On 07/09/2019 05:04 AM, Jason Wang wrote:
> On 2019/7/9 上午6:38, Daniel Borkmann wrote:
>> 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.kusak...@gmail.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
>
> Vnet headr sits just in front of xdp.data not xdp.data_hard_start. So it
> could be overwrote by metadata, that's why we need a copy here.
For the current code, you can adjust the xdp.data with a positive/negative
offset
already via bpf_xdp_adjust_head() helper. If vnet headr sits just in front of
xdp.data, couldn't this be overridden today as well then? Anyway, just wondering
how this is handled differently?
Thanks,
Daniel
