answers.txt: 6.828 Lab 4
Dan R. K. Ports <drkp@mit.edu>
2004/10/18:

Exercise 1:

1. The references to the variable e are valid both before and after
   the call to lcr3, because the virtual address e is mapped to the
   same physical location in both address spaces. e is a pointer to an
   environment, so it points to a virtual address in kernel memory,
   i.e. above KERNBASE. The mappings above KERNBASE in every address
   space are the same, so this virtual address continues to be valid
   after the address space change.


Challenge: 
   Implemented sfork. Duplicates all page mappings as shared
   (user-write in both processes, not copy-on-write) except those in
   the stack, which are marked copy-on-write just as with
   fork. Modified forktree to use sfork, and tested with pingpongs;
   both pass.

   (Yeah, I know this isn't a very interesting challenge problem. If
   only I had time this for some of the others...)