KVM: introduce wrapper functions for creating/destroying dirty bitmaps

This makes it easy to change the way of allocating/freeing dirty bitmaps.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

virt/kvm/kvm_main.c

@@ -444,6 +444,15 @@ static struct kvm *kvm_create_vm(void)
 	return ERR_PTR(r);
 }
 
+static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
+{
+	if (!memslot->dirty_bitmap)
+		return;
+
+	vfree(memslot->dirty_bitmap);
+	memslot->dirty_bitmap = NULL;
+}
+
 /*
  * Free any memory in @free but not in @dont.
  */
@@ -456,7 +465,7 @@ static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
 		vfree(free->rmap);
 
 	if (!dont || free->dirty_bitmap != dont->dirty_bitmap)
-		vfree(free->dirty_bitmap);
+		kvm_destroy_dirty_bitmap(free);
 
 
 	for (i = 0; i < KVM_NR_PAGE_SIZES - 1; ++i) {
@@ -467,7 +476,6 @@ static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
 	}
 
 	free->npages = 0;
-	free->dirty_bitmap = NULL;
 	free->rmap = NULL;
 }
 
@@ -529,6 +537,18 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
+{
+	unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(memslot);
+
+	memslot->dirty_bitmap = vmalloc(dirty_bytes);
+	if (!memslot->dirty_bitmap)
+		return -ENOMEM;
+
+	memset(memslot->dirty_bitmap, 0, dirty_bytes);
+	return 0;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -663,12 +683,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	/* Allocate page dirty bitmap if needed */
 	if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
-		unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(&new);
-
-		new.dirty_bitmap = vmalloc(dirty_bytes);
-		if (!new.dirty_bitmap)
+		if (kvm_create_dirty_bitmap(&new) < 0)
 			goto out_free;
-		memset(new.dirty_bitmap, 0, dirty_bytes);
 		/* destroy any largepage mappings for dirty tracking */
 		if (old.npages)
 			flush_shadow = 1;