[xdp-hints] Re: [PATCH bpf-next v4 03/15] bpf: Introduce device-bound XDP programs

[Martin KaFai Lau <martin.lau@linux.dev>]

On 12/12/22 6:35 PM, Stanislav Fomichev wrote:
> New flag BPF_F_XDP_DEV_BOUND_ONLY plus all the infra to have a way
> to associate a netdev with a BPF program at load time.
> 
> Some existing 'offloaded' routines are renamed to 'dev_bound' for
> consistency with the rest.
> 
> Also moved a bunch of code around to avoid forward declarations.

There are too many things in one patch.  It becomes quite hard to follow, eg. I 
have to go back-and-forth a few times within this patch to confirm what change 
is just a move.  Please put the "moved a bunch of code around to avoid forward 
declarations" in one individual patch and also the 
"late_initcall(bpf_offload_init)" change in another individual patch.

[ ... ]

> -int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
> +static int __bpf_offload_dev_netdev_register(struct bpf_offload_dev *offdev,
> +					     struct net_device *netdev)
> +{
> +	struct bpf_offload_netdev *ondev;
> +	int err;
> +
> +	ondev = kzalloc(sizeof(*ondev), GFP_KERNEL);
> +	if (!ondev)
> +		return -ENOMEM;
> +
> +	ondev->netdev = netdev;
> +	ondev->offdev = offdev;
> +	INIT_LIST_HEAD(&ondev->progs);
> +	INIT_LIST_HEAD(&ondev->maps);
> +
> +	err = rhashtable_insert_fast(&offdevs, &ondev->l, offdevs_params);
> +	if (err) {
> +		netdev_warn(netdev, "failed to register for BPF offload\n");
> +		goto err_unlock_free;
> +	}
> +
> +	if (offdev)
> +		list_add(&ondev->offdev_netdevs, &offdev->netdevs);
> +	return 0;
> +
> +err_unlock_free:
> +	up_write(&bpf_devs_lock);

No need to handle bpf_devs_lock in the "__" version of the register() helper? 
The goto label probably also needs another name, eg. "err_free".

> +	kfree(ondev);
> +	return err;
> +}
> +

[ ... ]

> +int bpf_prog_dev_bound_init(struct bpf_prog *prog, union bpf_attr *attr)
>   {
>   	struct bpf_offload_netdev *ondev;
>   	struct bpf_prog_offload *offload;
> @@ -87,7 +198,7 @@ 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_DEV_BOUND_ONLY)
>   		return -EINVAL;
>   
>   	offload = kzalloc(sizeof(*offload), GFP_USER);
> @@ -102,11 +213,25 @@ int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
>   	if (err)
>   		goto err_maybe_put;
>   
> +	prog->aux->offload_requested = !(attr->prog_flags & BPF_F_XDP_DEV_BOUND_ONLY);
> +
>   	down_write(&bpf_devs_lock);
>   	ondev = bpf_offload_find_netdev(offload->netdev);
>   	if (!ondev) {
> -		err = -EINVAL;
> -		goto err_unlock;
> +		if (!bpf_prog_is_offloaded(prog->aux)) {
> +			/* When only binding to the device, explicitly
> +			 * create an entry in the hashtable. See related
> +			 * bpf_dev_bound_try_remove_netdev.
> +			 */
> +			err = __bpf_offload_dev_netdev_register(NULL, offload->netdev);
> +			if (err)
> +				goto err_unlock;
> +			ondev = bpf_offload_find_netdev(offload->netdev);
> +		}
> +		if (!ondev) {

nit.  A bit confusing because the "ondev = bpf_offload_find_netdev(...)" above 
should not fail but "!ondev" is tested again here.  I think the intention is to 
fail on the 'bpf_prog_is_offloaded() == true' case. May be:

		if (bpf_prog_is_offloaded(prog->aux)) {
			err = -EINVAL;
			goto err_unlock;
		}
		/* When only binding to the device, explicitly
		 * ...
		 */
		err = __bpf_offload_dev_netdev_register(NULL, offload->netdev);
		if (err)
			goto err_unlock;
		ondev = bpf_offload_find_netdev(offload->netdev);

> +			err = -EINVAL;
> +			goto err_unlock;
> +		}
>   	}
>   	offload->offdev = ondev->offdev;
>   	prog->aux->offload = offload;
> @@ -209,27 +334,28 @@ bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt)
>   	up_read(&bpf_devs_lock);
>   }
>   
> -static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
> +static void bpf_dev_bound_try_remove_netdev(struct net_device *dev)
>   {
> -	struct bpf_prog_offload *offload = prog->aux->offload;
> -
> -	if (offload->dev_state)
> -		offload->offdev->ops->destroy(prog);
> +	struct bpf_offload_netdev *ondev;
>   
> -	/* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */
> -	bpf_prog_free_id(prog, true);
> +	if (!dev)
> +		return;
>   
> -	list_del_init(&offload->offloads);
> -	kfree(offload);
> -	prog->aux->offload = NULL;
> +	ondev = bpf_offload_find_netdev(dev);
> +	if (ondev && !ondev->offdev && list_empty(&ondev->progs))

hmm....list_empty(&ondev->progs) is tested here but will it be empty? ...

> +		__bpf_offload_dev_netdev_unregister(NULL, dev);
>   }
>   
> -void bpf_prog_offload_destroy(struct bpf_prog *prog)
> +void bpf_prog_dev_bound_destroy(struct bpf_prog *prog)
>   {
> +	rtnl_lock();
>   	down_write(&bpf_devs_lock);
> -	if (prog->aux->offload)
> -		__bpf_prog_offload_destroy(prog);
> +	if (prog->aux->offload) {
> +		bpf_dev_bound_try_remove_netdev(prog->aux->offload->netdev);

... the "prog" here is still linked to ondev->progs, right?
because __bpf_prog_dev_bound_destroy() is called later below.

nit. May be the bpf_dev_bound_try_remove_netdev() should be folded/merged back 
into bpf_prog_dev_bound_destroy() to make things more clear.

> +		__bpf_prog_dev_bound_destroy(prog); > +	}
>   	up_write(&bpf_devs_lock);
> +	rtnl_unlock();
>   }

[ ... ]

> +static int __init bpf_offload_init(void)
> +{
> +	int err;
> +
> +	down_write(&bpf_devs_lock);

lock is probably not needed.

> +	err = rhashtable_init(&offdevs, &offdevs_params);
> +	up_write(&bpf_devs_lock);
> +
> +	return err;
> +}
> +
> +late_initcall(bpf_offload_init);

[ ... ]

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 5d51999cba30..194f8116aad4 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 offloaded program without HW_MODE flag is not supported");
>   			return -EINVAL;
>   		}
> +		if (bpf_prog_is_dev_bound(new_prog->aux) && !bpf_offload_dev_match(new_prog, dev)) {
> +			NL_SET_ERR_MSG(extack, "Program bound to different device");
> +			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;
> @@ -10813,6 +10817,7 @@ void unregister_netdevice_many_notify(struct list_head *head,
>   		/* Shutdown queueing discipline. */
>   		dev_shutdown(dev);
>   
> +		bpf_dev_bound_netdev_unregister(dev);

Does it matter if bpf_dev_bound_netdev_unregister(dev) is called before 
dev_xdp_uninstall(dev)?  Asking because it seems more logic to unregister dev 
after detaching xdp progs.

>   		dev_xdp_uninstall(dev);
>   
>   		netdev_offload_xstats_disable_all(dev);