nfp: bpf: relax prog rejection through max_pkt_offset

NFP is refusing to offload programs whenever the MTU is set to a value
larger than the max packet bytes that fits in NFP Cluster Target Memory
(CTM). However, a eBPF program doesn't always need to access the whole
packet data.

Verifier has always calculated maximum direct packet access (DPA) offset,
and kept it in max_pkt_offset inside prog auxiliar information. This patch
relax prog rejection based on max_pkt_offset.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/netronome/nfp/bpf/offload.c

@@ -489,14 +489,15 @@ nfp_net_bpf_load(struct nfp_net *nn, struct bpf_prog *prog,
 		 struct netlink_ext_ack *extack)
 {
 	struct nfp_prog *nfp_prog = prog->aux->offload->dev_priv;
-	unsigned int max_mtu, max_stack, max_prog_len;
+	unsigned int fw_mtu, pkt_off, max_stack, max_prog_len;
 	dma_addr_t dma_addr;
 	void *img;
 	int err;
 
-	max_mtu = nn_readb(nn, NFP_NET_CFG_BPF_INL_MTU) * 64 - 32;
-	if (max_mtu < nn->dp.netdev->mtu) {
-		NL_SET_ERR_MSG_MOD(extack, "BPF offload not supported with MTU larger than HW packet split boundary");
+	fw_mtu = nn_readb(nn, NFP_NET_CFG_BPF_INL_MTU) * 64 - 32;
+	pkt_off = min(prog->aux->max_pkt_offset, nn->dp.netdev->mtu);
+	if (fw_mtu < pkt_off) {
+		NL_SET_ERR_MSG_MOD(extack, "BPF offload not supported with potential packet access beyond HW packet split boundary");
 		return -EOPNOTSUPP;
 	}