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Date: Mon, 1 Mar 2021 15:23:51 +0000
From: Lorenz Bauer <lmb@...udflare.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
duanxiongchun@...edance.com, wangdongdong.6@...edance.com,
jiang.wang@...edance.com, Cong Wang <cong.wang@...edance.com>,
Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf-next v7 4/9] skmsg: move sk_redir from TCP_SKB_CB to skb
On Tue, 23 Feb 2021 at 18:49, Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> From: Cong Wang <cong.wang@...edance.com>
>
> Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
> does not work for any other non-TCP protocols. We can move them to
> skb ext, but it introduces a memory allocation on fast path.
>
> Fortunately, we only need to a word-size to store all the information,
> because the flags actually only contains 1 bit so can be just packed
> into the lowest bit of the "pointer", which is stored as unsigned
> long.
>
> Inside struct sk_buff, '_skb_refdst' can be reused because skb dst is
> no longer needed after ->sk_data_ready() so we can just drop it.
Hi Cong Wang,
I saw this on patchwork:
include/linux/skbuff.h:932: warning: Function parameter or member
'_sk_redir' not described in 'sk_buff'
New warnings added
0a1
> include/linux/skbuff.h:932: warning: Function parameter or member '_sk_redir' not described in 'sk_buff'
Per-file breakdown
Source: https://patchwork.kernel.org/project/netdevbpf/patch/20210223184934.6054-5-xiyou.wangcong@gmail.com/
Maybe something to follow up on, I'm not sure what the conventions are here.
>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Lorenz Bauer <lmb@...udflare.com>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Acked-by: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
> include/linux/skbuff.h | 3 +++
> include/linux/skmsg.h | 38 ++++++++++++++++++++++++++++++++++++++
> include/net/tcp.h | 19 -------------------
> net/core/skmsg.c | 31 +++++++++++++++++++------------
> net/core/sock_map.c | 8 ++------
> 5 files changed, 62 insertions(+), 37 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 6d0a33d1c0db..bd84f799c952 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -755,6 +755,9 @@ struct sk_buff {
> void (*destructor)(struct sk_buff *skb);
> };
> struct list_head tcp_tsorted_anchor;
> +#ifdef CONFIG_NET_SOCK_MSG
> + unsigned long _sk_redir;
> +#endif
> };
>
> #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index 22e26f82de33..e0de45527bb6 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -455,4 +455,42 @@ static inline bool sk_psock_strp_enabled(struct sk_psock *psock)
> return false;
> return !!psock->saved_data_ready;
> }
> +
> +#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
> +
> +/* We only have one bit so far. */
> +#define BPF_F_PTR_MASK ~(BPF_F_INGRESS)
> +
> +static inline bool skb_bpf_ingress(const struct sk_buff *skb)
> +{
> + unsigned long sk_redir = skb->_sk_redir;
> +
> + return sk_redir & BPF_F_INGRESS;
> +}
> +
> +static inline void skb_bpf_set_ingress(struct sk_buff *skb)
> +{
> + skb->_sk_redir |= BPF_F_INGRESS;
> +}
> +
> +static inline void skb_bpf_set_redir(struct sk_buff *skb, struct sock *sk_redir,
> + bool ingress)
> +{
> + skb->_sk_redir = (unsigned long)sk_redir;
> + if (ingress)
> + skb->_sk_redir |= BPF_F_INGRESS;
> +}
> +
> +static inline struct sock *skb_bpf_redirect_fetch(const struct sk_buff *skb)
> +{
> + unsigned long sk_redir = skb->_sk_redir;
> +
> + return (struct sock *)(sk_redir & BPF_F_PTR_MASK);
> +}
> +
> +static inline void skb_bpf_redirect_clear(struct sk_buff *skb)
> +{
> + skb->_sk_redir = 0;
> +}
> +#endif /* CONFIG_NET_SOCK_MSG */
> #endif /* _LINUX_SKMSG_H */
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 947ef5da6867..075de26f449d 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -883,30 +883,11 @@ struct tcp_skb_cb {
> struct inet6_skb_parm h6;
> #endif
> } header; /* For incoming skbs */
> - struct {
> - __u32 flags;
> - struct sock *sk_redir;
> - } bpf;
> };
> };
>
> #define TCP_SKB_CB(__skb) ((struct tcp_skb_cb *)&((__skb)->cb[0]))
>
> -static inline bool tcp_skb_bpf_ingress(const struct sk_buff *skb)
> -{
> - return TCP_SKB_CB(skb)->bpf.flags & BPF_F_INGRESS;
> -}
> -
> -static inline struct sock *tcp_skb_bpf_redirect_fetch(struct sk_buff *skb)
> -{
