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Date: Fri, 26 Apr 2024 11:46:35 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
CC: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni
<pabeni@...hat.com>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Andrew Halaney <ahalaney@...hat.com>,
"Willem
de Bruijn" <willemdebruijn.kernel@...il.com>,
Martin KaFai Lau
<martin.lau@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, bpf
<bpf@...r.kernel.org>,
<kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support
clockid_t timestamp type
On 4/25/2024 9:37 PM, Martin KaFai Lau wrote:
> On 4/24/24 3:20 PM, Abhishek Chauhan wrote:
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index e464d0ebc9c1..3ad0de07d261 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -711,6 +711,8 @@ typedef unsigned char *sk_buff_data_t;
>> enum skb_tstamp_type {
>> SKB_CLOCK_REALTIME,
>> SKB_CLOCK_MONOTONIC,
>> + SKB_CLOCK_TAI,
>> + __SKB_CLOCK_MAX = SKB_CLOCK_TAI,
>> };
>> /**
>> @@ -831,8 +833,8 @@ enum skb_tstamp_type {
>> * @decrypted: Decrypted SKB
>> * @slow_gro: state present at GRO time, slower prepare step required
>> * @tstamp_type: When set, skb->tstamp has the
>> - * delivery_time in mono clock base Otherwise, the
>> - * timestamp is considered real clock base.
>> + * delivery_time in mono clock base or clock base of skb->tstamp.
>> + * Otherwise, the timestamp is considered real clock base
>> * @napi_id: id of the NAPI struct this skb came from
>> * @sender_cpu: (aka @napi_id) source CPU in XPS
>> * @alloc_cpu: CPU which did the skb allocation.
>> @@ -960,7 +962,7 @@ struct sk_buff {
>> /* private: */
>> __u8 __mono_tc_offset[0];
>> /* public: */
>> - __u8 tstamp_type:1; /* See skb_tstamp_type */
>> + __u8 tstamp_type:2; /* See skb_tstamp_type */
>> #ifdef CONFIG_NET_XGRESS
>> __u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
>> __u8 tc_skip_classify:1;
>> @@ -1090,15 +1092,17 @@ struct sk_buff {
>> #endif
>> #define PKT_TYPE_OFFSET offsetof(struct sk_buff, __pkt_type_offset)
>> -/* if you move tc_at_ingress or mono_delivery_time
>> +/* if you move tc_at_ingress or tstamp_type:2
>> * around, you also must adapt these constants.
>> */
>> #ifdef __BIG_ENDIAN_BITFIELD
>> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 7)
>> -#define TC_AT_INGRESS_MASK (1 << 6)
>> +#define SKB_TSTAMP_TYPE_MASK (3 << 6)
>> +#define SKB_TSTAMP_TYPE_RSH (6)
>> +#define TC_AT_INGRESS_RSH (5)
>
> TC_AT_INGRESS_RSH is not used.
>
Noted. I will remove it.
>> +#define TC_AT_INGRESS_MASK (1 << 5)
>> #else
>> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 0)
>> -#define TC_AT_INGRESS_MASK (1 << 1)
>> +#define SKB_TSTAMP_TYPE_MASK (3)
>> +#define TC_AT_INGRESS_MASK (1 << 2)
>> #endif
>> #define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset)
>> @@ -4204,6 +4208,12 @@ static inline void skb_set_tstamp_type_frm_clkid(struct sk_buff *skb,
>> case CLOCK_MONOTONIC:
>> skb->tstamp_type = SKB_CLOCK_MONOTONIC;
>> break;
>> + case CLOCK_TAI:
>> + skb->tstamp_type = SKB_CLOCK_TAI;
>> + break;
>> + default:
>> + WARN_ONCE(true, "clockid %d not supported", clockid);
>> + skb->tstamp_type = SKB_CLOCK_REALTIME;
>> }
>> }
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index cee0a7915c08..1376ed5ece10 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>
> The bpf.h needs to be sync to tools/include/uapi/linux/bpf.h.
Oh i see. There is a bpf.h in tools as well . I was not aware of this part. I will further check this.
> Otherwise, the bpf CI cannot compile the tests:
>
> https://patchwork.kernel.org/project/netdevbpf/patch/20240424222028.1080134-2-quic_abchauha@quicinc.com/
>
> Please monitor the bpf CI test result after submitting the patches.
