A computer system (10, 20) includes a processor which may initialize a secure execution mode by executing a security initialization instruction. Further, the processor may operate in the secure execution mode by executing a secure operating system code segment. The computer system also includes an input/output (I/O) interface (120, 220) coupled to the processor via an I/O link (225). The I/O interface may receive transactions performed as a result of the execution of the security initialization instruction. The transactions include at least a portion of the secure operating system code segment. The I/O interface may also determine whether the processor is a source of the transactions. The computer system further includes a security services processor (130) coupled to the I/O interface via a peripheral bus (135). The I/O interface may convey the transactions to the security services processor dependent upon determining that the processor is the source of the transactions.