mm/hmm: update HMM documentation

Update the HMM documentation to reflect the latest API and make a few
minor wording changes.

Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/linux/hmm.h

@@ -418,9 +418,10 @@ struct hmm_mirror_ops {
 	 *
 	 * @mirror: pointer to struct hmm_mirror
 	 *
-	 * This is called when the mm_struct is being released.
-	 * The callback should make sure no references to the mirror occur
-	 * after the callback returns.
+	 * This is called when the mm_struct is being released.  The callback
+	 * must ensure that all access to any pages obtained from this mirror
+	 * is halted before the callback returns. All future access should
+	 * fault.
 	 */
 	void (*release)(struct hmm_mirror *mirror);