Generalized address-space isolation

I think that an other approach could be related to DRAM encryption that certain CPUs support: if pages are encrypted with a task-specific key, we could imagine that depending on the task and execution level, there could be one or a few keys available that allow to access memory. In the worst case, even if the CPU was mislead into trying to prefetch data from wrong addresses, the observed data would be encrypted. One problem I'm seeing with encryption is the difficulty to share areas between tasks or with hardware devices, and I fear it could result in more copies.