Apparatus and method using hint capability for controlling micro-architectural control function

Capability storage circuitry 30, 32, 60, 34 stores at least one capability specifying a capability value and capability metadata indicative of constraints on valid use of the capability value. Capability checking circuitry 44 determines whether a capability-controlled operation to be performed by the processing circuitry with reference to a target capability is allowed, based on whether the capability-controlled operation satisfies the constraints indicated by the capability metadata of the target capability, and triggers an error handling response when the constraints are not satisfied. Micro-architectural control circuitry 40, 42, 23 controls a micro-architectural control function, other than determining whether the capability-controlled operation is allowed, depending on the capability metadata specified by a hint capability used to provide a hint to the micro-architectural control function.