1. A method of processing a guest event in a hypervisor-controlled system, the method comprising: triggering, based on the guest event, a first firmware service, the first firmware service being specific for the guest event in a firmware, the guest event being associated with a guest and with a guest state and a guest memory encrypted with a guest key; processing, by the firmware, information associated with the guest event, the information comprising information of the guest state and the guest memory, and presenting only a subset of the information of the guest state and the guest memory in decrypted form to a hypervisor, wherein the subset of the information is selected to suffice for the hypervisor to process the guest event; retaining, by the firmware, a part of the information of the guest state and the guest memory that is not being sent to the hypervisor; processing, by the hypervisor, the guest event based on the received subset of the information of the guest state and the guest memory and sending a process result to the firmware triggering a second firmware service, the second firmware service being specific for the guest event; processing, by the firmware, the received process result together with the part of the information of the guest state and the guest memory that was not sent to the hypervisor to generate a state or memory modification; and performing, by the firmware, the state or memory modification associated with the guest event at the guest memory in encrypted form.