Subject: Re: [RFC PATCHv2 bpf-next 1/2] xdp: add a new helper for dev map multicast support

From: Lorenzo Bianconi <[email-masked]>
Date: Fri, 24 Apr 2020 16:19:08 +0200

> This is a prototype for xdp multicast support. In this implemention we
> add a new helper to accept two maps, forward map and exclude map.
> We will redirect the packet to all the interfaces in *forward map*, but
> exclude the interfaces that in *exclude map*.
> 
> To achive this I add a new ex_map for struct bpf_redirect_info.
> in the helper I set tgt_value to NULL to make a difference with
> bpf_xdp_redirect_map()
> 
> We also add a flag *BPF_F_EXCLUDE_INGRESS* incase you don't want to
> create a exclude map for each interface and just want to exclude the
> ingress interface.
> 
> The general data path is kept in net/core/filter.c. The native data
> path is in kernel/bpf/devmap.c so we can use direct calls to
> get better performace.
> 
> v2: add new syscall bpf_xdp_redirect_map_multi() which could accept
> include/exclude maps directly.
> 
> Signed-off-by: Hangbin Liu <[email-masked]>
> ---
>  include/linux/bpf.h            |  20 ++++++
>  include/linux/filter.h         |   1 +
>  include/net/xdp.h              |   1 +
>  include/uapi/linux/bpf.h       |  23 ++++++-
>  kernel/bpf/devmap.c            | 114 +++++++++++++++++++++++++++++++++
>  kernel/bpf/verifier.c          |   6 ++
>  net/core/filter.c              |  98 ++++++++++++++++++++++++++--
>  net/core/xdp.c                 |  26 ++++++++
>  tools/include/uapi/linux/bpf.h |  23 ++++++-
>  9 files changed, 305 insertions(+), 7 deletions(-)
> 

[...]

> +{
> +
> +	switch (map->map_type) {
> +	case BPF_MAP_TYPE_DEVMAP:
> +		return dev_map_get_next_key(map, key, next_key);
> +	case BPF_MAP_TYPE_DEVMAP_HASH:
> +		return dev_map_hash_get_next_key(map, key, next_key);
> +	default:
> +		break;
> +	}
> +
> +	return -ENOENT;
> +}
> +
> +bool dev_in_exclude_map(struct bpf_dtab_netdev *obj, struct bpf_map *map,
> +			int exclude_ifindex)
> +{
> +	struct bpf_dtab_netdev *in_obj = NULL;
> +	u32 key, next_key;
> +	int err;
> +
> +	if (!map)
> +		return false;

doing so it seems mandatory to define an exclude_map even if we want just to do
not forward the packet to the "ingress" interface.
Moreover I was thinking that we can assume to never forward to in the incoming
interface. Doing so the code would be simpler I guess. Is there a use case for
it? (forward even to the ingress interface)

