KVM: Count the number of dirty pages for dirty logging

Needed for the next patch which uses this number to decide how to write
protect a slot.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -3466,10 +3466,9 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
 int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 				      struct kvm_dirty_log *log)
 {
-	int r, i;
+	int r;
 	struct kvm_memory_slot *memslot;
 	unsigned long n;
-	unsigned long is_dirty = 0;
 
 	mutex_lock(&kvm->slots_lock);
 
@@ -3484,11 +3483,8 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 
 	n = kvm_dirty_bitmap_bytes(memslot);
 
-	for (i = 0; !is_dirty && i < n/sizeof(long); i++)
-		is_dirty = memslot->dirty_bitmap[i];
-
 	/* If nothing is dirty, don't bother messing with page tables. */
-	if (is_dirty) {
+	if (memslot->nr_dirty_pages) {
 		struct kvm_memslots *slots, *old_slots;
 		unsigned long *dirty_bitmap;
 
@@ -3503,6 +3499,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 			goto out;
 		memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
 		slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
+		slots->memslots[log->slot].nr_dirty_pages = 0;
 		slots->generation++;
 
 		old_slots = kvm->memslots;

include/linux/kvm_host.h

@@ -181,6 +181,7 @@ struct kvm_memory_slot {
 	unsigned long *rmap;
 	unsigned long *dirty_bitmap;
 	unsigned long *dirty_bitmap_head;
+	unsigned long nr_dirty_pages;
 	struct kvm_lpage_info *lpage_info[KVM_NR_PAGE_SIZES - 1];
 	unsigned long userspace_addr;
 	int user_alloc;

virt/kvm/kvm_main.c

@@ -625,6 +625,7 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
 		return -ENOMEM;
 
 	memslot->dirty_bitmap_head = memslot->dirty_bitmap;
+	memslot->nr_dirty_pages = 0;
 	return 0;
 }
 #endif /* !CONFIG_S390 */
@@ -1491,7 +1492,8 @@ void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot,
 	if (memslot && memslot->dirty_bitmap) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 
-		__set_bit_le(rel_gfn, memslot->dirty_bitmap);
+		if (!__test_and_set_bit_le(rel_gfn, memslot->dirty_bitmap))
+			memslot->nr_dirty_pages++;
 	}
 }