Merge branch 'Add lookup_and_delete_elem support to BPF hash map types'

Denis Salopek says:

====================

This patch series extends the existing bpf_map_lookup_and_delete_elem()
functionality with 4 more map types:
 - BPF_MAP_TYPE_HASH,
 - BPF_MAP_TYPE_PERCPU_HASH,
 - BPF_MAP_TYPE_LRU_HASH and
 - BPF_MAP_TYPE_LRU_PERCPU_HASH.

Patch 1 adds most of its functionality and logic as well as
documentation.

As it was previously limited to only stacks and queues which do not
support the BPF_F_LOCK flag, patch 2 enables its usage by adding a new
libbpf API bpf_map_lookup_and_delete_elem_flags() based on the existing
bpf_map_lookup_elem_flags().

Patch 3 adds selftests for lookup_and_delete_elem().

Changes in patch 1:
v7: Minor formating nits, add Acked-by.
v6: Remove unneeded flag check, minor code/format fixes.
v5: Split patch to 3 patches. Extend BPF_MAP_LOOKUP_AND_DELETE_ELEM
documentation with this changes.
v4: Fix the return value for unsupported map types.
v3: Add bpf_map_lookup_and_delete_elem_flags() and enable BPF_F_LOCK
flag, change CHECKs to ASSERT_OKs, initialize variables to 0.
v2: Add functionality for LRU/per-CPU, add test_progs tests.

Changes in patch 2:
v7: No change.
v6: Add Acked-by.
v5: Move to the newest libbpf version (0.4.0).

Changes in patch 3:
v7: Remove ASSERT_GE macro which is already added in some other commit,
change ASSERT_OK to ASSERT_OK_PTR, add Acked-by.
v6: Remove PERCPU macros, add ASSERT_GE macro to test_progs.h, remove
leftover code.
v5: Use more appropriate macros. Better check for changed value.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

include/linux/bpf.h

@@ -70,6 +70,8 @@ struct bpf_map_ops {
 	void *(*map_lookup_elem_sys_only)(struct bpf_map *map, void *key);
 	int (*map_lookup_batch)(struct bpf_map *map, const union bpf_attr *attr,
 				union bpf_attr __user *uattr);
+	int (*map_lookup_and_delete_elem)(struct bpf_map *map, void *key,
+					  void *value, u64 flags);
 	int (*map_lookup_and_delete_batch)(struct bpf_map *map,
 					   const union bpf_attr *attr,
 					   union bpf_attr __user *uattr);

include/uapi/linux/bpf.h

@@ -527,6 +527,15 @@ union bpf_iter_link_info {
  *		Look up an element with the given *key* in the map referred to
  *		by the file descriptor *fd*, and if found, delete the element.
  *
+ *		For **BPF_MAP_TYPE_QUEUE** and **BPF_MAP_TYPE_STACK** map
+ *		types, the *flags* argument needs to be set to 0, but for other
+ *		map types, it may be specified as:
+ *
+ *		**BPF_F_LOCK**
+ *			Look up and delete the value of a spin-locked map
+ *			without returning the lock. This must be specified if
+ *			the elements contain a spinlock.
+ *
  *		The **BPF_MAP_TYPE_QUEUE** and **BPF_MAP_TYPE_STACK** map types
  *		implement this command as a "pop" operation, deleting the top
  *		element rather than one corresponding to *key*.
@@ -536,6 +545,10 @@ union bpf_iter_link_info {
  *		This command is only valid for the following map types:
  *		* **BPF_MAP_TYPE_QUEUE**
  *		* **BPF_MAP_TYPE_STACK**
+ *		* **BPF_MAP_TYPE_HASH**
+ *		* **BPF_MAP_TYPE_PERCPU_HASH**
+ *		* **BPF_MAP_TYPE_LRU_HASH**
+ *		* **BPF_MAP_TYPE_LRU_PERCPU_HASH**
  *
  *	Return
  *		Returns zero on success. On error, -1 is returned and *errno*

kernel/bpf/hashtab.c

@@ -1401,6 +1401,100 @@ static void htab_map_seq_show_elem(struct bpf_map *map, void *key,
 	rcu_read_unlock();
 }
 
