[PATCH bpf-next v2] bpf: increase supported cgroup storage value size

Stanislav Fomichev
2021-07-23T23:54:34Z

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).

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

Cc: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
kernel/bpf/local_storage.c | 11 +++++-
tools/testing/selftests/bpf/netcnt_common.h | 38 +++++++++++++++----
.../testing/selftests/bpf/progs/netcnt_prog.c | 29 +++++++-------
tools/testing/selftests/bpf/test_netcnt.c | 25 +++++++-----
4 files changed, 72 insertions(+), 31 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..dfcf184ff713 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, but allocate more to account for possible
+ * layout changes, different architectures, etc.
+ * It 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;

- __u64 prev_ts;
+ __u64 prev_ts;

- __u64 prev_packets;
- __u64 prev_bytes;
+ __u64 prev_packets;
+ __u64 prev_bytes;
+ } val;
+ __u8 data[PCPU_MIN_UNIT_SIZE];
+ };
};

struct net_cnt {
- __u64 packets;
- __u64 bytes;
+ union {
+ struct {
+ __u64 packets;
+ __u64 bytes;
+ } val;
+ __u8 data[BPF_LOCAL_STORAGE_MAX_VALUE_SIZE];
+ };
};

#endif
diff --git a/tools/testing/selftests/bpf/progs/netcnt_prog.c b/tools/testing/selftests/bpf/progs/netcnt_prog.c
index d071adf178bd..4b0884239892 100644
--- a/tools/testing/selftests/bpf/progs/netcnt_prog.c
+++ b/tools/testing/selftests/bpf/progs/netcnt_prog.c
@@ -34,34 +34,35 @@ int bpf_nextcnt(struct __sk_buff *skb)
cnt = bpf_get_local_storage(&netcnt, 0);
percpu_cnt = bpf_get_local_storage(&percpu_netcnt, 0);

- percpu_cnt->packets++;
- percpu_cnt->bytes += skb->len;
+ percpu_cnt->val.packets++;
+ percpu_cnt->val.bytes += skb->len;

- if (percpu_cnt->packets > MAX_PERCPU_PACKETS) {
- __sync_fetch_and_add(&cnt->packets,
- percpu_cnt->packets);
- percpu_cnt->packets = 0;
+ if (percpu_cnt->val.packets > MAX_PERCPU_PACKETS) {
+ __sync_fetch_and_add(&cnt->val.packets,
+ percpu_cnt->val.packets);
+ percpu_cnt->val.packets = 0;

- __sync_fetch_and_add(&cnt->bytes,
- percpu_cnt->bytes);
- percpu_cnt->bytes = 0;
+ __sync_fetch_and_add(&cnt->val.bytes,
+ percpu_cnt->val.bytes);
+ percpu_cnt->val.bytes = 0;
}

ts = bpf_ktime_get_ns();
- dt = ts - percpu_cnt->prev_ts;
+ dt = ts - percpu_cnt->val.prev_ts;

dt *= MAX_BPS;
dt /= NS_PER_SEC;

- if (cnt->bytes + percpu_cnt->bytes - percpu_cnt->prev_bytes < dt)
+ if (cnt->val.bytes + percpu_cnt->val.bytes -
+ percpu_cnt->val.prev_bytes < dt)
ret = 1;
else
ret = 0;

if (dt > REFRESH_TIME_NS) {
- percpu_cnt->prev_ts = ts;
- percpu_cnt->prev_packets = cnt->packets;
- percpu_cnt->prev_bytes = cnt->bytes;
+ percpu_cnt->val.prev_ts = ts;
+ percpu_cnt->val.prev_packets = cnt->val.packets;
+ percpu_cnt->val.prev_bytes = cnt->val.bytes;
}

return !!ret;
diff --git a/tools/testing/selftests/bpf/test_netcnt.c b/tools/testing/selftests/bpf/test_netcnt.c
index a7b9a69f4fd5..1138765406a5 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;
}
@@ -109,17 +115,17 @@ 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->val.packets;
+ bytes = netcnt->val.bytes;
for (cpu = 0; cpu < nproc; cpu++) {
- if (percpu_netcnt[cpu].packets > MAX_PERCPU_PACKETS) {
+ if (percpu_netcnt[cpu].val.packets > MAX_PERCPU_PACKETS) {
printf("Unexpected percpu value: %llu\n",
- percpu_netcnt[cpu].packets);
+ percpu_netcnt[cpu].val.packets);
goto err;
}

- packets += percpu_netcnt[cpu].packets;
- bytes += percpu_netcnt[cpu].bytes;
+ packets += percpu_netcnt[cpu].val.packets;
+ bytes += percpu_netcnt[cpu].val.bytes;
}

/* No packets should be lost */
@@ -142,6 +148,7 @@ int main(int argc, char **argv)
err:
cleanup_cgroup_environment();
free(percpu_netcnt);
+ free(netcnt);

out:
return error;
--
2.32.0.432.gabb21c7263-goog