Masking of architectural state associated with a realm

A data processing method comprising:

• processing software processes at one of a plurality of exception levels and in one of a plurality of realms, where each realm corresponds to at least a portion of at least one software process and is associated with a boundary exception level indicative of a most privileged exception level corresponding to the realm;
• and
• storing architectural state data in a plurality of registers;
• wherein in response to a realm-exiting exception condition occurring during processing of a given realm, the realm-exiting exception condition comprising an exception condition to be handled by an exception handler at a more privileged exception level than the boundary exception level of the given realm, triggering a state masking process for making inaccessible, to software processes processed at a more privileged exception level than the boundary exception level, architectural state data of a subset of registers selected depending on the boundary exception level of the given realm.

A non-transitory storage medium storing a computer program for controlling a host data processing apparatus to provide an instruction execution environment comprising:

• processing program logic configured to process software processes in the instruction execution environment at one of a plurality of exception levels and in one of a plurality of realms, where each realm corresponds to at least a portion of at least one software process and is associated with a boundary exception level indicative of a most privileged exception level corresponding to the realm;
• and
• a plurality of data structures to store architectural register state data;
• wherein in response to a realm-exiting exception condition occurring in the instruction execution environment during processing of a given realm, the realm-exiting exception condition comprising an exception condition to be handled by an exception handler at a more privileged exception level than the boundary exception level of the given realm, the processing program logic is configured to trigger a state masking process for making inaccessible, to software processes processed at a more privileged exception level than the boundary exception level, architectural register state data of a subset of data structures selected depending on the boundary exception level of the given realm.