Abstract: In a data processing system that includes a safe store buffer containing valid copies of all registers, processor transitions from a higher security routine to a lower security routine can be performed in fewer cycles by utilizing a plurality of sets of registers maintained in a round-robin system. Whenever a transition is made to a higher security environment, a switch is made to a different set of registers. Then, when a transition is made back to the lower security environment, a switch is made back to the previous set of registers. Writes to memory copies of registers are detected, and only those registers whose memory copies have been modified are restored from the memory copy.

Abstract: In a data processing system that includes a safe store buffer containing valid copies of all registers, processor transitions from a higher security routine to a lower security routine can be performed in fewer cycles by loading the safe store buffer from a safe store stack frame, then delaying loading registers either until actually utilized, or by a background process that loads registers utilizing unused memory cycles. A flag is used for each register that indicates whether the register contents are valid. This flag is cleared for each of the registers whenever such a state transition is made. Then, the flag is set for a register when it is referenced and made valid.