bitkeeper revision 1.1236.32.2 (42360b33-HudAOddVBt3ez4shMiyOw)

bitkeeper revision 1.1236.32.2 (42360b33-HudAOddVBt3ez4shMiyOw)

Initial fullshadow checkin.

Things still to do:
- reuse snapshots intelligently.
- minimize tlb flushes during resync.
- figure out when to free up no-longer-used L2 shadows, and
  generally deal with out-of-memory kinds of problems.

Some basic guidelines:
- With fullshadow on, you can not trust
  linear_pg_table unless you have first checked whether the VA
  in which you are interested is out-of-sync or not.
- Significant new functions/macros include:
  page_out_of_sync(mfn): returns true if page is out of sync.
  shadow_mark_out_of_sync: make a page be out of sync (allocating
     any necessary snapshots, etc)
  shadow_out_of_sync(va): returns true if the current mappings
     involved in va are out-of-sync.
  shadow_sync_va(): bring the pages involved in mapping a particular
     va back into sync.  Currently calls shadow_sync_all().
  shadow_sync_all(): bring all pages back in-sync.

Signed-off-by: michael.fetterman@cl.cam.ac.uk