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Date: Wed, 5 Feb 2020 12:10:43 +0800
From: Jason Wang <jasowang@...hat.com>
To: Yuya Kusakabe <yuya.kusakabe@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
hawk@...nel.org, john.fastabend@...il.com, kafai@...com,
mst@...hat.com, songliubraving@...com, yhs@...com, kuba@...nel.org,
andriin@...com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v4] virtio_net: add XDP meta data support
On 2020/2/4 下午3:16, 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 and copy vnet header to the front of xdp.data_hard_start
> to avoid overwriting it, where on program return with pass verdict,
> we call into skb_metadata_set().
>
> Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")
> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@...il.com>
> ---
> drivers/net/virtio_net.c | 47 ++++++++++++++++++++++++++++------------
> 1 file changed, 33 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 2fe7a3188282..5fdd6ea0e3f1 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)
hdr_valid means no XDP, so I think we can remove the check for metasize
here and add a comment instead?
> 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 +689,15 @@ 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 it by XDP meta data.
> + */
> + memcpy(xdp.data_hard_start - vi->hdr_len,
> + xdp.data - vi->hdr_len, vi->hdr_len);
I think we don't need this. And it looks to me there's a bug in the
current code.
Commit 436c9453a1ac0 ("virtio-net: keep vnet header zeroed after
processing XDP") leave the a corner case for receive_small() which still
use:
if (!delta) {
buf += header_offset;
memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
} /* keep zeroed vnet hdr since packet was changed by bpf */
Which seems wrong, we need check xdp_prog instead of delta.
With this fixed, there's no need to care about the vnet header here
since we don't know whether or not packet is modified by XDP.
> act = bpf_prog_run_xdp(xdp_prog, &xdp);
> stats->xdp_packets++;
>
> @@ -695,9 +706,11 @@ 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;
I think we should remove the xdp_set_data_meta_invalid() at least? And
move this initialization just after xdp.data is initialized.
Testing receive_small() requires to disable mrg_rxbuf, guest_tso4,
guest_tso6 and guest_ufo from qemu command line.
> xdpf = convert_to_xdp_frame(&xdp);
> if (unlikely(!xdpf))
> goto err_xdp;
> @@ -736,10 +749,12 @@ static struct sk_buff *receive_small(struct net_device *dev,
> skb_reserve(skb, headroom - delta);
> skb_put(skb, len);
> if (!delta) {
Need to check xdp_prog (need another patch).
> - 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 +775,8 @@ 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 +808,7 @@ 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 +855,8 @@ 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 +868,9 @@ 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 +880,15 @@ 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;
Any reason for doing this?
Thanks
> xdpf = convert_to_xdp_frame(&xdp);
> if (unlikely(!xdpf))
> goto err_xdp;
> @@ -921,7 +939,8 @@ 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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