Re: [RFC PATCH bpf-next v4 2/2] net: Add additional bit to support clockid_t timestamp type
From: Martin KaFai Lau
Date: Mon Apr 22 2024 - 14:49:47 EST
On 4/19/24 6:13 PM, Abhishek Chauhan (ABC) wrote:
On 4/18/2024 5:30 PM, Abhishek Chauhan (ABC) wrote:
On 4/18/2024 2:57 PM, Martin KaFai Lau wrote:
On 4/18/24 1:10 PM, Abhishek Chauhan (ABC) wrote:
#ifdef CONFIG_NET_XGRESS
__u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
__u8 tc_skip_classify:1;
@@ -1096,10 +1100,12 @@ struct sk_buff {
*/
#ifdef __BIG_ENDIAN_BITFIELD
#define SKB_MONO_DELIVERY_TIME_MASK (1 << 7)
-#define TC_AT_INGRESS_MASK (1 << 6)
+#define SKB_TAI_DELIVERY_TIME_MASK (1 << 6)
SKB_TSTAMP_TYPE_BIT2_MASK?
nit. Shorten it to just SKB_TSTAMP_TYPE_MASK?
Okay i will do the same. Noted!
#ifdef __BIG_ENDIAN_BITFIELD
#define SKB_TSTAMP_TYPE_MASK (3 << 6)
#define SKB_TSTAMP_TYPE_RSH (6) /* more on this later */
#else
#define SKB_TSTAMP_TYPE_MASK (3)
#endif
I was thinking to keep it as TAI because it will confuse developers. I hope thats okay.
I think it is not very useful to distinguish each bit since it is an enum value now. It becomes more like the "pkt_type:3" and its PKT_TYPE_MAX.
I see what you are saying.
+#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_TAI_DELIVERY_TIME_MASK (1 << 1)
+#define TC_AT_INGRESS_MASK (1 << 2)
#endif
#define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset)
@@ -4206,6 +4212,11 @@ static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
case CLOCK_MONOTONIC:
skb->tstamp_type = SKB_CLOCK_MONO;
break;
+ case CLOCK_TAI:
+ skb->tstamp_type = SKB_CLOCK_TAI;
+ break;
+ default:
+ WARN_ONCE(true, "clockid %d not supported", tstamp_type);
and set to 0 and default tstamp_type?
Actually thinking about it. I feel if its unsupported just fall back to default is the correct thing. I will take care of this.
}
}
>
@@ -9372,10 +9378,16 @@ static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
*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);
+ SKB_MONO_DELIVERY_TIME_MASK | SKB_TAI_DELIVERY_TIME_MASK, 2);
+ *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
+ SKB_MONO_DELIVERY_TIME_MASK, 3);
+ *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
+ SKB_TAI_DELIVERY_TIME_MASK, 4);
*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);
+ *insn++ = BPF_JMP_A(1);
+ *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_DELIVERY_TAI);
With SKB_TSTAMP_TYPE_MASK defined like above, this could be simplified like this (untested):
Let me think this through and raise it as part of the next rfc patch.
static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->dst_reg;
__u8 skb_reg = si->src_reg;
BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_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
return insn;
}
return insn;
}
@@ -9418,10 +9430,26 @@ 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);
+ /*check if all three bits are set*/
*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);
+ TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK |
+ SKB_TAI_DELIVERY_TIME_MASK);
+ /*if all 3 bits are set jump 3 instructions and clear the register */
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
+ TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK |
+ SKB_TAI_DELIVERY_TIME_MASK, 4);
+ /*Now check Mono is set with ingress mask if so clear */
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
+ TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 3);
+ /*Now Check tai is set with ingress mask if so clear */
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
+ TC_AT_INGRESS_MASK | SKB_TAI_DELIVERY_TIME_MASK, 2);
+ /*Now Check tai and mono are set if so clear */
+ *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
+ SKB_MONO_DELIVERY_TIME_MASK |
+ SKB_TAI_DELIVERY_TIME_MASK, 1);
Same as the bpf_convert_tstamp_type_read, this could be simplified with SKB_TSTAMP_TYPE_MASK.
Willem and Martin,
When do we clear the tstamp and make it 0 in bpf_convert_tstamp_read? meaning which configuration?
