* just verifies it is an address we can use.
*
* Since the kernel does everything in page size chunks ensure
* just verifies it is an address we can use.
*
* Since the kernel does everything in page size chunks ensure
* special cases crop of when we don't do this. The most
* insidious is getting overlapping destination addresses
* simply because addresses are changed to page size
* special cases crop of when we don't do this. The most
* insidious is getting overlapping destination addresses
* simply because addresses are changed to page size