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: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
---
In fact, this is a fix patch belonging to the net branch, which needs
to be backported to the stable branch.
drivers/net/virtio_net.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 443aa7b8f0ad..1203e4176b66 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3074,7 +3074,9 @@ 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;
@@ -3097,7 +3099,7 @@ 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;
}
--
2.19.1.6.gb485710b
