Re: [PATCH bpf-next v5 05/17] bpf: Introduce device-bound XDP programs

Stanislav Fomichev
2022-12-23T04:06:45Z

On Thu, Dec 22, 2022 at 4:19 PM Martin KaFai Lau <martin.lau@linux.dev> wrote:
>
> On 12/20/22 2:20 PM, Stanislav Fomichev wrote:
> > -int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
> > +int bpf_prog_dev_bound_init(struct bpf_prog *prog, union bpf_attr *attr)
> > {
> > struct bpf_offload_netdev *ondev;
> > struct bpf_prog_offload *offload;
> > @@ -199,7 +197,7 @@ 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);
> > @@ -214,11 +212,23 @@ 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);
>
> Just noticed bpf_prog_dev_bound_init() takes BPF_PROG_TYPE_SCHED_CLS. Not sure
> if there is device match check when attaching BPF_PROG_TYPE_SCHED_CLS. If not,
> does it make sense to reject dev bound only BPF_PROG_TYPE_SCHED_CLS?

No, good point, I haven't added a device match check to tc progs; will
add a check here to reject dev-bound progs at tc.

> > +
> > 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)) {
> > + err = -EINVAL;
> > + goto err_unlock;
> > + }
> > +
> > + /* When only binding to the device, explicitly
> > + * create an entry in the hashtable.
> > + */
> > + err = __bpf_offload_dev_netdev_register(NULL, offload->netdev);
> > + if (err)
> > + goto err_unlock;
> > + ondev = bpf_offload_find_netdev(offload->netdev);
> > }
> > offload->offdev = ondev->offdev;
> > prog->aux->offload = offload;
> > @@ -321,12 +331,41 @@ bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt)
> > up_read(&bpf_devs_lock);
> > }
> >
> > -void bpf_prog_offload_destroy(struct bpf_prog *prog)
> > +static void __bpf_prog_dev_bound_destroy(struct bpf_prog *prog)
> > +{
> > + struct bpf_prog_offload *offload = prog->aux->offload;
> > +
> > + if (offload->dev_state)
> > + offload->offdev->ops->destroy(prog);
> > +
> > + /* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */
> > + bpf_prog_free_id(prog, true);
> > +
> > + kfree(offload);
> > + prog->aux->offload = NULL;
> > +}
> > +
> > +void bpf_prog_dev_bound_destroy(struct bpf_prog *prog)
> > {
> > + struct bpf_offload_netdev *ondev;
> > + struct net_device *netdev;
> > +
> > + rtnl_lock();
> > down_write(&bpf_devs_lock);
> > - if (prog->aux->offload)
> > - __bpf_prog_offload_destroy(prog);
> > + if (prog->aux->offload) {
> > + list_del_init(&prog->aux->offload->offloads);
> > +
> > + netdev = prog->aux->offload->netdev;
>
> After saving the netdev, would it work to call __bpf_prog_offload_destroy() here
> instead of creating an almost identical __bpf_prog_dev_bound_destroy(). The
> idea is to call list_del_init() first but does not need the "offload" around to
> do the __bpf_offload_dev_netdev_unregister()?

Good idea, that might work, let me try..

> > + if (netdev) {

[..]

> I am thinking offload->netdev cannot be NULL. Did I overlook places that reset
> offload->netdev back to NULL? eg. In bpf_prog_offload_info_fill_ns(), it is not
> checking offload->netdev.
>
> > + ondev = bpf_offload_find_netdev(netdev);
>
> and ondev should not be NULL too?
>
> I am trying to ensure my understanding that all offload->netdev and ondev should
> be protected by bpf_devs_lock.

I think you're right and I'm just being overly cautious here.

> > + if (ondev && !ondev->offdev && list_empty(&ondev->progs))
> > + __bpf_offload_dev_netdev_unregister(NULL, netdev);
> > + }
> > +
> > + __bpf_prog_dev_bound_destroy(prog);
> > + }
> > up_write(&bpf_devs_lock);
> > + rtnl_unlock();
> > }
>