Commit 74e31ca8 authored Feb 19, 2019 by Jesper Dangaard Brouer Committed by Daniel Borkmann Feb 19, 2019

bpf: add skb->queue_mapping write access from tc clsact



The skb->queue_mapping already have read access, via __sk_buff->queue_mapping.

This patch allow BPF tc qdisc clsact write access to the queue_mapping via
tc_cls_act_is_valid_access.  Also handle that the value NO_QUEUE_MAPPING
is not allowed.

It is already possible to change this via TC filter action skbedit
tc-skbedit(8).  Due to the lack of TC examples, lets show one:

  # tc qdisc  add  dev ixgbe1 clsact
  # tc filter add  dev ixgbe1 ingress matchall action skbedit queue_mapping 5
  # tc filter list dev ixgbe1 ingress

The most common mistake is that XPS (Transmit Packet Steering) takes
precedence over setting skb->queue_mapping. XPS is configured per DEVICE
via /sys/class/net/DEVICE/queues/tx-*/xps_cpus via a CPU hex mask. To
disable set mask=00.

The purpose of changing skb->queue_mapping is to influence the selection of
the net_device "txq" (struct netdev_queue), which influence selection of
the qdisc "root_lock" (via txq->qdisc->q.lock) and txq->_xmit_lock. When
using the MQ qdisc the txq->qdisc points to different qdiscs and associated
locks, and HARD_TX_LOCK (txq->_xmit_lock), allowing for CPU scalability.

Due to lack of TC examples, lets show howto attach clsact BPF programs:

 # tc qdisc  add  dev ixgbe2 clsact
 # tc filter add  dev ixgbe2 egress bpf da obj XXX_kern.o sec tc_qmap2cpu
 # tc filter list dev ixgbe2 egress

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent 568f1967

net/core/filter.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -6279,6 +6279,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
		case bpf_ctx_range(struct __sk_buff, tc_classid):
		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):
		break;
		default:
		return false;
		@@ -6683,9 +6684,18 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
		break;

		case offsetof(struct __sk_buff, queue_mapping):
		if (type == BPF_WRITE) {
		*insn++ = BPF_JMP_IMM(BPF_JGE, si->src_reg, NO_QUEUE_MAPPING, 1);
		*insn++ = BPF_STX_MEM(BPF_H, si->dst_reg, si->src_reg,
		bpf_target_off(struct sk_buff,
		queue_mapping,
		2, target_size));
		} else {
		*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
		bpf_target_off(struct sk_buff, queue_mapping, 2,
		target_size));
		bpf_target_off(struct sk_buff,
		queue_mapping,
		2, target_size));
		}
		break;

		case offsetof(struct __sk_buff, vlan_present):

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