The embodiments relate to processing a guest event in a hypervisor-controlled system. A guest event triggers a first firmware service for the guest event in firmware. The guest event is associated with a guest, a guest key, and with a guest state and protected guest memory accessible only by the guest and the firmware. The firmware processes information associated with the guest event. The processed information includes information of the guest state and the protected guest memory. A subset of the processed information is received by a hypervisor to process the guest event, and a non-received portion of the information is retained by the firmware. The hypervisor processes the guest event based on the received subset and sends a process result to the firmware triggering a second firmware service for the guest event. The firmware processes the process result together with the retained information to generate modification associated with the guest event. The firmware performs the generated modification associated with the guest event at the protected guest memory.