IN  HANDLE ProcessHandle,
  IN OUT PULONG_PTR NumberOfPages,

Routine Description:

    This function allocates nonpaged physical pages for the specified
    subject process.

    No WSLEs are maintained for this range.

    The caller must check the NumberOfPages returned to determine how many
    pages were actually allocated (this number may be less than the requested

    On success, the user array is filled with the allocated physical page
    frame numbers (only up to the returned NumberOfPages is filled in).

    No PTEs are filled here - this gives the application the flexibility
    to order the address space with no metadata structure imposed by the Mm.
    Applications do this via NtMapUserPhysicalPages - ie:

        - Each physical page allocated is set in the process's bitmap.
          This provides remap, free and unmap a way to validate and rundown
          these frames.

          Unmaps may result in a walk of the entire bitmap, but that's ok as
          unmaps should be less frequent.  The win is it saves us from
          using up system virtual address space to manage these frames.

        - Note that the same physical frame may NOT be mapped at two different
          virtual addresses in the process.  This makes frees and unmaps
          substantially faster as no checks for aliasing need be performed.


    ProcessHandle - Supplies an open handle to a process object.

    NumberOfPages - Supplies a pointer to a variable that supplies the
                    desired size in pages of the allocation.  This is filled
                    with the actual number of pages allocated.
    UserPfnArray - Supplies a pointer to user memory to store the allocated
                   frame numbers into.

Return Value:

    Various NTSTATUS codes.