Re: [PATCH bpf-next v3] virtio_net: add XDP meta data support

From: Jason Wang <jasowang@redhat.com>
To: Yuya Kusakabe <yuya.kusakabe@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	davem@davemloft.net, Jesper Dangaard Brouer <hawk@kernel.org>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <kafai@fb.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	netdev@vger.kernel.org, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH bpf-next v3] virtio_net: add XDP meta data support
Date: Tue, 4 Feb 2020 11:31:39 +0800	[thread overview]
Message-ID: <8da1b560-3128-b885-b453-13de5c7431fb@redhat.com> (raw)
In-Reply-To: <CAGCJULNe_2tQRrSdO3BPS5_qvNnqgyU=33hFcVe8Tnxfzy57fA@mail.gmail.com>

On 2020/2/3 下午9:52, Yuya Kusakabe wrote:
> I'm sorry for the late reply.
>
> I saw the status of this patch is "Awaiting Upstream" on
> https://patchwork.ozlabs.org/patch/1126046/. What is "Awaiting
> Upstream"? Is there anything that I can do?

You can post a new version I think.

Thanks

>
> Thank you,
> Yuya
>
> On Wed, Jul 10, 2019 at 11:30 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On 2019/7/10 上午4:03, Daniel Borkmann wrote:
>>> 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.kusakabe@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?
>>
>> We will invalidate the vnet header in this case. But for the case of
>> metadata adjustment without header adjustment, we want to seek a way to
>> preserve that.
>>
>> Thanks
>>
>>
>>> Thanks,
>>> Daniel
>
>