Re: [PATCH 1/2] bpf: htab: Split htab_elem_lru and htab_elem_pcpu off of htab_elem

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 7/22/26 9:38 PM, T.J. Mercier wrote:
> The htab_elem struct is used as the per-element type for all BPF hash
> map types and includes bpf_lru_node in a union with a ptr_to_pptr
> pointer. For standard (non-LRU, non-PCPU) hash maps, the 24 byte union
> allocated for every element is entirely unused. For non-preallocated
> PCPU maps, ptr_to_pptr only requires 8 bytes, leaving 16 bytes of unused
> overhead in the union. For preallocated PCPU maps ptr_to_pptr is unused
> since elements are freed to the PCPU freelist.
> 
> Eliminate this per-element memory overhead by splitting htab_elem into
> dedicated structures for each map type:
>    - struct htab_elem: Minimal structure for standard hash maps and
>      preallocated PCPU maps (saves 24 bytes per element).
>    - struct htab_elem_pcpu: Structure for non-preallocated PCPU maps
>      containing ptr_to_pptr (saves 16 bytes per element).
>    - struct htab_elem_lru: Retains struct bpf_lru_node for LRU maps.
> 
> Because element sizes now vary by map type, add key_offset to struct
> bpf_htab to track the dynamic key offset. Update helper accessors and
> lookups to compute key and value offsets using htab->key_offset.
> 
> Pointers to struct htab_elem in the existing code (e.g. htab_elem_hash)
> serve as generic base element pointers. This is possible because
> htab_elem, htab_elem_pcpu, and htab_elem_lru share a common initial
> sequence, making pointer casts safe.
> 
> Signed-off-by: T.J. Mercier <tjmercier@google.com>
> ---
>  kernel/bpf/hashtab.c    | 318 +++++++++++++++++++++++++++-------------
>  kernel/bpf/map_in_map.c |  13 ++
>  kernel/bpf/map_in_map.h |   2 +
>  3 files changed, 234 insertions(+), 99 deletions(-)
> 
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 9f394e1aa2e8..57729c3dff3d 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -102,6 +102,7 @@ struct bpf_htab {
>  	bool use_percpu_counter;
>  	u32 n_buckets;	/* number of hash buckets */
>  	u32 elem_size;	/* size of each element in bytes */
> +	u32 key_offset;	/* offset of key in bytes */
>  	u32 hashrnd;
>  };
>  
> @@ -117,14 +118,41 @@ struct htab_elem {
>  			};
>  		};
>  	};
> +	u32 hash;
> +} __aligned(8);
> +
> +struct htab_elem_lru {
>  	union {
> -		/* pointer to per-cpu pointer */
> -		void *ptr_to_pptr;
> -		struct bpf_lru_node lru_node;
> +		struct hlist_nulls_node hash_node;
> +		struct {
> +			void *padding;
> +			union {
> +				struct pcpu_freelist_node fnode;
> +				struct htab_elem_lru *batch_flink;
> +			};
> +		};
>  	};
> +	struct bpf_lru_node lru_node;
>  	u32 hash;
> -	char key[] __aligned(8);
> -};
> +} __aligned(8);
> +
> +/* Only for non-preallocated PCPU maps. Preallocated PCPU maps don't need
> + * ptr_to_pptr, and use htab_elem.
> + */
> +struct htab_elem_pcpu {
> +	union {
> +		struct hlist_nulls_node hash_node;
> +		struct {
> +			void *padding;
> +			union {
> +				struct pcpu_freelist_node fnode;
> +				struct htab_elem_pcpu *batch_flink;
> +			};
> +		};
> +	};

Will it make the code more readable if we move this common part into a separate
struct (keep the name htab_elem to minimise the change) and reuse it across 
different variants: htab_elem_standard/htab_elem_pcpu/htab_elem_lru. This will allow removing 
those BUILD_BUG_ON() and be explicit about the comon part of the layout.

> +	void *ptr_to_pptr;
> +	u32 hash;

We can remove u32 hash field and instead add dynamic 
array `u8 data[] __aligned(8);` that going to store the same layout. 
I think that buys us clearer definition of dynamic
section of the structure that has different layout depending on the key size.

> +} __aligned(8);
>  
>  struct htab_btf_record {
>  	struct btf_record *record;
> @@ -136,6 +164,21 @@ static inline bool htab_is_prealloc(const struct bpf_htab *htab)
>  	return !(htab->map.map_flags & BPF_F_NO_PREALLOC);
>  }
>  
...
