PM / Hibernate: allow hibernation with PAGE_POISONING_ZERO

PAGE_POISONING_ZERO disables zeroing new pages on alloc, they are
poisoned (zeroed) as they become available.
In the hibernate use case, free pages will appear in the system without
being cleared, left there by the loading kernel.

This patch will make sure free pages are cleared on resume when
PAGE_POISONING_ZERO is enabled. We free the pages just after resume
because we can't do it later: going through any device resume code might
allocate some memory and invalidate the free pages bitmap.

Thus we don't need to disable hibernation when PAGE_POISONING_ZERO is
enabled.
Signed-off-by: NAnisse Astier <anisse@astier.eu>
Reviewed-by: NKees Cook <keescook@chromium.org>
Acked-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

kernel/power/hibernate.c

@@ -306,8 +306,10 @@ static int create_image(int platform_mode)
 	if (error)
 		printk(KERN_ERR "PM: Error %d creating hibernation image\n",
 			error);
-	if (!in_suspend)
+	if (!in_suspend) {
 		events_check_enabled = false;
+		clear_free_pages();
+	}
 
 	platform_leave(platform_mode);
 
@@ -1189,22 +1191,6 @@ static int __init nohibernate_setup(char *str)
 	return 1;
 }
 
-static int __init page_poison_nohibernate_setup(char *str)
-{
-#ifdef CONFIG_PAGE_POISONING_ZERO
-	/*
-	 * The zeroing option for page poison skips the checks on alloc.
-	 * since hibernation doesn't save free pages there's no way to
-	 * guarantee the pages will still be zeroed.
-	 */
-	if (!strcmp(str, "on")) {
-		pr_info("Disabling hibernation due to page poisoning\n");
-		return nohibernate_setup(str);
-	}
-#endif
-	return 1;
-}
-
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
@@ -1212,4 +1198,3 @@ __setup("hibernate=", hibernate_setup);
 __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
-__setup("page_poison=", page_poison_nohibernate_setup);

kernel/power/power.h

@@ -110,6 +110,8 @@ extern int create_basic_memory_bitmaps(void);
 extern void free_basic_memory_bitmaps(void);
 extern int hibernate_preallocate_memory(void);
 
+extern void clear_free_pages(void);
+
 /**
  *	Auxiliary structure used for reading the snapshot image data and
  *	metadata from and writing them to the list of page backup entries

kernel/power/snapshot.c

@@ -1132,6 +1132,28 @@ void free_basic_memory_bitmaps(void)
 	pr_debug("PM: Basic memory bitmaps freed\n");
 }
 
+void clear_free_pages(void)
+{
+#ifdef CONFIG_PAGE_POISONING_ZERO
+	struct memory_bitmap *bm = free_pages_map;
+	unsigned long pfn;
+
+	if (WARN_ON(!(free_pages_map)))
+		return;
+
+	memory_bm_position_reset(bm);
+	pfn = memory_bm_next_pfn(bm);
+	while (pfn != BM_END_OF_MAP) {
+		if (pfn_valid(pfn))
+			clear_highpage(pfn_to_page(pfn));
+
+		pfn = memory_bm_next_pfn(bm);
+	}
+	memory_bm_position_reset(bm);
+	pr_info("PM: free pages cleared after restore\n");
+#endif /* PAGE_POISONING_ZERO */
+}
+
 /**
  * snapshot_additional_pages - Estimate the number of extra pages needed.
  * @zone: Memory zone to carry out the computation for.

mm/Kconfig.debug

@@ -76,8 +76,6 @@ config PAGE_POISONING_ZERO
 	   no longer necessary to write zeros when GFP_ZERO is used on
 	   allocation.
 
-	   Enabling page poisoning with this option will disable hibernation
-
 	   If unsure, say N
 	bool