+static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
+					     void *value, bool is_lru_map,
+					     bool is_percpu, u64 flags)
+{
+	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
+	struct hlist_nulls_head *head;
+	unsigned long bflags;
+	struct htab_elem *l;
+	u32 hash, key_size;
+	struct bucket *b;
+	int ret;
+
+	key_size = map->key_size;
+
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
+	b = __select_bucket(htab, hash);
+	head = &b->head;
+
+	ret = htab_lock_bucket(htab, b, hash, &bflags);
+	if (ret)
+		return ret;
+
+	l = lookup_elem_raw(head, hash, key, key_size);
+	if (!l) {
+		ret = -ENOENT;
+	} else {
+		if (is_percpu) {
+			u32 roundup_value_size = round_up(map->value_size, 8);
+			void __percpu *pptr;
+			int off = 0, cpu;
+
+			pptr = htab_elem_get_ptr(l, key_size);
+			for_each_possible_cpu(cpu) {
+				bpf_long_memcpy(value + off,
+						per_cpu_ptr(pptr, cpu),
+						roundup_value_size);
+				off += roundup_value_size;
+			}
+		} else {
+			u32 roundup_key_size = round_up(map->key_size, 8);
+
+			if (flags & BPF_F_LOCK)
+				copy_map_value_locked(map, value, l->key +
+						      roundup_key_size,
+						      true);
+			else
+				copy_map_value(map, value, l->key +
+					       roundup_key_size);
+			check_and_init_map_lock(map, value);
+		}
+
+		hlist_nulls_del_rcu(&l->hash_node);
+		if (!is_lru_map)
+			free_htab_elem(htab, l);
+	}
+
+	htab_unlock_bucket(htab, b, hash, bflags);
+
+	if (is_lru_map && l)
+		bpf_lru_push_free(&htab->lru, &l->lru_node);
+
+	return ret;
+}
+
+static int htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
+					   void *value, u64 flags)
+{
+	return __htab_map_lookup_and_delete_elem(map, key, value, false, false,
+						 flags);
+}
+
+static int htab_percpu_map_lookup_and_delete_elem(struct bpf_map *map,
+						  void *key, void *value,
+						  u64 flags)
+{
+	return __htab_map_lookup_and_delete_elem(map, key, value, false, true,
+						 flags);
+}
+
+static int htab_lru_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
+					       void *value, u64 flags)
+{
+	return __htab_map_lookup_and_delete_elem(map, key, value, true, false,
+						 flags);
+}
+
+static int htab_lru_percpu_map_lookup_and_delete_elem(struct bpf_map *map,
+						      void *key, void *value,
+						      u64 flags)
+{
+	return __htab_map_lookup_and_delete_elem(map, key, value, true, true,
+						 flags);
+}
+
 static int
 __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 				   const union bpf_attr *attr,
@@ -1934,6 +2028,7 @@ const struct bpf_map_ops htab_map_ops = {
 	.map_free = htab_map_free,
 	.map_get_next_key = htab_map_get_next_key,
 	.map_lookup_elem = htab_map_lookup_elem,
+	.map_lookup_and_delete_elem = htab_map_lookup_and_delete_elem,
 	.map_update_elem = htab_map_update_elem,
 	.map_delete_elem = htab_map_delete_elem,
 	.map_gen_lookup = htab_map_gen_lookup,
@@ -1954,6 +2049,7 @@ const struct bpf_map_ops htab_lru_map_ops = {
 	.map_free = htab_map_free,
 	.map_get_next_key = htab_map_get_next_key,
 	.map_lookup_elem = htab_lru_map_lookup_elem,
+	.map_lookup_and_delete_elem = htab_lru_map_lookup_and_delete_elem,
 	.map_lookup_elem_sys_only = htab_lru_map_lookup_elem_sys,
 	.map_update_elem = htab_lru_map_update_elem,
 	.map_delete_elem = htab_lru_map_delete_elem,
@@ -2077,6 +2173,7 @@ const struct bpf_map_ops htab_percpu_map_ops = {
 	.map_free = htab_map_free,
 	.map_get_next_key = htab_map_get_next_key,
 	.map_lookup_elem = htab_percpu_map_lookup_elem,
+	.map_lookup_and_delete_elem = htab_percpu_map_lookup_and_delete_elem,
 	.map_update_elem = htab_percpu_map_update_elem,
 	.map_delete_elem = htab_map_delete_elem,
 	.map_seq_show_elem = htab_percpu_map_seq_show_elem,
@@ -2096,6 +2193,7 @@ const struct bpf_map_ops htab_lru_percpu_map_ops = {
 	.map_free = htab_map_free,
 	.map_get_next_key = htab_map_get_next_key,
 	.map_lookup_elem = htab_lru_percpu_map_lookup_elem,
+	.map_lookup_and_delete_elem = htab_lru_percpu_map_lookup_and_delete_elem,
 	.map_update_elem = htab_lru_percpu_map_update_elem,
 	.map_delete_elem = htab_lru_map_delete_elem,
 	.map_seq_show_elem = htab_percpu_map_seq_show_elem,

kernel/bpf/syscall.c

@@ -1483,7 +1483,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
 	return err;
 }
 
-#define BPF_MAP_LOOKUP_AND_DELETE_ELEM_LAST_FIELD value
+#define BPF_MAP_LOOKUP_AND_DELETE_ELEM_LAST_FIELD flags
 
 static int map_lookup_and_delete_elem(union bpf_attr *attr)
 {
@@ -1499,6 +1499,9 @@ static int map_lookup_and_delete_elem(union bpf_attr *attr)
 	if (CHECK_ATTR(BPF_MAP_LOOKUP_AND_DELETE_ELEM))
 		return -EINVAL;
 
+	if (attr->flags & ~BPF_F_LOCK)
+		return -EINVAL;
+
 	f = fdget(ufd);
 	map = __bpf_map_get(f);
 	if (IS_ERR(map))
@@ -1509,24 +1512,47 @@ static int map_lookup_and_delete_elem(union bpf_attr *attr)
 		goto err_put;
 	}
 
