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Date: Tue, 13 Dec 2022 15:25:26 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Stanislav Fomichev <sdf@...gle.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
song@...nel.org, yhs@...com, john.fastabend@...il.com,
kpsingh@...nel.org, haoluo@...gle.com, jolsa@...nel.org,
David Ahern <dsahern@...il.com>,
Jakub Kicinski <kuba@...nel.org>,
Willem de Bruijn <willemb@...gle.com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Anatoly Burakov <anatoly.burakov@...el.com>,
Alexander Lobakin <alexandr.lobakin@...el.com>,
Magnus Karlsson <magnus.karlsson@...il.com>,
Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 03/15] bpf: Introduce device-bound XDP
programs
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);
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