mm/mmu_notifier: mmu_notifier_range_update_to_read_only() helper

mm/mmu_notifier: mmu_notifier_range_update_to_read_only() helper

Helper to test if a range is updated to read only (it is still valid to
read from the range).  This is useful for device driver or anyone who wish
to optimize out update when they know that they already have the range map
read only.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Jérôme Glisse <[email protected]>
Reviewed-by: Ralph Campbell <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Cc: Christian König <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krcmar <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Christian Koenig <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>