Rick, Terri, Greg, and others, apologies I should have given out the PTF
numbers and a little more background on my earlier append.

APAR VM65396 PTF UM34851 is the one that introduced the prog check problem.
We discovered the problem February 26th, and marked VM65396 in error on
March 1st with VM65414 the PE fix to it. The correction to that error is
included in APAR VM65414 PTF UM34853, which closed on March 23rd.  For
other reasons, both of these APARs are Security/Integrity APARs, so see my
earlier append on the IBM Z Security portal.

However, the functional problem, other than being introduced by VM65396, is
not connected to the security/integrity aspects of these APARs. The
functional problem is related to a virtual processor coming out of SIE for
a fast path operation, as opposed to the typical normal exit from SIE. (For
those unfamiliar with SIE, think of it as dispatching or running a virtual
processor). Fast path exits are far more prevalent in a CMS environment
than in other guest operating systems, but it is possible. In all cases,
fast path exits are a subset, mostly a very small subset, of all exits.
There is a scenario where taking the fast path exit can erroneously cause
z/VM to present the 028 program check. The error further involves the upper
part of a register not being cleared. If this register's upper half
contains zeroes, it would not trigger the error condition, but over time,
it appears the upper half changes and the program checks start appearing.
So from that perspective it's a timing/workload dependent problem. This is
a simplification, but I hope it's enough for you to appreciate the aspects
you need to be aware.

The real solution is to apply VM65414's PTF which is available. A
mitigation would be to do a CP TRACE PROG 28 NOTERM NOPRINT RUN for the
virtual machines through the console or if logged off and on, through a
directory command statement.

Thank you for understanding the communication challenges in this space. I'm
sure you'll let us know if you need more info. :-)

Regards,
Bill
___________________________________________________________________________________________

Bill Bitner - z/VM Customer Focus and Care - 607-429-3286
bitn...@us.ibm.com
"Making systems practical and profitable for customers through
virtualization and its exploitation." - z/VM

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