Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 4-245
INSTRUCTION SET REFERENCE, N-Z
64-Bit Mode Exceptions
#GP(0) If the current privilege level is not 0 and the PCE flag in the CR4
register is clear.
If an invalid performance counter index is specified in ECX[30:0]
(see Table 4-2).