How to separate mount rights in nfsv4

[Asdo <asdo@shiftmail.org>]

Hello,
it's not clear to me how I can allow different access to different
machines in NFSv4.
Because nfsv4 needs a root export with fsid=0, and all other mounts
should be below that.

However, if the line with fsid=0 is not mountable to all nodes, also the
mounts below it will fail.
And if the line with fsid=0 is mountable to all nodes, all further lines
can provide no additional security!

Example; this is my current export:

/virtual_machines/kvm/export   
10.48.0.0/24(rw,no_root_squash,async,subtree_check,fsid=0)
/virtual_machines/kvm/export/hwnode1  
10.48.0.10(rw,no_root_squash,async,subtree_check)
/virtual_machines/kvm/export/hwnode2  
10.48.0.11(rw,no_root_squash,async,subtree_check)

I have two hardware nodes for virtual machines. Ideally each one of them
should be able to mount only its subdirectory, but the export shown
above is the only working one I could create.
However with the above export file the root user on hwnode1 can directly
mount /virtual_machines/kvm/export and see everything, even the files
that were for hwnode2 only.
OTOH if I set my fsid=0 line so that it's not mountable (e.g. changing
the IP or netmask), all lines below it stop working.

How should I do?

Thanks for your help