Re: [PATCH RFC 10/15] hw/virtio/vhost-shadow-virtqueue: range boundary in translation

On 24.07.26 00:30, 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 then it line with DMAMap and iova-tree
> convention.
>
> Signed-off-by: Connor Kite <[email protected]>
> ---
>   hw/virtio/vhost-shadow-virtqueue.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index 9e3c359f50..20e5c7d2f1 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -104,14 +104,14 @@ static bool vhost_svq_translate_addr(const VhostShadowVirtqueue *svq,
>               /* Search the GPA->IOVA tree */
>               needle = (DMAMap) {
>                   .translated_addr = gpas[i],
> -                .size = iovec[i].iov_len,
> +                .size = iovec[i].iov_len - 1,  /* Inclusive */
>               };
>               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 */
>               };
>               map = vhost_iova_tree_find_iova(svq->iova_tree, &needle);
>           }

It’s not immediately obvious what is ensuring that `iov_len` can never 
be 0. Sure, it would be wrong and makes no sense, but that is why I 
think an `assert(iovec[i].iov_len > 0)` would be appropriate.

(Looks like `virtqueue_map_desc()` is what rejects zero length, but that 
is not really local to this code path, so not immediately obvious.)

Hanna