On Sun, Sep 04, 2022 at 10:41:18PM +0200, Kumar Kartikeya Dwivedi wrote:
> Enable support for kptrs in local storage maps by wiring up the freeing
> of these kptrs from map value.
>
> Cc: Martin KaFai Lau <kafai@xxxxxx>
> Cc: KP Singh <kpsingh@xxxxxxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> include/linux/bpf_local_storage.h | 2 +-
> kernel/bpf/bpf_local_storage.c | 33 +++++++++++++++++++++++++++----
> kernel/bpf/syscall.c | 5 ++++-
> kernel/bpf/verifier.c | 9 ++++++---
> 4 files changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h
> index 7ea18d4da84b..6786d00f004e 100644
> --- a/include/linux/bpf_local_storage.h
> +++ b/include/linux/bpf_local_storage.h
> @@ -74,7 +74,7 @@ struct bpf_local_storage_elem {
> struct hlist_node snode; /* Linked to bpf_local_storage */
> struct bpf_local_storage __rcu *local_storage;
> struct rcu_head rcu;
> - /* 8 bytes hole */
> + struct bpf_map *map; /* Only set for bpf_selem_free_rcu */
> /* The data is stored in another cacheline to minimize
> * the number of cachelines access during a cache hit.
> */
> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> index 802fc15b0d73..4a725379d761 100644
> --- a/kernel/bpf/bpf_local_storage.c
> +++ b/kernel/bpf/bpf_local_storage.c
> @@ -74,7 +74,8 @@ bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
> gfp_flags | __GFP_NOWARN);
> if (selem) {
> if (value)
> - memcpy(SDATA(selem)->data, value, smap->map.value_size);
> + copy_map_value(&smap->map, SDATA(selem)->data, value);
> + /* No call to check_and_init_map_value as memory is zero init */
> return selem;
> }
>
> @@ -92,12 +93,27 @@ void bpf_local_storage_free_rcu(struct rcu_head *rcu)
> kfree_rcu(local_storage, rcu);
> }
>
> +static void check_and_free_fields(struct bpf_local_storage_elem *selem)
> +{
> + if (map_value_has_kptrs(selem->map))
> + bpf_map_free_kptrs(selem->map, SDATA(selem));
> +}
> +
> static void bpf_selem_free_rcu(struct rcu_head *rcu)
> {
> struct bpf_local_storage_elem *selem;
>
> selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
> - kfree_rcu(selem, rcu);
> + check_and_free_fields(selem);
> + kfree(selem);
> +}
> +
> +static void bpf_selem_free_tasks_trace_rcu(struct rcu_head *rcu)
> +{
> + struct bpf_local_storage_elem *selem;
> +
> + selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
> + call_rcu(&selem->rcu, bpf_selem_free_rcu);
> }
>
> /* local_storage->lock must be held and selem->local_storage == local_storage.
> @@ -150,10 +166,11 @@ bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
> SDATA(selem))
> RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
>
> + selem->map = &smap->map;
> if (use_trace_rcu)
> - call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
> + call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_tasks_trace_rcu);
> else
> - kfree_rcu(selem, rcu);
> + call_rcu(&selem->rcu, bpf_selem_free_rcu);
>
> return free_local_storage;
> }
> @@ -581,6 +598,14 @@ void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
> */
> synchronize_rcu();
>
> + /* When local storage map has kptrs, the call_rcu callback accesses
> + * kptr_off_tab, hence we need the bpf_selem_free_rcu callbacks to
> + * finish before we free it.
> + */
> + if (map_value_has_kptrs(&smap->map)) {
> + rcu_barrier();
> + bpf_map_free_kptr_off_tab(&smap->map);
probably needs conditional rcu_barrier_tasks_trace before rcu_barrier?
With or without it will be a significant delay in map freeing.
Maybe we should generalize the destroy_mem_alloc trick?
Patch 4 needs rebase. Applied patches 1-3.
The first 5 look great to me.
Pls follow up with kptr specific tests.
