Enable 5-level page tables support

configname: CONFIG_X86_5LEVEL

Linux Kernel Configuration
└─>Processor type and features
└─>Enable 5-level page tables support
In linux kernel since version 3.10 (release Date: 2013-06-30)  
5-level paging enables access to larger address space:
upto 128 PiB of virtual address space and 4 PiB of
physical address space.

It will be supported by future Intel CPUs.

Note: a kernel with this option enabled can only be booted
on machines that support the feature.

See Documentation/x86/x86_64/5level-paging.txt for more
information.

Say N if unsure.

depends
CONFIG_X86_64

is selected by
CONFIG_XEN_PVH