RHEL8/9: LPAR is not booting up after inactive LPM

Issue

• When booting an LPAR with processors in shared mode after performing an inactive LPM, the system hangs while loading Grub:

  IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM
  IBM IBM IBM IBM IBM IBM IBM                         IBM IBM IBM IBM IBM IBM IBM
  IBM IBM IBM IBM IBM IBM IBM    STARTING SOFTWARE    IBM IBM IBM IBM IBM IBM IBM
  IBM IBM IBM IBM IBM IBM IBM       PLEASE WAIT...    IBM IBM IBM IBM IBM IBM IBM
  IBM IBM IBM IBM IBM IBM IBM                         IBM IBM IBM IBM IBM IBM IBM
  IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM
  ...
  Elapsed time since release of system processors: 45155 mins 25 secs
  Calling ibm,client-architecture-support from grub...
  

• At this time the issue is found to affect RHEL 8.7 and RHEL 9.1.