netdev - Re: [PATCH ipsec-next 4/6] xfrm: add TX datapath support for IPsec full offload mode

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Date:   Fri, 13 May 2022 16:56:58 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Leon Romanovsky <leonro@...dia.com>,
        "David S . Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        <netdev@...r.kernel.org>, Raed Salem <raeds@...dia.com>,
        ipsec-devel <devel@...ux-ipsec.org>
Subject: Re: [PATCH ipsec-next 4/6] xfrm: add TX datapath support for IPsec
 full offload mode

On Tue, May 10, 2022 at 01:36:55PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> In IPsec full mode, the device is going to encrypt and encapsulate
> packets that are associated with offloaded policy. After successful
> policy lookup to indicate if packets should be offloaded or not,
> the stack forwards packets to the device to do the magic.
> 
> Signed-off-by: Raed Salem <raeds@...dia.com>
> Signed-off-by: Huy Nguyen <huyn@...dia.com>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---
>  net/xfrm/xfrm_output.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> index d4935b3b9983..2599f3dbac08 100644
> --- a/net/xfrm/xfrm_output.c
> +++ b/net/xfrm/xfrm_output.c
> @@ -718,6 +718,25 @@ int xfrm_output(struct sock *sk, struct sk_buff *skb)
>  		break;
>  	}
>  
> +	if (x->xso.type == XFRM_DEV_OFFLOAD_FULL) {
> +		struct dst_entry *dst = skb_dst_pop(skb);
> +
> +		if (!dst) {
> +			XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
> +			return -EHOSTUNREACH;
> +		}
> +
> +		skb_dst_set(skb, dst);
> +		err = skb_dst(skb)->ops->local_out(net, skb->sk, skb);
> +		if (unlikely(err != 1))
> +			return err;
> +
> +		if (!skb_dst(skb)->xfrm)
> +			return dst_output(net, skb->sk, skb);
> +
> +		return 0;
> +	}
> +

How do we know that we send the packet really to a device that
supports this type of offload? For crypto offload, we check that
in xfrm_dev_offload_ok() and I think something similar is required
here too.

Also, the offload type still requires software policies and states.
What if a device comes up that can do a real full offload, i.e.
in a way that the kernel acts just as a stub layer between IKE
and the device. Are we going to create XFRM_DEV_OFFLOAD_FULL_2
then? We need to make sure that this case cann be supported with
the new API too.