mm: introduce page_vma_mapped_walk()

Introduce a new interface to check if a page is mapped into a vma.  It
aims to address shortcomings of page_check_address{,_transhuge}.

Existing interface is not able to handle PTE-mapped THPs: it only finds
the first PTE.  The rest lefted unnoticed.

page_vma_mapped_walk() iterates over all possible mapping of the page in
the vma.

Link: http://lkml.kernel.org/r/20170129173858.45174-3-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 85742ac..a7bac4f2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2129,9 +2129,12 @@
 static void unfreeze_page(struct page *page)
 {
 	int i;
-
-	for (i = 0; i < HPAGE_PMD_NR; i++)
-		remove_migration_ptes(page + i, page + i, true);
+	if (PageTransHuge(page)) {
+		remove_migration_ptes(page, page, true);
+	} else {
+		for (i = 0; i < HPAGE_PMD_NR; i++)
+			remove_migration_ptes(page + i, page + i, true);
+	}
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,