vfio/type1: Fix missed frees and zero sized removes

With hugepage support we can only properly aligned and sized ranges.
We only guarantee that we can unmap the same ranges mapped and not
arbitrary sub-ranges.  This means we might not free anything or might
free more than requested.  The vfio unmap interface started storing
the unmapped size to return to userspace to handle this.  This patch
fixes a few places where we don't properly handle those cases, moves
a memory allocation to a place where failure is an option and checks
our loops to make sure we don't get into an infinite loop trying to
remove an overlap.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -370,6 +370,9 @@ static int vfio_remove_dma_overlap(struct vfio_iommu *iommu, dma_addr_t start,
 	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 @@ static int vfio_remove_dma_overlap(struct vfio_iommu *iommu, dma_addr_t start,
 			dma->vaddr += overlap;
 			dma->size -= overlap;
 			vfio_insert_dma(iommu, dma);
-		}
+		} else
+			kfree(dma);
+
 		*size = overlap;
 		return 0;
 	}
@@ -425,48 +430,41 @@ static int vfio_remove_dma_overlap(struct vfio_iommu *iommu, dma_addr_t start,
 		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 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 
 	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 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 	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 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 			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 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 			}
 		}
 
-		/* 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 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 		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 @@ static void vfio_iommu_type1_release(void *iommu_data)
 		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);