> @@ -428,6 +494,25 @@ static int htab_map_alloc_check(union bpf_attr *attr)
>  	BUILD_BUG_ON(offsetof(struct htab_elem, fnode.next) !=
>  		     offsetof(struct htab_elem, hash_node.pprev));
>  
> +	/* htab_elem pointers are used as base pointers for htab_elem_lru and
> +	 * htab_elem_pcpu. These structures must share a common initial sequence
> +	 * to ensure pointer casting between them is safe.
> +	 */
> +	BUILD_BUG_ON(offsetof(struct htab_elem, hash_node) !=
> +		     offsetof(struct htab_elem_lru, hash_node));
> +	BUILD_BUG_ON(offsetof(struct htab_elem, hash_node) !=
> +		     offsetof(struct htab_elem_pcpu, hash_node));
> +
> +	BUILD_BUG_ON(offsetof(struct htab_elem, padding) !=
> +		     offsetof(struct htab_elem_lru, padding));
> +	BUILD_BUG_ON(offsetof(struct htab_elem, padding) !=
> +		     offsetof(struct htab_elem_pcpu, padding));
> +
> +	BUILD_BUG_ON(offsetof(struct htab_elem, fnode) !=
> +		     offsetof(struct htab_elem_lru, fnode));
> +	BUILD_BUG_ON(offsetof(struct htab_elem, fnode) !=
> +		     offsetof(struct htab_elem_pcpu, fnode));
> +
>  	if (zero_seed && !capable(CAP_SYS_ADMIN))
>  		/* Guard against local DoS, and discourage production use. */
>  		return -EPERM;
> @@ -476,7 +561,7 @@ static void htab_mem_dtor(void *obj, void *ctx)
>  	if (IS_ERR_OR_NULL(hrec->record))
>  		return;
>  
> -	map_value = htab_elem_value(elem, hrec->key_size);
> +	map_value = (void *)elem + sizeof(struct htab_elem) + round_up(hrec->key_size, 8);
>  	bpf_obj_free_fields(hrec->record, map_value);
>  }
>  
> @@ -583,8 +668,14 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
>  
>  	htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
>  
> -	htab->elem_size = sizeof(struct htab_elem) +
> -			  round_up(htab->map.key_size, 8);
> +	if (htab_is_lru(htab))
> +		htab->key_offset = sizeof(struct htab_elem_lru);
> +	else if (percpu && !prealloc)
> +		htab->key_offset = sizeof(struct htab_elem_pcpu);
> +	else
> +		htab->key_offset = sizeof(struct htab_elem);
> +
> +	htab->elem_size = htab->key_offset + round_up(htab->map.key_size, 8);
>  	if (percpu)
>  		htab->elem_size += sizeof(void *);
>  	else
> @@ -692,14 +783,16 @@ static inline struct hlist_nulls_head *select_bucket(struct bpf_htab *htab, u32
>  }
>  
>  /* this lookup function can only be called with bucket lock taken */
> -static struct htab_elem *lookup_elem_raw(struct hlist_nulls_head *head, u32 hash,
> +static struct htab_elem *lookup_elem_raw(struct bpf_htab *htab,
> +					 struct hlist_nulls_head *head, u32 hash,
>  					 void *key, u32 key_size)
>  {
>  	struct hlist_nulls_node *n;
>  	struct htab_elem *l;
>  
>  	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
> -		if (l->hash == hash && !memcmp(&l->key, key, key_size))
> +		if (htab_elem_hash(htab, l) == hash &&
> +		    !memcmp(htab_elem_key(htab, l), key, key_size))
>  			return l;
>  
>  	return NULL;
> @@ -709,7 +802,8 @@ static struct htab_elem *lookup_elem_raw(struct hlist_nulls_head *head, u32 hash
>   * the unlikely event when elements moved from one bucket into another
>   * while link list is being walked
>   */
> -static struct htab_elem *lookup_nulls_elem_raw(struct hlist_nulls_head *head,
> +static struct htab_elem *lookup_nulls_elem_raw(struct bpf_htab *htab,
> +					       struct hlist_nulls_head *head,
>  					       u32 hash, void *key,
>  					       u32 key_size, u32 n_buckets)
>  {
> @@ -718,7 +812,8 @@ static struct htab_elem *lookup_nulls_elem_raw(struct hlist_nulls_head *head,
>  
>  again:
>  	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
> -		if (l->hash == hash && !memcmp(&l->key, key, key_size))
> +		if (htab_elem_hash(htab, l) == hash &&
> +		    !memcmp(htab_elem_key(htab, l), key, key_size))
>  			return l;
>  
>  	if (unlikely(get_nulls_value(n) != (hash & (n_buckets - 1))))
