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Subject: Re: [PATCH bpf-next v5] virtio_net: add XDP meta data support
To:     Jason Wang <jasowang@redhat.com>
Cc:     andriin@fb.com, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org,
        john.fastabend@gmail.com, kafai@fb.com, kuba@kernel.org,
        linux-kernel@vger.kernel.org, mst@redhat.com,
        netdev@vger.kernel.org, songliubraving@fb.com, yhs@fb.com
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From:   Yuya Kusakabe <yuya.kusakabe@gmail.com>
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Message-ID: <8fafd23d-4c80-539d-9f74-bc5cda0d5575@gmail.com>
Date:   Fri, 21 Feb 2020 17:36:08 +0900
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On 2/21/20 1:23 PM, Jason Wang wrote:
> 
> On 2020/2/20 下午4:55, Yuya Kusakabe wrote:
>> Implement support for transferring XDP meta data into skb for
>> virtio_net driver; before calling into the program, xdp.data_meta points
>> to xdp.data, where on program return with pass verdict, we call
>> into skb_metadata_set().
>>
>> Tested with the script at
>> https://github.com/higebu/virtio_net-xdp-metadata-test.
>>
>> Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")
> 
> 
> I'm not sure this is correct since virtio-net claims to not support metadata by calling xdp_set_data_meta_invalid()?

virtio_net doesn't support by calling xdp_set_data_meta_invalid() for now.

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/drivers/net/virtio_net.c?id=e42da4c62abb547d9c9138e0e7fcd1f36057b5e8#n686
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/drivers/net/virtio_net.c?id=e42da4c62abb547d9c9138e0e7fcd1f36057b5e8#n842

And xdp_set_data_meta_invalid() are added by de8f3a83b0a0.

$ git blame ./drivers/net/virtio_net.c | grep xdp_set_data_meta_invalid
de8f3a83b0a0f (Daniel Borkmann           2017-09-25 02:25:51 +0200  686)                xdp_set_data_meta_invalid(&xdp);
de8f3a83b0a0f (Daniel Borkmann           2017-09-25 02:25:51 +0200  842)                xdp_set_data_meta_invalid(&xdp);

So I added `Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")` to the comment.

> 
> 
>> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
>> ---
>> v5:
>>   - page_to_skb(): copy vnet header if hdr_valid without checking metasize.
>>   - receive_small(): do not copy vnet header if xdp_prog is availavle.
>>   - __virtnet_xdp_xmit_one(): remove the xdp_set_data_meta_invalid().
>>   - improve comments.
>> v4:
>>   - improve commit message
>> v3:
>>   - fix preserve the vnet header in receive_small().
>> v2:
>>   - keep copy untouched in page_to_skb().
>>   - preserve the vnet header in receive_small().
>>   - fix indentation.
>> ---
>>   drivers/net/virtio_net.c | 54 ++++++++++++++++++++++++----------------
>>   1 file changed, 33 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 2fe7a3188282..4ea0ae60c000 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -371,7 +371,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>                      struct receive_queue *rq,
>>                      struct page *page, unsigned int offset,
>>                      unsigned int len, unsigned int truesize,
>> -                   bool hdr_valid)
>> +                   bool hdr_valid, unsigned int metasize)
>>   {
>>       struct sk_buff *skb;
>>       struct virtio_net_hdr_mrg_rxbuf *hdr;
>> @@ -393,6 +393,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>       else
>>           hdr_padded_len = sizeof(struct padded_vnet_hdr);
>>   +    /* hdr_valid means no XDP, so we can copy the vnet header */
>>       if (hdr_valid)
>>           memcpy(hdr, p, hdr_len);
>>   @@ -405,6 +406,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>           copy = skb_tailroom(skb);
>>       skb_put_data(skb, p, copy);
>>   +    if (metasize) {
>> +        __skb_pull(skb, metasize);
>> +        skb_metadata_set(skb, metasize);
>> +    }
>> +
>>       len -= copy;
>>       offset += copy;
>>   @@ -450,10 +456,6 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>>       struct virtio_net_hdr_mrg_rxbuf *hdr;
>>       int err;
>>   -    /* virtqueue want to use data area in-front of packet */
>> -    if (unlikely(xdpf->metasize > 0))
>> -        return -EOPNOTSUPP;
>> -
>>       if (unlikely(xdpf->headroom < vi->hdr_len))
>>           return -EOVERFLOW;
>>   @@ -644,6 +646,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>       unsigned int delta = 0;
>>       struct page *xdp_page;
>>       int err;
>> +    unsigned int metasize = 0;
>>         len -= vi->hdr_len;
>>       stats->bytes += len;
>> @@ -683,8 +686,8 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>             xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;
>>           xdp.data = xdp.data_hard_start + xdp_headroom;
>> -        xdp_set_data_meta_invalid(&xdp);
>>           xdp.data_end = xdp.data + len;
>> +        xdp.data_meta = xdp.data;
>>           xdp.rxq = &rq->xdp_rxq;
>>           orig_data = xdp.data;
>>           act = bpf_prog_run_xdp(xdp_prog, &xdp);
>> @@ -695,6 +698,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>               /* Recalculate length in case bpf program changed it */
>>               delta = orig_data - xdp.data;
>>               len = xdp.data_end - xdp.data;
>> +            metasize = xdp.data - xdp.data_meta;
>>               break;
>>           case XDP_TX:
>>               stats->xdp_tx++;
>> @@ -735,11 +739,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>       }
>>       skb_reserve(skb, headroom - delta);
>>       skb_put(skb, len);
>> -    if (!delta) {
>> +    if (!xdp_prog) {
>>           buf += header_offset;
>>           memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
>>       } /* keep zeroed vnet hdr since packet was changed by bpf */
> 
> 
> I prefer to make this an independent patch and cc stable.
> 
> Other looks good.
> 
> Thanks

