Merge branch 'bpf-introduce-bpf_f_cpu-and-bpf_f_all_cpus-flags-for-percpu-maps'

Leon Hwang says:

====================
bpf: Introduce BPF_F_CPU and BPF_F_ALL_CPUS flags for percpu maps

This patch set introduces the BPF_F_CPU and BPF_F_ALL_CPUS flags for
percpu maps, as the requirement of BPF_F_ALL_CPUS flag for percpu_array
maps was discussed in the thread of
"[PATCH bpf-next v3 0/4] bpf: Introduce global percpu data"[1].

The goal of BPF_F_ALL_CPUS flag is to reduce data caching overhead in light
skeletons by allowing a single value to be reused to update values across all
CPUs. This avoids the M:N problem where M cached values are used to update a
map on N CPUs kernel.

The BPF_F_CPU flag is accompanied by *flags*-embedded cpu info, which
specifies the target CPU for the operation:

* For lookup operations: the flag field alongside cpu info enable querying
  a value on the specified CPU.
* For update operations: the flag field alongside cpu info enable
  updating value for specified CPU.

Links:
[1] https://lore.kernel.org/bpf/20250526162146.24429-1-leon.hwang@linux.dev/

Changes:
v12 -> v13:
* No changes, rebased on latest tree.

v11 -> v12:
* Dropped the v11 changes.
* Stabilized the lru_percpu_hash map test by keeping an extra spare entry,
  which can be used temporarily during updates to avoid unintended LRU
  evictions.

v10 -> v11:
* Support the combination of BPF_EXIST and BPF_F_CPU/BPF_F_ALL_CPUS for
  update operations.
* Fix unstable lru_percpu_hash map test using the combination of
  BPF_EXIST and BPF_F_CPU/BPF_F_ALL_CPUS to avoid LRU eviction
  (reported by Alexei).

v9 -> v10:
* Add tests to verify array and hash maps do not support BPF_F_CPU and
  BPF_F_ALL_CPUS flags.
* Address comment from Andrii:
  * Copy map value using copy_map_value_long for percpu_cgroup_storage
    maps in a separate patch.

v8 -> v9:
* Change value type from u64 to u32 in selftests.
* Address comments from Andrii:
  * Keep value_size unaligned and update everywhere for consistency when
    cpu flags are specified.
  * Update value by getting pointer for percpu hash and percpu
    cgroup_storage maps.

v7 -> v8:
* Address comments from Andrii:
  * Check BPF_F_LOCK when update percpu_array, percpu_hash and
    lru_percpu_hash maps.
  * Refactor flags check in __htab_map_lookup_and_delete_batch().
  * Keep value_size unaligned and copy value using copy_map_value() in
    __htab_map_lookup_and_delete_batch() when BPF_F_CPU is specified.
  * Update warn message in libbpf's validate_map_op().
  * Update comment of libbpf's bpf_map__lookup_elem().

v6 -> v7:
* Get correct value size for percpu_hash and lru_percpu_hash in
  update_batch API.
* Set 'count' as 'max_entries' in test cases for lookup_batch API.
* Address comment from Alexei:
  * Move cpu flags check into bpf_map_check_op_flags().

v5 -> v6:
* Move bpf_map_check_op_flags() from 'bpf.h' to 'syscall.c'.
* Address comments from Alexei:
  * Drop the refactoring code of data copying logic for percpu maps.
  * Drop bpf_map_check_op_flags() wrappers.

v4 -> v5:
* Address comments from Andrii:
  * Refactor data copying logic for all percpu maps.
  * Drop this_cpu_ptr() micro-optimization.
  * Drop cpu check in libbpf's validate_map_op().
  * Enhance bpf_map_check_op_flags() using *allowed flags* instead of
    'extra_flags_mask'.

v3 -> v4:
* Address comments from Andrii:
  * Remove unnecessary map_type check in bpf_map_value_size().
  * Reduce code churn.
  * Remove unnecessary do_delete check in
    __htab_map_lookup_and_delete_batch().
  * Introduce bpf_percpu_copy_to_user() and bpf_percpu_copy_from_user().
  * Rename check_map_flags() to bpf_map_check_op_flags() with
    extra_flags_mask.
  * Add human-readable pr_warn() explanations in validate_map_op().
  * Use flags in bpf_map__delete_elem() and
    bpf_map__lookup_and_delete_elem().
  * Drop "for alignment reasons".
v3 link: https://lore.kernel.org/bpf/20250821160817.70285-1-leon.hwang@linux.dev/

v2 -> v3:
* Address comments from Alexei:
  * Use BPF_F_ALL_CPUS instead of BPF_ALL_CPUS magic.
  * Introduce these two cpu flags for all percpu maps.
* Address comments from Jiri:
  * Reduce some unnecessary u32 cast.
  * Refactor more generic map flags check function.
  * A code style issue.
v2 link: https://lore.kernel.org/bpf/20250805163017.17015-1-leon.hwang@linux.dev/

v1 -> v2:
* Address comments from Andrii:
  * Embed cpu info as high 32 bits of *flags* totally.
  * Use ERANGE instead of E2BIG.
  * Few format issues.
====================

Link: https://patch.msgid.link/20260107022022.12843-1-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 23 insertions, 6 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 1eeb31c5b317..67e9e811de3a 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -307,7 +307,7 @@ 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;
@@ -325,11 +325,18 @@ 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(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;
 }
@@ -398,10 +405,11 @@ 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;
 	void __percpu *pptr;
-	int cpu, off = 0;
+	void *ptr, *val;
 	u32 size;
+	int cpu;
 
-	if (unlikely(map_flags > BPF_EXIST))
+	if (unlikely((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS))
 		/* unknown flags */
 		return -EINVAL;
 
@@ -422,11 +430,20 @@ 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;
+		ptr = per_cpu_ptr(pptr, cpu);
+		copy_map_value(map, ptr, value);
+		bpf_obj_free_fields(array->map.record, ptr);
+		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;
+		ptr = per_cpu_ptr(pptr, cpu);
+		val = (map_flags & BPF_F_ALL_CPUS) ? value : value + size * cpu;
+		copy_map_value(map, ptr, val);
+		bpf_obj_free_fields(array->map.record, ptr);
 	}
+unlock:
 	rcu_read_unlock();
 	return 0;
 }