Messages in this thread | | | Date | Thu, 10 Aug 2023 23:22:04 -0700 | Subject | Re: [PATCH bpf-next] bpf: Support default .validate() and .update() behavior for struct_ops links | From | Kui-Feng Lee <> |
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Overall, this patch make sense to me.
On 8/10/23 15:04, David Vernet wrote: > Currently, if a struct_ops map is loaded with BPF_F_LINK, it must also > define the .validate() and .update() callbacks in its corresponding > struct bpf_struct_ops in the kernel. Enabling struct_ops link is useful > in its own right to ensure that the map is unloaded if an application > crashes. For example, with sched_ext, we want to automatically unload > the host-wide scheduler if the application crashes. We would likely > never support updating elements of a sched_ext struct_ops map, so we'd > have to implement these callbacks showing that they _can't_ support > element updates just to benefit from the basic lifetime management of > struct_ops links. > > Let's enable struct_ops maps to work with BPF_F_LINK even if they > haven't defined these callbacks, by assuming that a struct_ops map > element cannot be updated by default. > > Signed-off-by: David Vernet <void@manifault.com> > --- > kernel/bpf/bpf_struct_ops.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c > index eaff04eefb31..3d2fb85186a9 100644 > --- a/kernel/bpf/bpf_struct_ops.c > +++ b/kernel/bpf/bpf_struct_ops.c > @@ -509,9 +509,12 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key, > } > > if (st_map->map.map_flags & BPF_F_LINK) { > - err = st_ops->validate(kdata); > - if (err) > - goto reset_unlock; > + err = 0; > + if (st_ops->validate) { > + err = st_ops->validate(kdata); > + if (err) > + goto reset_unlock; > + } > set_memory_rox((long)st_map->image, 1); > /* Let bpf_link handle registration & unregistration. > * > @@ -663,9 +666,6 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) > if (attr->value_size != vt->size) > return ERR_PTR(-EINVAL); > > - if (attr->map_flags & BPF_F_LINK && (!st_ops->validate || !st_ops->update)) > - return ERR_PTR(-EOPNOTSUPP); > - > t = st_ops->type; > > st_map_size = sizeof(*st_map) + > @@ -838,6 +838,11 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map > goto err_out; > } > > + if (!st_map->st_ops->update) { > + err = -EOPNOTSUPP; > + goto err_out; > + } > +
We can perform this check before calling mutex_lock(), and return -EOPNOTSUPP early.
> err = st_map->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data); > if (err) > goto err_out;
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