KVM: Refactor error handling for setting memory region

Replace a big pile o' gotos with returns to make it more obvious what
error code is being returned, and to prepare for refactoring the
functional, i.e. post-checks, portion of __kvm_set_memory_region().

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -1005,34 +1005,33 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	r = check_memory_region_flags(mem);
 	if (r)
-		goto out;
+		return r;
 
-	r = -EINVAL;
 	as_id = mem->slot >> 16;
 	id = (u16)mem->slot;
 
 	/* General sanity checks */
 	if (mem->memory_size & (PAGE_SIZE - 1))
-		goto out;
+		return -EINVAL;
 	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
-		goto out;
+		return -EINVAL;
 	/* We can read the guest memory with __xxx_user() later on. */
 	if ((id < KVM_USER_MEM_SLOTS) &&
 	    ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
 	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
 			mem->memory_size)))
-		goto out;
+		return -EINVAL;
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
-		goto out;
+		return -EINVAL;
 	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
-		goto out;
+		return -EINVAL;
 
 	slot = id_to_memslot(__kvm_memslots(kvm, as_id), id);
 	base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
 	npages = mem->memory_size >> PAGE_SHIFT;
 
 	if (npages > KVM_MEM_MAX_NR_PAGES)
-		goto out;
+		return -EINVAL;
 
 	new = old = *slot;
 
@@ -1049,20 +1048,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			if ((new.userspace_addr != old.userspace_addr) ||
 			    (npages != old.npages) ||
 			    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
-				goto out;
+				return -EINVAL;
 
 			if (base_gfn != old.base_gfn)
 				change = KVM_MR_MOVE;
 			else if (new.flags != old.flags)
 				change = KVM_MR_FLAGS_ONLY;
-			else { /* Nothing to change. */
+			else /* Nothing to change. */
-				r = 0;
+				return 0;
-				goto out;
-			}
 		}
 	} else {
 		if (!old.npages)
-			goto out;
+			return -EINVAL;
 
 		change = KVM_MR_DELETE;
 		new.base_gfn = 0;
@@ -1071,29 +1068,29 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
 		/* Check for overlaps */
-		r = -EEXIST;
 		kvm_for_each_memslot(slot, __kvm_memslots(kvm, as_id)) {
 			if (slot->id == id)
 				continue;
 			if (!((base_gfn + npages <= slot->base_gfn) ||
 			      (base_gfn >= slot->base_gfn + slot->npages)))
-				goto out;
+				return -EEXIST;
 		}
 	}
 
-	r = -ENOMEM;
-
 	/* Allocate/free page dirty bitmap as needed */
 	if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
 		new.dirty_bitmap = NULL;
 	else if (!new.dirty_bitmap) {
-		if (kvm_create_dirty_bitmap(&new) < 0)
+		r = kvm_create_dirty_bitmap(&new);
-			goto out;
+		if (r)
+			return r;
 	}
 
 	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
-	if (!slots)
+	if (!slots) {
+		r = -ENOMEM;
 		goto out_bitmap;
+	}
 	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
 
 	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
@@ -1144,7 +1141,6 @@ out_slots:
 out_bitmap:
 	if (new.dirty_bitmap && !old.dirty_bitmap)
 		kvm_destroy_dirty_bitmap(&new);
-out:
 	return r;
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);