bpf: Factor out htab_elem_value helper()

JIRA: https://issues.redhat.com/browse/RHEL-110274

Conflicts: changed context due to missing upstream commits
           4fa8d68 ("bpf: Convert hashtab.c to rqspinlock") and
           ea5b229 ("bpf: Remove migrate_{disable|enable} in ->map_for_each_callback").

commit ba2b31b
Author: Hou Tao <[email protected]>
Date:   Tue Apr 1 14:22:45 2025 +0800

    bpf: Factor out htab_elem_value helper()

    All hash maps store map key and map value together. The relative offset
    of the map value compared to the map key is round_up(key_size, 8).
    Therefore, factor out a common helper htab_elem_value() to calculate the
    address of the map value instead of duplicating the logic.

    Acked-by: Andrii Nakryiko <[email protected]>
    Signed-off-by: Hou Tao <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Alexei Starovoitov <[email protected]>

Signed-off-by: Viktor Malik <[email protected]>

Author: viktormalik

kernel/bpf/hashtab.c

@@ -194,20 +194,25 @@ static bool htab_is_percpu(const struct bpf_htab *htab)
 		htab->map.map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH;
 }
 
+static inline void *htab_elem_value(struct htab_elem *l, u32 key_size)
+{
+	return l->key + round_up(key_size, 8);
+}
+
 static inline void htab_elem_set_ptr(struct htab_elem *l, u32 key_size,
 				     void __percpu *pptr)
 {
-	*(void __percpu **)(l->key + roundup(key_size, 8)) = pptr;
+	*(void __percpu **)htab_elem_value(l, key_size) = pptr;
 }
 
 static inline void __percpu *htab_elem_get_ptr(struct htab_elem *l, u32 key_size)
 {
-	return *(void __percpu **)(l->key + roundup(key_size, 8));
+	return *(void __percpu **)htab_elem_value(l, key_size);
 }
 
 static void *fd_htab_map_get_ptr(const struct bpf_map *map, struct htab_elem *l)
 {
-	return *(void **)(l->key + roundup(map->key_size, 8));
+	return *(void **)htab_elem_value(l, map->key_size);
 }
 
 static struct htab_elem *get_htab_elem(struct bpf_htab *htab, int i)
@@ -234,10 +239,10 @@ static void htab_free_prealloced_timers_and_wq(struct bpf_htab *htab)
 		elem = get_htab_elem(htab, i);
 		if (btf_record_has_field(htab->map.record, BPF_TIMER))
 			bpf_obj_free_timer(htab->map.record,
-					   elem->key + round_up(htab->map.key_size, 8));
+					   htab_elem_value(elem, htab->map.key_size));
 		if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE))
 			bpf_obj_free_workqueue(htab->map.record,
-					       elem->key + round_up(htab->map.key_size, 8));
+					       htab_elem_value(elem, htab->map.key_size));
 		cond_resched();
 	}
 }
@@ -264,7 +269,8 @@ static void htab_free_prealloced_fields(struct bpf_htab *htab)
 				cond_resched();
 			}
 		} else {
-			bpf_obj_free_fields(htab->map.record, elem->key + round_up(htab->map.key_size, 8));
+			bpf_obj_free_fields(htab->map.record,
+					    htab_elem_value(elem, htab->map.key_size));
 			cond_resched();
 		}
 		cond_resched();
@@ -703,7 +709,7 @@ static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
 	struct htab_elem *l = __htab_map_lookup_elem(map, key);
 
 	if (l)
-		return l->key + round_up(map->key_size, 8);
+		return htab_elem_value(l, map->key_size);
 
 	return NULL;
 }
@@ -742,7 +748,7 @@ static __always_inline void *__htab_lru_map_lookup_elem(struct bpf_map *map,
 	if (l) {
 		if (mark)
 			bpf_lru_node_set_ref(&l->lru_node);
-		return l->key + round_up(map->key_size, 8);
+		return htab_elem_value(l, map->key_size);
 	}
 
 	return NULL;
@@ -793,7 +799,7 @@ static void check_and_free_fields(struct bpf_htab *htab,
 		for_each_possible_cpu(cpu)
 			bpf_obj_free_fields(htab->map.record, per_cpu_ptr(pptr, cpu));
 	} else {
-		void *map_value = elem->key + round_up(htab->map.key_size, 8);
+		void *map_value = htab_elem_value(elem, htab->map.key_size);
 
 		bpf_obj_free_fields(htab->map.record, map_value);
 	}
@@ -1070,11 +1076,9 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 			htab_elem_set_ptr(l_new, key_size, pptr);
 	} else if (fd_htab_map_needs_adjust(htab)) {
 		size = round_up(size, 8);
-		memcpy(l_new->key + round_up(key_size, 8), value, size);
+		memcpy(htab_elem_value(l_new, key_size), value, size);
 	} else {
-		copy_map_value(&htab->map,
-			       l_new->key + round_up(key_size, 8),
-			       value);
+		copy_map_value(&htab->map, htab_elem_value(l_new, key_size), value);
 	}
 
