For now, we have to call some helpers when we need to update the csum,
such as bpf_l4_csum_replace, bpf_l3_csum_replace, etc. These helpers are
not inlined, which causes poor performance.
In fact, we can define our own csum update functions in BPF program
instead of bpf_l3_csum_replace, which is totally inlined and efficient.
However, we can't do this for bpf_l4_csum_replace for now, as we can't
update skb->csum, which can make skb->csum invalid in the rx path with
CHECKSUM_COMPLETE mode.
What's more, we can't use the direct data access and have to use
skb_store_bytes() with the BPF_F_RECOMPUTE_CSUM flag in some case, such
as modifing the vni in the vxlan header and the underlay udp header has
no checksum.
With the read/write accessing to skb->csum and read accessing to
skb->ip_summed, now we can define the inlined csum update functions in
libbpf, which are much more efficient.
Signed-off-by: Menglong Dong <menglong8.dong@xxxxxxxxx>
---
include/linux/skbuff.h | 2 ++
include/uapi/linux/bpf.h | 2 ++
net/core/filter.c | 22 ++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 2 ++
4 files changed, 28 insertions(+)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ea5c8ab3ed00..a0ec404c7009 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1077,8 +1077,10 @@ struct sk_buff {
/* if you move pkt_type around you also must adapt those constants */
#ifdef __BIG_ENDIAN_BITFIELD
#define PKT_TYPE_MAX (7 << 5)
+#define IP_SUMMED_RSH 1
#else
#define PKT_TYPE_MAX 7
+#define IP_SUMMED_RSH 5
#endif
#define PKT_TYPE_OFFSET offsetof(struct sk_buff, __pkt_type_offset)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 754e68ca8744..b450e27f5a8d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6148,6 +6148,8 @@ struct __sk_buff {
__u8 tstamp_type;
__u32 :24; /* Padding, future use. */
__u64 hwtstamp;
+ __u32 csum;
+ __u32 ip_summed;
};
struct bpf_tunnel_key {
diff --git a/net/core/filter.c b/net/core/filter.c
index 24061f29c9dd..23c22d88da1b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8858,6 +8858,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
case bpf_ctx_range_till(struct __sk_buff, cb[0], cb[4]):
case bpf_ctx_range(struct __sk_buff, tstamp):
case bpf_ctx_range(struct __sk_buff, queue_mapping):
+ case bpf_ctx_range(struct __sk_buff, csum):
break;
default:
return false;
@@ -8885,6 +8886,8 @@ static bool tc_cls_act_is_valid_access(int off, int size,
*/
((struct bpf_prog *)prog)->tstamp_type_access = 1;
return size == sizeof(__u8);
+ case bpf_ctx_range_till(struct __sk_buff, csum, ip_summed):
+ return size == sizeof(__u32);
}
return bpf_skb_is_valid_access(off, size, type, prog, info);
@@ -9513,6 +9516,25 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
#endif
break;
+ case offsetof(struct __sk_buff, ip_summed):
+ *target_size = 1;
+ *insn++ = BPF_LDX_MEM(BPF_B, si->dst_reg, si->src_reg,
+ PKT_TYPE_OFFSET);
+ *insn++ = BPF_ALU32_IMM(BPF_RSH, si->dst_reg, IP_SUMMED_RSH);
+ *insn++ = BPF_ALU32_IMM(BPF_AND, si->dst_reg, 3);
+ break;
+
+ case offsetof(struct __sk_buff, csum):
+ if (type == BPF_WRITE)
+ *insn++ = BPF_EMIT_STORE(BPF_W, si,
+ bpf_target_off(struct sk_buff, csum, 4,
+ target_size));
+ else
+ *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
+ bpf_target_off(struct sk_buff, csum, 4,
+ target_size));
+ break;
+
case offsetof(struct __sk_buff, queue_mapping):
if (type == BPF_WRITE) {
u32 off = bpf_target_off(struct sk_buff, queue_mapping, 2, target_size);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7f24d898efbb..31fd5ee40864 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6148,6 +6148,8 @@ struct __sk_buff {
__u8 tstamp_type;
__u32 :24; /* Padding, future use. */
__u64 hwtstamp;
+ __u32 csum;
+ __u32 ip_summed;
};
struct bpf_tunnel_key {
--
2.39.2
