[PATCH bpf-next v6 3/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_array maps

[Leon Hwang <leon.hwang@linux.dev>]

Introduce support for the BPF_F_ALL_CPUS flag in percpu_array maps to
allow updating values for all CPUs with a single value for both
update_elem and update_batch APIs.

Introduce support for the BPF_F_CPU flag in percpu_array maps to allow:

* update value for specified CPU for both update_elem and update_batch
APIs.
* lookup value for specified CPU for both lookup_elem and lookup_batch
APIs.

The BPF_F_CPU flag is passed via:

* map_flags of lookup_elem and update_elem APIs along with embedded cpu
info.
* elem_flags of lookup_batch and update_batch APIs along with embedded
cpu info.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/linux/bpf.h   |  2 +-
 kernel/bpf/arraymap.c | 36 +++++++++++++++++++++++++++++-------
 kernel/bpf/syscall.c  |  9 +++++++--
 3 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 60c235836987d..b5143420ea947 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2697,7 +2697,7 @@ int map_set_for_each_callback_args(struct bpf_verifier_env *env,
 				   struct bpf_func_state *callee);
 
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
-int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
+int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value, u64 flags);
 int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
 			   u64 flags);
 int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 3d080916faf97..aa5c17c707f1c 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -295,14 +295,18 @@ static void *percpu_array_map_lookup_percpu_elem(struct bpf_map *map, void *key,
 	return per_cpu_ptr(array->pptrs[index & array->index_mask], cpu);
 }
 
-int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value)
+int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value, u64 map_flags)
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	u32 index = *(u32 *)key;
+	int err, cpu, off = 0;
 	void __percpu *pptr;
-	int cpu, off = 0;
 	u32 size;
 
+	err = bpf_map_check_cpu_flags(map_flags, false);
+	if (unlikely(err))
+		return err;
+
 	if (unlikely(index >= array->map.max_entries))
 		return -ENOENT;
 
@@ -313,11 +317,18 @@ int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value)
 	size = array->elem_size;
 	rcu_read_lock();
 	pptr = array->pptrs[index & array->index_mask];
+	if (map_flags & BPF_F_CPU) {
+		cpu = map_flags >> 32;
+		copy_map_value_long(map, value, per_cpu_ptr(pptr, cpu));
+		check_and_init_map_value(map, value);
+		goto unlock;
+	}
 	for_each_possible_cpu(cpu) {
 		copy_map_value_long(map, value + off, per_cpu_ptr(pptr, cpu));
 		check_and_init_map_value(map, value + off);
 		off += size;
 	}
+unlock:
 	rcu_read_unlock();
 	return 0;
 }
@@ -386,13 +397,13 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	u32 index = *(u32 *)key;
+	int err, cpu, off = 0;
 	void __percpu *pptr;
-	int cpu, off = 0;
 	u32 size;
 
-	if (unlikely(map_flags > BPF_EXIST))
-		/* unknown flags */
-		return -EINVAL;
+	err = bpf_map_check_cpu_flags(map_flags, true);
+	if (unlikely(err))
+		return err;
 
 	if (unlikely(index >= array->map.max_entries))
 		/* all elements were pre-allocated, cannot insert a new one */
@@ -411,11 +422,22 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
 	size = array->elem_size;
 	rcu_read_lock();
 	pptr = array->pptrs[index & array->index_mask];
+	if (map_flags & BPF_F_CPU) {
+		cpu = map_flags >> 32;
+		copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value);
+		bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
+		goto unlock;
+	}
 	for_each_possible_cpu(cpu) {
 		copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off);
 		bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu));
-		off += size;
+		/* same user-provided value is used if BPF_F_ALL_CPUS is
+		 * specified, otherwise value is an array of per-CPU values.
+		 */
+		if (!(map_flags & BPF_F_ALL_CPUS))
+			off += size;
 	}
+unlock:
 	rcu_read_unlock();
 	return 0;
 }
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index db841b38f0c22..6d0a08d63f175 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -133,7 +133,12 @@ bool bpf_map_write_active(const struct bpf_map *map)
 
 static bool bpf_map_supports_cpu_flags(enum bpf_map_type map_type)
 {
-	return false;
+	switch (map_type) {
+	case BPF_MAP_TYPE_PERCPU_ARRAY:
+		return true;
+	default:
+		return false;
+	}
 }
 
 static int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 allowed_flags)
@@ -338,7 +343,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
 	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
 		err = bpf_percpu_hash_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
-		err = bpf_percpu_array_copy(map, key, value);
+		err = bpf_percpu_array_copy(map, key, value, flags);
 	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE) {
 		err = bpf_percpu_cgroup_storage_copy(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) {
-- 
2.50.1