[PATCH] unpaged: get_user_pages VM_RESERVED

The PageReserved removal in 2.6.15-rc1 prohibited get_user_pages on the areas
flagged VM_RESERVED in place of PageReserved.  That is correct in theory - we
ought not to interfere with struct pages in such a reserved area; but in
practice it broke BTTV for one.

So revert to prohibiting only on VM_IO: if someone gets into trouble with
get_user_pages on VM_RESERVED, it'll just be a "don't do that".

You can argue that videobuf_mmap_mapper shouldn't set VM_RESERVED in the first
place, but now's not the time for breaking drivers without notice.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>