> +
> +	if (obj->dev->ifindex == exclude_ifindex)
> +		return true;
> +
> +	devmap_get_next_key(map, NULL, &key);
> +
> +	for (;;) {
> +		switch (map->map_type) {
> +		case BPF_MAP_TYPE_DEVMAP:
> +			in_obj = __dev_map_lookup_elem(map, key);
> +			break;
> +		case BPF_MAP_TYPE_DEVMAP_HASH:
> +			in_obj = __dev_map_hash_lookup_elem(map, key);
> +			break;
> +		default:
> +			break;
> +		}
> +
> +		if (in_obj && in_obj->dev->ifindex == obj->dev->ifindex)
> +			return true;
> +
> +		err = devmap_get_next_key(map, &key, &next_key);
> +
> +		if (err)
> +			break;
> +
> +		key = next_key;
> +	}
> +
> +	return false;
> +}
> +
> +int dev_map_enqueue_multi(struct xdp_buff *xdp, struct net_device *dev_rx,
> +			  struct bpf_map *map, struct bpf_map *ex_map,
> +			  bool exclude_ingress)
> +{
> +	struct bpf_dtab_netdev *obj = NULL;
> +	struct xdp_frame *xdpf, *nxdpf;
> +	struct net_device *dev;
> +	u32 key, next_key;
> +	int err;
> +
> +	devmap_get_next_key(map, NULL, &key);
> +
> +	xdpf = convert_to_xdp_frame(xdp);
> +	if (unlikely(!xdpf))
> +		return -EOVERFLOW;
> +
> +	for (;;) {
> +		switch (map->map_type) {
> +		case BPF_MAP_TYPE_DEVMAP:
> +			obj = __dev_map_lookup_elem(map, key);
> +			break;
> +		case BPF_MAP_TYPE_DEVMAP_HASH:
> +			obj = __dev_map_hash_lookup_elem(map, key);
> +			break;
> +		default:
> +			break;
> +		}
> +
> +		if (!obj || dev_in_exclude_map(obj, ex_map,
> +					       exclude_ingress ? dev_rx->ifindex : 0))
> +			goto find_next;
> +
> +		dev = obj->dev;
> +
> +		if (!dev->netdev_ops->ndo_xdp_xmit)
> +			return -EOPNOTSUPP;
> +
> +		err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
> +		if (unlikely(err))
> +			return err;
> +
> +		nxdpf = xdpf_clone(xdpf);
> +		if (unlikely(!nxdpf))
> +			return -ENOMEM;
> +
> +		bq_enqueue(dev, nxdpf, dev_rx);
> +
> +find_next:
> +		err = devmap_get_next_key(map, &key, &next_key);
> +		if (err)
> +			break;
> +		key = next_key;
> +	}

Do we need to free 'incoming' xdp buffer here? I think most of the drivers assume
the packet is owned by the stack if xdp_do_redirect returns 0

> +
> +	return 0;
> +}
> +
>  int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
>  			     struct bpf_prog *xdp_prog)
>  {
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 38cfcf701eeb..f77213a0e354 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3880,6 +3880,7 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  	case BPF_MAP_TYPE_DEVMAP:
>  	case BPF_MAP_TYPE_DEVMAP_HASH:
>  		if (func_id != BPF_FUNC_redirect_map &&
> +		    func_id != BPF_FUNC_redirect_map_multi &&
>  		    func_id != BPF_FUNC_map_lookup_elem)
>  			goto error;
>  		break;
> @@ -3970,6 +3971,11 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  		    map->map_type != BPF_MAP_TYPE_XSKMAP)
>  			goto error;
>  		break;
> +	case BPF_FUNC_redirect_map_multi:
> +		if (map->map_type != BPF_MAP_TYPE_DEVMAP &&
> +		    map->map_type != BPF_MAP_TYPE_DEVMAP_HASH)
> +			goto error;
> +		break;
>  	case BPF_FUNC_sk_redirect_map:
>  	case BPF_FUNC_msg_redirect_map:
>  	case BPF_FUNC_sock_map_update:
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 7d6ceaa54d21..94d1530e5ac6 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3473,12 +3473,17 @@ static const struct bpf_func_proto bpf_xdp_adjust_meta_proto = {
>  };
>  
>  static int __bpf_tx_xdp_map(struct net_device *dev_rx, void *fwd,
> -			    struct bpf_map *map, struct xdp_buff *xdp)
> +			    struct bpf_map *map, struct xdp_buff *xdp,
> +			    struct bpf_map *ex_map, bool exclude_ingress)
>  {
>  	switch (map->map_type) {
>  	case BPF_MAP_TYPE_DEVMAP:
>  	case BPF_MAP_TYPE_DEVMAP_HASH:
> -		return dev_map_enqueue(fwd, xdp, dev_rx);
> +		if (fwd)
> +			return dev_map_enqueue(fwd, xdp, dev_rx);
> +		else
> +			return dev_map_enqueue_multi(xdp, dev_rx, map, ex_map,
> +						     exclude_ingress);

I guess it would be better to do not make it the default case. Maybe you can
add a bit in flags to mark it for "multicast"

