Subject: Re: [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs

From: Jakub Kicinski <[email-masked]>
Date: Wed, 7 Dec 2022 21:00:19 -0800

The offload tests still pass after this, right?
TBH I don't remember this code well enough to spot major issues.

On Mon,  5 Dec 2022 18:45:45 -0800 Stanislav Fomichev wrote:
> There is an ndo handler per kfunc, the verifier replaces a call to the
> generic kfunc with a call to the per-device one.
> 
> For XDP, we define a new kfunc set (xdp_metadata_kfunc_ids) which
> implements all possible metatada kfuncs. Not all devices have to
> implement them. If kfunc is not supported by the target device,
> the default implementation is called instead.
> 
> Upon loading, if BPF_F_XDP_HAS_METADATA is passed via prog_flags,
> we treat prog_index as target device for kfunc resolution.

> @@ -2476,10 +2477,18 @@ void bpf_offload_dev_netdev_unregister(struct bpf_offload_dev *offdev,
>  				       struct net_device *netdev);
>  bool bpf_offload_dev_match(struct bpf_prog *prog, struct net_device *netdev);
>  
> +void *bpf_offload_resolve_kfunc(struct bpf_prog *prog, u32 func_id);

There seems to be some mis-naming going on. I expected:

  offloaded =~ nfp
  dev_bound == XDP w/ funcs

*_offload_resolve_kfunc looks misnamed? Unless you want to resolve 
for HW offload?

>  void unpriv_ebpf_notify(int new_state);
>  
>  #if defined(CONFIG_NET) && defined(CONFIG_BPF_SYSCALL)
>  int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr);
> +void bpf_offload_bound_netdev_unregister(struct net_device *dev);

ditto: offload_bound is a mix of terms no?

> @@ -1611,6 +1612,10 @@ struct net_device_ops {
>  	ktime_t			(*ndo_get_tstamp)(struct net_device *dev,
>  						  const struct skb_shared_hwtstamps *hwtstamps,
>  						  bool cycles);
> +	bool			(*ndo_xdp_rx_timestamp_supported)(const struct xdp_md *ctx);
> +	u64			(*ndo_xdp_rx_timestamp)(const struct xdp_md *ctx);
> +	bool			(*ndo_xdp_rx_hash_supported)(const struct xdp_md *ctx);
> +	u32			(*ndo_xdp_rx_hash)(const struct xdp_md *ctx);
>  };

Is this on the fast path? Can we do an indirection?
Put these ops in their own struct and add a pointer to that struct 
in net_device_ops? Purely for grouping reasons because the netdev
ops are getting orders of magnitude past the size where you can
actually find stuff in this struct.

>  	bpf_free_used_maps(aux);
>  	bpf_free_used_btfs(aux);
> -	if (bpf_prog_is_offloaded(aux))
> +	if (bpf_prog_is_dev_bound(aux))
>  		bpf_prog_offload_destroy(aux->prog);

This also looks a touch like a mix of terms (condition vs function
called).

> +static int __bpf_offload_init(void);
> +static int __bpf_offload_dev_netdev_register(struct bpf_offload_dev *offdev,
> +					     struct net_device *netdev);
> +static void __bpf_offload_dev_netdev_unregister(struct bpf_offload_dev *offdev,
> +						struct net_device *netdev);

fwd declarations are yuck

>  static int bpf_dev_offload_check(struct net_device *netdev)
>  {
>  	if (!netdev)
> @@ -87,13 +93,17 @@ int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
>  	    attr->prog_type != BPF_PROG_TYPE_XDP)
>  		return -EINVAL;
>  
> -	if (attr->prog_flags)
> +	if (attr->prog_flags & ~BPF_F_XDP_HAS_METADATA)
>  		return -EINVAL;
>  
>  	offload = kzalloc(sizeof(*offload), GFP_USER);
>  	if (!offload)
>  		return -ENOMEM;
>  
> +	err = __bpf_offload_init();
> +	if (err)
> +		return err;

leaks offload

> @@ -209,6 +233,19 @@ bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt)
>  	up_read(&bpf_devs_lock);
>  }
>  
> +static void maybe_remove_bound_netdev(struct net_device *dev)
> +{

func name prefix ?

> -struct bpf_offload_dev *
> -bpf_offload_dev_create(const struct bpf_prog_offload_ops *ops, void *priv)
> +static int __bpf_offload_init(void)
>  {
> -	struct bpf_offload_dev *offdev;
>  	int err;
>  
>  	down_write(&bpf_devs_lock);
> @@ -680,12 +740,25 @@ bpf_offload_dev_create(const struct bpf_prog_offload_ops *ops, void *priv)
>  		err = rhashtable_init(&offdevs, &offdevs_params);
>  		if (err) {
>  			up_write(&bpf_devs_lock);
> -			return ERR_PTR(err);
> +			return err;
>  		}
>  		offdevs_inited = true;
>  	}
>  	up_write(&bpf_devs_lock);
>  
> +	return 0;
> +}

Would late_initcall() or some such not work for this?

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 5b221568dfd4..862e03fcffa6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9228,6 +9228,10 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
>  			NL_SET_ERR_MSG(extack, "Using device-bound program without HW_MODE flag is not supported");

extack should get updated here, I reckon, maybe in previous patch

>  			return -EINVAL;
>  		}
> +		if (bpf_prog_is_dev_bound(new_prog->aux) && !bpf_offload_dev_match(new_prog, dev)) {

bound_dev_match() ?

> +			NL_SET_ERR_MSG(extack, "Cannot attach to a different target device");

different than.. ?

> +			return -EINVAL;
> +		}
>  		if (new_prog->expected_attach_type == BPF_XDP_DEVMAP) {
>  			NL_SET_ERR_MSG(extack, "BPF_XDP_DEVMAP programs can not be attached to a device");
>  			return -EINVAL;