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Date: Sun, 9 Apr 2017 01:17:26 -0400
From: Andy Gospodarek <andy@...yhouse.net>
To: David Miller <davem@...emloft.net>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
xdp-newbies@...r.kernel.org
Subject: Re: [PATCH net-next RFC] Generic XDP
On Sat, Apr 8, 2017 at 11:07 PM, David Miller <davem@...emloft.net> wrote:
>
> This provides a generic non-optimized XDP implementation when the
> device driver does not provide an optimized one.
>
> It is arguable that perhaps I should have required something like
> this as part of the initial XDP feature merge.
>
> I believe this is critical for two reasons:
>
> 1) Accessibility. More people can play with XDP with less
> dependencies. Yes I know we have XDP support in virtio_net, but
> that just creates another depedency for learning how to use this
> facility.
>
> I wrote this to make life easier for the XDP newbies.
>
> 2) As a model for what the expected semantics are. If there is a pure
> generic core implementation, it serves as a semantic example for
> driver folks adding XDP support.
>
> This is just a rough draft and is untested.
Overall I like the idea. It does reduce the complexity and would
allow anyone to kick the tires with XDP more easily. I did some quick
inspection of the offset calculations coming back from the program and
I _think_ that looks correct. It might also be too late. :-)
I should be able to run this on Monday and see how the performance
compares to the driver/native XDP case on some bnxt_en-based hardware.
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index cc07c3b..7cfb355 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1892,6 +1892,7 @@ struct net_device {
> struct lock_class_key *qdisc_tx_busylock;
> struct lock_class_key *qdisc_running_key;
> bool proto_down;
> + struct bpf_prog *xdp_prog;
> };
> #define to_net_dev(d) container_of(d, struct net_device, dev)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7efb417..e4c7927 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -95,6 +95,7 @@
> #include <linux/notifier.h>
> #include <linux/skbuff.h>
> #include <linux/bpf.h>
> +#include <linux/bpf_trace.h>
> #include <net/net_namespace.h>
> #include <net/sock.h>
> #include <net/busy_poll.h>
> @@ -4247,6 +4248,80 @@ static int __netif_receive_skb(struct sk_buff *skb)
> return ret;
> }
>
> +static struct static_key generic_xdp_needed __read_mostly;
> +
> +static int generic_xdp_install(struct net_device *dev, struct netdev_xdp *xdp)
> +{
> + struct bpf_prog *new = xdp->prog;
> + int ret = 0;
> +
> + switch (xdp->command) {
> + case XDP_SETUP_PROG: {
> + struct bpf_prog *old;
> +
> + old = xchg(&dev->xdp_prog, new);
> + if (old)
> + bpf_prog_put(old);
> +
> + if (old && !new)
> + static_key_slow_dec(&generic_xdp_needed);
> + else if (new && !old)
> + static_key_slow_inc(&generic_xdp_needed);
> + break;
> + }
> + case XDP_QUERY_PROG:
> + xdp->prog_attached = !!dev->xdp_prog;
> + ret = 0;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> +
> + return ret;
> +}
> +
> +static u32 netif_receive_generic_xdp(struct sk_buff *skb,
> + struct bpf_prog *xdp_prog)
> +{
> + struct xdp_buff xdp;
> + u32 act = XDP_DROP;
> + void *orig_data;
> + int hlen, off;
> +
> + if (skb_linearize(skb))
> + goto do_drop;
> +
> + hlen = skb_headlen(skb);
> + xdp.data = skb->data;
> + xdp.data_end = xdp.data + hlen;
> + xdp.data_hard_start = xdp.data - skb_headroom(skb);
> + orig_data = xdp.data;
> +
> + act = bpf_prog_run_xdp(xdp_prog, &xdp);
> +
> + off = xdp.data - orig_data;
> + if (off)
> + __skb_push(skb, off);
> +
> + switch (act) {
> + case XDP_PASS:
> + case XDP_TX:
> + break;
> +
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + case XDP_ABORTED:
> + trace_xdp_exception(skb->dev, xdp_prog, act);
> + case XDP_DROP:
> + do_drop:
> + kfree_skb(skb);
> + break;
> + }
> +
> + return act;
> +}
> +
> static int netif_receive_skb_internal(struct sk_buff *skb)
> {
> int ret;