+	if (attr->flags &&
+	    (map->map_type == BPF_MAP_TYPE_QUEUE ||
+	     map->map_type == BPF_MAP_TYPE_STACK)) {
+		err = -EINVAL;
+		goto err_put;
+	}
+
+	if ((attr->flags & BPF_F_LOCK) &&
+	    !map_value_has_spin_lock(map)) {
+		err = -EINVAL;
+		goto err_put;
+	}
+
 	key = __bpf_copy_key(ukey, map->key_size);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
 		goto err_put;
 	}
 
-	value_size = map->value_size;
+	value_size = bpf_map_value_size(map);
 
 	err = -ENOMEM;
 	value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
 	if (!value)
 		goto free_key;
 
+	err = -ENOTSUPP;
 	if (map->map_type == BPF_MAP_TYPE_QUEUE ||
 	    map->map_type == BPF_MAP_TYPE_STACK) {
 		err = map->ops->map_pop_elem(map, value);
-	} else {
-		err = -ENOTSUPP;
+	} else if (map->map_type == BPF_MAP_TYPE_HASH ||
+		   map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+		   map->map_type == BPF_MAP_TYPE_LRU_HASH ||
+		   map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
+		if (!bpf_map_is_dev_bound(map)) {
+			bpf_disable_instrumentation();
+			rcu_read_lock();
+			err = map->ops->map_lookup_and_delete_elem(map, key, value, attr->flags);
+			rcu_read_unlock();
+			bpf_enable_instrumentation();
+		}
 	}
 
 	if (err)

tools/include/uapi/linux/bpf.h

@@ -527,6 +527,15 @@ union bpf_iter_link_info {
  *		Look up an element with the given *key* in the map referred to
  *		by the file descriptor *fd*, and if found, delete the element.
  *
+ *		For **BPF_MAP_TYPE_QUEUE** and **BPF_MAP_TYPE_STACK** map
+ *		types, the *flags* argument needs to be set to 0, but for other
+ *		map types, it may be specified as:
+ *
+ *		**BPF_F_LOCK**
+ *			Look up and delete the value of a spin-locked map
+ *			without returning the lock. This must be specified if
+ *			the elements contain a spinlock.
+ *
  *		The **BPF_MAP_TYPE_QUEUE** and **BPF_MAP_TYPE_STACK** map types
  *		implement this command as a "pop" operation, deleting the top
  *		element rather than one corresponding to *key*.
@@ -536,6 +545,10 @@ union bpf_iter_link_info {
  *		This command is only valid for the following map types:
  *		* **BPF_MAP_TYPE_QUEUE**
  *		* **BPF_MAP_TYPE_STACK**
+ *		* **BPF_MAP_TYPE_HASH**
+ *		* **BPF_MAP_TYPE_PERCPU_HASH**
+ *		* **BPF_MAP_TYPE_LRU_HASH**
+ *		* **BPF_MAP_TYPE_LRU_PERCPU_HASH**
  *
  *	Return
  *		Returns zero on success. On error, -1 is returned and *errno*

tools/lib/bpf/bpf.c

@@ -458,6 +458,19 @@ int bpf_map_lookup_and_delete_elem(int fd, const void *key, void *value)
 	return sys_bpf(BPF_MAP_LOOKUP_AND_DELETE_ELEM, &attr, sizeof(attr));
 }
 
+int bpf_map_lookup_and_delete_elem_flags(int fd, const void *key, void *value, __u64 flags)
+{
+	union bpf_attr attr;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.map_fd = fd;
+	attr.key = ptr_to_u64(key);
+	attr.value = ptr_to_u64(value);
+	attr.flags = flags;
+
+	return sys_bpf(BPF_MAP_LOOKUP_AND_DELETE_ELEM, &attr, sizeof(attr));
+}
+
 int bpf_map_delete_elem(int fd, const void *key)
 {
 	union bpf_attr attr;

tools/lib/bpf/bpf.h

@@ -124,6 +124,8 @@ LIBBPF_API int bpf_map_lookup_elem_flags(int fd, const void *key, void *value,
 					 __u64 flags);
 LIBBPF_API int bpf_map_lookup_and_delete_elem(int fd, const void *key,
 					      void *value);
+LIBBPF_API int bpf_map_lookup_and_delete_elem_flags(int fd, const void *key,
+						    void *value, __u64 flags);
 LIBBPF_API int bpf_map_delete_elem(int fd, const void *key);
 LIBBPF_API int bpf_map_get_next_key(int fd, const void *key, void *next_key);
 LIBBPF_API int bpf_map_freeze(int fd);

tools/lib/bpf/libbpf.map

@@ -361,6 +361,7 @@ LIBBPF_0.4.0 {
 		bpf_linker__new;
 		bpf_map__initial_value;
 		bpf_map__inner_map;
+		bpf_map_lookup_and_delete_elem_flags;
 		bpf_object__gen_loader;
 		bpf_object__set_kversion;
 		bpf_tc_attach;