>  	case BPF_MAP_TYPE_CPUMAP:
>  		return cpu_map_enqueue(fwd, xdp, dev_rx);
>  	case BPF_MAP_TYPE_XSKMAP:
> @@ -3534,6 +3539,8 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>  		    struct bpf_prog *xdp_prog)
>  {
>  	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> +	bool exclude_ingress = !!(ri->flags & BPF_F_EXCLUDE_INGRESS);
> +	struct bpf_map *ex_map = READ_ONCE(ri->ex_map);
>  	struct bpf_map *map = READ_ONCE(ri->map);
>  	u32 index = ri->tgt_index;
>  	void *fwd = ri->tgt_value;
> @@ -3552,7 +3559,7 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>  
>  		err = dev_xdp_enqueue(fwd, xdp, dev);
>  	} else {
> -		err = __bpf_tx_xdp_map(dev, fwd, map, xdp);
> +		err = __bpf_tx_xdp_map(dev, fwd, map, xdp, ex_map, exclude_ingress);
>  	}
>  
>  	if (unlikely(err))
> @@ -3566,6 +3573,49 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>  }
>  EXPORT_SYMBOL_GPL(xdp_do_redirect);
>  
> +static int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
> +				  struct bpf_prog *xdp_prog,
> +				  struct bpf_map *map, struct bpf_map *ex_map,
> +				  bool exclude_ingress)
> +
> +{
> +	struct bpf_dtab_netdev *dst;
> +	struct sk_buff *nskb;
> +	u32 key, next_key;
> +	int err;
> +	void *fwd;
> +
> +	/* Get first key from forward map */
> +	map->ops->map_get_next_key(map, NULL, &key);
> +
> +	for (;;) {
> +		fwd = __xdp_map_lookup_elem(map, key);
> +		if (fwd) {
> +			dst = (struct bpf_dtab_netdev *)fwd;
> +			if (dev_in_exclude_map(dst, ex_map,
> +					       exclude_ingress ? dev->ifindex : 0))
> +				goto find_next;
> +
> +			nskb = skb_clone(skb, GFP_ATOMIC);
> +			if (!nskb)
> +				return -EOVERFLOW;
> +
> +			err = dev_map_generic_redirect(dst, nskb, xdp_prog);
> +			if (unlikely(err))
> +				return err;
> +		}
> +
> +find_next:
> +		err = map->ops->map_get_next_key(map, &key, &next_key);
> +		if (err)
> +			break;
> +
> +		key = next_key;
> +	}
> +
> +	return 0;
> +}
> +
>  static int xdp_do_generic_redirect_map(struct net_device *dev,
>  				       struct sk_buff *skb,
>  				       struct xdp_buff *xdp,
> @@ -3573,6 +3623,8 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
>  				       struct bpf_map *map)
>  {
>  	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> +	bool exclude_ingress = !!(ri->flags & BPF_F_EXCLUDE_INGRESS);
> +	struct bpf_map *ex_map = READ_ONCE(ri->ex_map);
>  	u32 index = ri->tgt_index;
>  	void *fwd = ri->tgt_value;
>  	int err = 0;
> @@ -3583,9 +3635,16 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
>  
>  	if (map->map_type == BPF_MAP_TYPE_DEVMAP ||
>  	    map->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
> -		struct bpf_dtab_netdev *dst = fwd;
> +		if (fwd) {
> +			struct bpf_dtab_netdev *dst = fwd;
> +
> +			err = dev_map_generic_redirect(dst, skb, xdp_prog);
> +		} else {
> +			/* Deal with multicast maps */
> +			err = dev_map_redirect_multi(dev, skb, xdp_prog, map,
> +						     ex_map, exclude_ingress);
> +		}
>  
> -		err = dev_map_generic_redirect(dst, skb, xdp_prog);
>  		if (unlikely(err))
>  			goto err;
>  	} else if (map->map_type == BPF_MAP_TYPE_XSKMAP) {
> @@ -3699,6 +3758,33 @@ static const struct bpf_func_proto bpf_xdp_redirect_map_proto = {
>  	.arg3_type      = ARG_ANYTHING,
>  };
>  
> +BPF_CALL_3(bpf_xdp_redirect_map_multi, struct bpf_map *, map,
> +	   struct bpf_map *, ex_map, u64, flags)
> +{
> +	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> +
