CONFIG_X86_64 (not configurable)

modulename: sys_x86_64.ko

and/or

hv_apic.ko

configname: CONFIG_X86_64

Linux Kernel Configuration
└─>X86_64
In linux kernel since version 2.6.12  
source code:
arch/x86/kernel/sys_x86_64.c

depends
CONFIG_64BIT