> @@ -747,17 +842,18 @@ static void *__htab_map_lookup_elem(struct bpf_map *map, void *key)
>  
>  	head = select_bucket(htab, hash);
>  
> -	l = lookup_nulls_elem_raw(head, hash, key, key_size, htab->n_buckets);
> +	l = lookup_nulls_elem_raw(htab, head, hash, key, key_size, htab->n_buckets);
>  
>  	return l;
>  }
>  
>  static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l = __htab_map_lookup_elem(map, key);
>  
>  	if (l)
> -		return htab_elem_value(l, map->key_size);
> +		return htab_elem_value(htab, l);
>  
>  	return NULL;
>  }
> @@ -775,6 +871,7 @@ static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
>   */
>  static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct bpf_insn *insn = insn_buf;
>  	const int ret = BPF_REG_0;
>  
> @@ -783,7 +880,7 @@ static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
>  	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
> -				offsetof(struct htab_elem, key) +
> +				htab->key_offset +
>  				round_up(map->key_size, 8));
>  	return insn - insn_buf;
>  }
> @@ -791,12 +888,13 @@ static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
>  static __always_inline void *__htab_lru_map_lookup_elem(struct bpf_map *map,
>  							void *key, const bool mark)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l = __htab_map_lookup_elem(map, key);
>  
>  	if (l) {
>  		if (mark)
> -			bpf_lru_node_set_ref(&l->lru_node);
> -		return htab_elem_value(l, map->key_size);
> +			bpf_lru_node_set_ref(htab_elem_lru_node(l));
> +		return htab_elem_value(htab, l);
>  	}
>  
>  	return NULL;
> @@ -815,6 +913,7 @@ static void *htab_lru_map_lookup_elem_sys(struct bpf_map *map, void *key)
>  static int htab_lru_map_gen_lookup(struct bpf_map *map,
>  				   struct bpf_insn *insn_buf)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct bpf_insn *insn = insn_buf;
>  	const int ret = BPF_REG_0;
>  	const int ref_reg = BPF_REG_1;
> @@ -824,15 +923,15 @@ static int htab_lru_map_gen_lookup(struct bpf_map *map,
>  	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);
>  	*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,
> -			      offsetof(struct htab_elem, lru_node) +
> +			      offsetof(struct htab_elem_lru, lru_node) +
>  			      offsetof(struct bpf_lru_node, ref));
>  	*insn++ = BPF_JMP_IMM(BPF_JNE, ref_reg, 0, 1);
>  	*insn++ = BPF_ST_MEM(BPF_B, ret,
> -			     offsetof(struct htab_elem, lru_node) +
> +			     offsetof(struct htab_elem_lru, lru_node) +
>  			     offsetof(struct bpf_lru_node, ref),
>  			     1);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
> -				offsetof(struct htab_elem, key) +
> +				htab->key_offset +
>  				round_up(map->key_size, 8));
>  	return insn - insn_buf;
>  }
> @@ -844,13 +943,13 @@ static void check_and_cancel_fields(struct bpf_htab *htab,
>  		return;
>  
>  	if (htab_is_percpu(htab)) {
> -		void __percpu *pptr = htab_elem_get_ptr(elem, htab->map.key_size);
> +		void __percpu *pptr = htab_elem_get_ptr(htab, elem);
>  		int cpu;
>  
>  		for_each_possible_cpu(cpu)
>  			bpf_obj_cancel_fields(&htab->map, per_cpu_ptr(pptr, cpu));
>  	} else {
> -		void *map_value = htab_elem_value(elem, htab->map.key_size);
> +		void *map_value = htab_elem_value(htab, elem);
>  
>  		bpf_obj_cancel_fields(&htab->map, map_value);
>  	}
> @@ -869,8 +968,8 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
>  	struct bucket *b;
>  	int ret;
>  
> -	tgt_l = container_of(node, struct htab_elem, lru_node);
> -	b = __select_bucket(htab, tgt_l->hash);
> +	tgt_l = (struct htab_elem *)container_of(node, struct htab_elem_lru, lru_node);
> +	b = __select_bucket(htab, htab_elem_hash(htab, tgt_l));
>  	head = &b->head;
>  
>  	ret = htab_lock_bucket(b, &flags);
> @@ -912,7 +1011,7 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>  	head = select_bucket(htab, hash);
