CONFIG_KVM_GUEST is not available for the selected architecture x86.
Result is shown for architecture powerpc

KVM Guest support

modulename: kvm.ko

configname: CONFIG_KVM_GUEST

Linux Kernel Configuration
└─>Platform support
└─>KVM Guest support
In linux kernel since version 2.6.26 (release Date: 2008-07-13)
This option enables various optimizations for running under the KVM
hypervisor. Overhead for the kernel when not running inside KVM should
be minimal.

In case of doubt, say Y