Memory bus attached Input/Output (‘I/O’) subsystem management in a computing system, the computing system including an I/O subsystem communicatively coupled to a memory bus, including: detecting, by an I/O subsystem device driver, a hibernation request; setting, by the I/O subsystem device driver, a predetermined memory address to a value indicating that the I/O subsystem is not to service system requests; detecting, by the I/O subsystem device driver, that the I/O subsystem device driver has been restarted; and setting, by the I/O subsystem device driver, the predetermined memory address to a value indicating that the I/O subsystem can resume servicing system requests.