linux-kernel - Re: [PATCH] xfrm: Add pre-encap fragmentation for packet offload

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Message-ID: <20241126132220.GB1245331@unreal>
Date: Tue, 26 Nov 2024 15:22:20 +0200
From: Leon Romanovsky <leonro@...dia.com>
To: Steffen Klassert <steffen.klassert@...unet.com>
CC: Ilia Lin <ilia.lin@...nel.org>, <herbert@...dor.apana.org.au>,
	<davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfrm: Add pre-encap fragmentation for packet offload

On Tue, Nov 26, 2024 at 01:51:42PM +0100, Steffen Klassert wrote:
> On Sun, Nov 24, 2024 at 11:35:31AM +0200, Ilia Lin wrote:
> > In packet offload mode the raw packets will be sent to the NiC,
> > and will not return to the Network Stack. In event of crossing
> > the MTU size after the encapsulation, the NiC HW may not be
> > able to fragment the final packet.
> > Adding mandatory pre-encapsulation fragmentation for both
> > IPv4 and IPv6, if tunnel mode with packet offload is configured
> > on the state.
> > 
> > Signed-off-by: Ilia Lin <ilia.lin@...nel.org>
> > ---
> >  net/ipv4/xfrm4_output.c | 31 +++++++++++++++++++++++++++++--
> >  net/ipv6/xfrm6_output.c |  8 ++++++--
> >  2 files changed, 35 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
> > index 3cff51ba72bb0..a4271e0dd51bb 100644
> > --- a/net/ipv4/xfrm4_output.c
> > +++ b/net/ipv4/xfrm4_output.c
> > @@ -14,17 +14,44 @@
> >  #include <net/xfrm.h>
> >  #include <net/icmp.h>
> >  
> > +static int __xfrm4_output_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
> > +{
> > +	return xfrm_output(sk, skb);
> > +}
> > +
> >  static int __xfrm4_output(struct net *net, struct sock *sk, struct sk_buff *skb)
> >  {
> > -#ifdef CONFIG_NETFILTER
> > -	struct xfrm_state *x = skb_dst(skb)->xfrm;
> > +	struct dst_entry *dst = skb_dst(skb);
> > +	struct xfrm_state *x = dst->xfrm;
> > +	unsigned int mtu;
> > +	bool toobig;
> >  
> > +#ifdef CONFIG_NETFILTER
> >  	if (!x) {
> >  		IPCB(skb)->flags |= IPSKB_REROUTED;
> >  		return dst_output(net, sk, skb);
> >  	}
> >  #endif
> >  
> > +	if (x->props.mode != XFRM_MODE_TUNNEL || x->xso.type != XFRM_DEV_OFFLOAD_PACKET)
> > +		goto skip_frag;
> > +
> > +	mtu = xfrm_state_mtu(x, dst_mtu(skb_dst(skb)));
> > +
> > +	toobig = skb->len > mtu && !skb_is_gso(skb);
> > +
> > +	if (!skb->ignore_df && toobig && skb->sk) {
> > +		xfrm_local_error(skb, mtu);
> > +		kfree_skb(skb);
> > +		return -EMSGSIZE;
> > +	}
> > +
> > +	if (toobig) {
> > +		IPCB(skb)->frag_max_size = mtu;
> > +		return ip_do_fragment(net, sk, skb, __xfrm4_output_finish);
> > +	}
> 
> This would fragment the packet even if the DF bit is set.
> 
> Please no further packet offload stuff in generic code.

+ 100000

Thanks

>