Read/Write migration entries: Implement correct behavior in copy_one_pte

Migration entries with write permission must become SWP_MIGRATION_READ
entries if a COW mapping is processed. The migration entries from which
the copy is being made must also become SWP_MIGRATION_READ. This mimicks
the copying of pte for an anonymous page.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.17-rc1-mm2/mm/memory.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/memory.c	2006-04-17 16:23:50.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/memory.c	2006-04-17 17:25:50.000000000 -0700
@@ -434,7 +434,9 @@ copy_one_pte(struct mm_struct *dst_mm, s
 	/* pte contains position in swap or file, so copy. */
 	if (unlikely(!pte_present(pte))) {
 		if (!pte_file(pte)) {
-			swap_duplicate(pte_to_swp_entry(pte));
+			swp_entry_t entry = pte_to_swp_entry(pte);
+
+			swap_duplicate(entry);
 			/* make sure dst_mm is on swapoff's mmlist. */
 			if (unlikely(list_empty(&dst_mm->mmlist))) {
 				spin_lock(&mmlist_lock);
@@ -443,6 +445,19 @@ copy_one_pte(struct mm_struct *dst_mm, s
 						 &src_mm->mmlist);
 				spin_unlock(&mmlist_lock);
 			}
+			if (is_migration_entry(entry) &&
+					is_cow_mapping(vm_flags)) {
+				page = migration_entry_to_page(entry);
+
+				/*
+				 * COW mappings require pages in both parent
+				*  and child to be set to read.
+				 */
+				entry = make_migration_entry(page,
+	`					SWP_MIGRATION_READ);
+				pte = swp_entry_to_pte(entry);
+				set_pte_at(src_mm, addr, src_pte, pte);
+			}
 		}
 		goto out_set_pte;
 	}