Subject: Re: [PATCH net-next 3/3] cls_flower: Allow flow offloading though masked key exist.

From: Ido Schimmel <[email-masked]>
Date: Fri, 19 Jun 2020 16:35:48 +0300

On Fri, Jun 19, 2020 at 03:11:56PM +0530, dsatish wrote:
> A packet reaches OVS user space, only if, either there is no rule in
> datapath/hardware or there is race condition that the flow is added
> to hardware but before it is processed another packet arrives.
> 
> It is possible hardware as part of its limitations/optimizations
> remove certain flows.

Which driver is doing this? I don't believe it's valid to remove filters
from hardware and not tell anyone about it.

> To handle such cases where the hardware lost
> the flows, tc can offload to hardware if it receives a flow for which
> there exists an entry in its flow table. To handle such cases TC when
> it returns EEXIST error, also programs the flow in hardware, if
> hardware offload is enabled.
> 
> Signed-off-by: Chandra Kesava <[email-masked]>
> Signed-off-by: Prathibha Nagooru <[email-masked]>
> Signed-off-by: Satish Dhote <[email-masked]>
> ---
>  net/sched/cls_flower.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> index f1a5352cbb04..d718233cd5b9 100644
> --- a/net/sched/cls_flower.c
> +++ b/net/sched/cls_flower.c
> @@ -431,7 +431,8 @@ static void fl_hw_destroy_filter(struct tcf_proto *tp, struct cls_fl_filter *f,
>  
>  static int fl_hw_replace_filter(struct tcf_proto *tp,
>  				struct cls_fl_filter *f, bool rtnl_held,
> -				struct netlink_ext_ack *extack)
> +				struct netlink_ext_ack *extack,
> +				unsigned long cookie)
>  {
>  	struct tcf_block *block = tp->chain->block;
>  	struct flow_cls_offload cls_flower = {};
> @@ -444,7 +445,7 @@ static int fl_hw_replace_filter(struct tcf_proto *tp,
>  
>  	tc_cls_common_offload_init(&cls_flower.common, tp, f->flags, extack);
>  	cls_flower.command = FLOW_CLS_REPLACE;
> -	cls_flower.cookie = (unsigned long) f;
> +	cls_flower.cookie = cookie;
>  	cls_flower.rule->match.dissector = &f->mask->dissector;
>  	cls_flower.rule->match.mask = &f->mask->key;
>  	cls_flower.rule->match.key = &f->mkey;
> @@ -2024,11 +2025,25 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
>  	fl_init_unmasked_key_dissector(&fnew->unmasked_key_dissector);
>  
>  	err = fl_ht_insert_unique(fnew, fold, &in_ht);
> -	if (err)
> +	if (err) {
> +		/* It is possible Hardware lost the flow even though TC has it,
> +		 * and flow miss in hardware causes controller to offload flow again.
> +		 */
> +		if (err == -EEXIST && !tc_skip_hw(fnew->flags)) {
> +			struct cls_fl_filter *f =
> +				__fl_lookup(fnew->mask, &fnew->mkey);
> +
> +			if (f)
> +				fl_hw_replace_filter(tp, fnew, rtnl_held,
> +						     extack,
> +						     (unsigned long)(f));
> +		}
>  		goto errout_mask;
> +	}
>  
>  	if (!tc_skip_hw(fnew->flags)) {
> -		err = fl_hw_replace_filter(tp, fnew, rtnl_held, extack);
> +		err = fl_hw_replace_filter(tp, fnew, rtnl_held, extack,
> +					   (unsigned long)fnew);
>  		if (err)
>  			goto errout_ht;
>  	}
> -- 
> 2.17.1
>