> - return TCP_SKB_CB(skb)->bpf.sk_redir;
> -}
> -
> -static inline void tcp_skb_bpf_redirect_clear(struct sk_buff *skb)
> -{
> - TCP_SKB_CB(skb)->bpf.sk_redir = NULL;
> -}
> -
> extern const struct inet_connection_sock_af_ops ipv4_specific;
>
> #if IS_ENABLED(CONFIG_IPV6)
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index 8822001ab3dc..409258367bea 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -525,7 +525,8 @@ static void sk_psock_backlog(struct work_struct *work)
> len = skb->len;
> off = 0;
> start:
> - ingress = tcp_skb_bpf_ingress(skb);
> + ingress = skb_bpf_ingress(skb);
> + skb_bpf_redirect_clear(skb);
> do {
> ret = -EIO;
> if (likely(psock->sk->sk_socket))
> @@ -631,7 +632,12 @@ void __sk_psock_purge_ingress_msg(struct sk_psock *psock)
>
> static void sk_psock_zap_ingress(struct sk_psock *psock)
> {
> - __skb_queue_purge(&psock->ingress_skb);
> + struct sk_buff *skb;
> +
> + while ((skb = __skb_dequeue(&psock->ingress_skb)) != NULL) {
> + skb_bpf_redirect_clear(skb);
> + kfree_skb(skb);
> + }
> __sk_psock_purge_ingress_msg(psock);
> }
>
> @@ -754,7 +760,7 @@ static void sk_psock_skb_redirect(struct sk_buff *skb)
> struct sk_psock *psock_other;
> struct sock *sk_other;
>
> - sk_other = tcp_skb_bpf_redirect_fetch(skb);
> + sk_other = skb_bpf_redirect_fetch(skb);
> /* This error is a buggy BPF program, it returned a redirect
> * return code, but then didn't set a redirect interface.
> */
> @@ -804,9 +810,10 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb)
> * TLS context.
> */
> skb->sk = psock->sk;
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> skb->sk = NULL;
> }
> sk_psock_tls_verdict_apply(skb, psock->sk, ret);
> @@ -818,7 +825,6 @@ EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read);
> static void sk_psock_verdict_apply(struct sk_psock *psock,
> struct sk_buff *skb, int verdict)
> {
> - struct tcp_skb_cb *tcp;
> struct sock *sk_other;
> int err = -EIO;
>
> @@ -830,8 +836,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
> goto out_free;
> }
>
> - tcp = TCP_SKB_CB(skb);
> - tcp->bpf.flags |= BPF_F_INGRESS;
> + skb_bpf_set_ingress(skb);
>
> /* If the queue is empty then we can submit directly
> * into the msg queue. If its not empty we have to
> @@ -892,9 +897,10 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
> skb_set_owner_r(skb, sk);
> prog = READ_ONCE(psock->progs.skb_verdict);
> if (likely(prog)) {
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> }
> sk_psock_verdict_apply(psock, skb, ret);
> out:
> @@ -1011,9 +1017,10 @@ static int sk_psock_verdict_recv(read_descriptor_t *desc, struct sk_buff *skb,
> skb_set_owner_r(skb, sk);
> prog = READ_ONCE(psock->progs.skb_verdict);
> if (likely(prog)) {
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> }
> sk_psock_verdict_apply(psock, skb, ret);
> out:
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 1a28a5c2c61e..dbfcd7006338 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -657,7 +657,6 @@ const struct bpf_func_proto bpf_sock_map_update_proto = {
> BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
> struct bpf_map *, map, u32, key, u64, flags)
> {
> - struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> struct sock *sk;
>
> if (unlikely(flags & ~(BPF_F_INGRESS)))
> @@ -667,8 +666,7 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
> if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
> return SK_DROP;
>
> - tcb->bpf.flags = flags;
> - tcb->bpf.sk_redir = sk;
> + skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
> return SK_PASS;
> }
>
> @@ -1250,7 +1248,6 @@ const struct bpf_func_proto bpf_sock_hash_update_proto = {
> BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
> struct bpf_map *, map, void *, key, u64, flags)
> {
> - struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> struct sock *sk;
>
> if (unlikely(flags & ~(BPF_F_INGRESS)))
> @@ -1260,8 +1257,7 @@ BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
> if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
> return SK_DROP;
>
> - tcb->bpf.flags = flags;
> - tcb->bpf.sk_redir = sk;
> + skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
> return SK_PASS;
> }
>
> --
> 2.25.1
>
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
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