net/af_iucv: build SG skbs for TRANS_HIPER sockets

The TX path no longer falls apart when some of its SG skbs are later
linearized by lower layers of the stack. So enable the use of SG skbs
in iucv_sock_sendmsg() again.

This effectively reverts
commit dc5367bc ("net/af_iucv: don't use paged skbs for TX on HiperSockets").
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/iucv/af_iucv.c

@@ -256,7 +256,9 @@ static int afiucv_hs_send(struct iucv_message *imsg, struct sock *sock,
 			err = -EMSGSIZE;
 			goto err_free;
 		}
-		skb_trim(skb, skb->dev->mtu);
+		err = pskb_trim(skb, skb->dev->mtu);
+		if (err)
+			goto err_free;
 	}
 	skb->protocol = cpu_to_be16(ETH_P_AF_IUCV);
 
@@ -996,7 +998,7 @@ static int iucv_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 	if (iucv->transport == AF_IUCV_TRANS_HIPER) {
 		headroom = sizeof(struct af_iucv_trans_hdr) +
 			   LL_RESERVED_SPACE(iucv->hs_dev);
-		linear = len;
+		linear = min(len, PAGE_SIZE - headroom);
 	} else {
 		if (len < PAGE_SIZE) {
 			linear = len;