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Date:   Tue, 2 Jul 2019 10:00:27 +0900
From:   Yuya Kusakabe <yuya.kusakabe@...il.com>
To:     Jason Wang <jasowang@...hat.com>, davem@...emloft.net
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] virtio_net: add XDP meta data support

On 7/1/19 6:30 PM, Jason Wang wrote:
> 
> On 2019/6/27 下午4:06, Yuya Kusakabe wrote:
>> This adds XDP meta data support to both receive_small() and
>> receive_mergeable().
>>
>> Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")
>> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@...il.com>
>> ---
>>   drivers/net/virtio_net.c | 40 +++++++++++++++++++++++++++++-----------
>>   1 file changed, 29 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 4f3de0ac8b0b..e787657fc568 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;
>> @@ -393,17 +393,25 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>       else
>>           hdr_padded_len = sizeof(struct padded_vnet_hdr);
>>   -    if (hdr_valid)
>> +    if (hdr_valid && !metasize)
>>           memcpy(hdr, p, hdr_len);
>>         len -= hdr_len;
>>       offset += hdr_padded_len;
>>       p += hdr_padded_len;
>>   -    copy = len;
>> +    copy = len + metasize;
>>       if (copy > skb_tailroom(skb))
>>           copy = skb_tailroom(skb);
>> -    skb_put_data(skb, p, copy);
>> +
>> +    if (metasize) {
>> +        skb_put_data(skb, p - metasize, copy);
> 
> 
> I would rather keep copy untouched above, and use copy + metasize here, then you can save the following decrement  as well. Or tweak the caller the count the meta in to offset, then we need only deal with skb_pull() and skb_metadata_set() here.

I think the latter is better, because copy + metasize must be smaller than skb tailroom size.

> 
>> +        __skb_pull(skb, metasize);
>> +        skb_metadata_set(skb, metasize);
>> +        copy -= metasize;
>> +    } else {
>> +        skb_put_data(skb, p, copy);
>> +    }
>>         len -= copy;
>>       offset += copy;
>> @@ -644,6 +652,7 @@ 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 +692,8 @@ 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);
>> @@ -695,9 +704,11 @@ 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++;
>> +            xdp.data_meta = xdp.data;
> 
> 
> Why need this?

Because virtnet_xdp_xmit() doesn't support XDP meta data as below. And I suppose that we don't need to support XDP metadata for XDP_TX.

static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
				   struct send_queue *sq,
				   struct xdp_frame *xdpf)
{
	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;


> 
>>               xdpf = convert_to_xdp_frame(&xdp);
>>               if (unlikely(!xdpf))
>>                   goto err_xdp;
>> @@ -735,11 +746,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>       }
>>       skb_reserve(skb, headroom - delta);
>>       skb_put(skb, len);
>> -    if (!delta) {
>> +    if (!delta && !metasize) {
>>           buf += header_offset;
>>           memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
>>       } /* keep zeroed vnet hdr since packet was changed by bpf */
> 
> 
> Is there any method to preserve the vnet header here? We probably don't want to lose it for XDP_PASS when packet is not modified.

I'll try to keep the vnet header with moving the meta data to the front of the vnet header.

> 
>>   +    if (metasize)
>> +        skb_metadata_set(skb, metasize);
>> +
>>   err:
>>       return skb;
>>   @@ -761,7 +775,7 @@ static struct sk_buff *receive_big(struct net_device *dev,
>>   {
>>       struct page *page = buf;
>>       struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len,
>> -                      PAGE_SIZE, true);
>> +                      PAGE_SIZE, true, 0);
>>         stats->bytes += len - vi->hdr_len;
>>       if (unlikely(!skb))
>> @@ -793,6 +807,7 @@ 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 +854,8 @@ 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);
>> @@ -859,18 +874,20 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>                * adjusted
>>                */
>>               len = xdp.data_end - xdp.data + vi->hdr_len;
>> +            metasize = xdp.data - xdp.data_meta;
>>               /* 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);
>> +                           offset, len,
>> +                           PAGE_SIZE, false, metasize);
> 
> 
> Indentation is wired.

Sorry. I'll fix it.

> 
> Thanks
> 
> 
>>                   return head_skb;
>>               }
>>               break;
>>           case XDP_TX:
>>               stats->xdp_tx++;
>> +            xdp.data_meta = xdp.data;
>>               xdpf = convert_to_xdp_frame(&xdp);
>>               if (unlikely(!xdpf))
>>                   goto err_xdp;
>> @@ -921,7 +938,8 @@ 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))

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