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Date: Tue, 9 Jul 2019 00:38:49 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Yuya Kusakabe <yuya.kusakabe@...il.com>,
Jason Wang <jasowang@...hat.com>
Cc: ast@...nel.org, davem@...emloft.net, hawk@...nel.org,
jakub.kicinski@...ronome.com, john.fastabend@...il.com,
kafai@...com, mst@...hat.com, netdev@...r.kernel.org,
songliubraving@...com, yhs@...com
Subject: Re: [PATCH bpf-next v3] virtio_net: add XDP meta data support
On 07/02/2019 04:11 PM, Yuya Kusakabe wrote:
> On 7/2/19 5:33 PM, Jason Wang wrote:
>> On 2019/7/2 下午4:16, 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>
>>> ---
>>> 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 | 45 +++++++++++++++++++++++++++-------------
>>> 1 file changed, 31 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 4f3de0ac8b0b..03a1ae6fe267 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;
>>> @@ -393,7 +393,7 @@ 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;
>>> @@ -405,6 +405,11 @@ 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;
>>> @@ -644,6 +649,7 @@ 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;
>>> @@ -683,10 +689,13 @@ 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;
>>> + /* Copy the vnet header to the front of data_hard_start to avoid
>>> + * overwriting by XDP meta data */
>>> + memcpy(xdp.data_hard_start - vi->hdr_len, xdp.data - vi->hdr_len, vi->hdr_len);
I'm not fully sure if I'm following this one correctly, probably just missing
something. Isn't the vnet header based on how we set up xdp.data_hard_start
earlier already in front of it? Wouldn't we copy invalid data from xdp.data -
vi->hdr_len into the vnet header at that point (given there can be up to 256
bytes of headroom between the two)? If it's relative to xdp.data and headroom
is >0, then BPF prog could otherwise mangle this; something doesn't add up to
me here. Could you clarify? Thx
>> What happens if we have a large metadata that occupies all headroom here?
>>
>> Thanks
>
> Do you mean a large "XDP" metadata? If a large metadata is a large "XDP" metadata, I think we can not use a metadata that occupies all headroom. The size of metadata limited by bpf_xdp_adjust_meta() as below.
> bpf_xdp_adjust_meta() in net/core/filter.c:
> if (unlikely((metalen & (sizeof(__u32) - 1)) ||
> (metalen > 32)))
> return -EACCES;
>
> Thanks.
>
>>
>>
>>> act = bpf_prog_run_xdp(xdp_prog, &xdp);
>>> stats->xdp_packets++;
>>> @@ -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;
>>> xdpf = convert_to_xdp_frame(&xdp);
>>> if (unlikely(!xdpf))
>>> goto err_xdp;
>>> @@ -736,10 +747,12 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>> skb_reserve(skb, headroom - delta);
>>> skb_put(skb, len);
>>> if (!delta) {
>>> - buf += header_offset;
>>> - memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
>>> + memcpy(skb_vnet_hdr(skb), buf + VIRTNET_RX_PAD, vi->hdr_len);
>>> } /* keep zeroed vnet hdr since packet was changed by bpf */
>>> + if (metasize)
>>> + skb_metadata_set(skb, metasize);
>>> +
>>> err:
>>> return skb;
>>> @@ -760,8 +773,8 @@ 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 +806,7 @@ 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 +853,8 @@ 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);
>>> @@ -852,8 +866,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>> * adjustments. Note other cases do not build an
>>> * skb and avoid using offset
>>> */
>>> - offset = xdp.data -
>>> - page_address(xdp_page) - vi->hdr_len;
>>> + metasize = xdp.data - xdp.data_meta;
>>> + offset = xdp.data - page_address(xdp_page) -
>>> + vi->hdr_len - metasize;
>>> /* recalculate len if xdp.data or xdp.data_end were
>>> * adjusted
>>> @@ -863,14 +878,15 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>> 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;
>>> 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 +937,8 @@ 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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