Re: RFC: multiple address spaces for one process

[Jeremy Fitzhardinge <jeremy@xensource.com>]

Carsten Otte wrote:
> The big difference here is that LinuxOnLinux does represent guest 
> virtual addressing in these mm structs where all other kernel based 
> VMMs do represent guest physical in the user address space. That 
> somewhat disqualifies LinuxOnLinux to share the commonality.
> Whether or not proposed patch makes sense for shaddow page tables is 
> unknown to me, since we have nested paging on s390. 

 From an interface perspective, I think nested paging and shadow 
pagetables should be identical; after all, shadow pagetables are just a 
software implementation of nested pagetables.  There seem to be 3 
distinct types of VMM pagetable:

   1. UML/LoL vmas-as-pagetable/tlb
   2. shadow/nested paging
   3. direct paging

The multiple address space patch definitely makes sense for 1, but 2&3 
both implement the alternate address space by directly pointing the 
CPU's paging hardware at a new pagetable, rather than going via the 
Linux VM.

    J

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