Re: [PATCH net-next 2/4] net: implement generic cpumap

This change implements CPUMAP redirect support for generic XDP programs.
The idea is to reuse the cpu map entry's queue that is used to push
native xdp frames for redirecting skb to a different CPU. This will
match native XDP behavior (in that RPS is invoked again for packet
reinjected into networking stack).

To be able to determine whether the incoming skb is from the driver or
cpumap, we reuse skb->redirected bit that skips generic XDP processing
when it is set. To always make use of this, CONFIG_NET_REDIRECT guard on
it has been lifted and it is always available.

From the redirect side, we add the skb to ptr_ring with its lowest bit
set to 1.  This should be safe as skb is not 1-byte aligned. This allows
kthread to discern between xdp_frames and sk_buff. On consumption of the
ptr_ring item, the lowest bit is unset.

In the end, the skb is simply added to the list that kthread is anyway
going to maintain for xdp_frames converted to skb, and then received
again by using netif_receive_skb_list.

Bulking optimization for generic cpumap is left as an exercise for a
future patch for now.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h    |   8 +++
 include/linux/skbuff.h |  10 +--
 kernel/bpf/cpumap.c    | 151 +++++++++++++++++++++++++++++++++++++----
 net/core/filter.c      |   6 +-
 4 files changed, 154 insertions(+), 21 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f309fc1509f2..46e6587d3ee6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1513,6 +1513,8 @@ bool dev_map_can_have_prog(struct bpf_map *map);
 void __cpu_map_flush(void);
 int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
 		    struct net_device *dev_rx);
+int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
+			     struct sk_buff *skb);
 bool cpu_map_prog_allowed(struct bpf_map *map);
 
 /* Return map's numa specified by userspace */

@@ -1710,6 +1712,12 @@ static inline int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu,
 	return 0;
 }
 
+static inline int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
+					   struct sk_buff *skb)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline bool cpu_map_prog_allowed(struct bpf_map *map)
 {
 	return false;

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index b2db9cd9a73f..f19190820e63 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -863,8 +863,8 @@ struct sk_buff {
 	__u8			tc_skip_classify:1;
 	__u8			tc_at_ingress:1;
 #endif
-#ifdef CONFIG_NET_REDIRECT
 	__u8			redirected:1;
+#ifdef CONFIG_NET_REDIRECT
 	__u8			from_ingress:1;
 #endif
 #ifdef CONFIG_TLS_DEVICE

@@ -4664,17 +4664,13 @@ static inline __wsum lco_csum(struct sk_buff *skb)
 
 static inline bool skb_is_redirected(const struct sk_buff *skb)
 {
-#ifdef CONFIG_NET_REDIRECT
 	return skb->redirected;
-#else
-	return false;
-#endif
 }
 
 static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
 {
-#ifdef CONFIG_NET_REDIRECT
 	skb->redirected = 1;
+#ifdef CONFIG_NET_REDIRECT
 	skb->from_ingress = from_ingress;
 	if (skb->from_ingress)
 		skb->tstamp = 0;

@@ -4683,9 +4679,7 @@ static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
 
 static inline void skb_reset_redirect(struct sk_buff *skb)
 {
-#ifdef CONFIG_NET_REDIRECT
 	skb->redirected = 0;
-#endif
 }
 
 static inline bool skb_csum_is_sctp(struct sk_buff *skb)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index a1a0c4e791c6..f016daf8fdcc 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c

@@ -16,6 +16,7 @@
  * netstack, and assigning dedicated CPUs for this stage.  This
  * basically allows for 10G wirespeed pre-filtering via bpf.
  */
+#include <linux/bitops.h>
 #include <linux/bpf.h>
 #include <linux/filter.h>
 #include <linux/ptr_ring.h>

@@ -79,6 +80,29 @@ struct bpf_cpu_map {
 
 static DEFINE_PER_CPU(struct list_head, cpu_map_flush_list);
 
