Re: [dpdk-dev] [PATCH] net/virtio: set offload flag for jumbo frames

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 1/30/19 4:26 PM, Jens Freimann wrote:
> Port configuration fails when offload flags don't match the expected
> value, e.g. when max-pkt-len is set to a value that should enable
> receive port offloading but doesn't.
> 
> This can be triggered by running testpmd e.g. with --max-pkt-len=2000.
> It will fail with "Ethdev port_id=0 requested Rx offloads 0x800 doesn't
> match Rx offloads capabilities 0x20d in rte_eth_dev_configure()"
> 
> To fix this there are two cases to consider:
> 
> 1. VIRTIO_NET_F_MTU is negotiated. Then we need to check if the
>     requested max. packet length fits into the MTU. If yes we set the
>     offload flag.
> 2. VIRTIO_NET_F_MTU is not negotiated. We can set the offload flag.

I think we need to Cc: stable and point to the commit introducing the
regression. I think it is the one introducing the use of
DEV_RX_OFFLOAD_JUMBO_FRAME in Virtio PMD.
> 
> Signed-off-by: Jens Freimann <jfreimann@redhat.com>
> ---
>   drivers/net/virtio/virtio_ethdev.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> index 7c4c1df00..e0d6542d4 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -2351,6 +2351,17 @@ virtio_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
>   	if ((host_features & tso_mask) == tso_mask)
>   		dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_TCP_LRO;
>   
> +	if (host_features & (1ULL << VIRTIO_NET_F_MTU)) {
> +		struct virtio_net_config config;
> +		vtpci_read_dev_config(hw,
> +				offsetof(struct virtio_net_config, mtu),
> +				&config.mtu, sizeof(config.mtu));
> +		if (dev->data->dev_conf.rxmode.max_rx_pkt_len <= config.mtu)

That is not exactly right, MTU does not take into account the Ethernet
header, the VLAN tag and the virtio-net header.

See virtio_mtu_set() for example.

> +			dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> +	} else {
> +		dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> +	}
> +
>   	dev_info->tx_offload_capa = DEV_TX_OFFLOAD_MULTI_SEGS |
>   				    DEV_TX_OFFLOAD_VLAN_INSERT;
>   	if (host_features & (1ULL << VIRTIO_NET_F_CSUM)) {
>