diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 8a2be4e..98231d1 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -370,6 +370,9 @@
 	struct vfio_dma *split;
 	int ret;
 
+	if (!*size)
+		return 0;
+
 	/*
 	 * Existing dma region is completely covered, unmap all.  This is
 	 * the likely case since userspace tends to map and unmap buffers
@@ -411,7 +414,9 @@
 			dma->vaddr += overlap;
 			dma->size -= overlap;
 			vfio_insert_dma(iommu, dma);
-		}
+		} else
+			kfree(dma);
+
 		*size = overlap;
 		return 0;
 	}
@@ -425,48 +430,41 @@
 		if (ret)
 			return ret;
 
-		/*
-		 * We may have unmapped the entire vfio_dma if the user is
-		 * trying to unmap a sub-region of what was originally
-		 * mapped.  If anything left, we can resize in place since
-		 * iova is unchanged.
-		 */
-		if (overlap < dma->size)
-			dma->size -= overlap;
-		else
-			vfio_remove_dma(iommu, dma);
-
+		dma->size -= overlap;
 		*size = overlap;
 		return 0;
 	}
 
 	/* Split existing */
+	split = kzalloc(sizeof(*split), GFP_KERNEL);
+	if (!split)
+		return -ENOMEM;
+
 	offset = start - dma->iova;
 
 	ret = vfio_unmap_unpin(iommu, dma, start, size);
 	if (ret)
 		return ret;
 
-	WARN_ON(!*size);
+	if (!*size) {
+		kfree(split);
+		return -EINVAL;
+	}
+
 	tmp = dma->size;
 
-	/*
-	 * Resize the lower vfio_dma in place, insert new for remaining
-	 * upper segment.
-	 */
+	/* Resize the lower vfio_dma in place, before the below insert */
 	dma->size = offset;
 
-	if (offset + *size < tmp) {
-		split = kzalloc(sizeof(*split), GFP_KERNEL);
-		if (!split)
-			return -ENOMEM;
-
+	/* Insert new for remainder, assuming it didn't all get unmapped */
+	if (likely(offset + *size < tmp)) {
 		split->size = tmp - offset - *size;
 		split->iova = dma->iova + offset + *size;
 		split->vaddr = dma->vaddr + offset + *size;
 		split->prot = dma->prot;
 		vfio_insert_dma(iommu, split);
-	}
+	} else
+		kfree(split);
 
 	return 0;
 }
@@ -483,7 +481,7 @@
 
 	if (unmap->iova & mask)
 		return -EINVAL;
-	if (unmap->size & mask)
+	if (!unmap->size || unmap->size & mask)
 		return -EINVAL;
 
 	WARN_ON(mask & PAGE_MASK);
@@ -493,7 +491,7 @@
 	while ((dma = vfio_find_dma(iommu, unmap->iova, unmap->size))) {
 		size = unmap->size;
 		ret = vfio_remove_dma_overlap(iommu, unmap->iova, &size, dma);
-		if (ret)
+		if (ret || !size)
 			break;
 		unmapped += size;
 	}
@@ -635,7 +633,6 @@
 			if (tmp && tmp->prot == prot &&
 			    tmp->vaddr + tmp->size == vaddr) {
 				tmp->size += size;
-
 				iova = tmp->iova;
 				size = tmp->size;
 				vaddr = tmp->vaddr;
@@ -643,19 +640,28 @@
 			}
 		}
 
-		/* Check if we abut a region above - nothing above ~0 + 1 */
+		/*
+		 * Check if we abut a region above - nothing above ~0 + 1.
+		 * If we abut above and below, remove and free.  If only
+		 * abut above, remove, modify, reinsert.
+		 */
 		if (likely(iova + size)) {
 			struct vfio_dma *tmp;
-
 			tmp = vfio_find_dma(iommu, iova + size, 1);
 			if (tmp && tmp->prot == prot &&
 			    tmp->vaddr == vaddr + size) {
 				vfio_remove_dma(iommu, tmp);
-				if (dma)
+				if (dma) {
 					dma->size += tmp->size;
-				else
+					kfree(tmp);
+				} else {
 					size += tmp->size;
-				kfree(tmp);
+					tmp->size = size;
+					tmp->iova = iova;
+					tmp->vaddr = vaddr;
+					vfio_insert_dma(iommu, tmp);
+					dma = tmp;
+				}
 			}
 		}
 
@@ -681,11 +687,10 @@
 		iova = map->iova;
 		size = map->size;
 		while ((tmp = vfio_find_dma(iommu, iova, size))) {
-			if (vfio_remove_dma_overlap(iommu, iova, &size, tmp)) {
-				pr_warn("%s: Error rolling back failed map\n",
-					__func__);
+			int r = vfio_remove_dma_overlap(iommu, iova,
+							&size, tmp);
+			if (WARN_ON(r || !size))
 				break;
-			}
 		}
 	}
 
@@ -813,6 +818,8 @@
 		struct vfio_dma *dma = rb_entry(node, struct vfio_dma, node);
 		size_t size = dma->size;
 		vfio_remove_dma_overlap(iommu, dma->iova, &size, dma);
+		if (WARN_ON(!size))
+			break;
 	}
 
 	iommu_domain_free(iommu->domain);