Commit e814b958 authored by Heng Qi's avatar Heng Qi Committed by David S. Miller
Browse files

virtio-net: fix calculation of MTU for single-buffer xdp 



When single-buffer xdp is loaded, the size of the buffer filled each time
is 'sz = (PAGE_SIZE - headroom - tailroom)', which is the maximum packet
length that the driver allows the device to pass in. Otherwise, the packet
with a length greater than sz will come in, so num_buf will be greater than
or equal to 2, and xdp_linearize_page() will be performed and the packet
will be dropped because the total length is greater than PAGE_SIZE. So the
maximum value of MTU for single-buffer xdp is 'max_sz = sz - ETH_HLEN'.

Signed-off-by: default avatarHeng Qi <hengqi@linux.alibaba.com>
Reviewed-by: default avatarXuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 484beac2

drivers/net/virtio_net.c

+4 −2
Original line number Diff line number Diff line
@@ -3081,7 +3081,9 @@ static int virtnet_restore_guest_offloads(struct virtnet_info *vi) 
static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,

			   struct netlink_ext_ack *extack)

{

	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);

	unsigned int room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +

					   sizeof(struct skb_shared_info));

	unsigned int max_sz = PAGE_SIZE - room - ETH_HLEN;

	struct virtnet_info *vi = netdev_priv(dev);

	struct bpf_prog *old_prog;

	u16 xdp_qp = 0, curr_qp;
@@ -3106,7 +3108,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog, 


	if (dev->mtu > max_sz) {

		NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");

		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);

		netdev_warn(dev, "XDP requires MTU less than %u\n", max_sz);

		return -EINVAL;

	}