> @@ -4258,6 +4333,21 @@ static int netif_receive_skb_internal(struct sk_buff *skb)
>
> rcu_read_lock();
>
> + if (static_key_false(&generic_xdp_needed)) {
> + struct bpf_prog *xdp_prog = READ_ONCE(skb->dev->xdp_prog);
> +
> + if (xdp_prog) {
> + u32 act = netif_receive_generic_xdp(skb, xdp_prog);
> +
> + if (act != XDP_PASS) {
> + rcu_read_unlock();
> + if (act == XDP_TX)
> + dev_queue_xmit(skb);
> + return NET_RX_DROP;
> + }
> + }
> + }
> +
> #ifdef CONFIG_RPS
> if (static_key_false(&rps_needed)) {
> struct rps_dev_flow voidflow, *rflow = &voidflow;
> @@ -6718,6 +6808,7 @@ EXPORT_SYMBOL(dev_change_proto_down);
> */
> int dev_change_xdp_fd(struct net_device *dev, int fd, u32 flags)
> {
> + int (*xdp_op)(struct net_device *dev, struct netdev_xdp *xdp);
> const struct net_device_ops *ops = dev->netdev_ops;
> struct bpf_prog *prog = NULL;
> struct netdev_xdp xdp;
> @@ -6725,14 +6816,16 @@ int dev_change_xdp_fd(struct net_device *dev, int fd, u32 flags)
>
> ASSERT_RTNL();
>
> - if (!ops->ndo_xdp)
> - return -EOPNOTSUPP;
> + xdp_op = ops->ndo_xdp;
> + if (!xdp_op)
> + xdp_op = generic_xdp_install;
> +
> if (fd >= 0) {
> if (flags & XDP_FLAGS_UPDATE_IF_NOEXIST) {
> memset(&xdp, 0, sizeof(xdp));
> xdp.command = XDP_QUERY_PROG;
>
> - err = ops->ndo_xdp(dev, &xdp);
> + err = xdp_op(dev, &xdp);
> if (err < 0)
> return err;
> if (xdp.prog_attached)
> @@ -6748,7 +6841,7 @@ int dev_change_xdp_fd(struct net_device *dev, int fd, u32 flags)
> xdp.command = XDP_SETUP_PROG;
> xdp.prog = prog;
>
> - err = ops->ndo_xdp(dev, &xdp);
> + err = xdp_op(dev, &xdp);
> if (err < 0 && prog)
> bpf_prog_put(prog);
>
> @@ -7807,6 +7900,11 @@ void free_netdev(struct net_device *dev)
> free_percpu(dev->pcpu_refcnt);
> dev->pcpu_refcnt = NULL;
>
> + if (dev->xdp_prog) {
> + bpf_prog_put(dev->xdp_prog);
> + static_key_slow_dec(&generic_xdp_needed);
> + }
> +
> /* Compatibility with error handling in drivers */
> if (dev->reg_state == NETREG_UNINITIALIZED) {
> netdev_freemem(dev);
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index b2bd4c9..fe1abba 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -896,15 +896,12 @@ static size_t rtnl_port_size(const struct net_device *dev,
> return port_self_size;
> }
>
> -static size_t rtnl_xdp_size(const struct net_device *dev)
> +static size_t rtnl_xdp_size(void)
> {
> size_t xdp_size = nla_total_size(0) + /* nest IFLA_XDP */
> nla_total_size(1); /* XDP_ATTACHED */
>
> - if (!dev->netdev_ops->ndo_xdp)
> - return 0;
> - else
> - return xdp_size;
> + return xdp_size;
> }
>
> static noinline size_t if_nlmsg_size(const struct net_device *dev,
> @@ -943,7 +940,7 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
> + nla_total_size(MAX_PHYS_ITEM_ID_LEN) /* IFLA_PHYS_PORT_ID */
> + nla_total_size(MAX_PHYS_ITEM_ID_LEN) /* IFLA_PHYS_SWITCH_ID */
> + nla_total_size(IFNAMSIZ) /* IFLA_PHYS_PORT_NAME */
> - + rtnl_xdp_size(dev) /* IFLA_XDP */
> + + rtnl_xdp_size() /* IFLA_XDP */
> + nla_total_size(4) /* IFLA_EVENT */
> + nla_total_size(1); /* IFLA_PROTO_DOWN */
>
> @@ -1252,20 +1249,25 @@ static int rtnl_fill_link_ifmap(struct sk_buff *skb, struct net_device *dev)
>
> static int rtnl_xdp_fill(struct sk_buff *skb, struct net_device *dev)
> {
> - struct netdev_xdp xdp_op = {};
> struct nlattr *xdp;
> int err;
> + u8 val;
>
> - if (!dev->netdev_ops->ndo_xdp)
> - return 0;
> xdp = nla_nest_start(skb, IFLA_XDP);
> if (!xdp)
> return -EMSGSIZE;
> - xdp_op.command = XDP_QUERY_PROG;
> - err = dev->netdev_ops->ndo_xdp(dev, &xdp_op);
> - if (err)
> - goto err_cancel;
> - err = nla_put_u8(skb, IFLA_XDP_ATTACHED, xdp_op.prog_attached);
> + if (dev->netdev_ops->ndo_xdp) {
> + struct netdev_xdp xdp_op = {};
> +
> + xdp_op.command = XDP_QUERY_PROG;
> + err = dev->netdev_ops->ndo_xdp(dev, &xdp_op);
> + if (err)
> + goto err_cancel;
> + val = xdp_op.prog_attached;
> + } else {
> + val = dev->xdp_prog ? 1 : 0;
> + }
> + err = nla_put_u8(skb, IFLA_XDP_ATTACHED, val);
> if (err)
> goto err_cancel;
>
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