RE: [PATCH v19 bpf-next 10/23] net: mvneta: enable jumbo frames if the loaded XDP program support mb

From: John Fastabend <john.fastabend@gmail.com>
To: Lorenzo Bianconi <lorenzo@kernel.org>,
	bpf@vger.kernel.org, netdev@vger.kernel.org
Cc: lorenzo.bianconi@redhat.com, davem@davemloft.net,
	kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net,
	shayagr@amazon.com, john.fastabend@gmail.com, dsahern@kernel.org,
	brouer@redhat.com, echaudro@redhat.com, jasowang@redhat.com,
	alexander.duyck@gmail.com, saeed@kernel.org,
	maciej.fijalkowski@intel.com, magnus.karlsson@intel.com,
	tirthendu.sarkar@intel.com, toke@redhat.com
Subject: RE: [PATCH v19 bpf-next 10/23] net: mvneta: enable jumbo frames if the loaded XDP program support mb
Date: Sun, 05 Dec 2021 19:18:03 -0800	[thread overview]
Message-ID: <61ad80eb139f9_444e2082e@john.notmuch> (raw)
In-Reply-To: <47932365c53acbf359c26944f0bec363928d342f.1638272238.git.lorenzo@kernel.org>

Lorenzo Bianconi wrote:
> Enable the capability to receive jumbo frames even if the interface is
> running in XDP mode if the loaded program declare to properly support
> xdp multi-buff. At same time reject a xdp program not supporting xdp
> multi-buffer if the driver is running in xdp multi-buffer mode.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---

Allow me to enumerate the cases as a sanity check.

 mb prog on driver w/out mb support:

    The program will never receive a non-linear buffer so no
    trouble here. If user tries to configure MTU >1500 an error
    will be thrown by driver same as always.

 !mb prog on driver w/out mb support.

    This is the normal case, no change.

 mb prog on driver with mb support.

    Allowed and user may now set MTU >1500.    

 !mb prog on driver with mb support

    Allowed and now driver must throw an error on MTU >1500

OK works for me. Thanks.

Acked-by: John Fastabend <john.fastabend@gmail.com>

>  drivers/net/ethernet/marvell/mvneta.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 332699960b53..98db3d03116a 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -3750,6 +3750,7 @@ static void mvneta_percpu_disable(void *arg)
>  static int mvneta_change_mtu(struct net_device *dev, int mtu)
>  {
>  	struct mvneta_port *pp = netdev_priv(dev);
> +	struct bpf_prog *prog = pp->xdp_prog;
>  	int ret;
>  
>  	if (!IS_ALIGNED(MVNETA_RX_PKT_SIZE(mtu), 8)) {
> @@ -3758,8 +3759,11 @@ static int mvneta_change_mtu(struct net_device *dev, int mtu)
>  		mtu = ALIGN(MVNETA_RX_PKT_SIZE(mtu), 8);
>  	}
>  
> -	if (pp->xdp_prog && mtu > MVNETA_MAX_RX_BUF_SIZE) {
> -		netdev_info(dev, "Illegal MTU value %d for XDP mode\n", mtu);
> +	if (prog && !prog->aux->xdp_mb && mtu > MVNETA_MAX_RX_BUF_SIZE) {
> +		netdev_info(dev,
> +			    "Illegal MTU %d for XDP prog without multi-buf\n",
> +			    mtu);
> +
>  		return -EINVAL;
>  	}
>  
> @@ -4428,8 +4432,9 @@ static int mvneta_xdp_setup(struct net_device *dev, struct bpf_prog *prog,
>  	struct mvneta_port *pp = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
>  
> -	if (prog && dev->mtu > MVNETA_MAX_RX_BUF_SIZE) {
> -		NL_SET_ERR_MSG_MOD(extack, "MTU too large for XDP");
> +	if (prog && !prog->aux->xdp_mb && dev->mtu > MVNETA_MAX_RX_BUF_SIZE) {
> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "prog does not support XDP multi-buff");
>  		return -EOPNOTSUPP;
>  	}
>  
> -- 
> 2.31.1