RE: [PATCH v3] net: hyperv: add support for vlans in netvsc driver

[Haiyang Zhang <haiyangz@microsoft.com>]

> -----Original Message-----
> From: Sriram Krishnan <srirakr2@cisco.com>
> Sent: Monday, July 20, 2020 12:46 PM
> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> Wei Liu <wei.liu@kernel.org>
> Cc: mbumgard@cisco.com; ugm@cisco.com; nimm@cisco.com; xe-linux-
> external@cisco.com; David S. Miller <davem@davemloft.net>; Jakub Kicinski
> <kuba@kernel.org>; linux-hyperv@vger.kernel.org; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org
> Subject: [PATCH v3] net: hyperv: add support for vlans in netvsc driver
> 
> Vlan tagged packets are getting dropped when used with DPDK that uses
> the AF_PACKET interface on a hyperV guest.
> 
> The packet layer uses the tpacket interface to communicate the vlans
> information to the upper layers. On Rx path, these drivers can read the
> vlan info from the tpacket header but on the Tx path, this information
> is still within the packet frame and requires the paravirtual drivers to
> push this back into the NDIS header which is then used by the host OS to
> form the packet.
> 
> This transition from the packet frame to NDIS header is currently missing
> hence causing the host OS to drop the all vlan tagged packets sent by
> the drivers that use AF_PACKET (ETH_P_ALL) such as DPDK.
> 
> Here is an overview of the changes in the vlan header in the packet path:
> 
> The RX path (userspace handles everything):
>   1. RX VLAN packet is stripped by HOST OS and placed in NDIS header
>   2. Guest Kernel RX hv_netvsc packets and moves VLAN info from NDIS
>      header into kernel SKB
>   3. Kernel shares packets with user space application with PACKET_MMAP.
>      The SKB VLAN info is copied to tpacket layer and indication set
>      TP_STATUS_VLAN_VALID.
>   4. The user space application will re-insert the VLAN info into the frame.
> 
> The TX path:
>   1. The user space application has the VLAN info in the frame.
>   2. Guest kernel gets packets from the application with PACKET_MMAP.
>   3. The kernel later sends the frame to the hv_netvsc driver. The only way
>      to send VLANs is when the SKB is setup & the VLAN is is stripped from the
>      frame.
>   4. TX VLAN is re-inserted by HOST OS based on the NDIS header. If it sees
>      a VLAN in the frame the packet is dropped.
> 
> Cc: xe-linux-external@cisco.com
> Cc: Sriram Krishnan <srirakr2@cisco.com>
> Signed-off-by: Sriram Krishnan <srirakr2@cisco.com>
> ---
>  drivers/net/hyperv/netvsc_drv.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index 6267f706e8ee..2a25b4352369 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -605,6 +605,29 @@ static int netvsc_xmit(struct sk_buff *skb, struct
> net_device *net, bool xdp_tx)
>  		*hash_info = hash;
>  	}
> 
> +	/* When using AF_PACKET we need to remove VLAN from frame
> +	 * and indicate VLAN information in SKB so HOST OS will
> +	 * transmit the VLAN frame
> +	 */
> +	if (skb->protocol == htons(ETH_P_8021Q)) {
> +		u16 vlan_tci = 0;
> +		skb_reset_mac_header(skb);
> +		if (eth_type_vlan(eth_hdr(skb)->h_proto)) {
> +			int pop_err;
> +			pop_err = __skb_vlan_pop(skb, &vlan_tci);
> +			if (likely(pop_err == 0)) {
> +				__vlan_hwaccel_put_tag(skb,
> htons(ETH_P_8021Q), vlan_tci);
> +
> +				/* Update the NDIS header pkt lengths */
> +				packet->total_data_buflen -= VLAN_HLEN;

packet->total_bytes should be updated too.

Thanks,
- Haiyang