>
>> @@ -6209,6 +6209,7 @@ union { \
>> enum {
>> BPF_SKB_TSTAMP_UNSPEC,
>> BPF_SKB_TSTAMP_DELIVERY_MONO, /* tstamp has mono delivery time */
>> + BPF_SKB_TSTAMP_DELIVERY_TAI, /* tstamp has tai delivery time */
>> /* For any BPF_SKB_TSTAMP_* that the bpf prog cannot handle,
>> * the bpf prog should handle it like BPF_SKB_TSTAMP_UNSPEC
>> * and try to deduce it by ingress, egress or skb->sk->sk_clockid.
>
> SKB_CLOCK_TAI is properly defined as an enum now and there is a
> WARN for clock other than REAL, MONO, and TAI. I think it is
> time to remove UNSPEC and give it back the proper name REALTIME.
>
> I want to take this chance to do some renaming:
>
> /* The enum used in skb->tstamp_type. It specifies the clock type
> * of the time stored in the skb->tstamp.
> */
> enum {
> BPF_SKB_TSTAMP_UNSPEC = 0, /* DEPRECATED */
> BPF_SKB_TSTAMP_DELIVERY_MONO = 1, /* DEPRECATED */
> BPF_SKB_CLOCK_REALTIME = 0, /* Realtime clock */
> BPF_SKB_CLOCK_MONOTONIC = 1, /* Monotonic clock */
> BPF_SKB_CLOCK_TAI = 2, /* TAI clock */
> /* For any future BPF_SKB_CLOCK_* that the bpf prog cannot handle,
> * the bpf prog can try to deduce it by ingress/egress/skb->sk->sk_clockid.
> */
> };
>
Okay let me evalute this and get back
>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 957c2fc724eb..c67622f4fe98 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -7733,6 +7733,12 @@ BPF_CALL_3(bpf_skb_set_tstamp, struct sk_buff *, skb,
>> skb->tstamp = tstamp;
>> skb->tstamp_type = SKB_CLOCK_MONOTONIC;
>> break;
>> + case BPF_SKB_TSTAMP_DELIVERY_TAI:
>> + if (!tstamp)
>> + return -EINVAL;
>> + skb->tstamp = tstamp;
>> + skb->tstamp_type = SKB_CLOCK_TAI;
>> + break;
>> case BPF_SKB_TSTAMP_UNSPEC:
>> if (tstamp)
>
> Allow to store any realtime tstamp here since BPF_SKB_TSTAMP_UNSPEC
> becomes BPF_SKB_CLOCK_REALTIME.
>
> Like:
>
> BPF_CALL_3(bpf_skb_set_tstamp, struct sk_buff *, skb,
> u64, tstamp, u32, tstamp_type)
> {
> /* ... */
> case BPF_SKB_CLOCK_TAI:
> if (!tstamp)
> return -EINVAL;
> skb->tstamp = tstamp;
> skb->tstamp_type = SKB_CLOCK_TAI;
> break;
> case BPF_SKB_CLOCK_REALTIME:
> skb->tstamp = tstamp;
> skb->tstamp_type = SKB_CLOCK_REALTIME;
> break;
>
> /* ... */
> }
Noted!
>
>> return -EINVAL;
>
>> @@ -9388,17 +9394,17 @@ static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
>> {
>> __u8 value_reg = si->dst_reg;
>> __u8 skb_reg = si->src_reg;
>> - /* AX is needed because src_reg and dst_reg could be the same */
>> - __u8 tmp_reg = BPF_REG_AX;
>> -
>> - *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
>> - SKB_BF_MONO_TC_OFFSET);
>> - *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
>> - SKB_MONO_DELIVERY_TIME_MASK, 2);
>> - *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_UNSPEC);
>> - *insn++ = BPF_JMP_A(1);
>> - *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_DELIVERY_MONO);
>> -
>> + BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
>
> Add these also:
>
Noted!
