linux-kernel - Re: [PATCH v6] hv_netvsc: add support for vlans in AF

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Date:   Wed, 22 Jul 2020 17:58:30 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     srirakr2@...co.com
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, mbumgard@...co.com, ugm@...co.com,
        nimm@...co.com, xe-linux-external@...co.com, kuba@...nel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] hv_netvsc: add support for vlans in AF_PACKET mode

From: Sriram Krishnan <srirakr2@...co.com>
Date: Wed, 22 Jul 2020 21:08:44 +0530

> 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 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@...co.com
> Cc: Sriram Krishnan <srirakr2@...co.com>
> Signed-off-by: Sriram Krishnan <srirakr2@...co.com>

Applied to net-next, thank you.