A fix is available
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 * **************************************************************** 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 number
VM66400
Reported component name
VM CP
Reported component ID
568411202
Reported release
640
Status
CLOSED PER
PE
YesPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2020-06-10
Closed date
2020-07-28
Last modified date
2021-06-29
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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Document Information
Modified date:
30 June 2021