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: Anisse Astier <anisse@astier.eu>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index b02228411d57..4f0f0604f1c4 100644
--- a/kernel/power/snapshot.c
+++ b/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.