[PATCH] kmemcheck: store shadow-memory pointers in each page

[Vegard Nossum]

Prior to this patch, the pointer to the shadow-memory area was stored only in
the head page of each (compound) allocation.

This patch is a prerequisite for SLAB support, since SLAB does not use
__GFP_COMP.

For this reason, we need to store one shadow-memory pointer per page. Note
that the shadow memory must still be allocated in a single block, since
mark_shadow() and friends assume that shadow memory is contiguous across page
boundaries.

Also remove some useless code.

Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxx>
---
 arch/x86/kernel/kmemcheck.c |    6 +++---
 mm/slub_kmemcheck.c         |   26 ++++++++++----------------
 2 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/kmemcheck.c b/arch/x86/kernel/kmemcheck.c
index ebdbe20..f03024a 100644
--- a/arch/x86/kernel/kmemcheck.c
+++ b/arch/x86/kernel/kmemcheck.c
@@ -280,7 +280,6 @@ address_get_shadow(unsigned long address)
 {
 	pte_t *pte;
 	struct page *page;
-	struct page *head;
 
 	if (!virt_addr_valid(address))
 		return NULL;
@@ -290,8 +289,9 @@ address_get_shadow(unsigned long address)
 		return NULL;
 
 	page = virt_to_page(address);
-	head = compound_head(page);
-	return head->shadow + ((void *) address - page_address(head));
+	if (!page->shadow)
+		return NULL;
+	return page->shadow + (address & (PAGE_SIZE - 1));
 }
 
 static int
diff --git a/mm/slub_kmemcheck.c b/mm/slub_kmemcheck.c
index 1fa8168..2fe33ab 100644
--- a/mm/slub_kmemcheck.c
+++ b/mm/slub_kmemcheck.c
@@ -9,6 +9,7 @@ void kmemcheck_alloc_shadow(struct kmem_cache *s, gfp_t flags, int node,
 {
 	struct page *shadow;
 	int order, pages;
+	int i;
 
 	order = compound_order(page);
 	pages = 1 << order;
@@ -17,9 +18,6 @@ void kmemcheck_alloc_shadow(struct kmem_cache *s, gfp_t flags, int node,
 	 * With kmemcheck enabled, we need to allocate a memory area for the
 	 * shadow bits as well.
 	 */
-
-	flags |= __GFP_COMP;
-
 	shadow = alloc_pages_node(node, flags, order);
 	if (!shadow) {
 		if (printk_ratelimit())
@@ -28,7 +26,8 @@ void kmemcheck_alloc_shadow(struct kmem_cache *s, gfp_t flags, int node,
 		return;
 	}
 
-	page->shadow = page_address(shadow);
+	for(i = 0; i < pages; ++i)
+		page[i].shadow = page_address(&shadow[i]);
 
 	/*
 	 * Mark it as non-present for the MMU so that our accesses to
@@ -45,29 +44,24 @@ void kmemcheck_alloc_shadow(struct kmem_cache *s, gfp_t flags, int node,
 		kmemcheck_mark_uninitialized_pages(page, pages);
 	else
 		kmemcheck_mark_unallocated_pages(page, pages);
-
-	mod_zone_page_state(page_zone(shadow),
-		(s->flags & SLAB_RECLAIM_ACCOUNT) ?
-		NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
-		pages);
 }
 
 void kmemcheck_free_shadow(struct kmem_cache *s, struct page *page)
 {
-	struct page *shadow = virt_to_page(page->shadow);
+	struct page *shadow;
 	int order, pages;
+	int i;
 
 	order = compound_order(page);
 	pages = 1 << order;
 
 	kmemcheck_show_pages(page, pages);
 
-	__ClearPageSlab(shadow);
-	mod_zone_page_state(page_zone(shadow),
-		(s->flags & SLAB_RECLAIM_ACCOUNT) ?
-		NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
-		-pages);
-	reset_page_mapcount(shadow);
+	shadow = virt_to_page(page[0].shadow);
+
+	for(i = 0; i < pages; ++i)
+		page[i].shadow = NULL;
+
 	__free_pages(shadow, order);
 }
 
-- 
1.5.4.1

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