soft-dirty: call mmu notifiers when write-protecting ptes

soft-dirty: call mmu notifiers when write-protecting ptes

As noticed by Xiao, since soft-dirty clear command modifies page tables we
have to flush tlbs and call mmu notifiers.  While the former is done by
the clear_refs engine itself, the latter is to be done.

One thing to note about this -- in order not to call per-page invalidate
notifier (_all_ address space is about to be changed), the
_invalidate_range_start and _end are used.  But for those start and end
are not known exactly.  To address this, the same trick as in exit_mmap()
is used -- start is 0 and end is (unsigned long)-1.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>