix.MICS.PARMS(SYSID) be kept up-to-date
              with respect to the operating system level of
              all of your systems.