Intel 64 and IA-32 Architectures Software Developers Manual Volume 2A, Instruction Set Reference, A-M

3-700 Vol. 2
INSTRUCTION SET REFERENCE, A-M
64-Bit Mode Exceptions
#GP(0) If the current privilege level is not 0.
If RCX
≠ 0 and CPUID.05H.ECX[0] = 0.
#UD If CPUID.01H:ECX.MONITOR[bit 3] = 0.
If the F3H, F2H, 66H or LOCK prefix is used.