When the bpf prog does not check the skb->tstamp_type. It is
the "if (!prog->tstamp_type_access)" in bpf_convert_tstamp_read().
If bpf prog does not check the skb->tstamp_type and it is at ingress,
bpf prog expects recv tstamp (ie. real clock), so it needs to clear
out the tstamp (i.e read as 0 tstamp).
I see previously(current upstream code) if mono_delivery is set and tc_ingress_mask is set
upstream code used to set the tstamp as 0.
Which means with addition of tai mask the new implementation should take care of following cases(correct me if i am wrong)
1. ( tai mask set + ingress mask set ) = Clear tstamp
2. ( mono mask set + ingress mask set ) = Clear tstamp
3. ( mono mask set + tai mask set + ingress mask set ) = Clear tstamp
4. ( No mask set ) = Clear tstamp
5. ( Tai mask set + mono mask set ) = Clear tstamp
No need to check the individual mono and tai bit here. Check the
tstamp_type as a whole. Like in pseudo C:
if (skb->tc_at_ingress && skb->tstamp_type)
value_reg = 0;
untested code for tstamp_read() and tstamp_write():
static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->dst_reg;
__u8 skb_reg = si->src_reg;
#ifdef CONFIG_NET_XGRESS
/* If the tstamp_type is read,
* the bpf prog is aware the tstamp could have delivery time.
* Thus, read skb->tstamp as is if tstamp_type_access is true.
*/
if (!prog->tstamp_type_access) {
/* 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, TC_AT_INGRESS_MASK, 1);
/* goto <read> */
BPF_JMP_A(4);
*insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, SKB_TSTAMP_TYPE_MASK, 1);
/* goto <read> */
BPF_JMP_A(2);
/* skb->tc_at_ingress && skb->tstamp_type,
* read 0 as the (rcv) timestamp.
*/
*insn++ = BPF_MOV64_IMM(value_reg, 0);
*insn++ = BPF_JMP_A(1);
}
#endif
/* <read>: value_reg = skb->tstamp */
*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_prog *prog,
const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->src_reg;
__u8 skb_reg = si->dst_reg;
#ifdef CONFIG_NET_XGRESS
/* If the tstamp_type is read,
* 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.
*/
if (!prog->tstamp_type_access) {
__u8 tmp_reg = BPF_REG_AX;
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, SKB_BF_MONO_TC_OFFSET);
/* Writing __sk_buff->tstamp as ingress, goto <clear> */
*insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg, TC_AT_INGRESS_MASK, 1);
/* goto <store> */
*insn++ = BPF_JMP_A(2);
/* <clear>: skb->tstamp_type */
*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
/* <store>: skb->tstamp = tstamp */
*insn++ = BPF_RAW_INSN(BPF_CLASS(si->code) | BPF_DW | BPF_MEM,
skb_reg, value_reg, offsetof(struct sk_buff, tstamp), si->imm);
return insn;
}
This leaves us with only two values which can be support which is 0x1 and 0x2
This means the tstamp_type should be either 0x1(mono) and tstamp_type 0x2 (tai) to set the value_reg with tstamp
Is my understanding correct ?
Do you think the below simplified version looks okay ?
static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->dst_reg;
__u8 skb_reg = si->src_reg;
BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
#ifdef CONFIG_NET_XGRESS
/* If the tstamp_type is read,
* the bpf prog is aware the tstamp could have delivery time.
* Thus, read skb->tstamp as is if tstamp_type_access is true.
*/
if (!prog->tstamp_type_access) {
/* 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);
/* check if all three bits are set*/
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
TC_AT_INGRESS_MASK | SKB_TSTAMP_TYPE_MASK);
/* If the value of tmp_reg is 7,6,5,4,3,0 which means invalid
* configuration set the tstamp to 0, value 0x1 and 0x2
* is correct configuration
*/
#ifdef __BIG_ENDIAN_BITFIELD
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0x1 << SKB_TSTAMP_TYPE_RSH, 3);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0x2 << SKB_TSTAMP_TYPE_RSH, 2);
#endif
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0x1, 3);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0x2, 2);
#endif
/* skb->tc_at_ingress && skb->tstamp_type:2,
* 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;
}