>  
>  	/* lookup the key */
> -	l = lookup_nulls_elem_raw(head, hash, key, key_size, htab->n_buckets);
> +	l = lookup_nulls_elem_raw(htab, head, hash, key, key_size, htab->n_buckets);
>  
>  	if (!l)
>  		goto find_first_elem;
> @@ -923,7 +1022,7 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>  
>  	if (next_l) {
>  		/* if next elem in this hash list is non-zero, just return it */
> -		memcpy(next_key, next_l->key, key_size);
> +		memcpy(next_key, htab_elem_key(htab, next_l), key_size);
>  		return 0;
>  	}
>  
> @@ -941,7 +1040,7 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>  					  struct htab_elem, hash_node);
>  		if (next_l) {
>  			/* if it's not empty, just return it */
> -			memcpy(next_key, next_l->key, key_size);
> +			memcpy(next_key, htab_elem_key(htab, next_l), key_size);
>  			return 0;
>  		}
>  	}
> @@ -955,7 +1054,7 @@ static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)
>  	check_and_cancel_fields(htab, l);
>  
>  	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
> -		bpf_mem_cache_free(&htab->pcpu_ma, l->ptr_to_pptr);
> +		bpf_mem_cache_free(&htab->pcpu_ma, htab_elem_get_ptr_to_pptr(l));
>  	bpf_mem_cache_free(&htab->ma, l);
>  }
>  
> @@ -965,7 +1064,7 @@ static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
>  	void *ptr;
>  
>  	if (map->ops->map_fd_put_ptr) {
> -		ptr = fd_htab_map_get_ptr(map, l);
> +		ptr = fd_htab_map_get_ptr(htab, l);
>  		map->ops->map_fd_put_ptr(map, ptr, true);
>  	}
>  }
> @@ -1117,10 +1216,10 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
>  		}
>  	}
>  
> -	memcpy(l_new->key, key, key_size);
> +	memcpy(htab_elem_key(htab, l_new), key, key_size);
>  	if (percpu) {
>  		if (prealloc) {
> -			pptr = htab_elem_get_ptr(l_new, key_size);
> +			pptr = htab_elem_get_ptr(htab, l_new);
>  		} else {
>  			/* alloc_percpu zero-fills */
>  			void *ptr = bpf_mem_cache_alloc(&htab->pcpu_ma);
> @@ -1130,26 +1229,26 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
>  				l_new = ERR_PTR(-ENOMEM);
>  				goto dec_count;
>  			}
> -			l_new->ptr_to_pptr = ptr;
> +			htab_elem_set_ptr_to_pptr(l_new, ptr);
>  			pptr = *(void __percpu **)ptr;
>  		}
>  
>  		pcpu_init_value(htab, pptr, value, onallcpus, map_flags);
>  
>  		if (!prealloc)
> -			htab_elem_set_ptr(l_new, key_size, pptr);
> +			htab_elem_set_ptr(htab, l_new, pptr);
>  	} else if (fd_htab_map_needs_adjust(htab)) {
>  		size = round_up(size, 8);
> -		memcpy(htab_elem_value(l_new, key_size), value, size);
> +		memcpy(htab_elem_value(htab, l_new), value, size);
>  	} else if (map_flags & BPF_F_LOCK) {
>  		copy_map_value_locked(&htab->map,
> -				      htab_elem_value(l_new, key_size),
> +				      htab_elem_value(htab, l_new),
>  				      value, false);
>  	} else {
> -		copy_map_value(&htab->map, htab_elem_value(l_new, key_size), value);
> +		copy_map_value(&htab->map, htab_elem_value(htab, l_new), value);
>  	}
>  
> -	l_new->hash = hash;
> +	htab_elem_set_hash(htab, l_new, hash);
>  	return l_new;
>  dec_count:
>  	dec_elem_count(htab);
> @@ -1199,7 +1298,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>  		if (unlikely(!btf_record_has_field(map->record, BPF_SPIN_LOCK)))
>  			return -EINVAL;
>  		/* find an element without taking the bucket lock */
> -		l_old = lookup_nulls_elem_raw(head, hash, key, key_size,
> +		l_old = lookup_nulls_elem_raw(htab, head, hash, key, key_size,
>  					      htab->n_buckets);
>  		ret = check_flags(htab, l_old, map_flags);
>  		if (ret)
> @@ -1207,7 +1306,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>  		if (l_old) {
>  			/* grab the element lock and update value in place */
>  			copy_map_value_locked(map,
> -					      htab_elem_value(l_old, key_size),
> +					      htab_elem_value(htab, l_old),
