Messages in this thread | | | Date | Thu, 14 Mar 2024 09:10:10 -0700 | Subject | Re: [PATCH v4 iwl-net] i40e: Prevent setting MTU if greater than MFS | From | Brett Creeley <> |
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On 3/13/2024 2:07 AM, Erwan Velu wrote: > Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. > > > Commit 6871a7de705 ("[intelxl] Use admin queue to set port MAC address > and maximum frame size") from iPXE project set the MFS to 0x600 = 1536. > See https://github.com/ipxe/ipxe/commit/6871a7de705 > > At boot time the i40e driver complains about it with > the following message but continues. > > MFS for port 1 has been set below the default: 600 > > If the MTU size is increased, the driver accepts it but large packets will > not be processed by the firmware generating tx_errors. The issue is pretty > silent for users. i.e doing TCP in such context will generates lots of > retransmissions until the proper window size (below 1500) will be used. > > To fix this case, it would have been ideal to increase the MFS, > via i40e_aqc_opc_set_mac_config, incoming patch will take care of it. > > At least, commit prevents setting up an MTU greater than the current MFS. > It will avoid being in the position of having an MTU set to 9000 on the > netdev with a firmware refusing packets larger than 1536. > > A typical trace looks like: > [ 377.548696] i40e 0000:5d:00.0 eno5: Error changing mtu to 9000, Max is 1500. MFS is too small. > > Signed-off-by: Erwan Velu <e.velu@criteo.com> > --- > drivers/net/ethernet/intel/i40e/i40e_main.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c > index f86578857e8a..85ecf2f3de18 100644 > --- a/drivers/net/ethernet/intel/i40e/i40e_main.c > +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c > @@ -2946,7 +2946,7 @@ static int i40e_change_mtu(struct net_device *netdev, int new_mtu) > struct i40e_netdev_priv *np = netdev_priv(netdev); > struct i40e_vsi *vsi = np->vsi; > struct i40e_pf *pf = vsi->back; > - int frame_size; > + int frame_size, mfs, max_mtu; > > frame_size = i40e_max_vsi_frame_size(vsi, vsi->xdp_prog); > if (new_mtu > frame_size - I40E_PACKET_HDR_PAD) { > @@ -2955,6 +2955,14 @@ static int i40e_change_mtu(struct net_device *netdev, int new_mtu) > return -EINVAL; > } > > + mfs = pf->hw.phy.link_info.max_frame_size; > + max_mtu = mfs - I40E_PACKET_HDR_PAD;
If this is how the max_mtu is determined, does it make sense to set this before registering the netdev, i.e. netdev->max_mtu in i40e_config_netdev()?
Thanks,
Brett
> + if (new_mtu > max_mtu) { > + netdev_err(netdev, "Error changing mtu to %d, Max is %d. MFS is too small.\n", > + new_mtu, max_mtu); > + return -EINVAL; > + } > + > netdev_dbg(netdev, "changing MTU from %d to %d\n", > netdev->mtu, new_mtu); > netdev->mtu = new_mtu; > -- > 2.44.0 > >
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