在 2022/12/27 下午8:20, Heng Qi 写道:
在 2022/12/27 下午2:32, Jason Wang 写道:
在 2022/12/20 22:14, Heng Qi 写道:
When the xdp program sets xdp.frags, which means it can process
multi-buffer packets over larger MTU, so we continue to support xdp.
But for single-buffer xdp, we should keep checking for MTU.
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 443aa7b8f0ad..c5c4e9db4ed3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device
*dev, struct bpf_prog *prog,
return -EINVAL;
}
- if (dev->mtu > max_sz) {
- NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");
+ if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) {
Not related to this patch, but I see:
unsigned long int max_sz = PAGE_SIZE - sizeof(struct
padded_vnet_hdr);
Which is suspicious, do we need to count reserved headroom/tailroom
as well?
This seems to be suspicious. After loading xdp, the size of the filled
avail buffer
is (PAGE_SIZE - headroom - tailroom), so the size of the received used
buffer, ie MTU,
should also be (PAGE_SIZE - headroom - tailroom).
Hi Jason, this is indeed a problem. After verification, packet drop will
indeed occur. To avoid this,
the size of MTU should be (PAGE_SIZE - headroom - tailroom - ethhdr =
4096 - 256 -320 - 14 =3506).
Because when there is xdp, each filling is 3520 (PAGE_SIZE - room), if
the value of (MTU + 14) is
greater than 3520 (because the MTU does not contain the ethernet
header), then the packet with a
length greater than 3520 will come in, so num_buf will still be greater
than or equal to 2, and then
xdp_linearize_page() will be performed and the packet will be dropped
because the total length is
greater than PAGE_SIZE.
I will make a separate bugfix patch to fix this later.
Thanks.
Thanks.
Thanks
+ NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP
without frags");
netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
return -EINVAL;
}