>  					      value, false);
>  			return 0;
>  		}
> @@ -1221,7 +1320,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>  	if (ret)
>  		return ret;
>  
> -	l_old = lookup_elem_raw(head, hash, key, key_size);
> +	l_old = lookup_elem_raw(htab, head, hash, key, key_size);
>  
>  	ret = check_flags(htab, l_old, map_flags);
>  	if (ret)
> @@ -1235,7 +1334,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
>  		 * and update element in place
>  		 */
>  		copy_map_value_locked(map,
> -				      htab_elem_value(l_old, key_size),
> +				      htab_elem_value(htab, l_old),
>  				      value, false);
>  		ret = 0;
>  		goto err;
> @@ -1275,7 +1374,7 @@ static void htab_lru_push_free(struct bpf_htab *htab, struct htab_elem *elem)
>  {
>  	check_and_cancel_fields(htab, elem);
>  	bpf_map_dec_elem_count(&htab->map);
> -	bpf_lru_push_free(&htab->lru, &elem->lru_node);
> +	bpf_lru_push_free(&htab->lru, htab_elem_lru_node(elem));
>  }
>  
>  static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
> @@ -1310,13 +1409,13 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
>  	l_new = prealloc_lru_pop(htab, key, hash);
>  	if (!l_new)
>  		return -ENOMEM;
> -	copy_map_value(&htab->map, htab_elem_value(l_new, map->key_size), value);
> +	copy_map_value(&htab->map, htab_elem_value(htab, l_new), value);
>  
>  	ret = htab_lock_bucket(b, &flags);
>  	if (ret)
>  		goto err_lock_bucket;
>  
> -	l_old = lookup_elem_raw(head, hash, key, key_size);
> +	l_old = lookup_elem_raw(htab, head, hash, key, key_size);
>  
>  	ret = check_flags(htab, l_old, map_flags);
>  	if (ret)
> @@ -1327,7 +1426,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
>  	 */
>  	hlist_nulls_add_head_rcu(&l_new->hash_node, head);
>  	if (l_old) {
> -		bpf_lru_node_set_ref(&l_new->lru_node);
> +		bpf_lru_node_set_ref(htab_elem_lru_node(l_new));
>  		hlist_nulls_del_rcu(&l_old->hash_node);
>  	}
>  	ret = 0;
> @@ -1383,7 +1482,7 @@ static long htab_map_update_elem_in_place(struct bpf_map *map, void *key,
>  	if (ret)
>  		return ret;
>  
> -	l_old = lookup_elem_raw(head, hash, key, key_size);
> +	l_old = lookup_elem_raw(htab, head, hash, key, key_size);
>  
>  	ret = check_flags(htab, l_old, map_flags);
>  	if (ret)
> @@ -1392,10 +1491,10 @@ static long htab_map_update_elem_in_place(struct bpf_map *map, void *key,
>  	if (l_old) {
>  		/* Update value in-place */
>  		if (percpu) {
> -			pcpu_copy_value(htab, htab_elem_get_ptr(l_old, key_size),
> +			pcpu_copy_value(htab, htab_elem_get_ptr(htab, l_old),
>  					value, onallcpus, map_flags);
>  		} else {
> -			void **inner_map_pptr = htab_elem_value(l_old, key_size);
> +			void **inner_map_pptr = htab_elem_value(htab, l_old);
>  
>  			old_map_ptr = *inner_map_pptr;
>  			WRITE_ONCE(*inner_map_pptr, *(void **)value);
> @@ -1456,20 +1555,20 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
>  	if (ret)
>  		goto err_lock_bucket;
>  
> -	l_old = lookup_elem_raw(head, hash, key, key_size);
> +	l_old = lookup_elem_raw(htab, head, hash, key, key_size);
>  
>  	ret = check_flags(htab, l_old, map_flags);
>  	if (ret)
>  		goto err;
>  
>  	if (l_old) {
> -		bpf_lru_node_set_ref(&l_old->lru_node);
> +		bpf_lru_node_set_ref(htab_elem_lru_node(l_old));
>  
>  		/* per-cpu hash map can update value in-place */
> -		pcpu_copy_value(htab, htab_elem_get_ptr(l_old, key_size),
> +		pcpu_copy_value(htab, htab_elem_get_ptr(htab, l_old),
>  				value, onallcpus, map_flags);
>  	} else {
> -		pcpu_init_value(htab, htab_elem_get_ptr(l_new, key_size),
> +		pcpu_init_value(htab, htab_elem_get_ptr(htab, l_new),
>  				value, onallcpus, map_flags);
>  		hlist_nulls_add_head_rcu(&l_new->hash_node, head);
>  		l_new = NULL;
> @@ -1480,7 +1579,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
>  err_lock_bucket:
>  	if (l_new) {
