KAISER: hiding the kernel from user space

> if a syscall is about to become as expensive as IPC on L4... would the (theoretical) performance of the respective kernels be similar after KAISER?

Most of the KAISER performance impact is purely from the cost of manipulating the hardware. L4 and other kernels would pay the same cost Linux would.

It's not fair to compare a non-hardened kernel to a hardened one, though. It's apples-to-oranges.