> +	if (unlikely(!map || flags > BPF_F_EXCLUDE_INGRESS))
> +		return XDP_ABORTED;
> +
> +	ri->tgt_index = 0;
> +	ri->tgt_value = NULL;
> +	ri->flags = flags;
> +
> +	WRITE_ONCE(ri->map, map);
> +	WRITE_ONCE(ri->ex_map, ex_map);
> +
> +	return XDP_REDIRECT;
> +}
> +
> +static const struct bpf_func_proto bpf_xdp_redirect_map_multi_proto = {
> +	.func           = bpf_xdp_redirect_map_multi,
> +	.gpl_only       = false,
> +	.ret_type       = RET_INTEGER,
> +	.arg1_type      = ARG_CONST_MAP_PTR,
> +	.arg1_type      = ARG_CONST_MAP_PTR,
> +	.arg3_type      = ARG_ANYTHING,
> +};
> +
>  static unsigned long bpf_skb_copy(void *dst_buff, const void *skb,
>  				  unsigned long off, unsigned long len)
>  {
> @@ -6304,6 +6390,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_xdp_redirect_proto;
>  	case BPF_FUNC_redirect_map:
>  		return &bpf_xdp_redirect_map_proto;
> +	case BPF_FUNC_redirect_map_multi:
> +		return &bpf_xdp_redirect_map_multi_proto;
>  	case BPF_FUNC_xdp_adjust_tail:
>  		return &bpf_xdp_adjust_tail_proto;
>  	case BPF_FUNC_fib_lookup:
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 4c7ea85486af..70dfb4910f84 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -496,3 +496,29 @@ struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp)
>  	return xdpf;
>  }
>  EXPORT_SYMBOL_GPL(xdp_convert_zc_to_xdp_frame);
> +
> +struct xdp_frame *xdpf_clone(struct xdp_frame *xdpf)
> +{
> +	unsigned int headroom, totalsize;
> +	struct xdp_frame *nxdpf;
> +	struct page *page;
> +	void *addr;
> +
> +	headroom = xdpf->headroom + sizeof(*xdpf);
> +	totalsize = headroom + xdpf->len;
> +
> +	if (unlikely(totalsize > PAGE_SIZE))
> +		return NULL;
> +	page = dev_alloc_page();
> +	if (!page)
> +		return NULL;
> +	addr = page_to_virt(page);
> +
> +	memcpy(addr, xdpf, totalsize);
> +
> +	nxdpf = addr;
> +	nxdpf->data = addr + headroom;
> +
> +	return nxdpf;
> +}
> +EXPORT_SYMBOL_GPL(xdpf_clone);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 2e29a671d67e..1dbe42290223 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3025,6 +3025,21 @@ union bpf_attr {
>   *		* **-EOPNOTSUPP**	Unsupported operation, for example a
>   *					call from outside of TC ingress.
>   *		* **-ESOCKTNOSUPPORT**	Socket type not supported (reuseport).
> + *
> + * int bpf_redirect_map_multi(struct bpf_map *map, struct bpf_map *ex_map, u64 flags)
> + * 	Description
> + * 		Redirect the packet to all the interfaces in *map*, and
> + * 		exclude the interfaces that in *ex_map*. The *ex_map* could
> + * 		be NULL.
> + *
> + * 		Currently the *flags* only supports *BPF_F_EXCLUDE_INGRESS*,
> + * 		which could exlcude redirect to the ingress device.
> + *
> + * 		See also bpf_redirect_map(), which supports redirecting
> + * 		packet to a specific ifindex in the map.
> + * 	Return
> + * 		**XDP_REDIRECT** on success, or **XDP_ABORTED** on error.
> + *
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -3151,7 +3166,8 @@ union bpf_attr {
>  	FN(xdp_output),			\
>  	FN(get_netns_cookie),		\
>  	FN(get_current_ancestor_cgroup_id),	\
> -	FN(sk_assign),
> +	FN(sk_assign),			\
> +	FN(redirect_map_multi),
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> @@ -3280,6 +3296,11 @@ enum bpf_lwt_encap_mode {
>  	BPF_LWT_ENCAP_IP,
>  };
>  
> +/* BPF_FUNC_redirect_map_multi flags. */
> +enum {
> +	BPF_F_EXCLUDE_INGRESS		= (1ULL << 0),
> +};
> +
>  #define __bpf_md_ptr(type, name)	\
>  union {					\
>  	type name;			\
> -- 
> 2.19.2
>