>  		bpf_map_dec_elem_count(&htab->map);
> -		bpf_lru_push_free(&htab->lru, &l_new->lru_node);
> +		bpf_lru_push_free(&htab->lru, htab_elem_lru_node(l_new));
>  	}
>  	return ret;
>  }
> @@ -1521,7 +1620,7 @@ static long htab_map_delete_elem(struct bpf_map *map, void *key)
>  	if (ret)
>  		return ret;
>  
> -	l = lookup_elem_raw(head, hash, key, key_size);
> +	l = lookup_elem_raw(htab, head, hash, key, key_size);
>  	if (l)
>  		hlist_nulls_del_rcu(&l->hash_node);
>  	else
> @@ -1556,7 +1655,7 @@ static long htab_lru_map_delete_elem(struct bpf_map *map, void *key)
>  	if (ret)
>  		return ret;
>  
> -	l = lookup_elem_raw(head, hash, key, key_size);
> +	l = lookup_elem_raw(htab, head, hash, key, key_size);
>  
>  	if (l)
>  		hlist_nulls_del_rcu(&l->hash_node);
> @@ -1602,7 +1701,7 @@ static void htab_free_malloced_internal_structs(struct bpf_htab *htab)
>  		hlist_nulls_for_each_entry(l, n, head, hash_node) {
>  			/* We only free internal structs on uref dropping to zero */
>  			bpf_map_free_internal_structs(&htab->map,
> -						      htab_elem_value(l, htab->map.key_size));
> +						      htab_elem_value(htab, l));
>  		}
>  		cond_resched_rcu();
>  	}
> @@ -1697,7 +1796,7 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
>  	if (ret)
>  		return ret;
>  
> -	l = lookup_elem_raw(head, hash, key, key_size);
> +	l = lookup_elem_raw(htab, head, hash, key, key_size);
>  	if (!l) {
>  		ret = -ENOENT;
>  		goto out_unlock;
> @@ -1708,14 +1807,14 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
>  		void __percpu *pptr;
>  		int off = 0, cpu;
>  
> -		pptr = htab_elem_get_ptr(l, key_size);
> +		pptr = htab_elem_get_ptr(htab, l);
>  		for_each_possible_cpu(cpu) {
>  			copy_map_value_long(&htab->map, value + off, per_cpu_ptr(pptr, cpu));
>  			check_and_init_map_value(&htab->map, value + off);
>  			off += roundup_value_size;
>  		}
>  	} else {
> -		void *src = htab_elem_value(l, map->key_size);
> +		void *src = htab_elem_value(htab, l);
>  
>  		if (flags & BPF_F_LOCK)
>  			copy_map_value_locked(map, value, src, true);
> @@ -1898,13 +1997,13 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>  		goto next_batch;
>  
>  	hlist_nulls_for_each_entry_safe(l, n, head, hash_node) {
> -		memcpy(dst_key, l->key, key_size);
> +		memcpy(dst_key, htab_elem_key(htab, l), key_size);
>  
>  		if (is_percpu) {
>  			int off = 0, cpu;
>  			void __percpu *pptr;
>  
> -			pptr = htab_elem_get_ptr(l, map->key_size);
> +			pptr = htab_elem_get_ptr(htab, l);
>  			if (elem_map_flags & BPF_F_CPU) {
>  				cpu = elem_map_flags >> 32;
>  				copy_map_value(&htab->map, dst_val, per_cpu_ptr(pptr, cpu));
> @@ -1918,7 +2017,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
>  				}
>  			}
>  		} else {
> -			value = htab_elem_value(l, key_size);
> +			value = htab_elem_value(htab, l);
>  			if (is_fd_htab(htab)) {
>  				struct bpf_map **inner_map = value;
>  
> @@ -2183,12 +2282,12 @@ static int __bpf_hash_map_seq_show(struct seq_file *seq, struct htab_elem *elem)
>  		ctx.meta = &meta;
>  		ctx.map = info->map;
>  		if (elem) {
> -			ctx.key = elem->key;
> +			ctx.key = htab_elem_key(info->htab, elem);
>  			if (!info->percpu_value_buf) {
> -				ctx.value = htab_elem_value(elem, map->key_size);
> +				ctx.value = htab_elem_value(info->htab, elem);
>  			} else {
>  				roundup_value_size = round_up(map->value_size, 8);
> -				pptr = htab_elem_get_ptr(elem, map->key_size);
> +				pptr = htab_elem_get_ptr(info->htab, elem);
>  				for_each_possible_cpu(cpu) {
>  					copy_map_value_long(map, info->percpu_value_buf + off,
>  							    per_cpu_ptr(pptr, cpu));
> @@ -2293,13 +2392,13 @@ static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_
>  		rcu_read_lock();
>  		head = &b->head;
>  		hlist_nulls_for_each_entry_safe(elem, n, head, hash_node) {
