kernel/include/linux/bpf_local_storage.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (c) 2019 Facebook
 * Copyright 2020 Google LLC.
 */

#ifndef _BPF_LOCAL_STORAGE_H
#define _BPF_LOCAL_STORAGE_H

#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/rculist.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/types.h>
#include <linux/bpf_mem_alloc.h>
#include <uapi/linux/btf.h>

#define BPF_LOCAL_STORAGE_CACHE_SIZE	16

#define bpf_rcu_lock_held()                                                    \
	(rcu_read_lock_held() || rcu_read_lock_trace_held() ||                 \
	 rcu_read_lock_bh_held())
struct bpf_local_storage_map_bucket {
	struct hlist_head list;
	raw_spinlock_t lock;
};

/* Thp map is not the primary owner of a bpf_local_storage_elem.
 * Instead, the container object (eg. sk->sk_bpf_storage) is.
 *
 * The map (bpf_local_storage_map) is for two purposes
 * 1. Define the size of the "local storage".  It is
 *    the map's value_size.
 *
 * 2. Maintain a list to keep track of all elems such
 *    that they can be cleaned up during the map destruction.
 *
 * When a bpf local storage is being looked up for a
 * particular object,  the "bpf_map" pointer is actually used
 * as the "key" to search in the list of elem in
 * the respective bpf_local_storage owned by the object.
 *
 * e.g. sk->sk_bpf_storage is the mini-map with the "bpf_map" pointer
 * as the searching key.
 */
struct bpf_local_storage_map {
	struct bpf_map map;
	/* Lookup elem does not require accessing the map.
	 *
	 * Updating/Deleting requires a bucket lock to
	 * link/unlink the elem from the map.  Having
	 * multiple buckets to improve contention.
	 */
	struct bpf_local_storage_map_bucket *buckets;
	u32 bucket_log;
	u16 elem_size;
	u16 cache_idx;
	struct bpf_mem_alloc selem_ma;
	struct bpf_mem_alloc storage_ma;
	bool bpf_ma;
};

struct bpf_local_storage_data {
	/* smap is used as the searching key when looking up
	 * from the object's bpf_local_storage.
	 *
	 * Put it in the same cacheline as the data to minimize
	 * the number of cachelines accessed during the cache hit case.
	 */
	struct bpf_local_storage_map __rcu *smap;
	u8 data[] __aligned(8);
};

/* Linked to bpf_local_storage and bpf_local_storage_map */
struct bpf_local_storage_elem {
	struct hlist_node map_node;	/* Linked to bpf_local_storage_map */
	struct hlist_node snode;	/* Linked to bpf_local_storage */
	struct bpf_local_storage __rcu *local_storage;
	union {
		struct rcu_head rcu;
		struct hlist_node free_node;	/* used to postpone
						 * bpf_selem_free
						 * after raw_spin_unlock
						 */
	};
	/* 8 bytes hole */
	/* The data is stored in another cacheline to minimize
	 * the number of cachelines access during a cache hit.
	 */
	struct bpf_local_storage_data sdata ____cacheline_aligned;
};

struct bpf_local_storage {
	struct bpf_local_storage_data __rcu *cache[BPF_LOCAL_STORAGE_CACHE_SIZE];
	struct bpf_local_storage_map __rcu *smap;
	struct hlist_head list; /* List of bpf_local_storage_elem */
	void *owner;		/* The object that owns the above "list" of
				 * bpf_local_storage_elem.
				 */
	struct rcu_head rcu;
	raw_spinlock_t lock;	/* Protect adding/removing from the "list" */
};

/* U16_MAX is much more than enough for sk local storage
 * considering a tcp_sock is ~2k.
 */
#define BPF_LOCAL_STORAGE_MAX_VALUE_SIZE				       \
	min_t(u32,                                                             \
	      (KMALLOC_MAX_SIZE - MAX_BPF_STACK -                              \
	       sizeof(struct bpf_local_storage_elem)),                         \
	      (U16_MAX - sizeof(struct bpf_local_storage_elem)))

#define SELEM(_SDATA)                                                          \
	container_of((_SDATA), struct bpf_local_storage_elem, sdata)
#define SDATA(_SELEM) (&(_SELEM)->sdata)

#define BPF_LOCAL_STORAGE_CACHE_SIZE	16

struct bpf_local_storage_cache {
	spinlock_t idx_lock;
	u64 idx_usage_counts[BPF_LOCAL_STORAGE_CACHE_SIZE];
};

#define DEFINE_BPF_STORAGE_CACHE(name)				\
static struct bpf_local_storage_cache name = {			\
	.idx_lock = __SPIN_LOCK_UNLOCKED(name.idx_lock),	\
}

/* Helper functions for bpf_local_storage */
int bpf_local_storage_map_alloc_check(union bpf_attr *attr);

struct bpf_map *
bpf_local_storage_map_alloc(union bpf_attr *attr,
			    struct bpf_local_storage_cache *cache,
			    bool bpf_ma);

void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
				      struct bpf_local_storage_map *smap,
				      struct bpf_local_storage_elem *selem);
/* If cacheit_lockit is false, this lookup function is lockless */
static inline struct bpf_local_storage_data *
bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
			 struct bpf_local_storage_map *smap,
			 bool cacheit_lockit)
{
	struct bpf_local_storage_data *sdata;
	struct bpf_local_storage_elem *selem;

	/* Fast path (cache hit) */
	sdata = rcu_dereference_check(local_storage->cache[smap->cache_idx],
				      bpf_rcu_lock_held());
	if (sdata && rcu_access_pointer(sdata->smap) == smap)
		return sdata;

	/* Slow path (cache miss) */
	hlist_for_each_entry_rcu(selem, &local_storage->list, snode,
				  rcu_read_lock_trace_held())
		if (rcu_access_pointer(SDATA(selem)->smap) == smap)
			break;

	if (!selem)
		return NULL;
	if (cacheit_lockit)
		__bpf_local_storage_insert_cache(local_storage, smap, selem);
	return SDATA(selem);
}

void bpf_local_storage_destroy(struct bpf_local_storage *local_storage);

void bpf_local_storage_map_free(struct bpf_map *map,
				struct bpf_local_storage_cache *cache,
				int __percpu *busy_counter);

int bpf_local_storage_map_check_btf(const struct bpf_map *map,
				    const struct btf *btf,
				    const struct btf_type *key_type,
				    const struct btf_type *value_type);

void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
				   struct bpf_local_storage_elem *selem);

void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now);

void bpf_selem_link_map(struct bpf_local_storage_map *smap,
			struct bpf_local_storage_elem *selem);

struct bpf_local_storage_elem *
bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner, void *value,
		bool charge_mem, bool swap_uptrs, gfp_t gfp_flags);

void bpf_selem_free(struct bpf_local_storage_elem *selem,
		    struct bpf_local_storage_map *smap,
		    bool reuse_now);

int
bpf_local_storage_alloc(void *owner,
			struct bpf_local_storage_map *smap,
			struct bpf_local_storage_elem *first_selem,
			gfp_t gfp_flags);

struct bpf_local_storage_data *
bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
			 void *value, u64 map_flags, bool swap_uptrs, gfp_t gfp_flags);

u64 bpf_local_storage_map_mem_usage(const struct bpf_map *map);

#endif /* _BPF_LOCAL_STORAGE_H */