 	l_new->hash = hash;
@@ -1137,7 +1141,7 @@ 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,
-					      l_old->key + round_up(key_size, 8),
+					      htab_elem_value(l_old, key_size),
 					      value, false);
 			return 0;
 		}
@@ -1165,7 +1169,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 		 * and update element in place
 		 */
 		copy_map_value_locked(map,
-				      l_old->key + round_up(key_size, 8),
+				      htab_elem_value(l_old, key_size),
 				      value, false);
 		ret = 0;
 		goto err;
@@ -1251,8 +1255,7 @@ 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,
-		       l_new->key + round_up(map->key_size, 8), value);
+	copy_map_value(&htab->map, htab_elem_value(l_new, map->key_size), value);
 
 	ret = htab_lock_bucket(htab, b, hash, &flags);
 	if (ret)
@@ -1533,10 +1536,10 @@ static void htab_free_malloced_timers_and_wq(struct bpf_htab *htab)
 			/* We only free timer on uref dropping to zero */
 			if (btf_record_has_field(htab->map.record, BPF_TIMER))
 				bpf_obj_free_timer(htab->map.record,
-						   l->key + round_up(htab->map.key_size, 8));
+						   htab_elem_value(l, htab->map.key_size));
 			if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE))
 				bpf_obj_free_workqueue(htab->map.record,
-						       l->key + round_up(htab->map.key_size, 8));
+						       htab_elem_value(l, htab->map.key_size));
 		}
 		cond_resched_rcu();
 	}
@@ -1652,15 +1655,12 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
 			off += roundup_value_size;
 		}
 	} else {
-		u32 roundup_key_size = round_up(map->key_size, 8);
+		void *src = htab_elem_value(l, map->key_size);
 
 		if (flags & BPF_F_LOCK)
-			copy_map_value_locked(map, value, l->key +
-					      roundup_key_size,
-					      true);
+			copy_map_value_locked(map, value, src, true);
 		else
-			copy_map_value(map, value, l->key +
-				       roundup_key_size);
+			copy_map_value(map, value, src);
 		/* Zeroing special fields in the temp buffer */
 		check_and_init_map_value(map, value);
 	}
@@ -1715,12 +1715,12 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 				   bool is_percpu)
 {
 	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
-	u32 bucket_cnt, total, key_size, value_size, roundup_key_size;
 	void *keys = NULL, *values = NULL, *value, *dst_key, *dst_val;
 	void __user *uvalues = u64_to_user_ptr(attr->batch.values);
 	void __user *ukeys = u64_to_user_ptr(attr->batch.keys);
 	void __user *ubatch = u64_to_user_ptr(attr->batch.in_batch);
 	u32 batch, max_count, size, bucket_size, map_id;
+	u32 bucket_cnt, total, key_size, value_size;
 	struct htab_elem *node_to_free = NULL;
 	u64 elem_map_flags, map_flags;
 	struct hlist_nulls_head *head;
@@ -1755,7 +1755,6 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 		return -ENOENT;
 
 	key_size = htab->map.key_size;
-	roundup_key_size = round_up(htab->map.key_size, 8);
 	value_size = htab->map.value_size;
 	size = round_up(value_size, 8);
 	if (is_percpu)
@@ -1847,7 +1846,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 				off += size;
 			}
 		} else {
-			value = l->key + roundup_key_size;
+			value = htab_elem_value(l, key_size);
 			if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) {
 				struct bpf_map **inner_map = value;
 
@@ -2098,11 +2097,11 @@ static void *bpf_hash_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 static int __bpf_hash_map_seq_show(struct seq_file *seq, struct htab_elem *elem)
 {
 	struct bpf_iter_seq_hash_map_info *info = seq->private;
-	u32 roundup_key_size, roundup_value_size;
 	struct bpf_iter__bpf_map_elem ctx = {};
 	struct bpf_map *map = info->map;
 	struct bpf_iter_meta meta;
 	int ret = 0, off = 0, cpu;
+	u32 roundup_value_size;
 	struct bpf_prog *prog;
 	void __percpu *pptr;
 
@@ -2112,10 +2111,9 @@ static int __bpf_hash_map_seq_show(struct seq_file *seq, struct htab_elem *elem)
 		ctx.meta = &meta;
 		ctx.map = info->map;
 		if (elem) {
-			roundup_key_size = round_up(map->key_size, 8);
 			ctx.key = elem->key;
 			if (!info->percpu_value_buf) {
-				ctx.value = elem->key + roundup_key_size;
+				ctx.value = htab_elem_value(elem, map->key_size);
 			} else {
 				roundup_value_size = round_up(map->value_size, 8);
 				pptr = htab_elem_get_ptr(elem, map->key_size);
@@ -2200,7 +2198,6 @@ static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_
 	struct hlist_nulls_head *head;
 	struct hlist_nulls_node *n;
 	struct htab_elem *elem;
-	u32 roundup_key_size;
 	int i, num_elems = 0;
 	void __percpu *pptr;
 	struct bucket *b;
@@ -2213,7 +2210,6 @@ static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_
 
 	is_percpu = htab_is_percpu(htab);
 
-	roundup_key_size = round_up(map->key_size, 8);
 	/* disable migration so percpu value prepared here will be the
 	 * same as the one seen by the bpf program with bpf_map_lookup_elem().
 	 */
@@ -2230,7 +2226,7 @@ static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_
 				pptr = htab_elem_get_ptr(elem, map->key_size);
 				val = this_cpu_ptr(pptr);
 			} else {
-				val = elem->key + roundup_key_size;
+				val = htab_elem_value(elem, map->key_size);
 			}
 			num_elems++;
 			ret = callback_fn((u64)(long)map, (u64)(long)key,