> -			key = elem->key;
> +			key = htab_elem_key(htab, elem);
>  			if (is_percpu) {
>  				/* current cpu value for percpu map */
> -				pptr = htab_elem_get_ptr(elem, map->key_size);
> +				pptr = htab_elem_get_ptr(htab, elem);
>  				val = this_cpu_ptr(pptr);
>  			} else {
> -				val = htab_elem_value(elem, map->key_size);
> +				val = htab_elem_value(htab, elem);
>  			}
>  			num_elems++;
>  			ret = callback_fn((u64)(long)map, (u64)(long)key,
> @@ -2403,10 +2502,11 @@ const struct bpf_map_ops htab_lru_map_ops = {
>  /* Called from eBPF program */
>  static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l = __htab_map_lookup_elem(map, key);
>  
>  	if (l)
> -		return this_cpu_ptr(htab_elem_get_ptr(l, map->key_size));
> +		return this_cpu_ptr(htab_elem_get_ptr(htab, l));
>  	else
>  		return NULL;
>  }
> @@ -2414,6 +2514,7 @@ static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
>  /* inline bpf_map_lookup_elem() call for per-CPU hashmap */
>  static int htab_percpu_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct bpf_insn *insn = insn_buf;
>  
>  	if (!bpf_jit_supports_percpu_insn())
> @@ -2424,7 +2525,7 @@ static int htab_percpu_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn
>  	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0,
> -				offsetof(struct htab_elem, key) + roundup(map->key_size, 8));
> +				htab->key_offset + roundup(map->key_size, 8));
>  	*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
>  	*insn++ = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
>  
> @@ -2433,6 +2534,7 @@ static int htab_percpu_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn
>  
>  static void *htab_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *key, u32 cpu)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l;
>  
>  	if (cpu >= nr_cpu_ids)
> @@ -2440,18 +2542,19 @@ static void *htab_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *key,
>  
>  	l = __htab_map_lookup_elem(map, key);
>  	if (l)
> -		return per_cpu_ptr(htab_elem_get_ptr(l, map->key_size), cpu);
> +		return per_cpu_ptr(htab_elem_get_ptr(htab, l), cpu);
>  	else
>  		return NULL;
>  }
>  
>  static void *htab_lru_percpu_map_lookup_elem(struct bpf_map *map, void *key)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l = __htab_map_lookup_elem(map, key);
>  
>  	if (l) {
> -		bpf_lru_node_set_ref(&l->lru_node);
> -		return this_cpu_ptr(htab_elem_get_ptr(l, map->key_size));
> +		bpf_lru_node_set_ref(htab_elem_lru_node(l));
> +		return this_cpu_ptr(htab_elem_get_ptr(htab, l));
>  	}
>  
>  	return NULL;
> @@ -2459,6 +2562,7 @@ static void *htab_lru_percpu_map_lookup_elem(struct bpf_map *map, void *key)
>  
>  static void *htab_lru_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *key, u32 cpu)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l;
>  
>  	if (cpu >= nr_cpu_ids)
> @@ -2466,8 +2570,8 @@ static void *htab_lru_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *k
>  
>  	l = __htab_map_lookup_elem(map, key);
>  	if (l) {
> -		bpf_lru_node_set_ref(&l->lru_node);
> -		return per_cpu_ptr(htab_elem_get_ptr(l, map->key_size), cpu);
> +		bpf_lru_node_set_ref(htab_elem_lru_node(l));
> +		return per_cpu_ptr(htab_elem_get_ptr(htab, l), cpu);
>  	}
>  
>  	return NULL;
> @@ -2475,6 +2579,7 @@ static void *htab_lru_percpu_map_lookup_percpu_elem(struct bpf_map *map, void *k
>  
>  int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value, u64 map_flags)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l;
>  	void __percpu *pptr;
>  	int ret = -ENOENT;
> @@ -2494,7 +2599,7 @@ int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value, u64 map_fl
>  	/* We do not mark LRU map element here in order to not mess up
>  	 * eviction heuristics when user space does a map walk.
