reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git/commit/?id=8d43a66fdb5007eb7f368b20a2ca44395e8e47d9
        git remote add bcain https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git
        git fetch --no-tags bcain bcain/qemu_boot
        git checkout 8d43a66fdb5007eb7f368b20a2ca44395e8e47d9

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash mm/