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net: xdp: support xdp generic on virtual devices
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XDP generic allows users to test XDP programs and/or run them with
degraded performance on devices that do not yet support XDP. For
testing I typically test eBPF programs using a set of veth devices.
This allows testing topologies that would otherwise be difficult to
setup especially in the early stages of development.

This patch adds a xdp generic hook to the netif_rx_internal()
function which is called from dev_forward_skb(). With this addition
attaching XDP programs to veth devices works as expected! Also I
noticed multiple drivers using netif_rx(). These devices will also
benefit and generic XDP will work for them as well.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Tested-by: Andy Gospodarek <andy@greyhouse.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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John Fastabend authored and David S. Miller committed Jul 17, 2017
1 parent 90382dc commit d445516
Showing 1 changed file with 113 additions and 95 deletions.
208 changes: 113 additions & 95 deletions net/core/dev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3865,13 +3865,122 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
return NET_RX_DROP;
}

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 struct static_key generic_xdp_needed __read_mostly;

static int do_xdp_generic(struct sk_buff *skb)
{
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) {
if (act == XDP_TX)
generic_xdp_tx(skb, xdp_prog);
return XDP_DROP;
}
}
return XDP_PASS;
}

static int netif_rx_internal(struct sk_buff *skb)
{
int ret;

net_timestamp_check(netdev_tstamp_prequeue, skb);

trace_netif_rx(skb);

if (static_key_false(&generic_xdp_needed)) {
int ret = do_xdp_generic(skb);

if (ret != XDP_PASS)
return NET_RX_DROP;
}

#ifdef CONFIG_RPS
if (static_key_false(&rps_needed)) {
struct rps_dev_flow voidflow, *rflow = &voidflow;
Expand Down Expand Up @@ -4338,8 +4447,6 @@ 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 *old = rtnl_dereference(dev->xdp_prog);
Expand Down Expand Up @@ -4373,89 +4480,6 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_xdp *xdp)
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;
Expand All @@ -4468,17 +4492,11 @@ 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);
int ret = do_xdp_generic(skb);

if (act != XDP_PASS) {
rcu_read_unlock();
if (act == XDP_TX)
generic_xdp_tx(skb, xdp_prog);
return NET_RX_DROP;
}
if (ret != XDP_PASS) {
rcu_read_unlock();
return NET_RX_DROP;
}
}

Expand Down

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