>  	 */
> -	pptr = htab_elem_get_ptr(l, map->key_size);
> +	pptr = htab_elem_get_ptr(htab, l);
>  	if (map_flags & BPF_F_CPU) {
>  		cpu = map_flags >> 32;
>  		copy_map_value(map, value, per_cpu_ptr(pptr, cpu));
> @@ -2532,6 +2637,7 @@ int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
>  static void htab_percpu_map_seq_show_elem(struct bpf_map *map, void *key,
>  					  struct seq_file *m)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct htab_elem *l;
>  	void __percpu *pptr;
>  	int cpu;
> @@ -2546,7 +2652,7 @@ static void htab_percpu_map_seq_show_elem(struct bpf_map *map, void *key,
>  
>  	btf_type_seq_show(map->btf, map->btf_key_type_id, key, m);
>  	seq_puts(m, ": {\n");
> -	pptr = htab_elem_get_ptr(l, map->key_size);
> +	pptr = htab_elem_get_ptr(htab, l);
>  	for_each_possible_cpu(cpu) {
>  		seq_printf(m, "\tcpu%d: ", cpu);
>  		btf_type_seq_show(map->btf, map->btf_value_type_id,
> @@ -2620,7 +2726,7 @@ static void fd_htab_map_free(struct bpf_map *map)
>  		head = select_bucket(htab, i);
>  
>  		hlist_nulls_for_each_entry_safe(l, n, head, hash_node) {
> -			void *ptr = fd_htab_map_get_ptr(map, l);
> +			void *ptr = fd_htab_map_get_ptr(htab, l);
>  
>  			map->ops->map_fd_put_ptr(map, ptr, false);
>  		}
> @@ -2705,6 +2811,7 @@ static void *htab_of_map_lookup_elem(struct bpf_map *map, void *key)
>  static int htab_of_map_gen_lookup(struct bpf_map *map,
>  				  struct bpf_insn *insn_buf)
>  {
> +	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>  	struct bpf_insn *insn = insn_buf;
>  	const int ret = BPF_REG_0;
>  
> @@ -2713,7 +2820,7 @@ static int htab_of_map_gen_lookup(struct bpf_map *map,
>  	*insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
>  	*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);
>  	*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
> -				offsetof(struct htab_elem, key) +
> +				htab->key_offset +
>  				round_up(map->key_size, 8));
>  	*insn++ = BPF_LDX_MEM(BPF_DW, ret, ret, 0);
>  
> @@ -3533,3 +3640,16 @@ const struct bpf_map_ops rhtab_map_ops = {
>  	.map_btf_id = &rhtab_map_btf_ids[0],
>  	.iter_seq_info = &rhash_iter_seq_info,
>  };
> +
> +size_t bpf_htab_map_meta_size(void)
> +{
> +	return sizeof(struct bpf_htab);
> +}
> +
> +void bpf_htab_map_meta_init(struct bpf_map *inner_map_meta, struct bpf_map *inner_map)
> +{
> +	struct bpf_htab *inner_htab_meta = container_of(inner_map_meta, struct bpf_htab, map);
> +	struct bpf_htab *inner_htab = container_of(inner_map, struct bpf_htab, map);
> +
> +	inner_htab_meta->key_offset = inner_htab->key_offset;
> +}
> diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c
> index d2cbab4bdf64..b2db5d0c98be 100644
> --- a/kernel/bpf/map_in_map.c
> +++ b/kernel/bpf/map_in_map.c
> @@ -7,6 +7,15 @@
>  
>  #include "map_in_map.h"
>  
> +static bool bpf_map_type_is_htab(enum bpf_map_type type)
> +{
> +	return type == BPF_MAP_TYPE_HASH ||
> +	       type == BPF_MAP_TYPE_PERCPU_HASH ||
> +	       type == BPF_MAP_TYPE_LRU_HASH ||
> +	       type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
> +	       type == BPF_MAP_TYPE_HASH_OF_MAPS;
> +}
> +
>  struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
>  {
>  	struct bpf_map *inner_map, *inner_map_meta;
> @@ -29,6 +38,8 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
>  	/* In some cases verifier needs to access beyond just base map. */
>  	if (inner_map->ops == &array_map_ops || inner_map->ops == &percpu_array_map_ops)
>  		inner_map_meta_size = sizeof(struct bpf_array);
> +	else if (bpf_map_type_is_htab(inner_map->map_type))
> +		inner_map_meta_size = bpf_htab_map_meta_size();
>  
>  	inner_map_meta = kzalloc(inner_map_meta_size, GFP_USER);
>  	if (!inner_map_meta)
> @@ -70,6 +81,8 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
>  		inner_array_meta->index_mask = inner_array->index_mask;
>  		inner_array_meta->elem_size = inner_array->elem_size;
>  		inner_map_meta->bypass_spec_v1 = inner_map->bypass_spec_v1;
> +	} else if (bpf_map_type_is_htab(inner_map->map_type)) {
> +		bpf_htab_map_meta_init(inner_map_meta, inner_map);
>  	}
>  	return inner_map_meta;
>  }
> diff --git a/kernel/bpf/map_in_map.h b/kernel/bpf/map_in_map.h
> index 7d61602354de..1edc205772d8 100644
> --- a/kernel/bpf/map_in_map.h
> +++ b/kernel/bpf/map_in_map.h
> @@ -15,5 +15,7 @@ void *bpf_map_fd_get_ptr(struct bpf_map *map, struct file *map_file,
>  			 int ufd);
>  void bpf_map_fd_put_ptr(struct bpf_map *map, void *ptr, bool need_defer);
>  u32 bpf_map_fd_sys_lookup_elem(void *ptr);
> +size_t bpf_htab_map_meta_size(void);
> +void bpf_htab_map_meta_init(struct bpf_map *inner_map_meta, struct bpf_map *inner_map);
>  
>  #endif