+static void *__ptr_set_bit(void *ptr, int bit)
+{
+	unsigned long __ptr = (unsigned long)ptr;
+
+	__ptr |= BIT(bit);
+	return (void *)__ptr;
+}
+
+static void *__ptr_clear_bit(void *ptr, int bit)
+{
+	unsigned long __ptr = (unsigned long)ptr;
+
+	__ptr &= ~BIT(bit);
+	return (void *)__ptr;
+}
+
+static int __ptr_test_bit(void *ptr, int bit)
+{
+	unsigned long __ptr = (unsigned long)ptr;
+
+	return __ptr & BIT(bit);
+}

 static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
 {
 	u32 value_size = attr->value_size;

@@ -168,6 +192,64 @@ static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
 	}
 }
 
+static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
+				    void **frames, int skb_n,
+				    struct xdp_cpumap_stats *stats,
+				    struct list_head *listp)
+{
+	struct xdp_rxq_info rxq = {};
+	struct xdp_buff xdp;
+	int err, i;
+	u32 act;
+
+	xdp.rxq = &rxq;
+
+	if (!rcpu->prog)
+		goto insert;
+
+	for (i = 0; i < skb_n; i++) {
+		struct sk_buff *skb = frames[i];
+
+		rxq.dev = skb->dev;
+
+		act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
+		switch (act) {
+		case XDP_PASS:
+			list_add_tail(&skb->list, listp);
+			break;
+		case XDP_REDIRECT:
+			err = xdp_do_generic_redirect(skb->dev, skb, &xdp,
+						      rcpu->prog);
+			if (unlikely(err)) {
+				kfree_skb(skb);
+				stats->drop++;
+			} else {
+				stats->redirect++;
+			}
+			return;
+		default:
+			bpf_warn_invalid_xdp_action(act);
+			fallthrough;
+		case XDP_ABORTED:
+			trace_xdp_exception(skb->dev, rcpu->prog, act);
+			fallthrough;
+		case XDP_DROP:
+			kfree_skb(skb);
+			stats->drop++;
+			return;
+		}
+	}
+
+	return;
+
+insert:
+	for (i = 0; i < skb_n; i++) {
+		struct sk_buff *skb = frames[i];
+
+		list_add_tail(&skb->list, listp);
+	}
+}
+
 static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 				    void **frames, int n,
 				    struct xdp_cpumap_stats *stats)

@@ -179,8 +261,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 	if (!rcpu->prog)
 		return n;
 
-	rcu_read_lock_bh();
-
 	xdp_set_return_frame_no_direct();
 	xdp.rxq = &rxq;
 

@@ -227,17 +307,36 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 		}
 	}
 
+	xdp_clear_return_frame_no_direct();
+
+	return nframes;
+}
+
+#define CPUMAP_BATCH 8
+
+static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu,
+				void **frames, int xdp_n, int skb_n,
+				struct xdp_cpumap_stats *stats,
+				struct list_head *list)
+{
+	int nframes;
+
+	rcu_read_lock_bh();
+
+	nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, xdp_n, stats);
+
 	if (stats->redirect)
-		xdp_do_flush_map();
+		xdp_do_flush();
 
-	xdp_clear_return_frame_no_direct();
+	if (unlikely(skb_n))
+		cpu_map_bpf_prog_run_skb(rcpu, frames + CPUMAP_BATCH, skb_n,
+					 stats, list);
 
-	rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
+	rcu_read_unlock_bh();
 
 	return nframes;
 }
 
-#define CPUMAP_BATCH 8
 
 static int cpu_map_kthread_run(void *data)
 {

@@ -254,9 +353,9 @@ static int cpu_map_kthread_run(void *data)
 		struct xdp_cpumap_stats stats = {}; /* zero stats */
 		unsigned int kmem_alloc_drops = 0, sched = 0;
 		gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
-		void *frames[CPUMAP_BATCH];
+		int i, n, m, nframes, xdp_n, skb_n;
+		void *frames[CPUMAP_BATCH * 2];