VM66400: PEVM66154 USER HANGS WITH CPU LIMITING

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• In some cases a guest with CPU limiting (LIMITHARD, CPUPOOL,
  RESPOOL) can hang.
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of z/VM                            *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  ****************************************************************
  * RECOMMENDATION: APPLY PTF                                    *
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  Incorrect code in HCPCFM can lead to a z/VM guest virtual
  machine hang condition if the guest needs to be limited when
  trying to promote from instruction stream (i-stream)
  serialization to Console-Function-Mode (CFM) serialization.
  
  The code in HCPCFM, shortly after label CFMRD, incorrectly
  checks whether 2 bits (VMDCFWT and VMDSIMWT) are on in VMDRSTAT,
  in order to determine whether or not a CFM promote operation is
  pending.  The test used a CLI instruction which would only match
  if VMDRSTAT contained exactly those two bits, with no other bits
  on.
  
  Prior to VM66154, there were no known scenarios where any other
  bit would be on in VMDRSTAT when a promote was pending.  VM66154
  moved the VMDLIMMV bit, a flag indicating whether a VMDBK
  required CPU limiting, into VMDRSTAT.  If this bit is on when a
  CFM promote is attempted, the guest can become hung.
  
  If CPU limiting is used on a guest after applying VM66154 (or
  running with base z/VM 7.2, as the code for VM66154 is in the
  base) then any guest being limited can potentially become hung.
  CPU limiting includes SET SHARE with the LIMITHARD option,
  SET CPUPOOL, and SET RESPOOL with the CPU option.
  

Problem conclusion

• Code in HCPCFM has been modified so that the presence of other
  bits on in VMDRSTAT will not affect the check on whether
  VMDCFWT and VMDSIMWT are both on.
  
  Additionally, 2 other tests of VMDRSTAT in HCPCFM have been
  modified to ignore VMDLIMMV and VMDSIMAB when looking to see
  if the VMDBK has additional work, as these bits are not
  indicative of the type of work HCPCFM is looking for.
  

Temporary fix

• *********
  * HIPER *
  *********
  FOR RELEASE VM/ESA CP/ESA R640 :
  PREREQ: VM66154
  CO-REQ: NONE
  IF-REQ: NONE
  FOR RELEASE VM/ESACP/ESAR710 :
  PREREQ: VM66154
  CO-REQ: NONE
  IF-REQ: NONE
  FOR RELEASE VM/ESA CP/ESA R720 :
  PREREQ: NONE
  CO-REQ: NONE
  IF-REQ: NONE
  

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UM35704 UM35705 UM35706

Modules/Macros

• HCPCFM
  

Fix information

• Fixed component name

  VM CP

• Fixed component ID

  568411202

Applicable component levels

• R640 PSY UM35704

     UP20/08/12 P 2001 ­

• R710 PSY UM35705

     UP20/08/12 P 2101 ­

• R720 PSY UM35706

     UP20/08/12 P 2101 ­

Fix is available

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