First of all, I'm very happy to see people start working on this!
Thanks you Brenden!
On Fri, 1 Apr 2016 18:21:57 -0700
Brenden Blanco <bbla...@plumgrid.com> wrote:
> Add support for the BPF_PROG_TYPE_PHYS_DEV hook in mlx4 driver. Since
> bpf programs require a skb context to navigate the packet, build a
> percpu fake skb with the minimal fields. This avoids the costly
> allocation for packets that end up being dropped.
>
> Since mlx4 is so far the only user of this pseudo skb, the build
> function is defined locally.
>
> Signed-off-by: Brenden Blanco <bbla...@plumgrid.com>
> ---
[...]
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 86bcfe5..03fe005 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
[...]
> @@ -764,6 +765,8 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct
> mlx4_en_cq *cq, int bud
> if (budget <= 0)
> return polled;
>
> + prog = READ_ONCE(priv->prog);
> +
> /* We assume a 1:1 mapping between CQEs and Rx descriptors, so Rx
> * descriptor offset can be deduced from the CQE index instead of
> * reading 'cqe->index' */
> @@ -840,6 +843,21 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct
> mlx4_en_cq *cq, int bud
> l2_tunnel = (dev->hw_enc_features & NETIF_F_RXCSUM) &&
> (cqe->vlan_my_qpn & cpu_to_be32(MLX4_CQE_L2_TUNNEL));
>
> + /* A bpf program gets first chance to drop the packet. It may
> + * read bytes but not past the end of the frag. A non-zero
> + * return indicates packet should be dropped.
> + */
> + if (prog) {
> + struct ethhdr *ethh;
> +
I think you need to DMA sync RX-page before you can safely access
packet data in page (on all arch's).
> + ethh = (struct ethhdr *)(page_address(frags[0].page) +
> + frags[0].page_offset);
> + if (mlx4_call_bpf(prog, ethh, length)) {
AFAIK length here covers all the frags[n].page, thus potentially
causing the BPF program to access memory out of bound (crash).
Having several page fragments is AFAIK an optimization for jumbo-frames
on PowerPC (which is a bit annoying for you use-case ;-)).
> + priv->stats.rx_dropped++;
> + goto next;
> + }
> + }
> +
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
