On Tue, 2021-06-22 at 12:52 +0800, Jason Wang wrote:
> 
> 
> I cook two patches. Please see and check if they fix the problem. 
> (compile test only for me).

I did the second one slightly differently (below) but those are what I
came up with too, which seems to be working.

@@ -2331,7 +2344,7 @@ static int tun_xdp_one(struct tun_struct *tun,
 {
        unsigned int datasize = xdp->data_end - xdp->data;
        struct tun_xdp_hdr *hdr = xdp->data_hard_start;
-       struct virtio_net_hdr *gso = &hdr->gso;
+       struct virtio_net_hdr *gso = NULL;
        struct bpf_prog *xdp_prog;
        struct sk_buff *skb = NULL;
        u32 rxhash = 0, act;
@@ -2340,9 +2353,12 @@ static int tun_xdp_one(struct tun_struct *tun,
        bool skb_xdp = false;
        struct page *page;
 
+       if (tun->flags & IFF_VNET_HDR)
+               gso = &hdr->gso;
+
        xdp_prog = rcu_dereference(tun->xdp_prog);
        if (xdp_prog) {
-               if (gso->gso_type) {
+               if (gso && gso->gso_type) {
                        skb_xdp = true;
                        goto build;
                }
@@ -2388,14 +2406,18 @@ static int tun_xdp_one(struct tun_struct *tun,
        skb_reserve(skb, xdp->data - xdp->data_hard_start);
        skb_put(skb, xdp->data_end - xdp->data);
 
-       if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
+       if (!gso)
+               skb_reset_mac_header(skb);
+       else if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
                atomic_long_inc(&tun->rx_frame_errors);
                kfree_skb(skb);