> BUILD_BUG_ON(SKB_CLOCK_REALTIME != BPF_SKB_CLOCK_REALTIME);
> BUILD_BUG_ON(SKB_CLOCK_MONOTONIC != BPF_SKB_CLOCK_MONOTONIC);
> BUILD_BUG_ON(SKB_CLOCK_TAI != BPF_SKB_CLOCK_TAI);
>
>> + *insn++ = BPF_LDX_MEM(BPF_B, value_reg, skb_reg, SKB_BF_MONO_TC_OFFSET);
>> + *insn++ = BPF_ALU32_IMM(BPF_AND, value_reg, SKB_TSTAMP_TYPE_MASK);
>> +#ifdef __BIG_ENDIAN_BITFIELD
>> + *insn++ = BPF_ALU32_IMM(BPF_RSH, value_reg, SKB_TSTAMP_TYPE_RSH);
>> +#else
>> + BUILD_BUG_ON(!(SKB_TSTAMP_TYPE_MASK & 0x1));
>> +#endif
>> + *insn++ = BPF_JMP32_IMM(BPF_JNE, value_reg, SKB_TSTAMP_TYPE_MASK, 1);
>> + /* Both the bits set then mark it BPF_SKB_TSTAMP_UNSPEC */
>> + *insn++ = BPF_MOV64_IMM(value_reg, BPF_SKB_TSTAMP_UNSPEC);
>
> The kernel should not have both bits set in skb->tstamp_type. No need to
> add two extra bpf insns to check this. If there is a bug in the kernel,
> it is better to be uncovered instead of hiding it under BPF_SKB_TSTAMP_UNSPEC (which
> is renamed to BPF_SKB_CLOCK_REALTIME anyway).
> Hence, the last two bpf insns should be removed.
>
Got it !.
>> return insn;
>> }
>> @@ -9430,6 +9436,7 @@ static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
>> __u8 value_reg = si->dst_reg;
>> __u8 skb_reg = si->src_reg;
>> +BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
>
> It is a dup of the one in bpf_convert_tstamp_type_read and can be removed.
>
Noted!
>> #ifdef CONFIG_NET_XGRESS
>> /* If the tstamp_type is read,
>> * the bpf prog is aware the tstamp could have delivery time.
>> @@ -9440,11 +9447,12 @@ static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
>> __u8 tmp_reg = BPF_REG_AX;
>> *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, SKB_BF_MONO_TC_OFFSET);
>> - *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
>> - TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK);
>> - *insn++ = BPF_JMP32_IMM(BPF_JNE, tmp_reg,
>> - TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 2);
>> - /* skb->tc_at_ingress && skb->tstamp_type:1,
>> + /* check if ingress mask bits is set */
>> + *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1);
>> + *insn++ = BPF_JMP_A(4);
>> + *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, SKB_TSTAMP_TYPE_MASK, 1);
>> + *insn++ = BPF_JMP_A(2);
>> + /* skb->tc_at_ingress && skb->tstamp_type:2,
>> * read 0 as the (rcv) timestamp.
>> */
>> *insn++ = BPF_MOV64_IMM(value_reg, 0);
>> @@ -9469,7 +9477,7 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
>> * the bpf prog is aware the tstamp could have delivery time.
>> * Thus, write skb->tstamp as is if tstamp_type_access is true.
>> * Otherwise, writing at ingress will have to clear the
>> - * mono_delivery_time (skb->tstamp_type:1)bit also.
>> + * mono_delivery_time (skb->tstamp_type:2)bit also.
>> */
>> if (!prog->tstamp_type_access) {
>> __u8 tmp_reg = BPF_REG_AX;
>> @@ -9479,8 +9487,8 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
>> *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1);
>> /* goto <store> */
>> *insn++ = BPF_JMP_A(2);
>> - /* <clear>: mono_delivery_time or (skb->tstamp_type:1) */
>> - *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, ~SKB_MONO_DELIVERY_TIME_MASK);
>> + /* <clear>: skb->tstamp_type:2 */
>> + *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, ~SKB_TSTAMP_TYPE_MASK);
>> *insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg, SKB_BF_MONO_TC_OFFSET);
>> }
>> #endif
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index 591226dcde26..f195b31d6e75 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -1457,7 +1457,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>> skb->priority = (cork->tos != -1) ? cork->priority: READ_ONCE(sk->sk_priority);
>> skb->mark = cork->mark;
>> - skb->tstamp = cork->transmit_time;
>> + skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
>
> hmm... I think this will break for tcp. This sequence in particular:
>
> tcp_v4_timewait_ack()
> tcp_v4_send_ack()
> ip_send_unicast_reply()
> ip_push_pending_frames()
> ip_finish_skb()
> __ip_make_skb()
> /* sk_clockid is REAL but cork->transmit_time should be in mono */
> skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);;
>
> I think I hit it from time to time when running the test in this patch set.
