> How about sPMP is only used if satp.MODE=BARE or virtualization is
> enabled and hgatp.MODE=BARE? That would enable the trusted hypervisor
> case, while disallowing an S-mode operating system from enabling both
> paging and sPMP at the same time.
>
> Jonathan
>
I'd be ok with this, but I don't see what we gain from it, in the end
the hw will still use sPMP + MMU in case the hypervisor uses sPMP and
the guest uses paging, because we still want sPMP to be active when
guest is running.
It for instance rules out the case where M-mode uses PMP, HS-mode uses sPMP and paging, and VS-mode also uses sPMP and paging. That would be 5 stages of protection for every access! (Which is way worse than it sounds because each level of walking a page table also has to be validated)
