> Single address space OS's in a broader sense have been made unviable by Spectre vulnerabilities; This is valid only for current CPUs and probably can be fixe

> Single address space OS's in a broader sense have been made unviable by Spectre vulnerabilities; This is valid only for current CPUs and probably can be fixed. For example, current CPUs do not do speculative accesses for memory-mapped IO, and it means that similar method could be used to prevent access to kernel or other processes memory. There could be registers that contain lower and upper bounds of accessible memory, and they could be checked before accessing it.