netdev - Re: [PATCH nf-next,RFC v4] netfilter: nf_flow

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Date:   Wed, 24 Jan 2018 17:31:36 -0800
From:   Jakub Kicinski <kubakici@...pl>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        f.fainelli@...il.com, ronye@...lanox.com,
        simon.horman@...ronome.com, jiri@...lanox.com, nbd@....name,
        john@...ozen.org, fw@...len.de
Subject: Re: [PATCH nf-next,RFC v4] netfilter: nf_flow_table: add hardware
 offload support

On Thu, 25 Jan 2018 01:09:41 +0100, Pablo Neira Ayuso wrote:
> This patch adds the infrastructure to offload flows to hardware, in case
> the nic/switch comes with built-in flow tables capabilities.
> 
> If the hardware comes with no hardware flow tables or they have
> limitations in terms of features, the existing infrastructure falls back
> to the software flow table implementation.
> 
> The software flow table garbage collector skips entries that resides in
> the hardware, so the hardware will be responsible for releasing this
> flow table entry too via flow_offload_dead().
> 
> Hardware configuration, either to add or to delete entries, is done from
> the hardware offload workqueue, to ensure this is done from user context
> given that we may sleep when grabbing the mdio mutex.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>

I wonder how do you deal with device/table removal?  I know regrettably
little about internals of nftables.  I assume the table cannot be
removed/module unloaded as long as there are flow entries?  And on
device removal all flows pertaining to the removed ifindex will be
automatically flushed?

Still there could be outstanding work items targeting the device, so
this WARN_ON:

+	indev = dev_get_by_index(net, ifindex);
+	if (WARN_ON(!indev))
+		return 0;

looks possible to trigger.

On the general architecture - I think it's worth documenting somewhere
clearly that unlike TC offloads and most NDOs add/del of NFT flows are
not protected by rtnl_lock.

> v4: More work in progress
> - Decouple nf_flow_table_hw from nft_flow_offload via rcu hooks
> - Consolidate ->ndo invocations, now they happen from the hw worker.
> - Fix bug in list handling, use list_replace_init()
> - cleanup entries on nf_flow_table_hw module removal
> - add NFT_FLOWTABLE_F_HW flag to flowtables to explicit signal that user wants
>   to offload entries to hardware.
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index ed0799a12bf2..be0c12acc3f0 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -859,6 +859,13 @@ struct dev_ifalias {
>  	char ifalias[];
>  };
>  
> +struct flow_offload;
> +
> +enum flow_offload_type {
> +	FLOW_OFFLOAD_ADD	= 0,
> +	FLOW_OFFLOAD_DEL,
> +};
> +
>  /*
>   * This structure defines the management hooks for network devices.
>   * The following hooks can be defined; unless noted otherwise, they are
> @@ -1316,6 +1323,8 @@ struct net_device_ops {
>  	int			(*ndo_bridge_dellink)(struct net_device *dev,
>  						      struct nlmsghdr *nlh,
>  						      u16 flags);
> +	int			(*ndo_flow_offload)(enum flow_offload_type type,
> +						    struct flow_offload *flow);

nit: should there be kdoc for the new NDO?  ndo kdoc comment doesn't
     look like it would be recognized by tools anyway though..

nit: using "flow" as the name rings slightly grandiose to me :)  
     I would appreciate a nf_ prefix for clarity.  Drivers will have 
     to juggle a number of "flow" things, it would make the code easier
     to follow if names were prefixed clearly, I feel.

>  	int			(*ndo_change_carrier)(struct net_device *dev,
>  						      bool new_carrier);
>  	int			(*ndo_get_phys_port_id)(struct net_device *dev,