>
do you think i need to check for protocol type here . since tcp uses Mono and the rest according to the new design is based on
sk->sk_clockid
if (iph->protocol == IPPROTO_TCP)
skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, CLOCK_MONOTONIC);
else
skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
> [ ... ]
>
>> diff --git a/tools/testing/selftests/bpf/progs/test_tc_dtime.c b/tools/testing/selftests/bpf/progs/test_tc_dtime.c
>> index 74ec09f040b7..19dba6d88265 100644
>> --- a/tools/testing/selftests/bpf/progs/test_tc_dtime.c
>> +++ b/tools/testing/selftests/bpf/progs/test_tc_dtime.c
>
> Please separate the selftests/bpf changes into another patch.
>
I will do that.
>> @@ -227,6 +227,12 @@ int egress_host(struct __sk_buff *skb)
>> inc_dtimes(EGRESS_ENDHOST);
>> else
>> inc_errs(EGRESS_ENDHOST);
>> + } else if (skb_proto(skb_type) == IPPROTO_UDP) {
>> + if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI &&
>> + skb->tstamp)
>> + inc_dtimes(EGRESS_ENDHOST);
>> + else
>> + inc_errs(EGRESS_ENDHOST);
>> } else {
>> if (skb->tstamp_type == BPF_SKB_TSTAMP_UNSPEC &&
>> skb->tstamp)
>> @@ -255,6 +261,9 @@ int ingress_host(struct __sk_buff *skb)
>> if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO &&
>> skb->tstamp == EGRESS_FWDNS_MAGIC)
>> inc_dtimes(INGRESS_ENDHOST);
>> + else if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI &&
>> + skb->tstamp == EGRESS_FWDNS_MAGIC)
>> + inc_dtimes(INGRESS_ENDHOST);
>> else
>> inc_errs(INGRESS_ENDHOST);
>> @@ -323,12 +332,14 @@ int ingress_fwdns_prio101(struct __sk_buff *skb)
>> /* Should have handled in prio100 */
>> return TC_ACT_SHOT;
>> - if (skb_proto(skb_type) == IPPROTO_UDP)
>> + if (skb_proto(skb_type) == IPPROTO_UDP &&
>> + skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_TAI)
>> expected_dtime = 0;
>
> The IPPROTO_UDP check and expected_dtime can be removed. The UDP test
> can expect the same EGRESS_ENDHOST_MAGIC in the skb->tstamp since
> the TAI tstamp is also forwarded from egress to ingress now.
>
>> if (skb->tstamp_type) {
>> if (fwdns_clear_dtime() ||
>> - skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_MONO ||
>> + (skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_MONO &&
>> + skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_TAI) ||
>> skb->tstamp != expected_dtime)
>> inc_errs(INGRESS_FWDNS_P101);
>> else
>> @@ -338,7 +349,8 @@ int ingress_fwdns_prio101(struct __sk_buff *skb)
>> inc_errs(INGRESS_FWDNS_P101);
>> }
>> - if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO) {
>> + if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO ||
>> + skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI) {
>
> No need to check BPF_SKB_TSTAMP_DELIVERY_TAI such that the
> bpf_skb_set_tstamp() helper can still be tested.
>
> There are some other minor changes needed for the test_tc_dtime.c and
> the tc_redirect.c. I quickly made the changes and put them here (first patch):
>
> https://git.kernel.org/pub/scm/linux/kernel/git/martin.lau/bpf-next.git/log/?h=skb.tstamp_type
>
Thanks for your help Martin. I will check the changes you have made in BPF test framework and see what i have missed.
>
>
>> skb->tstamp = INGRESS_FWDNS_MAGIC;
>> } else {
>> if (bpf_skb_set_tstamp(skb, INGRESS_FWDNS_MAGIC,
>> @@ -370,7 +382,8 @@ int egress_fwdns_prio101(struct __sk_buff *skb)
>> if (skb->tstamp_type) {
>> if (fwdns_clear_dtime() ||
>> - skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_MONO ||
>> + (skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_MONO &&
>> + skb->tstamp_type != BPF_SKB_TSTAMP_DELIVERY_TAI) ||
>> skb->tstamp != INGRESS_FWDNS_MAGIC)
>> inc_errs(EGRESS_FWDNS_P101);
>> else
>> @@ -380,7 +393,8 @@ int egress_fwdns_prio101(struct __sk_buff *skb)
>> inc_errs(EGRESS_FWDNS_P101);
>> }
>> - if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO) {
>> + if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO ||
>> + skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI) {
>> skb->tstamp = EGRESS_FWDNS_MAGIC;
>> } else {
>> if (bpf_skb_set_tstamp(skb, EGRESS_FWDNS_MAGIC,
>
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