I see. So I need to revert to delta from xdp_prog?

Thank you.

> 
>>   +    if (metasize)
>> +        skb_metadata_set(skb, metasize);
>> +
>>   err:
>>       return skb;
>>   @@ -760,8 +767,8 @@ static struct sk_buff *receive_big(struct net_device *dev,
>>                      struct virtnet_rq_stats *stats)
>>   {
>>       struct page *page = buf;
>> -    struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len,
>> -                      PAGE_SIZE, true);
>> +    struct sk_buff *skb =
>> +        page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0);
>>         stats->bytes += len - vi->hdr_len;
>>       if (unlikely(!skb))
>> @@ -793,6 +800,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>       unsigned int truesize;
>>       unsigned int headroom = mergeable_ctx_to_headroom(ctx);
>>       int err;
>> +    unsigned int metasize = 0;
>>         head_skb = NULL;
>>       stats->bytes += len - vi->hdr_len;
>> @@ -839,8 +847,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>           data = page_address(xdp_page) + offset;
>>           xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len;
>>           xdp.data = data + vi->hdr_len;
>> -        xdp_set_data_meta_invalid(&xdp);
>>           xdp.data_end = xdp.data + (len - vi->hdr_len);
>> +        xdp.data_meta = xdp.data;
>>           xdp.rxq = &rq->xdp_rxq;
>>             act = bpf_prog_run_xdp(xdp_prog, &xdp);
>> @@ -848,24 +856,27 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>             switch (act) {
>>           case XDP_PASS:
>> +            metasize = xdp.data - xdp.data_meta;
>> +
>>               /* recalculate offset to account for any header
>> -             * adjustments. Note other cases do not build an
>> -             * skb and avoid using offset
>> +             * adjustments and minus the metasize to copy the
>> +             * metadata in page_to_skb(). Note other cases do not
>> +             * build an skb and avoid using offset
>>                */
>> -            offset = xdp.data -
>> -                    page_address(xdp_page) - vi->hdr_len;
>> +            offset = xdp.data - page_address(xdp_page) -
>> +                 vi->hdr_len - metasize;
>>   -            /* recalculate len if xdp.data or xdp.data_end were
>> -             * adjusted
>> +            /* recalculate len if xdp.data, xdp.data_end or
>> +             * xdp.data_meta were adjusted
>>                */
>> -            len = xdp.data_end - xdp.data + vi->hdr_len;
>> +            len = xdp.data_end - xdp.data + vi->hdr_len + metasize;
>>               /* We can only create skb based on xdp_page. */
>>               if (unlikely(xdp_page != page)) {
>>                   rcu_read_unlock();
>>                   put_page(page);
>> -                head_skb = page_to_skb(vi, rq, xdp_page,
>> -                               offset, len,
>> -                               PAGE_SIZE, false);
>> +                head_skb = page_to_skb(vi, rq, xdp_page, offset,
>> +                               len, PAGE_SIZE, false,
>> +                               metasize);
>>                   return head_skb;
>>               }
>>               break;
>> @@ -921,7 +932,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>           goto err_skb;
>>       }
>>   -    head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog);
>> +    head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
>> +                   metasize);
>>       curr_skb = head_skb;
>>         if (unlikely(!curr_skb))
>