Directed interrupt for multilevel virtualization

A computer system for providing an interrupt signal to a first guest operating system executed using one or more processors of a plurality of processors of a computer system assigned for usage by the first guest operating system, the computer system being configured to perform a method, said method comprising:

• receiving, by a bus attachment device of the computer system from a first bus connected module of a plurality of bus connected modules operationally coupled to the plurality of processors via the bus attachment device, a first interrupt signal with an interrupt target ID, the interrupt target ID identifying one processor of the plurality of processors assigned for usage by the first guest operating system as a first target processor to handle the first interrupt signal;
• checking, by the bus attachment device, whether the first target processor is scheduled for usage by the first guest operating system;
• translating, by the bus attachment device based on the first target processor being scheduled for usage by the first guest operating system, the interrupt target ID to a logical processor ID and forwarding the first interrupt signal to the first target processor to handle, the forwarding using the logical processor ID resulting from the translating to address the first target processor directly;
• and
• forwarding, by the bus attachment device based on the first target processor not being scheduled for usage by the first guest operating system, the first interrupt signal to the first guest operating system using broadcasting, the broadcasting comprising selecting by the bus attachment device a forwarding vector entry of a first set of forwarding vector entries which is assigned to the interrupt target ID and updating the forwarding vector entry such that it indicates that a directed interrupt summary indicator to which it is assigned is to be updated in order to indicate for the first guest operating system that there is a first interrupt signal addressed to the interrupt target ID to be handled.

A computer-implemented method of providing an interrupt signal to a first guest operating system executed using one or more processors of a plurality of processors of a computer system assigned for usage by the first guest operating system, the computer-implemented method comprising:

• receiving, by a bus attachment device of the computer system from a first bus connected module of a plurality of bus connected modules operationally coupled to the plurality of processors via the bus attachment device, a first interrupt signal with an interrupt target ID, the interrupt target ID identifying one processor of the plurality of processors assigned for usage by the first guest operating system as a first target processor to handle the first interrupt signal;
• checking, by the bus attachment device, whether the first target processor is scheduled for usage by the first guest operating system;
• translating, by the bus attachment device based on the first target processor being scheduled for usage by the first guest operating system, the interrupt target ID to a logical processor ID and forwarding the first interrupt signal to the first target processor to handle, the forwarding using the logical processor ID resulting from the translating to address the first target processor directly;
• and
• forwarding, by the bus attachment device based on the first target processor not being scheduled for usage by the first guest operating system, the first interrupt signal to the first guest operating system using broadcasting, the broadcasting comprising selecting by the bus attachment device a forwarding vector entry of a first set of forwarding vector entries which is assigned to the interrupt target ID and updating the forwarding vector entry such that it indicates that a directed interrupt summary indicator to which it is assigned is to be updated in order to indicate for the first operating system that there is a first interrupt signal addressed to the interrupt target ID to be handled.