CONFIG_S390_GUEST is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT or s390

s390 guest support for KVM (EXPERIMENTAL)

configname: CONFIG_S390_GUEST

Linux Kernel Configuration
└─>Base setup
└─>s390 guest support for KVM (EXPERIMENTAL)
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
Select this option if you want to run the kernel as a guest under
the KVM hypervisor. This will add detection for KVM as well as a
virtio transport. If KVM is detected, the virtio console will be
the default console.


depends
CONFIG_64BIT
CONFIG_EXPERIMENTAL