[PATCH] vhost-vdpa: reject zero-size unmap

[Weimin Xiong <xiongwm2026@163.com>]

From: xiongweimin <xiongweimin@kylinos.cn>

Reject unmap requests with size == 0 to prevent iova + size - 1
from underflowing to U64_MAX, which would incorrectly unmap the
entire IOTLB range.

This fix also covers the error rollback path in vhost_vdpa_va_map:
when the first VMA lookup fails, map_iova equals iova, resulting
in a zero-size unmap that would otherwise clear the whole IOTLB.

Signed-off-by: xiongweimin <xiongweimin@kylinos.cn>
---
 drivers/vhost/vdpa.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index bb96b1aa5..f49bf1cfb 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1035,6 +1035,9 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v,
 	const struct vdpa_config_ops *ops = vdpa->config;
 	u32 asid = iotlb_to_asid(iotlb);
 
+	if (!size)
+		return;
+
 	vhost_vdpa_iotlb_unmap(v, iotlb, iova, iova + size - 1, asid);
 
 	if (ops->set_map) {
--
2.39.3