kvm: commonize allocation of the new memory slots

commit f2a81036 upstream.

The two kmemdup invocations can be unified.  I find that the new
placement of the comment makes it easier to see what happens.
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

virt/kvm/kvm_main.c

@@ -858,11 +858,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			goto out_free;
 	}
 
-	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
 	slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
 			GFP_KERNEL);
 	if (!slots)
 		goto out_free;
+
+	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
 		slot = id_to_memslot(slots, mem->slot);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
@@ -878,26 +879,19 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		 * 	- kvm_is_visible_gfn (mmu_check_roots)
 		 */
 		kvm_arch_flush_shadow_memslot(kvm, slot);
-		slots = old_memslots;
-	}
 
-	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
-	if (r)
-		goto out_slots;
-
-	r = -ENOMEM;
 		/*
 		 * We can re-use the old_memslots from above, the only difference
 		 * from the currently installed memslots is the invalid flag.  This
 		 * will get overwritten by update_memslots anyway.
 		 */
-	if (!slots) {
-		slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
-				GFP_KERNEL);
-		if (!slots)
-			goto out_free;
+		slots = old_memslots;
 	}
 
+	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
+	if (r)
+		goto out_slots;
+
 	/* actual memory is freed via old in kvm_free_physmem_slot below */
 	if (change == KVM_MR_DELETE) {
 		new.dirty_bitmap = NULL;