Re: [PATCH v2] hw/virtio/vhost-shadow-virtqueue: range boundary in translation

On Mon, Aug 17, 2026 at 04:31:47PM -0700, Connor Kite wrote:
>iova-tree expects inclusive range sizing when maps are allocated or searched.
>Currently, svqs use exclusive sizing when searching their
>vhost-iova-tree for a match to the region to be translated.  This could
>lead to errors if the region to be translated is at the edge of an iova
>region.
>
>Fix this by reducing `needle.size` by 1 in
>vhost_svq_translate_addr to bring it in line with DMAMap and iova-tree
>convention.
>
>The only current user of svq->iova_tree is hw/virtio/vhost-vdpa.c, which
>also treats size as inclusive when using the tree API.  In progress work
>on vhost-user isolation mode in hw/virtio.vhost-vdpa.c also uses
>inclusive sizing when interacting with the tree.
>
>This patch is an updated version of one from the patch series "vhost-user:
>isolated memory".  The patch has been isolated from the series as it
>is not tightly coupled with the rest of the series.
>
>Signed-off-by: Connor Kite <[email protected]>
>Reviewed-by: Stefan Hajnoczi <[email protected]>
>---
>V2 Differences:
>- Context added about users of svq->iova_tree and their adoption of
>  inclusive sizing
>
> hw/virtio/vhost-shadow-virtqueue.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
>diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
>index bcb7f2ffc7..c8831d52be 100644
>--- a/hw/virtio/vhost-shadow-virtqueue.c
>+++ b/hw/virtio/vhost-shadow-virtqueue.c
>@@ -99,19 +99,25 @@ static bool vhost_svq_translate_addr(const VhostShadowVirtqueue *svq,
>         const DMAMap *map;
>         DMAMap needle;
>
>+        if (unlikely(iovec[i].iov_len == 0)) {
>+            qemu_log_mask(LOG_GUEST_ERROR,
>+                          "Zero-sized buffer made available by guest");
>+            return false;
>+        }
>+
>         /* Check if the descriptor is backed by guest memory  */
>         if (gpas) {
>             /* Search the GPA->IOVA tree */
>             needle = (DMAMap) {
>                 .translated_addr = gpas[i],
>-                .size = iovec[i].iov_len,
>+                .size = iovec[i].iov_len - 1,  /* Inclusive */
                                                ^
nit: double spaces here...

>             };
>             map = vhost_iova_tree_find_gpa(svq->iova_tree, &needle);
>         } else {
>             /* Search the IOVA->HVA tree */
>             needle = (DMAMap) {
>                 .translated_addr = (hwaddr)(uintptr_t)iovec[i].iov_base,
>-                .size = iovec[i].iov_len,
>+                .size = iovec[i].iov_len - 1, /* Inclusive */
                                                ^
... single here.
If you need to respin, maybe we can be consistent and fix it.

Anyway with Akihiko's comments fixed:

Reviewed-by: Stefano Garzarella <[email protected]>

Thanks for the fix!
Stefano