Swapping

index 4a52d6e..a155c2b 100644
@@ -565,8 +565,9 @@ static inline int is_error_hpa(hpa_t hpa) { return hpa >> HPA_MSB; }
 hpa_t gva_to_hpa(struct kvm_vcpu *vcpu, gva_t gva);
 struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva);
 
-extern hpa_t bad_page_address;
+extern struct page *bad_page;
 
+int is_error_page(struct page *page);
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
 int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,

index a0f8366..bfa201c 100644
@@ -1012,6 +1012,12 @@ static int kvm_vm_ioctl_set_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
 	return r;
 }
 
+int is_error_page(struct page *page)
+{
+	return page == bad_page;
+}
+EXPORT_SYMBOL_GPL(is_error_page);
+
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
 {
 	int i;

@@ -1053,7 +1059,7 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 	gfn = unalias_gfn(kvm, gfn);
 	slot = __gfn_to_memslot(kvm, gfn);
 	if (!slot)
-		return NULL;
+		return bad_page;
 	return slot->phys_mem[gfn - slot->base_gfn];
 }
 EXPORT_SYMBOL_GPL(gfn_to_page);

@@ -1073,7 +1079,7 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (!page)
+	if (is_error_page(page))
 		return -EFAULT;
 	page_virt = kmap_atomic(page, KM_USER0);
 

@@ -1111,7 +1117,7 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn, const void *data,
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (!page)
+	if (is_error_page(page))
 		return -EFAULT;
 	page_virt = kmap_atomic(page, KM_USER0);
 

@@ -1149,7 +1155,7 @@ int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (!page)
+	if (is_error_page(page))
 		return -EFAULT;
 	page_virt = kmap_atomic(page, KM_USER0);
 

@@ -3075,7 +3081,7 @@ static struct page *kvm_vm_nopage(struct vm_area_struct *vma,
 
 	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 	page = gfn_to_page(kvm, pgoff);
-	if (!page)
+	if (is_error_page(page))
 		return NOPAGE_SIGBUS;
 	get_page(page);
 	if (type != NULL)

@@ -3390,7 +3396,7 @@ static struct sys_device kvm_sysdev = {
 	.cls = &kvm_sysdev_class,
 };
 
-hpa_t bad_page_address;
+struct page *bad_page;
 
 static inline
 struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)

@@ -3519,7 +3525,6 @@ EXPORT_SYMBOL_GPL(kvm_exit_x86);
 
 static __init int kvm_init(void)
 {
-	static struct page *bad_page;
 	int r;
 
 	r = kvm_mmu_module_init();

@@ -3530,16 +3535,13 @@ static __init int kvm_init(void)
 
 	kvm_arch_init();
 
-	bad_page = alloc_page(GFP_KERNEL);
+	bad_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
 
 	if (bad_page == NULL) {
 		r = -ENOMEM;
 		goto out;
 	}
 
-	bad_page_address = page_to_pfn(bad_page) << PAGE_SHIFT;
-	memset(__va(bad_page_address), 0, PAGE_SIZE);
-
 	return 0;
 
 out:

@@ -3552,7 +3554,7 @@ out4:
 static __exit void kvm_exit(void)
 {
 	kvm_exit_debug();
-	__free_page(pfn_to_page(bad_page_address >> PAGE_SHIFT));
+	__free_page(bad_page);
 	kvm_mmu_module_exit();
 }
 

index cfbeec8..e6a9b4a 100644
@@ -850,23 +850,17 @@ static void page_header_update_slot(struct kvm *kvm, void *pte, gpa_t gpa)
 	__set_bit(slot, &page_head->slot_bitmap);
 }
 
-hpa_t safe_gpa_to_hpa(struct kvm *kvm, gpa_t gpa)
-{
-	hpa_t hpa = gpa_to_hpa(kvm, gpa);
-
-	return is_error_hpa(hpa) ? bad_page_address | (gpa & ~PAGE_MASK): hpa;
-}
-
 hpa_t gpa_to_hpa(struct kvm *kvm, gpa_t gpa)
 {
 	struct page *page;
+	hpa_t hpa;
 
 	ASSERT((gpa & HPA_ERR_MASK) == 0);
 	page = gfn_to_page(kvm, gpa >> PAGE_SHIFT);
-	if (!page)
-		return gpa | HPA_ERR_MASK;
-	return ((hpa_t)page_to_pfn(page) << PAGE_SHIFT)
-		| (gpa & (PAGE_SIZE-1));
+	hpa = ((hpa_t)page_to_pfn(page) << PAGE_SHIFT) | (gpa & (PAGE_SIZE-1));
+	if (is_error_page(page))
+		return hpa | HPA_ERR_MASK;
+	return hpa;
 }
 
 hpa_t gva_to_hpa(struct kvm_vcpu *vcpu, gva_t gva)

index a9e687b..58fd35a 100644
@@ -92,8 +92,6 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
 			    struct kvm_vcpu *vcpu, gva_t addr,
 			    int write_fault, int user_fault, int fetch_fault)
 {
-	hpa_t hpa;
-	struct kvm_memory_slot *slot;
 	pt_element_t *ptep;
 	pt_element_t root;
 	gfn_t table_gfn;

@@ -118,9 +116,8 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
 	walker->table_gfn[walker->level - 1] = table_gfn;
 	pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
 		 walker->level - 1, table_gfn);
-	slot = gfn_to_memslot(vcpu->kvm, table_gfn);
-	hpa = safe_gpa_to_hpa(vcpu->kvm, root & PT64_BASE_ADDR_MASK);
-	walker->page = pfn_to_page(hpa >> PAGE_SHIFT);
+	walker->page = gfn_to_page(vcpu->kvm, (root & PT64_BASE_ADDR_MASK)
+				   >> PAGE_SHIFT);
 	walker->table = kmap_atomic(walker->page, KM_USER0);
 
 	ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||

@@ -130,7 +127,6 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
 
 	for (;;) {
 		int index = PT_INDEX(addr, walker->level);
-		hpa_t paddr;
 
 		ptep = &walker->table[index];
 		walker->index = index;

@@ -179,8 +175,7 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
 		walker->inherited_ar &= walker->table[index];
 		table_gfn = (*ptep & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
 		kunmap_atomic(walker->table, KM_USER0);
-		paddr = safe_gpa_to_hpa(vcpu->kvm, table_gfn << PAGE_SHIFT);
-		walker->page = pfn_to_page(paddr >> PAGE_SHIFT);
+		walker->page = gfn_to_page(vcpu->kvm, table_gfn);
 		walker->table = kmap_atomic(walker->page, KM_USER0);
 		--walker->level;
 		walker->table_gfn[walker->level - 1] = table_gfn;