[bpf-next,v3,0/3] xsk: build skb by page

v3:
    Optimized code

v2:
    1. add priv_flags IFF_TX_SKB_NO_LINEAR instead of netdev_feature
    2. split the patch to three:
        a. add priv_flags IFF_TX_SKB_NO_LINEAR
        b. virtio net add priv_flags IFF_TX_SKB_NO_LINEAR
        c. When there is support this flag, construct skb without linear space
    3. use ERR_PTR() and PTR_ERR() to handle the err

v1 message log:
---------------

This patch is used to construct skb based on page to save memory copy
overhead.

This has one problem:

We construct the skb by fill the data page as a frag into the skb. In
this way, the linear space is empty, and the header information is also
in the frag, not in the linear space, which is not allowed for some
network cards. For example, Mellanox Technologies MT27710 Family
[ConnectX-4 Lx] will get the following error message:

    mlx5_core 0000:3b:00.1 eth1: Error cqe on cqn 0x817, ci 0x8, qn 0x1dbb, opcode 0xd, syndrome 0x1, vendor syndrome 0x68
    00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00000030: 00 00 00 00 60 10 68 01 0a 00 1d bb 00 0f 9f d2
    WQE DUMP: WQ size 1024 WQ cur size 0, WQE index 0xf, len: 64
    00000000: 00 00 0f 0a 00 1d bb 03 00 00 00 08 00 00 00 00
    00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00000020: 00 00 00 2b 00 08 00 00 00 00 00 05 9e e3 08 00
    00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    mlx5_core 0000:3b:00.1 eth1: ERR CQE on SQ: 0x1dbb

I also tried to use build_skb to construct skb, but because of the
existence of skb_shinfo, it must be behind the linear space, so this
method is not working. We can't put skb_shinfo on desc->addr, it will be
exposed to users, this is not safe.

Finally, I added a feature NETIF_F_SKB_NO_LINEAR to identify whether the
network card supports the header information of the packet in the frag
and not in the linear space.

---------------- Performance Testing ------------

The test environment is Aliyun ECS server.
Test cmd:
```
xdpsock -i eth0 -t  -S -s <msg size>
```

Test result data:

size    64      512     1024    1500
copy    1916747 1775988 1600203 1440054
page    1974058 1953655 1945463 1904478
percent 3.0%    10.0%   21.58%  32.3%

Xuan Zhuo (3):
  net: add priv_flags for allow tx skb without linear
  virtio-net: support IFF_TX_SKB_NO_LINEAR
  xsk: build skb by page

 drivers/net/virtio_net.c  |   3 +-
 include/linux/netdevice.h |   3 ++
 net/xdp/xsk.c             | 104 ++++++++++++++++++++++++++++++++++++++--------
 3 files changed, 91 insertions(+), 19 deletions(-)

--
1.8.3.1

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Date: Thu, 21 Jan 2021 21:47:07 +0800

> In some cases, we hope to construct skb directly based on the existing
> memory without copying data. In this case, the page will be placed
> directly in the skb, and the linear space of skb is empty. But
> unfortunately, many the network card does not support this operation.
> For example Mellanox Technologies MT27710 Family [ConnectX-4 Lx] will
> get the following error message:
> 
>     mlx5_core 0000:3b:00.1 eth1: Error cqe on cqn 0x817, ci 0x8, qn 0x1dbb, opcode 0xd, syndrome 0x1, vendor syndrome 0x68
>     00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000030: 00 00 00 00 60 10 68 01 0a 00 1d bb 00 0f 9f d2
>     WQE DUMP: WQ size 1024 WQ cur size 0, WQE index 0xf, len: 64
>     00000000: 00 00 0f 0a 00 1d bb 03 00 00 00 08 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 2b 00 08 00 00 00 00 00 05 9e e3 08 00
>     00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     mlx5_core 0000:3b:00.1 eth1: ERR CQE on SQ: 0x1dbb
> 
> So a priv_flag is added here to indicate whether the network card
> supports this feature.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Suggested-by: Alexander Lobakin <alobakin@pm.me>

Acked-by: Alexander Lobakin <alobakin@pm.me>

> ---
>  include/linux/netdevice.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index ef51725..135db8f 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1525,6 +1525,7 @@ struct net_device_ops {
>   * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
>   * @IFF_L3MDEV_RX_HANDLER: only invoke the rx handler of L3 master device
>   * @IFF_LIVE_RENAME_OK: rename is allowed while device is up and running
> + * @IFF_TX_SKB_NO_LINEAR: allow tx skb linear is empty
>   */
>  enum netdev_priv_flags {
>  	IFF_802_1Q_VLAN			= 1<<0,
> @@ -1558,6 +1559,7 @@ enum netdev_priv_flags {
>  	IFF_FAILOVER_SLAVE		= 1<<28,
>  	IFF_L3MDEV_RX_HANDLER		= 1<<29,
>  	IFF_LIVE_RENAME_OK		= 1<<30,
> +	IFF_TX_SKB_NO_LINEAR		= 1<<31,
>  };
>  
>  #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
> @@ -1590,6 +1592,7 @@ enum netdev_priv_flags {
>  #define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
>  #define IFF_L3MDEV_RX_HANDLER		IFF_L3MDEV_RX_HANDLER
>  #define IFF_LIVE_RENAME_OK		IFF_LIVE_RENAME_OK
> +#define IFF_TX_SKB_NO_LINEAR		IFF_TX_SKB_NO_LINEAR
>  
>  /**
>   *	struct net_device - The DEVICE structure.
> -- 
> 1.8.3.1

Thanks,
Al