diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index e8fe103..b65511e 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -236,6 +236,7 @@
 	struct kvm_vcpu vcpus[KVM_MAX_VCPUS];
 	int memory_config_version;
 	int busy;
+	unsigned long rmap_overflow;
 };
 
 struct kvm_stat {
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index bc88c33..f2a6b6f 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -638,6 +638,7 @@
 						     | __GFP_ZERO);
 			if (!new.phys_mem[i])
 				goto out_free;
+ 			new.phys_mem[i]->private = 0;
 		}
 	}
 
diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 790423c..0f27beb 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -27,6 +27,7 @@
 #include "kvm.h"
 
 #define pgprintk(x...) do { } while (0)
+#define rmap_printk(x...) do { } while (0)
 
 #define ASSERT(x)							\
 	if (!(x)) {							\
@@ -125,6 +126,13 @@
 #define PT_DIRECTORY_LEVEL 2
 #define PT_PAGE_TABLE_LEVEL 1
 
+#define RMAP_EXT 4
+
+struct kvm_rmap_desc {
+	u64 *shadow_ptes[RMAP_EXT];
+	struct kvm_rmap_desc *more;
+};
+
 static int is_write_protection(struct kvm_vcpu *vcpu)
 {
 	return vcpu->cr0 & CR0_WP_MASK;
@@ -150,6 +158,120 @@
 	return pte & PT_SHADOW_IO_MARK;
 }
 
+static int is_rmap_pte(u64 pte)
+{
+	return (pte & (PT_WRITABLE_MASK | PT_PRESENT_MASK))
+		== (PT_WRITABLE_MASK | PT_PRESENT_MASK);
+}
+
+/*
+ * Reverse mapping data structures:
+ *
+ * If page->private bit zero is zero, then page->private points to the
+ * shadow page table entry that points to page_address(page).
+ *
+ * If page->private bit zero is one, (then page->private & ~1) points
+ * to a struct kvm_rmap_desc containing more mappings.
+ */
+static void rmap_add(struct kvm *kvm, u64 *spte)
+{
+	struct page *page;
+	struct kvm_rmap_desc *desc;
+	int i;
+
+	if (!is_rmap_pte(*spte))
+		return;
+	page = pfn_to_page((*spte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT);
+	if (!page->private) {
+		rmap_printk("rmap_add: %p %llx 0->1\n", spte, *spte);
+		page->private = (unsigned long)spte;
+	} else if (!(page->private & 1)) {
+		rmap_printk("rmap_add: %p %llx 1->many\n", spte, *spte);
+		desc = kzalloc(sizeof *desc, GFP_NOWAIT);
+		if (!desc)
+			BUG(); /* FIXME: return error */
+		desc->shadow_ptes[0] = (u64 *)page->private;
+		desc->shadow_ptes[1] = spte;
+		page->private = (unsigned long)desc | 1;
+	} else {
+		rmap_printk("rmap_add: %p %llx many->many\n", spte, *spte);
+		desc = (struct kvm_rmap_desc *)(page->private & ~1ul);
+		while (desc->shadow_ptes[RMAP_EXT-1] && desc->more)
+			desc = desc->more;
+		if (desc->shadow_ptes[RMAP_EXT-1]) {
+			desc->more = kzalloc(sizeof *desc->more, GFP_NOWAIT);
+			if (!desc->more)
+				BUG(); /* FIXME: return error */
+			desc = desc->more;
+		}
+		for (i = 0; desc->shadow_ptes[i]; ++i)
+			;
+		desc->shadow_ptes[i] = spte;
+	}
+}
+
+static void rmap_desc_remove_entry(struct page *page,
+				   struct kvm_rmap_desc *desc,
+				   int i,
+				   struct kvm_rmap_desc *prev_desc)
+{
+	int j;
+
+	for (j = RMAP_EXT - 1; !desc->shadow_ptes[j] && j > i; --j)
+		;
+	desc->shadow_ptes[i] = desc->shadow_ptes[j];
+	desc->shadow_ptes[j] = 0;
+	if (j != 0)
+		return;
+	if (!prev_desc && !desc->more)
+		page->private = (unsigned long)desc->shadow_ptes[0];
+	else
+		if (prev_desc)
+			prev_desc->more = desc->more;
+		else
+			page->private = (unsigned long)desc->more | 1;
+	kfree(desc);
+}
+
+static void rmap_remove(struct kvm *kvm, u64 *spte)
+{
+	struct page *page;
+	struct kvm_rmap_desc *desc;
+	struct kvm_rmap_desc *prev_desc;
+	int i;
+
+	if (!is_rmap_pte(*spte))
+		return;
+	page = pfn_to_page((*spte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT);
+	if (!page->private) {
+		printk(KERN_ERR "rmap_remove: %p %llx 0->BUG\n", spte, *spte);
+		BUG();
+	} else if (!(page->private & 1)) {
+		rmap_printk("rmap_remove:  %p %llx 1->0\n", spte, *spte);
+		if ((u64 *)page->private != spte) {
+			printk(KERN_ERR "rmap_remove:  %p %llx 1->BUG\n",
+			       spte, *spte);
+			BUG();
+		}
+		page->private = 0;
+	} else {
+		rmap_printk("rmap_remove:  %p %llx many->many\n", spte, *spte);
+		desc = (struct kvm_rmap_desc *)(page->private & ~1ul);
+		prev_desc = NULL;
+		while (desc) {
+			for (i = 0; i < RMAP_EXT && desc->shadow_ptes[i]; ++i)
+				if (desc->shadow_ptes[i] == spte) {
+					rmap_desc_remove_entry(page, desc, i,
+							       prev_desc);
+					return;
+				}
+			prev_desc = desc;
+			desc = desc->more;
+		}
+		BUG();
+	}
+}
+
 static void kvm_mmu_free_page(struct kvm_vcpu *vcpu, hpa_t page_hpa)
 {
 	struct kvm_mmu_page *page_head = page_header(page_hpa);
@@ -229,27 +351,27 @@
 static void release_pt_page_64(struct kvm_vcpu *vcpu, hpa_t page_hpa,
 			       int level)
 {
+	u64 *pos;
+	u64 *end;
+
 	ASSERT(vcpu);
 	ASSERT(VALID_PAGE(page_hpa));
 	ASSERT(level <= PT64_ROOT_LEVEL && level > 0);
 
