Re: [PATCH bpf-next v3] bpf: increase supported cgroup storage value size

Current max cgroup storage value size is 4k (PAGE_SIZE). The other local
storages accept up to 64k (BPF_LOCAL_STORAGE_MAX_VALUE_SIZE). Let's align
max cgroup value size with the other storages.

For percpu, the max is 32k (PCPU_MIN_UNIT_SIZE) because percpu
allocator is not happy about larger values.

netcnt test is extended to exercise those maximum values
(non-percpu max size is close to, but not real max).

v3:
* refine SIZEOF_BPF_LOCAL_STORAGE_ELEM comment (Yonghong Song)
* anonymous struct in percpu_net_cnt & net_cnt (Yonghong Song)
* reorder free (Yonghong Song)

v2:
* cap max_value_size instead of BUILD_BUG_ON (Martin KaFai Lau)

Cc: Martin KaFai Lau <redacted>
Cc: Yonghong Song <redacted>
Signed-off-by: Stanislav Fomichev <redacted>
---
 kernel/bpf/local_storage.c                  | 11 +++++-
 tools/testing/selftests/bpf/netcnt_common.h | 38 +++++++++++++++++----
 tools/testing/selftests/bpf/test_netcnt.c   | 17 ++++++---
 3 files changed, 53 insertions(+), 13 deletions(-)

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 7ed2a14dc0de..035e9e3a7132 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c

@@ -1,6 +1,7 @@
 //SPDX-License-Identifier: GPL-2.0
 #include <linux/bpf-cgroup.h>
 #include <linux/bpf.h>
+#include <linux/bpf_local_storage.h>
 #include <linux/btf.h>
 #include <linux/bug.h>
 #include <linux/filter.h>

@@ -283,9 +284,17 @@ static int cgroup_storage_get_next_key(struct bpf_map *_map, void *key,

 static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 {
+       __u32 max_value_size = BPF_LOCAL_STORAGE_MAX_VALUE_SIZE;
        int numa_node = bpf_map_attr_numa_node(attr);
        struct bpf_cgroup_storage_map *map;

+       /* percpu is bound by PCPU_MIN_UNIT_SIZE, non-percu
+        * is the same as other local storages.
+        */
+       if (attr->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE)
+               max_value_size = min_t(__u32, max_value_size,
+                                      PCPU_MIN_UNIT_SIZE);
+
        if (attr->key_size != sizeof(struct bpf_cgroup_storage_key) &&
            attr->key_size != sizeof(__u64))
                return ERR_PTR(-EINVAL);

@@ -293,7 +302,7 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
        if (attr->value_size == 0)
                return ERR_PTR(-EINVAL);

-       if (attr->value_size > PAGE_SIZE)
+       if (attr->value_size > max_value_size)
                return ERR_PTR(-E2BIG);

        if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK ||

diff --git a/tools/testing/selftests/bpf/netcnt_common.h b/tools/testing/selftests/bpf/netcnt_common.h
index 81084c1c2c23..87f5b97e1932 100644
--- a/tools/testing/selftests/bpf/netcnt_common.h
+++ b/tools/testing/selftests/bpf/netcnt_common.h

@@ -6,19 +6,43 @@

 #define MAX_PERCPU_PACKETS 32

+/* sizeof(struct bpf_local_storage_elem):
+ *
+ * It really is about 128 bytes on x86_64, but allocate more to account for
+ * possible layout changes, different architectures, etc.
+ * The kernel will wrap up to PAGE_SIZE internally anyway.
+ */
+#define SIZEOF_BPF_LOCAL_STORAGE_ELEM          256
+
+/* Try to estimate kernel's BPF_LOCAL_STORAGE_MAX_VALUE_SIZE: */
+#define BPF_LOCAL_STORAGE_MAX_VALUE_SIZE       (0xFFFF - \
+                                                SIZEOF_BPF_LOCAL_STORAGE_ELEM)
+
+#define PCPU_MIN_UNIT_SIZE                     32768
+
 struct percpu_net_cnt {
-       __u64 packets;
-       __u64 bytes;
+       union {

+               struct {
+                       __u64 packets;
+                       __u64 bytes;
+               };
+               __u8 data[BPF_LOCAL_STORAGE_MAX_VALUE_SIZE];
+       };
 };

 #endif

diff --git a/tools/testing/selftests/bpf/test_netcnt.c b/tools/testing/selftests/bpf/test_netcnt.c
index a7b9a69f4fd5..372afccf2d17 100644
--- a/tools/testing/selftests/bpf/test_netcnt.c
+++ b/tools/testing/selftests/bpf/test_netcnt.c

@@ -33,11 +33,11 @@ static int bpf_find_map(const char *test, struct bpf_object *obj,

 int main(int argc, char **argv)
 {
-       struct percpu_net_cnt *percpu_netcnt;
+       struct percpu_net_cnt *percpu_netcnt = NULL;
        struct bpf_cgroup_storage_key key;
+       struct net_cnt *netcnt = NULL;
        int map_fd, percpu_map_fd;
        int error = EXIT_FAILURE;
-       struct net_cnt netcnt;
        struct bpf_object *obj;
        int prog_fd, cgroup_fd;
        unsigned long packets;

@@ -52,6 +52,12 @@ int main(int argc, char **argv)
                goto err;
        }

+       netcnt = malloc(sizeof(*netcnt));

+       if (!netcnt) {
+               printf("Not enough memory for non-per-cpu area\n");
+               goto err;
+       }
+
        if (bpf_prog_load(BPF_PROG, BPF_PROG_TYPE_CGROUP_SKB,
                          &obj, &prog_fd)) {
                printf("Failed to load bpf program\n");

@@ -96,7 +102,7 @@ int main(int argc, char **argv)
                goto err;
        }

-       if (bpf_map_lookup_elem(map_fd, &key, &netcnt)) {
+       if (bpf_map_lookup_elem(map_fd, &key, netcnt)) {
                printf("Failed to lookup cgroup storage\n");
                goto err;
        }

@@ -109,8 +115,8 @@ int main(int argc, char **argv)
        /* Some packets can be still in per-cpu cache, but not more than
         * MAX_PERCPU_PACKETS.
         */
-       packets = netcnt.packets;
-       bytes = netcnt.bytes;
+       packets = netcnt->packets;
+       bytes = netcnt->bytes;
        for (cpu = 0; cpu < nproc; cpu++) {
                if (percpu_netcnt[cpu].packets > MAX_PERCPU_PACKETS) {
                        printf("Unexpected percpu value: %llu\n",

@@ -141,6 +147,7 @@ int main(int argc, char **argv)

 err:
        cleanup_cgroup_environment();
+       free(netcnt);
        free(percpu_netcnt);

 out:
--

2.32.0.432.gabb21c7263-goog