The original one-shot page patch (git-e321f65) did not account for the
possibility of pagefaults happening while copying memory in the
kernel. This allowed a simple cp(1) from vbfs to hang the system,
since VM was repeatedly requesting the same page from the file system.
With this fix, VM no longer tries to fetch the same memory-mapped page
from VFS more than once per memory handling request from the kernel.
In addition to fixing the original issue, this change should make
handling memory somewhat more robust and ever-so-slightly faster.
Test74 has been extended with a simple test for this case.
Change-Id: I6e565f3750141e51b52ec98c938f8e1aa40070d0
