net: Generic XDP
This provides a generic SKB based non-optimized XDP path which is used
if either the driver lacks a specific XDP implementation, or the user
requests it via a new IFLA_XDP_FLAGS value named XDP_FLAGS_SKB_MODE.
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.
One thing I have not tried to address here is the issue of
XDP_PACKET_HEADROOM, thanks to Daniel for spotting that. It seems
incredibly expensive to do a skb_cow(skb, XDP_PACKET_HEADROOM) or
whatever even if the XDP program doesn't try to push headers at all.
I think we really need the verifier to somehow propagate whether
certain XDP helpers are used or not.
v5:
- Handle both negative and positive offset after running prog
- Fix mac length in XDP_TX case (Alexei)
- Use rcu_dereference_protected() in free_netdev (kbuild test robot)
v4:
- Fix MAC header adjustmnet before calling prog (David Ahern)
- Disable LRO when generic XDP is installed (Michael Chan)
- Bypass qdisc et al. on XDP_TX and record the event (Alexei)
- Do not perform generic XDP on reinjected packets (DaveM)
v3:
- Make sure XDP program sees packet at MAC header, push back MAC
header if we do XDP_TX. (Alexei)
- Elide GRO when generic XDP is in use. (Alexei)
- Add XDP_FLAG_SKB_MODE flag which the user can use to request generic
XDP even if the driver has an XDP implementation. (Alexei)
- Report whether SKB mode is in use in rtnl_xdp_fill() via XDP_FLAGS
attribute. (Daniel)
v2:
- Add some "fall through" comments in switch statements based
upon feedback from Andrew Lunn
- Use RCU for generic xdp_prog, thanks to Johannes Berg.
Tested-by: Andy Gospodarek <andy@greyhouse.net>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index db6e315..1b3317c 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>
@@ -4251,6 +4252,125 @@ 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 = rtnl_dereference(dev->xdp_prog);
+
+ rcu_assign_pointer(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);
+ dev_disable_lro(dev);
+ }
+ break;
+ }
+
+ case XDP_QUERY_PROG:
+ xdp->prog_attached = !!rcu_access_pointer(dev->xdp_prog);
+ 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;
+ u32 mac_len;
+
+ /* Reinjected packets coming from act_mirred or similar should
+ * not get XDP generic processing.
+ */
+ if (skb_cloned(skb))
+ return XDP_PASS;
+
+ if (skb_linearize(skb))
+ goto do_drop;
+
+ /* The XDP program wants to see the packet starting at the MAC
+ * header.
+ */
+ mac_len = skb->data - skb_mac_header(skb);
+ hlen = skb_headlen(skb) + mac_len;
+ xdp.data = skb->data - mac_len;
+ xdp.data_end = xdp.data + hlen;
+ xdp.data_hard_start = skb->data - skb_headroom(skb);
+ orig_data = xdp.data;
+
+ act = bpf_prog_run_xdp(xdp_prog, &xdp);
+
+ off = xdp.data - orig_data;
+ if (off > 0)
+ __skb_pull(skb, off);
+ else if (off < 0)
+ __skb_push(skb, -off);
+
+ switch (act) {
+ case XDP_TX:
+ __skb_push(skb, mac_len);
+ /* fall through */
+ case XDP_PASS:
+ break;
+
+ default:
+ bpf_warn_invalid_xdp_action(act);
+ /* fall through */
+ case XDP_ABORTED:
+ trace_xdp_exception(skb->dev, xdp_prog, act);
+ /* fall through */
+ case XDP_DROP:
+ do_drop:
+ kfree_skb(skb);
+ break;
+ }
+
+ return act;
+}
+
+/* When doing generic XDP we have to bypass the qdisc layer and the
+ * network taps in order to match in-driver-XDP behavior.
+ */
+static void generic_xdp_tx(struct sk_buff *skb, struct bpf_prog *xdp_prog)
+{
+ struct net_device *dev = skb->dev;
+ struct netdev_queue *txq;
+ bool free_skb = true;
+ int cpu, rc;
+
+ txq = netdev_pick_tx(dev, skb, NULL);
+ cpu = smp_processor_id();
+ HARD_TX_LOCK(dev, txq, cpu);
+ if (!netif_xmit_stopped(txq)) {
+ rc = netdev_start_xmit(skb, dev, txq, 0);
+ if (dev_xmit_complete(rc))
+ free_skb = false;
+ }
+ HARD_TX_UNLOCK(dev, txq);
+ if (free_skb) {
+ trace_xdp_exception(dev, xdp_prog, XDP_TX);
+ kfree_skb(skb);
+ }
+}
+
static int netif_receive_skb_internal(struct sk_buff *skb)
{
int ret;
@@ -4262,6 +4382,21 @@ 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 = rcu_dereference(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)
+ generic_xdp_tx(skb, xdp_prog);
+ return NET_RX_DROP;
+ }
+ }
+ }
+
#ifdef CONFIG_RPS
if (static_key_false(&rps_needed)) {
struct rps_dev_flow voidflow, *rflow = &voidflow;
@@ -4494,7 +4629,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
enum gro_result ret;
int grow;
- if (!(skb->dev->features & NETIF_F_GRO))
+ if (netif_elide_gro(skb->dev))
goto normal;
if (skb->csum_bad)
@@ -6723,6 +6858,7 @@ 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;
@@ -6730,14 +6866,16 @@ 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 || (flags & XDP_FLAGS_SKB_MODE))
+ 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)
@@ -6753,7 +6891,7 @@ 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);
@@ -7793,6 +7931,7 @@ EXPORT_SYMBOL(alloc_netdev_mqs);
void free_netdev(struct net_device *dev)
{
struct napi_struct *p, *n;
+ struct bpf_prog *prog;
might_sleep();
netif_free_tx_queues(dev);
@@ -7811,6 +7950,12 @@ void free_netdev(struct net_device *dev)
free_percpu(dev->pcpu_refcnt);
dev->pcpu_refcnt = NULL;
+ prog = rcu_dereference_protected(dev->xdp_prog, 1);
+ if (prog) {
+ bpf_prog_put(prog);
+ static_key_slow_dec(&generic_xdp_needed);
+ }
+
/* Compatibility with error handling in drivers */
if (dev->reg_state == NETREG_UNINITIALIZED) {
netdev_freemem(dev);