Re: [PATCH net-next v2 3/5] bpf: cpumap: implement generic cpumap

Kumar Kartikeya Dwivedi
2021-06-22T20:24:39Z

On Wed, Jun 23, 2021 at 01:25:25AM IST, Kumar Kartikeya Dwivedi wrote:
> 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.
>
> Since cpumap entry progs are now supported, also remove check in
> generic_xdp_install for the cpumap.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
> include/linux/bpf.h | 9 +++-
> include/linux/skbuff.h | 10 +---
> kernel/bpf/cpumap.c | 115 +++++++++++++++++++++++++++++++++++------
> net/core/dev.c | 3 +-
> net/core/filter.c | 6 ++-
> 5 files changed, 115 insertions(+), 28 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f309fc1509f2..095aaa104c56 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1513,7 +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);
> -bool cpu_map_prog_allowed(struct bpf_map *map);
> +int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
> + struct sk_buff *skb);
>
> /* Return map's numa specified by userspace */
> static inline int bpf_map_attr_numa_node(const union bpf_attr *attr)
> @@ -1710,6 +1711,12 @@ 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..57f751212a9d 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>
> @@ -168,6 +169,49 @@ 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,
> + struct list_head *listp,
> + struct xdp_cpumap_stats *stats)
> +{
> + struct xdp_buff xdp;
> + struct sk_buff *skb;
> + u32 act;
> + int err;
> +
> + if (!rcpu->prog)
> + return;
> +
> + list_for_each_entry(skb, listp, list) {

Oops, this should be list_for_each_entry_safe, I forgot to run format-patch
after fixing this...

Resending, sorry for the noise.

> + act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
> + switch (act) {
> + case XDP_PASS:
> + break;
> + case XDP_REDIRECT:
> + skb_list_del_init(skb);
> + 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:
> + skb_list_del_init(skb);
> + kfree_skb(skb);
> + stats->drop++;
> + return;
> + }
> + }
> +}
> +
> 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 +223,6 @@ 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 +269,34 @@ 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, 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(!list_empty(list)))
> + cpu_map_bpf_prog_run_skb(rcpu, list, stats);
>
> - 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 +313,9 @@ 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;
> + int i, n, m, nframes, xdp_n;
> void *frames[CPUMAP_BATCH];
> void *skbs[CPUMAP_BATCH];
> - int i, n, m, nframes;
> LIST_HEAD(list);
>
> /* Release CPU reschedule checks */
> @@ -280,9 +339,20 @@ static int cpu_map_kthread_run(void *data)
> */
> n = __ptr_ring_consume_batched(rcpu->queue, frames,
> CPUMAP_BATCH);
> - for (i = 0; i < n; i++) {
> + for (i = 0, xdp_n = 0; i < n; i++) {
> void *f = frames[i];
> - struct page *page = virt_to_page(f);
> + struct page *page;
> +
> + if (unlikely(__ptr_test_bit(0, &f))) {
> + struct sk_buff *skb = f;
> +
> + __ptr_clear_bit(0, &skb);
> + list_add_tail(&skb->list, &list);
> + continue;
> + }
> +
> + frames[xdp_n++] = f;
> + page = virt_to_page(f);
>
> /* Bring struct page memory area to curr CPU. Read by
> * build_skb_around via page_is_pfmemalloc(), and when
> @@ -292,7 +362,7 @@ static int cpu_map_kthread_run(void *data)
> }
>
> /* Support running another XDP prog on this CPU */
> - nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, n, &stats);
> + nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, &stats, &list);
> if (nframes) {
> m = kmem_cache_alloc_bulk(skbuff_head_cache, gfp, nframes, skbs);
> if (unlikely(m == 0)) {
> @@ -330,12 +400,6 @@ static int cpu_map_kthread_run(void *data)
> return 0;
> }
>
> -bool cpu_map_prog_allowed(struct bpf_map *map)
> -{
> - return map->map_type == BPF_MAP_TYPE_CPUMAP &&
> - map->value_size != offsetofend(struct bpf_cpumap_val, qsize);
> -}
> -
> static int __cpu_map_load_bpf_program(struct bpf_cpu_map_entry *rcpu, int fd)
> {
> struct bpf_prog *prog;
> @@ -696,6 +760,25 @@ int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
> return 0;
> }
>
> +int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
> + struct sk_buff *skb)
> +{
> + int ret;
> +
> + __skb_pull(skb, skb->mac_len);
> + skb_set_redirected(skb, false);
> + __ptr_set_bit(0, &skb);
> +
> + ret = ptr_ring_produce(rcpu->queue, skb);
> + if (ret < 0)
> + goto trace;
> +
> + wake_up_process(rcpu->kthread);
> +trace:
> + trace_xdp_cpumap_enqueue(rcpu->map_id, !ret, !!ret, rcpu->cpu);
> + return ret;
> +}
> +
> void __cpu_map_flush(void)
> {
> struct list_head *flush_list = this_cpu_ptr(&cpu_map_flush_list);
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c34ff1dbf6e6..a00421e9ee16 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5642,8 +5642,7 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
> * have a bpf_prog installed on an entry
> */
> for (i = 0; i < new->aux->used_map_cnt; i++) {
> - if (dev_map_can_have_prog(new->aux->used_maps[i]) ||
> - cpu_map_prog_allowed(new->aux->used_maps[i])) {
> + if (dev_map_can_have_prog(new->aux->used_maps[i])) {
> mutex_unlock(&new->aux->used_maps_mutex);
> return -EINVAL;
> }
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 0b13d8157a8f..4a21fde3028f 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4038,8 +4038,12 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
> goto err;
> consume_skb(skb);
> break;
> + case BPF_MAP_TYPE_CPUMAP:
> + err = cpu_map_generic_redirect(fwd, skb);
> + if (unlikely(err))
> + goto err;
> + break;
> default:
> - /* TODO: Handle BPF_MAP_TYPE_CPUMAP */
> err = -EBADRQC;
> goto err;
> }
> --
> 2.31.1
>

--
Kartikeya