From: Daniel Borkmann <daniel@iogearbox.net>
To: Martin KaFai Lau <kafai@fb.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
David Miller <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
kernel-team@fb.com, Willem de Bruijn <willemb@google.com>
Subject: Re: [PATCH v4 net-next 5/8] bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress
Date: Wed, 16 Feb 2022 00:30:53 +0100 [thread overview]
Message-ID: <f0d76498-0bb1-36a6-0c8c-b334f6fb13c2@iogearbox.net> (raw)
In-Reply-To: <20220211071303.890169-1-kafai@fb.com>
On 2/11/22 8:13 AM, Martin KaFai Lau wrote:
> The current tc-bpf@ingress reads and writes the __sk_buff->tstamp
> as a (rcv) timestamp. This patch is to backward compatible with the
> (rcv) timestamp expectation when the skb->tstamp has a mono delivery_time.
>
> If needed, the patch first saves the mono delivery_time. Depending on
> the static key "netstamp_needed_key", it then resets the skb->tstamp to
> either 0 or ktime_get_real() before running the tc-bpf@ingress. After
> the tc-bpf prog returns, if the (rcv) timestamp in skb->tstamp has not
> been changed, it will restore the earlier saved mono delivery_time.
>
> The current logic to run tc-bpf@ingress is refactored to a new
> bpf_prog_run_at_ingress() function and shared between cls_bpf and act_bpf.
> The above new delivery_time save/restore logic is also done together in
> this function.
>
> Signed-off-by: Martin KaFai Lau <kafai@fb.com>
> ---
> include/linux/filter.h | 28 ++++++++++++++++++++++++++++
> net/sched/act_bpf.c | 5 +----
> net/sched/cls_bpf.c | 6 +-----
> 3 files changed, 30 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index d23e999dc032..e43e1701a80e 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -699,6 +699,34 @@ static inline void bpf_compute_data_pointers(struct sk_buff *skb)
> cb->data_end = skb->data + skb_headlen(skb);
> }
>
> +static __always_inline u32 bpf_prog_run_at_ingress(const struct bpf_prog *prog,
> + struct sk_buff *skb)
> +{
> + ktime_t tstamp, saved_mono_dtime = 0;
> + int filter_res;
> +
> + if (unlikely(skb->mono_delivery_time)) {
> + saved_mono_dtime = skb->tstamp;
> + skb->mono_delivery_time = 0;
> + if (static_branch_unlikely(&netstamp_needed_key))
> + skb->tstamp = tstamp = ktime_get_real();
> + else
> + skb->tstamp = tstamp = 0;
> + }
> +
> + /* It is safe to push/pull even if skb_shared() */
> + __skb_push(skb, skb->mac_len);
> + bpf_compute_data_pointers(skb);
> + filter_res = bpf_prog_run(prog, skb);
> + __skb_pull(skb, skb->mac_len);
> +
> + /* __sk_buff->tstamp was not changed, restore the delivery_time */
> + if (unlikely(saved_mono_dtime) && skb_tstamp(skb) == tstamp)
> + skb_set_delivery_time(skb, saved_mono_dtime, true);
So above detour is for skb->tstamp backwards compatibility so users will see real time.
I don't see why we special case {cls,act}_bpf-only, given this will also be the case
for other subsystems (e.g. netfilter) when they read access plain skb->tstamp and get
the egress one instead of ktime_get_real() upon deferred skb_clear_delivery_time().
If we would generally ignore it, then the above bpf_prog_run_at_ingress() save/restore
detour is not needed (so patch 5/6 should be dropped). (Meaning, if we need to special
case {cls,act}_bpf only, we could also have gone for simpler bpf-only solution..)
> + return filter_res;
> +}
> +
> /* Similar to bpf_compute_data_pointers(), except that save orginal
> * data in cb->data and cb->meta_data for restore.
> */
> diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
> index a77d8908e737..14c3bd0a5088 100644
> --- a/net/sched/act_bpf.c
> +++ b/net/sched/act_bpf.c
> @@ -45,10 +45,7 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act,
>
> filter = rcu_dereference(prog->filter);
> if (at_ingress) {
> - __skb_push(skb, skb->mac_len);
> - bpf_compute_data_pointers(skb);
> - filter_res = bpf_prog_run(filter, skb);
> - __skb_pull(skb, skb->mac_len);
> + filter_res = bpf_prog_run_at_ingress(filter, skb);
> } else {
> bpf_compute_data_pointers(skb);
> filter_res = bpf_prog_run(filter, skb);
> diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
> index df19a847829e..036b2e1f74af 100644
> --- a/net/sched/cls_bpf.c
> +++ b/net/sched/cls_bpf.c
> @@ -93,11 +93,7 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
> if (tc_skip_sw(prog->gen_flags)) {
> filter_res = prog->exts_integrated ? TC_ACT_UNSPEC : 0;
> } else if (at_ingress) {
> - /* It is safe to push/pull even if skb_shared() */
> - __skb_push(skb, skb->mac_len);
> - bpf_compute_data_pointers(skb);
> - filter_res = bpf_prog_run(prog->filter, skb);
> - __skb_pull(skb, skb->mac_len);
> + filter_res = bpf_prog_run_at_ingress(prog->filter, skb);
> } else {
> bpf_compute_data_pointers(skb);
> filter_res = bpf_prog_run(prog->filter, skb);
>
next prev parent reply other threads:[~2022-02-15 23:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-11 7:12 [PATCH v4 net-next 0/8] Preserve mono delivery time (EDT) in skb->tstamp Martin KaFai Lau
2022-02-11 7:12 ` [PATCH v4 net-next 1/8] net: Add skb->mono_delivery_time to distinguish mono delivery_time from (rcv) timestamp Martin KaFai Lau
2022-02-12 19:13 ` Cong Wang
2022-02-12 23:27 ` Martin KaFai Lau
2022-02-15 20:49 ` Daniel Borkmann
2022-02-16 6:11 ` Martin KaFai Lau
2022-02-11 7:12 ` [PATCH v4 net-next 2/8] net: Add skb_clear_tstamp() to keep the mono delivery_time Martin KaFai Lau
2022-02-11 7:12 ` [PATCH v4 net-next 3/8] net: Set skb->mono_delivery_time and clear it after sch_handle_ingress() Martin KaFai Lau
2022-02-15 21:04 ` Daniel Borkmann
2022-02-11 7:12 ` [PATCH v4 net-next 4/8] net: Postpone skb_clear_delivery_time() until knowing the skb is delivered locally Martin KaFai Lau
2022-02-11 7:13 ` [PATCH v4 net-next 5/8] bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress Martin KaFai Lau
2022-02-15 23:30 ` Daniel Borkmann [this message]
2022-02-16 5:51 ` Martin KaFai Lau
2022-02-17 0:03 ` Daniel Borkmann
2022-02-17 1:50 ` Martin KaFai Lau
2022-02-17 6:52 ` Martin KaFai Lau
2022-02-11 7:13 ` [PATCH v4 net-next 6/8] bpf: Clear skb->mono_delivery_time bit if needed after running tc-bpf@egress Martin KaFai Lau
2022-02-11 7:13 ` [PATCH v4 net-next 7/8] bpf: Add __sk_buff->delivery_time_type and bpf_skb_set_delivery_time() Martin KaFai Lau
2022-02-11 7:13 ` [PATCH v4 net-next 8/8] bpf: selftests: test skb->tstamp in redirect_neigh Martin KaFai Lau
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