[PATCH v6 3/3] vhost/net: discard IOTLB when ACCESS_PLATFORM is cleared

[Jia Jia <physicalmtea@gmail.com>]

Apply the common device IOTLB teardown when userspace clears
VIRTIO_F_ACCESS_PLATFORM. This drops stale translations and avoids
rebuilding an existing IOTLB during feature updates that keep
ACCESS_PLATFORM enabled.

The transition invalidates cached vring access even with an attached
backend. The backend remains attached, but userspace must configure the
vring addresses for the new address mode after a successful live
transition.

Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")

Link: https://lore.kernel.org/all/20260726141158.1652386-1-physicalmtea@gmail.com/

Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vhost/net.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 77b59f49bddb..64671cf77a35 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -1673,6 +1673,7 @@ static long vhost_net_reset_owner(struct vhost_net *n)
 static int vhost_net_set_features(struct vhost_net *n, const u64 *features)
 {
 	size_t vhost_hlen, sock_hlen, hdr_len;
+	int ret = -EFAULT;
 	int i;
 
 	hdr_len = virtio_features_test_bit(features, VIRTIO_NET_F_MRG_RXBUF) ||
@@ -1701,8 +1702,11 @@ static int vhost_net_set_features(struct vhost_net *n, const u64 *features)
 		goto out_unlock;
 
 	if (virtio_features_test_bit(features, VIRTIO_F_ACCESS_PLATFORM)) {
-		if (vhost_init_device_iotlb(&n->dev))
+		ret = vhost_init_device_iotlb(&n->dev);
+		if (ret)
 			goto out_unlock;
+	} else {
+		vhost_clear_device_iotlb(&n->dev);
 	}
 
 	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
@@ -1718,7 +1722,7 @@ static int vhost_net_set_features(struct vhost_net *n, const u64 *features)
 
 out_unlock:
 	mutex_unlock(&n->dev.mutex);
-	return -EFAULT;
+	return ret;
 }
 
 static long vhost_net_set_owner(struct vhost_net *n)