diff options
| author | Martin KaFai Lau <kafai@fb.com> | 2022-03-02 11:56:28 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2022-03-03 14:38:48 +0000 |
| commit | 7449197d600d30d038b1ce6285ab4747096eac7f (patch) | |
| tree | db9b98b78d4502e54adf2c3cbfc79536f28c1c09 /net/sched | |
| parent | cd14e9b7b8d312dfbf75ce1f78552902e51b9045 (diff) | |
bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress
The current tc-bpf@ingress reads and writes the __sk_buff->tstamp
as a (rcv) timestamp which currently could either be 0 (not available)
or ktime_get_real(). This patch is to backward compatible with the
(rcv) timestamp expectation at ingress. If the skb->tstamp has
the delivery_time, the bpf insn rewrite will read 0 for tc-bpf
running at ingress as it is not available. When writing at ingress,
it will also clear the skb->mono_delivery_time bit.
/* BPF_READ: a = __sk_buff->tstamp */
if (!skb->tc_at_ingress || !skb->mono_delivery_time)
a = skb->tstamp;
else
a = 0
/* BPF_WRITE: __sk_buff->tstamp = a */
if (skb->tc_at_ingress)
skb->mono_delivery_time = 0;
skb->tstamp = a;
[ A note on the BPF_CGROUP_INET_INGRESS which can also access
skb->tstamp. At that point, the skb is delivered locally
and skb_clear_delivery_time() has already been done,
so the skb->tstamp will only have the (rcv) timestamp. ]
If the tc-bpf@egress writes 0 to skb->tstamp, the skb->mono_delivery_time
has to be cleared also. It could be done together during
convert_ctx_access(). However, the latter patch will also expose
the skb->mono_delivery_time bit as __sk_buff->delivery_time_type.
Changing the delivery_time_type in the background may surprise
the user, e.g. the 2nd read on __sk_buff->delivery_time_type
may need a READ_ONCE() to avoid compiler optimization. Thus,
in expecting the needs in the latter patch, this patch does a
check on !skb->tstamp after running the tc-bpf and clears the
skb->mono_delivery_time bit if needed. The earlier discussion
on v4 [0].
The bpf insn rewrite requires the skb's mono_delivery_time bit and
tc_at_ingress bit. They are moved up in sk_buff so that bpf rewrite
can be done at a fixed offset. tc_skip_classify is moved together with
tc_at_ingress. To get one bit for mono_delivery_time, csum_not_inet is
moved down and this bit is currently used by sctp.
[0]: https://lore.kernel.org/bpf/20220217015043.khqwqklx45c4m4se@kafai-mbp.dhcp.thefacebook.com/
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
| -rw-r--r-- | net/sched/act_bpf.c | 2 | ||||
| -rw-r--r-- | net/sched/cls_bpf.c | 2 |
2 files changed, 4 insertions, 0 deletions
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c index a77d8908e737..fea2d78b9ddc 100644 --- a/net/sched/act_bpf.c +++ b/net/sched/act_bpf.c @@ -53,6 +53,8 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act, bpf_compute_data_pointers(skb); filter_res = bpf_prog_run(filter, skb); } + if (unlikely(!skb->tstamp && skb->mono_delivery_time)) + skb->mono_delivery_time = 0; if (skb_sk_is_prefetched(skb) && filter_res != TC_ACT_OK) skb_orphan(skb); diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c index df19a847829e..c85b85a192bf 100644 --- a/net/sched/cls_bpf.c +++ b/net/sched/cls_bpf.c @@ -102,6 +102,8 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, bpf_compute_data_pointers(skb); filter_res = bpf_prog_run(prog->filter, skb); } + if (unlikely(!skb->tstamp && skb->mono_delivery_time)) + skb->mono_delivery_time = 0; if (prog->exts_integrated) { res->class = 0; |