1. In a logically partitioned host computer system comprising host processors (host CPUs), a method for a configuration change of a topology of a plurality of guest processors (guest CPUs) of a guest configuration, the method comprising: a guest processor of the guest configuration fetching a perform topology function instruction defined for a computer architecture, the perform topology function instruction comprising an opcode field specifying a function to be performed; executing function to be performed of the perform topology function instruction comprising: requesting a specified polarization change of the configuration of the topology of the guest processors of the guest configuration; responsive to the requested specified polarization change being accepted, initiating a change of the topology of the guest processors of the guest configuration according to the specified polarization change and setting a condition code to a first condition code value, the first condition code value indicating a topology-change initiated; and responsive to the requested specified polarization change not being accepted, setting the condition code to a second condition code value, the second condition code value indicating a topology-change is rejected.