When you link the application with the Mirage runtime (what you refer to as "libOS") you create a new kernel. You then run that kernel directly on Xen (like you

When you link the application with the Mirage runtime (what you refer to as "libOS") you create a new kernel. You then run that kernel directly on Xen (like you would run a Linux domU), so yes they run in kernel land. I'm not convinced that 'Xen + Mirage unikernel' has a performance advantage over 'Linux baremetal + Mirage direct mode', but I definetely see an advantage compared to 'Xen + Linux domU + Mirage direct mode'.