CONFIG_XTENSA_KSEG_512M is not available for thedefaultarchitecture x86.
Result is shown for architecture xtensa

512MB cached + 512MB uncached

configname: CONFIG_XTENSA_KSEG_512M

KSEG layout
└─>512MB cached + 512MB uncached
In linux kernel since version 4.1 (release Date: 2015-06-21)  
TLB way 6 maps 512MB starting at KSEG_PADDR to 0xa0000000
with cache and to 0xc0000000 without cache.
KSEG_PADDR must be aligned to 256MB.