Very interesting!  Can you describe when case 1 happens?
(I thought pmap_enter was ONLY called by vm_fault!)

Charles M. Hannum writes:
 > 
 > Here's a somewhat long-winded explanation, just to make sure I cover
 > all the points.
 > 
 > There are two different reasons why we map pages:
 > 
 > 1) because we expect to need the page Some Time Later.  This can
 >    happen when, e.g., `prefaulting' pages.  In this case the
 >    `access_type' is set to 0 and no special action is performed by the
 >    pmap.
 > 
 > 2) because we need the page Right Now, possibly because we got a
 >    fault.  In this case, we know that the page is going to be accessed
 >    immediately after the fault handler returns (or, in some cases,
 >    immediately after pmap_enter() returns, as in /dev/mem handling).
...