Actually we have designed the rid virtualization mechanism but is not in this implementation yet. Actually in this area we don't have difference between your approach (starting_rid/ending_rid for each domain) and high 4 bits indicating domain ID. Merge this problem is quit easy.

I am afraid supporting for both solution is extremely high burden as VMMU is a too fundmental thing. For example: How to support hypercall information passing between guest and HV? You are using poorman's exception handler now that is OK for temply debug effort. But as we discussed, it has critical problem/limitations.

The solution to solve that in our vMMU is that we keep all guest TLBs in HV internal data structure, and we have defined a seperate TLB section type like ForeignMap(Term in X86 XEN)/Hypercall sharedPage in vTLB. Xenolinux or Device model or others can insert special maps for that. This type of section will not be automatically purged when the collision chain is full. In this way guest will not see tlb miss for "uaccess" in HV to access guest data. How to solve that in global VHPT? I am afraid it is really hard. Why do we want to spend more time to discard existing approach and investigate on no hints direction?

BTW, how do you support MMIO map for DOM-N if the domain-N is a non modified Linux? I am afraid global VHPT will also eventually need a similar vTLB data struture to support.