netdev - Re: [net-next 1/6] ixgbe: Do not allow LRO or MTU change with XDP

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Date:   Thu, 26 Jul 2018 14:21:08 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net, Tony Nguyen <anthony.l.nguyen@...el.com>,
        netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
        jogreene@...hat.com
Subject: Re: [net-next 1/6] ixgbe: Do not allow LRO or MTU change with XDP

On Thu, 26 Jul 2018 10:40:45 -0700, Jeff Kirsher wrote:
> From: Tony Nguyen <anthony.l.nguyen@...el.com>
> 
> XDP does not support jumbo frames or LRO.  These checks are being made
> outside the driver when an XDP program is loaded, however, there is
> nothing preventing these from changing after an XDP program is loaded.
> Add the checks so that while an XDP program is loaded, do not allow MTU
> to be changed or LRO to be enabled.
> 
> Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
> Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 5a6600f7b382..c42256e91997 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -6469,6 +6469,11 @@ static int ixgbe_change_mtu(struct net_device *netdev, int new_mtu)
>  {
>  	struct ixgbe_adapter *adapter = netdev_priv(netdev);
>  
> +	if (adapter->xdp_prog) {
> +		e_warn(probe, "MTU cannot be changed while XDP program is loaded\n");
> +		return -EPERM;

EPERM looks wrong, EINVAL is common.  Also most drivers will just check
the bounds like you do in ixgbe_xdp_setup(), allowing the change if new
MTU still fits constraints.

FWIW are the IXGBE_FLAG_SRIOV_ENABLED and IXGBE_FLAG_DCB_ENABLED flag
changes also covered while xdp is enabled?  Quick grep doesn't reveal
them being checked against xdp_prog other than in ixgbe_xdp_setup().

> +	}
> +
>  	/*
>  	 * For 82599EB we cannot allow legacy VFs to enable their receive
>  	 * paths when MTU greater than 1500 is configured.  So display a
> @@ -9407,6 +9412,11 @@ static netdev_features_t ixgbe_fix_features(struct net_device *netdev,
>  	if (!(adapter->flags2 & IXGBE_FLAG2_RSC_CAPABLE))
>  		features &= ~NETIF_F_LRO;
>  
> +	if (adapter->xdp_prog && (features & NETIF_F_LRO)) {
> +		e_dev_err("LRO is not supported with XDP\n");
> +		features &= ~NETIF_F_LRO;
> +	}
> +
>  	return features;
>  }
>