[v4 3/6] mm: uninitialized struct page poisoning sanity checking

[Pavel Tatashin]

During boot we poison struct page memory in order to ensure that no one is
accessing this memory until the struct pages are initialized in
__init_single_page().

This patch adds more scrutiny to this checking by making sure that flags
do not equal the poison pattern when they are accessed.  The pattern is all
ones.

Since node id is also stored in struct page, and may be accessed quite
early, we add this enforcement into page_to_nid() function as well.
Note, this is applicable only when NODE_NOT_IN_PAGE_FLAGS=n

Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/mm.h         |  4 +++-
 include/linux/page-flags.h | 22 +++++++++++++++++-----
 mm/memblock.c              |  2 +-
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..ad71136a6494 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -896,7 +896,9 @@ extern int page_to_nid(const struct page *page);
 #else
 static inline int page_to_nid(const struct page *page)
 {
-	return (page->flags >> NODES_PGSHIFT) & NODES_MASK;
+	struct page *p = (struct page *)page;
+
+	return (PF_POISONED_CHECK(p)->flags >> NODES_PGSHIFT) & NODES_MASK;
 }
 #endif
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 50c2b8786831..e34a27727b9a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -156,9 +156,18 @@ static __always_inline int PageCompound(struct page *page)
 	return test_bit(PG_head, &page->flags) || PageTail(page);
 }
 
+#define	PAGE_POISON_PATTERN	-1l
+static inline int PagePoisoned(const struct page *page)
+{
+	return page->flags == PAGE_POISON_PATTERN;
+}
+
 /*
  * Page flags policies wrt compound pages
  *
+ * PF_POISONED_CHECK
+ *     check if this struct page poisoned/uninitialized
+ *
  * PF_ANY:
  *     the page flag is relevant for small, head and tail pages.
  *
@@ -176,17 +185,20 @@ static __always_inline int PageCompound(struct page *page)
  * PF_NO_COMPOUND:
  *     the page flag is not relevant for compound pages.
  */
-#define PF_ANY(page, enforce)	page
-#define PF_HEAD(page, enforce)	compound_head(page)
+#define PF_POISONED_CHECK(page) ({					\
+		VM_BUG_ON_PGFLAGS(PagePoisoned(page), page);		\
+		page; })
+#define PF_ANY(page, enforce)	PF_POISONED_CHECK(page)
+#define PF_HEAD(page, enforce)	PF_POISONED_CHECK(compound_head(page))
 #define PF_ONLY_HEAD(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(PageTail(page), page);		\
-		page;})
+		PF_POISONED_CHECK(page); })
 #define PF_NO_TAIL(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);	\
-		compound_head(page);})
+		PF_POISONED_CHECK(compound_head(page)); })
 #define PF_NO_COMPOUND(page, enforce) ({				\
 		VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page);	\
-		page;})
+		PF_POISONED_CHECK(page); })
 
 /*
  * Macros to create function definitions for page flags
diff --git a/mm/memblock.c b/mm/memblock.c
index 5a9ca2a1751b..d85c8754e0ce 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1373,7 +1373,7 @@ void * __init memblock_virt_alloc_try_nid_raw(
 					   min_addr, max_addr, nid);
 #ifdef CONFIG_DEBUG_VM
 	if (ptr && size > 0)
-		memset(ptr, 0xff, size);
+		memset(ptr, PAGE_POISON_PATTERN, size);
 #endif
 	return ptr;
 }
-- 
2.16.1