Correction. The s390 server did not have two virtual CPUs. It had a *LIMIT* of two virtual CPUs. In other words, its CP directory entry contained
MACH XA 2 This statement creates only one virtual CPU, but allows a second one to be defined, if desired, by means of the CP DEFINE CPU command. I changed it to MACH XA and observed the change in behavior. However, this merely caused it to fail in a different way. Also, I just upgraded from z/VM 5.3.0 to z/VM 5.4.0, with current maintenance (about one month old), and the problem remains.
