actually this is my conf file :
TIMEOUT 30
DEFAULT primary
MENU TITLE L4T boot options
#LABEL primary
#MENU LABEL primary kernel
#LINUX /boot/Image
#INITRD /boot/initrd
#APPEND ${cbootargs}
LABEL primary
MENU LABEL primary kernel
LINUX /boot/Image_kvm
FDT /boot/tegra210-p3448-0000-p3449-0000-b01-kvm.dtb
INITRD /boot/initrd
APPEND ${cbootargs}
it does not work.