Failed to mount /: 0

When running `kraft up -p kvm -m x86_64 -t python3 --memory 1024 demo` it fails to boot with the following error: 

```
SeaBIOS (version 1.14.0-2)
Booting from ROM...
[   69.438952] CRIT: [libvfscore] rootfs.c @ 85   : Failed to mount /: 0
[   69.561104] ERR:  [libukboot] boot.c @ 92   : Init function at 0x11e360 returned error -1
```
Any suggestions on debugging? Thanks. 