On 3/2/22 8:56 PM, Martin KaFai Lau wrote:
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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
---
include/linux/skbuff.h | 18 +++++++----
net/core/filter.c | 71 ++++++++++++++++++++++++++++++++++++------
net/sched/act_bpf.c | 2 ++
net/sched/cls_bpf.c | 2 ++
4 files changed, 77 insertions(+), 16 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4b5b926a81f2..5445860e1ba6 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -941,8 +941,12 @@ struct sk_buff {
__u8 vlan_present:1; /* See PKT_VLAN_PRESENT_BIT */
__u8 csum_complete_sw:1;
__u8 csum_level:2;
- __u8 csum_not_inet:1;
__u8 dst_pending_confirm:1;
+ __u8 mono_delivery_time:1;
+#ifdef CONFIG_NET_CLS_ACT
+ __u8 tc_skip_classify:1;
+ __u8 tc_at_ingress:1;
+#endif
#ifdef CONFIG_IPV6_NDISC_NODETYPE
__u8 ndisc_nodetype:2;
#endif
@@ -953,10 +957,6 @@ struct sk_buff {
#ifdef CONFIG_NET_SWITCHDEV
__u8 offload_fwd_mark:1;
__u8 offload_l3_fwd_mark:1;
-#endif
-#ifdef CONFIG_NET_CLS_ACT
- __u8 tc_skip_classify:1;
- __u8 tc_at_ingress:1;
#endif
__u8 redirected:1;
#ifdef CONFIG_NET_REDIRECT
@@ -969,7 +969,7 @@ struct sk_buff {
__u8 decrypted:1;
#endif
__u8 slow_gro:1;
- __u8 mono_delivery_time:1;
+ __u8 csum_not_inet:1;
#ifdef CONFIG_NET_SCHED
__u16 tc_index; /* traffic control index */
@@ -1047,10 +1047,16 @@ struct sk_buff {
/* if you move pkt_vlan_present around you also must adapt these constants */
#ifdef __BIG_ENDIAN_BITFIELD
#define PKT_VLAN_PRESENT_BIT 7
+#define TC_AT_INGRESS_MASK (1 << 0)
+#define SKB_MONO_DELIVERY_TIME_MASK (1 << 2)
#else
#define PKT_VLAN_PRESENT_BIT 0
+#define TC_AT_INGRESS_MASK (1 << 7)
+#define SKB_MONO_DELIVERY_TIME_MASK (1 << 5)
#endif
#define PKT_VLAN_PRESENT_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
+#define TC_AT_INGRESS_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
+#define SKB_MONO_DELIVERY_TIME_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
Just nit, but given PKT_VLAN_PRESENT_OFFSET, TC_AT_INGRESS_OFFSET and SKB_MONO_DELIVERY_TIME_OFFSET
are all the same offsetof(struct sk_buff, __pkt_vlan_present_offset), maybe lets use just one single
define? If anyone moves them out, they would have to adopt as per comment.
#ifdef __KERNEL__
/*
diff --git a/net/core/filter.c b/net/core/filter.c
index cfcf9b4d1ec2..5072733743e9 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8859,6 +8859,65 @@ static struct bpf_insn *bpf_convert_shinfo_access(const struct bpf_insn *si,
return insn;
}
+static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_insn *si,
+ struct bpf_insn *insn)
+{
+ __u8 value_reg = si->dst_reg;
+ __u8 skb_reg = si->src_reg;
+
+#ifdef CONFIG_NET_CLS_ACT
+ __u8 tmp_reg = BPF_REG_AX;
+
+ *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_OFFSET);
+ *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK);
nit: As far as I can see, can't si->dst_reg be used instead of AX?
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 5);
+ /* @ingress, read __sk_buff->tstamp as the (rcv) timestamp,
+ * so check the skb->mono_delivery_time.
+ */
+ *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
+ SKB_MONO_DELIVERY_TIME_OFFSET);
+ *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
+ SKB_MONO_DELIVERY_TIME_MASK);
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 2);
+ /* skb->mono_delivery_time is set, read 0 as the (rcv) timestamp. */
+ *insn++ = BPF_MOV64_IMM(value_reg, 0);
+ *insn++ = BPF_JMP_A(1);
+#endif
+
+ *insn++ = BPF_LDX_MEM(BPF_DW, value_reg, skb_reg,
+ offsetof(struct sk_buff, tstamp));
+ return insn;
+}
+
+static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_insn *si,
+ struct bpf_insn *insn)
+{
+ __u8 value_reg = si->src_reg;
+ __u8 skb_reg = si->dst_reg;
+
+#ifdef CONFIG_NET_CLS_ACT
+ __u8 tmp_reg = BPF_REG_AX;
+
+ *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_OFFSET);
+ *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK);
Can't we get rid of tcf_bpf_act() and cls_bpf_classify() changes altogether by just doing:
/* BPF_WRITE: __sk_buff->tstamp = a */
skb->mono_delivery_time = !skb->tc_at_ingress && a;
skb->tstamp = a;
(Untested) pseudo code:
// or see comment on common SKB_FLAGS_OFFSET define or such
BUILD_BUG_ON(TC_AT_INGRESS_OFFSET != SKB_MONO_DELIVERY_TIME_OFFSET)
BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, SKB_MONO_DELIVERY_TIME_OFFSET)
BPF_ALU32_IMM(BPF_OR, tmp_reg, SKB_MONO_DELIVERY_TIME_MASK)
BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, <clear>)
BPF_JMP32_REG(BPF_JGE, value_reg, tmp_reg, <store>)
<clear>:
BPF_ALU32_IMM(BPF_AND, tmp_reg, ~SKB_MONO_DELIVERY_TIME_MASK)
<store>:
BPF_STX_MEM(BPF_B, skb_reg, tmp_reg, SKB_MONO_DELIVERY_TIME_OFFSET)
BPF_STX_MEM(BPF_DW, skb_reg, value_reg, offsetof(struct sk_buff, tstamp))
(There's a small hack with the BPF_JGE for tmp_reg, so constant blinding for AX doesn't
get into our way.)
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 3);
+ /* Writing __sk_buff->tstamp at ingress as the (rcv) timestamp.
+ * Clear the skb->mono_delivery_time.
+ */
+ *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
+ SKB_MONO_DELIVERY_TIME_OFFSET);
+ *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
+ ~SKB_MONO_DELIVERY_TIME_MASK);
+ *insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg,
+ SKB_MONO_DELIVERY_TIME_OFFSET);
+#endif
+
+ /* skb->tstamp = tstamp */
+ *insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg,
+ offsetof(struct sk_buff, tstamp));
+ return insn;
+}
+
static u32 bpf_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
@@ -9167,17 +9226,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
BUILD_BUG_ON(sizeof_field(struct sk_buff, tstamp) != 8);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_DW,
- si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff,
- tstamp, 8,
- target_size));
+ insn = bpf_convert_tstamp_write(si, insn);
else
- *insn++ = BPF_LDX_MEM(BPF_DW,
- si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff,
- tstamp, 8,
- target_size));
+ insn = bpf_convert_tstamp_read(si, insn);
break;
case offsetof(struct __sk_buff, gso_segs):
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;
