Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1677

STI—Set Interrupt Flag (Continued)
Real Address Mode Exceptions
None.
Virtual 8086 Mode Exceptions
#GP(0)
Volume 4: Base IA-32 Instruction Reference
If the CPL is greater (has less privilege) than the IOPL of the current
program or procedure.
4:375