-	if (level == 1)
-		memset(__va(page_hpa), 0, PAGE_SIZE);
-	else {
-		u64 *pos;
-		u64 *end;
+	for (pos = __va(page_hpa), end = pos + PT64_ENT_PER_PAGE;
+	     pos != end; pos++) {
+		u64 current_ent = *pos;
 
-		for (pos = __va(page_hpa), end = pos + PT64_ENT_PER_PAGE;
-		     pos != end; pos++) {
-			u64 current_ent = *pos;
-
-			*pos = 0;
-			if (is_present_pte(current_ent))
+		if (is_present_pte(current_ent)) {
+			if (level != 1)
 				release_pt_page_64(vcpu,
 						  current_ent &
 						  PT64_BASE_ADDR_MASK,
 						  level - 1);
+			else
+				rmap_remove(vcpu->kvm, pos);
 		}
+		*pos = 0;
 	}
 	kvm_mmu_free_page(vcpu, page_hpa);
 }
@@ -275,6 +397,7 @@
 			page_header_update_slot(vcpu->kvm, table, v);
 			table[index] = p | PT_PRESENT_MASK | PT_WRITABLE_MASK |
 								PT_USER_MASK;
+			rmap_add(vcpu->kvm, &table[index]);
 			return 0;
 		}
 
@@ -437,6 +560,7 @@
 	} else {
 		*shadow_pte |= paddr;
 		page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
+		rmap_add(vcpu->kvm, shadow_pte);
 	}
 }
 
@@ -489,6 +613,7 @@
 		u64 *table = __va(page_addr);
 
 		if (level == PT_PAGE_TABLE_LEVEL ) {
+			rmap_remove(vcpu->kvm, &table[index]);
 			table[index] = 0;
 			return;
 		}
@@ -679,8 +804,9 @@
 		pt = __va(page->page_hpa);
 		for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
 			/* avoid RMW */
-			if (pt[i] & PT_WRITABLE_MASK)
+			if (pt[i] & PT_WRITABLE_MASK) {
+				rmap_remove(kvm, &pt[i]);
 				pt[i] &= ~PT_WRITABLE_MASK;
-
+			}
 	}
 }
diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 09bb9b4..8c48528 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -261,6 +261,7 @@
 	mark_page_dirty(vcpu->kvm, gfn);
 	*shadow_ent |= PT_WRITABLE_MASK;
 	*guest_ent |= PT_DIRTY_MASK;
+	rmap_add(vcpu->kvm, shadow_ent);
 
 	return 1;
 }