Re: RFC: multiple address spaces for one process

Jeremy Fitzhardinge
2007-06-30T16:30:42Z

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