> Suppose you control the entire stack though, from the bare metal up. (Correct me if I'm wrong, but) Toro doesn't seem to run on real hardware, you have to run it atop QEMU or Firecracker. In that case, what difference does it make if your application makes I/O requests through paravirtualized interfaces of the hypervisor or talks directly to the host via system calls? Both ultimately lead to the host OS servicing the request. There isn't any notable difference between the kernel/hypervisor and the user/kernel boundary in modern processors either; most of the time, privilege escalations come from errors in the software running in the privileged modes of the processor.

Toro can run on baremetal although I stopped to support on that a few years ago. I tagged in master the commit when this happened. Also, I removed the TCP/IP Stack in favor to VSOCK. Those changes, though, could be reversed in case there is interest on those features.