netdev - Re: [PATCH] net: tun: fix tun_xdp_one() for IFF

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Date:   Tue, 22 Jun 2021 09:10:03 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Jason Wang <jasowang@...hat.com>, netdev <netdev@...r.kernel.org>
CC:     Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH] net: tun: fix tun_xdp_one() for IFF_TUN mode



On 22 June 2021 08:51:43 BST, Jason Wang <jasowang@...hat.com> wrote:
>
>在 2021/6/22 下午3:24, David Woodhouse 写道:
>> 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);
>
>
>This should work as well.

I'll rip out the rest of my debugging hacks and check that these two are sufficient, and that I hadn't accidentally papered over something else as I debugged it.

Then I'll look at the case of having no virtio_net_hdr on either side, and also different sized headers on the tun device (why does it even support that?).

And the test case, of course. 

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.