CONFIG_64BIT_PHYS_ADDR is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
Support for 64-bit physical address space
configname: CONFIG_64BIT_PHYS_ADDR
Linux/MIPS Kernel Configuration
└─>CPU selection
└─>Support for 64-bit physical address space
In linux kernel since version 2.6.12
depends
CONFIG_MIPS32CONFIG_CPU_MIPS32 or CONFIG_CPU_MIPS64 or CONFIG_CPU_R10000 or CONFIG_CPU_R4X00 or CONFIG_CPU_R5000 or CONFIG_CPU_RM7000 or CONFIG_CPU_RM9000 or CONFIG_CPU_SB1 or CONFIG_32BIT or CONFIG_CPU_MIPS32_R1 or CONFIG_CPU_MIPS64_R1