reproduce:
        # https://github.com/davidhildenbrand/linux/commit/2a876920cbbc3c1ed61d1cd847cfc939f7b7d003
        git remote add davidhildenbrand https://github.com/davidhildenbrand/linux
        git fetch --no-tags davidhildenbrand virtio-mem-s390x-new
        git checkout 2a876920cbbc3c1ed61d1cd847cfc939f7b7d003
        make W=1 O=/tmp/kselftest headers
        make W=1 O=/tmp/kselftest -C tools/testing/selftests
        make W=1 O=/tmp/kselftest -C tools/testing/selftests/bpf