mm: rename migrate_pgmap_owner

MMU notifier ranges have a migrate_pgmap_owner field which is used by
drivers to store a pointer.  This is subsequently used by the driver
callback to filter MMU_NOTIFY_MIGRATE events.  Other notifier event types
can also benefit from this filtering, so rename the 'migrate_pgmap_owner'
field to 'owner' and create a new notifier initialisation function to
initialise this field.

Link: https://lkml.kernel.org/r/20210616105937.23201-6-apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Suggested-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 09e2850..3df7930 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -332,7 +332,7 @@
    walks to fill in the ``args->src`` array with PFNs to be migrated.
    The ``invalidate_range_start()`` callback is passed a
    ``struct mmu_notifier_range`` with the ``event`` field set to
-   ``MMU_NOTIFY_MIGRATE`` and the ``migrate_pgmap_owner`` field set to
+   ``MMU_NOTIFY_MIGRATE`` and the ``owner`` field set to
    the ``args->pgmap_owner`` field passed to migrate_vma_setup(). This is
    allows the device driver to skip the invalidation callback and only
    invalidate device private MMU mappings that are actually migrating.