reproduce (this is a W=1 build):
        # https://github.com/sean-jc/linux/commit/5a0b230804678a2841b6ce4a072651976a7b7c7f
        git remote add sean-jc https://github.com/sean-jc/linux
        git fetch --no-tags sean-jc x86/guest_cpufeatures
        git checkout 5a0b230804678a2841b6ce4a072651976a7b7c7f
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/kvm/