vfio/type1: massage unmap iteration

Modify the iteration in vfio_dma_do_unmap so it does not depend on deletion
of each dma entry.  Add a variant of vfio_find_dma that returns the entry
with the lowest iova in the search range to initialize the iteration.  No
externally visible change, but this behavior is needed in the subsequent
update-vaddr patch.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -173,6 +173,31 @@ static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
 	return NULL;
 }
 
+static struct rb_node *vfio_find_dma_first_node(struct vfio_iommu *iommu,
+						dma_addr_t start, size_t size)
+{
+	struct rb_node *res = NULL;
+	struct rb_node *node = iommu->dma_list.rb_node;
+	struct vfio_dma *dma_res = NULL;
+
+	while (node) {
+		struct vfio_dma *dma = rb_entry(node, struct vfio_dma, node);
+
+		if (start < dma->iova + dma->size) {
+			res = node;
+			dma_res = dma;
+			if (start >= dma->iova)
+				break;
+			node = node->rb_left;
+		} else {
+			node = node->rb_right;
+		}
+	}
+	if (res && size && dma_res->iova >= start + size)
+		res = NULL;
+	return res;
+}
+
 static void vfio_link_dma(struct vfio_iommu *iommu, struct vfio_dma *new)
 {
 	struct rb_node **link = &iommu->dma_list.rb_node, *parent = NULL;
@@ -1079,6 +1104,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 	dma_addr_t iova = unmap->iova;
 	unsigned long size = unmap->size;
 	bool unmap_all = unmap->flags & VFIO_DMA_UNMAP_FLAG_ALL;
+	struct rb_node *n;
 
 	mutex_lock(&iommu->lock);
 
@@ -1149,7 +1175,13 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 	}
 
 	ret = 0;
-	while ((dma = vfio_find_dma(iommu, iova, size))) {
+	n = vfio_find_dma_first_node(iommu, iova, size);
+
+	while (n) {
+		dma = rb_entry(n, struct vfio_dma, node);
+		if (dma->iova >= iova + size)
+			break;
+
 		if (!iommu->v2 && iova > dma->iova)
 			break;
 		/*
@@ -1194,6 +1226,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 		}
 
 		unmapped += dma->size;
+		n = rb_next(n);
 		vfio_remove_dma(iommu, dma);
 	}