[PATCH net-next v2 1/5] net: core: split out code to run generic XDP prog

Kumar Kartikeya Dwivedi
2021-06-22T19:57:10Z

This helper can later be utilized in code that runs cpumap and devmap
programs in generic redirect mode and adjust skb based on changes made
to xdp_buff.

When returning XDP_REDIRECT/XDP_TX, it invokes __skb_push, so whenever a
generic redirect path invokes devmap/cpumap prog if set, it must
__skb_pull again as we expect mac header to be pulled.

It also drops the skb_reset_mac_len call after do_xdp_generic, as the
mac_header and network_header are advanced by the same offset, so the
difference (mac_len) remains constant.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
NB: I am not too sure why the skb_reset_mac_len was there, so I removed it since
the offset addition/subtraction should be same for network_header and
mac_header, but I could be missing something important...
---
include/linux/netdevice.h | 2 +
net/core/dev.c | 84 ++++++++++++++++++++++++---------------
2 files changed, 55 insertions(+), 31 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index be1dcceda5e4..90472ea70db2 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3984,6 +3984,8 @@ static inline void dev_consume_skb_any(struct sk_buff *skb)
__dev_kfree_skb_any(skb, SKB_REASON_CONSUMED);
}

+u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
+ struct bpf_prog *xdp_prog);
void generic_xdp_tx(struct sk_buff *skb, struct bpf_prog *xdp_prog);
int do_xdp_generic(struct bpf_prog *xdp_prog, struct sk_buff *skb);
int netif_rx(struct sk_buff *skb);
diff --git a/net/core/dev.c b/net/core/dev.c
index 50531a2d0b20..c34ff1dbf6e6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4717,45 +4717,18 @@ static struct netdev_rx_queue *netif_get_rxqueue(struct sk_buff *skb)
return rxqueue;
}

-static u32 netif_receive_generic_xdp(struct sk_buff *skb,
- struct xdp_buff *xdp,
- struct bpf_prog *xdp_prog)
+u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
+ struct bpf_prog *xdp_prog)
{
void *orig_data, *orig_data_end, *hard_start;
struct netdev_rx_queue *rxqueue;
- u32 metalen, act = XDP_DROP;
bool orig_bcast, orig_host;
u32 mac_len, frame_sz;
__be16 orig_eth_type;
struct ethhdr *eth;
+ u32 metalen, act;
int off;

- /* Reinjected packets coming from act_mirred or similar should
- * not get XDP generic processing.
- */
- if (skb_is_redirected(skb))
- return XDP_PASS;
-
- /* XDP packets must be linear and must have sufficient headroom
- * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
- * native XDP provides, thus we need to do it here as well.
- */
- if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
- skb_headroom(skb) < XDP_PACKET_HEADROOM) {
- int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
- int troom = skb->tail + skb->data_len - skb->end;
-
- /* In case we have to go down the path and also linearize,
- * then lets do the pskb_expand_head() work just once here.
- */
- if (pskb_expand_head(skb,
- hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
- troom > 0 ? troom + 128 : 0, GFP_ATOMIC))
- goto do_drop;
- if (skb_linearize(skb))
- goto do_drop;
- }
-
/* The XDP program wants to see the packet starting at the MAC
* header.
*/
@@ -4810,6 +4783,13 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
skb->protocol = eth_type_trans(skb, skb->dev);
}

+ /* Redirect/Tx gives L2 packet, code that will reuse skb must __skb_pull
+ * before calling us again on redirect path. We do not call do_redirect
+ * as we leave that up to the caller.
+ *
+ * Caller is responsible for managing lifetime of skb (i.e. calling
+ * kfree_skb in response to actions it cannot handle/XDP_DROP).
+ */
switch (act) {
case XDP_REDIRECT:
case XDP_TX:
@@ -4820,6 +4800,49 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
if (metalen)
skb_metadata_set(skb, metalen);
break;
+ }
+
+ return act;
+}
+
+static u32 netif_receive_generic_xdp(struct sk_buff *skb,
+ struct xdp_buff *xdp,
+ struct bpf_prog *xdp_prog)
+{
+ u32 act = XDP_DROP;
+
+ /* Reinjected packets coming from act_mirred or similar should
+ * not get XDP generic processing.
+ */
+ if (skb_is_redirected(skb))
+ return XDP_PASS;
+
+ /* XDP packets must be linear and must have sufficient headroom
+ * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
+ * native XDP provides, thus we need to do it here as well.
+ */
+ if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
+ skb_headroom(skb) < XDP_PACKET_HEADROOM) {
+ int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
+ int troom = skb->tail + skb->data_len - skb->end;
+
+ /* In case we have to go down the path and also linearize,
+ * then lets do the pskb_expand_head() work just once here.
+ */
+ if (pskb_expand_head(skb,
+ hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
+ troom > 0 ? troom + 128 : 0, GFP_ATOMIC))
+ goto do_drop;
+ if (skb_linearize(skb))
+ goto do_drop;
+ }
+
+ act = bpf_prog_run_generic_xdp(skb, xdp, xdp_prog);
+ switch (act) {
+ case XDP_REDIRECT:
+ case XDP_TX:
+ case XDP_PASS:
+ break;
default:
bpf_warn_invalid_xdp_action(act);
fallthrough;
@@ -5285,7 +5308,6 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
ret = NET_RX_DROP;
goto out;
}
- skb_reset_mac_len(skb);
}

if (eth_type_vlan(skb->protocol)) {
--
2.31.1