qemu-system-aarch64: -enable-kvm: No machine specified, and there is no default Use -machine help to list supported machines

$ qemu-system-aarch64 -M help
akita                Sharp SL-C1000 (Akita) PDA (PXA270)
...
z2                   Zipit Z2 (PXA27x)

$ qemu-system-aarch64 -M virt -cpu help
 arm1026
 ...
 ti925t

qemu-system-aarch64 -M ? 

[root@localhost cloud_images]# qemu-system-aarch64 -M ? 
Supported machines are:
akita                Sharp SL-C1000 (Akita) PDA (PXA270)
ast2500-evb          Aspeed AST2500 EVB (ARM1176)
ast2600-evb          Aspeed AST2600 EVB (Cortex A7)
borzoi               Sharp SL-C3100 (Borzoi) PDA (PXA270)
canon-a1100          Canon PowerShot A1100 IS
cheetah              Palm Tungsten|E aka. Cheetah PDA (OMAP310)
collie               Sharp SL-5500 (Collie) PDA (SA-1110)
connex               Gumstix Connex (PXA255)
cubieboard           cubietech cubieboard (Cortex-A8)
emcraft-sf2          SmartFusion2 SOM kit from Emcraft (M2S010)
highbank             Calxeda Highbank (ECX-1000)
imx25-pdk            ARM i.MX25 PDK board (ARM926)

[root@localhost cloud_images]# qemu-system-aarch64  -name vm2 -enable-kvm  -M virt  -cpu host -smp 2 -m 4096 -object memory-backend-file,id=mem,size=4096M,mem-path=/mnt/huge,share=on -numa node,memdev=mem -mem-prealloc -drive file=/home/osimg/ubuntu16.img  -chardev socket,path=/tmp/vm2_qga0.sock,server,nowait,id=vm2_qga0 -device virtio-serial -device virtserialport,chardev=vm2_qga0,name=org.qemu.guest_agent.2 -daemonize -monitor unix:/tmp/vm2_monitor.sock,server,nowait -net nic,macaddr=00:00:00:08:e8:aa,addr=1f -net user,hostfwd=tcp:127.0.0.1:6002-:22 -chardev socket,id=char0,path=./vhost-net,server -netdev type=vhost-user,id=netdev0,chardev=char0,vhostforce -device virtio-net-pci,netdev=netdev0,mac=52:54:00:00:00:01,mrg_rxbuf=on,rx_queue_size=1024,tx_queue_size=1024 -vnc :10
qemu-system-aarch64: -chardev socket,id=char0,path=./vhost-net,server: info: QEMU waiting for connection on: disconnected:unix:./vhost-net,server