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bpf: add lookup/update support for per-cpu hash and array maps

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The functions bpf_map_lookup_elem(map, key, value) and
bpf_map_update_elem(map, key, value, flags) need to get/set
values from all-cpus for per-cpu hash and array maps,
so that user space can aggregate/update them as necessary.

Example of single counter aggregation in user space:
  unsigned int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
  long values[nr_cpus];
  long value = 0;

  bpf_lookup_elem(fd, key, values);
  for (i = 0; i < nr_cpus; i++)
    value += values[i];

The user space must provide round_up(value_size, 8) * nr_cpus
array to get/set values, since kernel will use 'long' copy
of per-cpu values to try to copy good counters atomically.
It's a best-effort, since bpf programs and user space are racing
to access the same memory.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2016-02-01 22:39:55 -08:00 committed by David S. Miller
parent a10423b87a
commit 15a07b3381
4 changed files with 201 additions and 26 deletions
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23
include/linux/bpf.h
View File

@ -183,6 +183,29 @@ int bpf_prog_new_fd(struct bpf_prog *prog);
int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
int bpf_obj_get_user(const char __user *pathname);
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_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,
u64 flags);
/* memcpy that is used with 8-byte aligned pointers, power-of-8 size and
* forced to use 'long' read/writes to try to atomically copy long counters.
* Best-effort only. No barriers here, since it _will_ race with concurrent
* updates from BPF programs. Called from bpf syscall and mostly used with
* size 8 or 16 bytes, so ask compiler to inline it.
*/
static inline void bpf_long_memcpy(void *dst, const void *src, u32 size)
{
const long *lsrc = src;
long *ldst = dst;
size /= sizeof(long);
while (size--)
*ldst++ = *lsrc++;
}
/* verify correctness of eBPF program */
int bpf_check(struct bpf_prog **fp, union bpf_attr *attr);
#else

64
kernel/bpf/arraymap.c
View File

@ -130,6 +130,32 @@ static void *percpu_array_map_lookup_elem(struct bpf_map *map, void *key)
return this_cpu_ptr(array->pptrs[index]);
}
int bpf_percpu_array_copy(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;
u32 size;
if (unlikely(index >= array->map.max_entries))
return -ENOENT;
/* per_cpu areas are zero-filled and bpf programs can only
* access 'value_size' of them, so copying rounded areas
* will not leak any kernel data
*/
size = round_up(map->value_size, 8);
rcu_read_lock();
pptr = array->pptrs[index];
for_each_possible_cpu(cpu) {
bpf_long_memcpy(value + off, per_cpu_ptr(pptr, cpu), size);
off += size;
}
rcu_read_unlock();
return 0;
}
/* Called from syscall */
static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
@ -177,6 +203,44 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
return 0;
}
int bpf_percpu_array_update(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;
void __percpu *pptr;
int cpu, off = 0;
u32 size;
if (unlikely(map_flags > BPF_EXIST))
/* unknown flags */
return -EINVAL;
if (unlikely(index >= array->map.max_entries))
/* all elements were pre-allocated, cannot insert a new one */
return -E2BIG;
if (unlikely(map_flags == BPF_NOEXIST))
/* all elements already exist */
return -EEXIST;
/* the user space will provide round_up(value_size, 8) bytes that
* will be copied into per-cpu area. bpf programs can only access
* value_size of it. During lookup the same extra bytes will be
* returned or zeros which were zero-filled by percpu_alloc,
* so no kernel data leaks possible
*/
size = round_up(map->value_size, 8);
rcu_read_lock();
pptr = array->pptrs[index];
for_each_possible_cpu(cpu) {
bpf_long_memcpy(per_cpu_ptr(pptr, cpu), value + off, size);
off += size;
}
rcu_read_unlock();
return 0;
}
/* Called from syscall or from eBPF program */
static int array_map_delete_elem(struct bpf_map *map, void *key)
{

83
kernel/bpf/hashtab.c
View File

@ -290,7 +290,7 @@ static void free_htab_elem(struct htab_elem *l, bool percpu, u32 key_size)
static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
void *value, u32 key_size, u32 hash,
bool percpu)
bool percpu, bool onallcpus)
{
u32 size = htab->map.value_size;
struct htab_elem *l_new;
@ -312,8 +312,18 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
return NULL;
}
/* copy true value_size bytes */
memcpy(this_cpu_ptr(pptr), value, htab->map.value_size);
if (!onallcpus) {
/* copy true value_size bytes */
memcpy(this_cpu_ptr(pptr), value, htab->map.value_size);
} else {
int off = 0, cpu;
for_each_possible_cpu(cpu) {
bpf_long_memcpy(per_cpu_ptr(pptr, cpu),
value + off, size);
off += size;
}
}
htab_elem_set_ptr(l_new, key_size, pptr);
} else {
memcpy(l_new->key + round_up(key_size, 8), value, size);
@ -368,7 +378,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
/* allocate new element outside of the lock, since
* we're most likley going to insert it
*/
l_new = alloc_htab_elem(htab, key, value, key_size, hash, false);
l_new = alloc_htab_elem(htab, key, value, key_size, hash, false, false);
if (!l_new)
return -ENOMEM;
@ -402,8 +412,9 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
return ret;
}
static int htab_percpu_map_update_elem(struct bpf_map *map, void *key,
void *value, u64 map_flags)
static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
void *value, u64 map_flags,
bool onallcpus)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct htab_elem *l_new = NULL, *l_old;
@ -436,12 +447,25 @@ static int htab_percpu_map_update_elem(struct bpf_map *map, void *key,
goto err;
if (l_old) {
void __percpu *pptr = htab_elem_get_ptr(l_old, key_size);
u32 size = htab->map.value_size;
/* per-cpu hash map can update value in-place */
memcpy(this_cpu_ptr(htab_elem_get_ptr(l_old, key_size)),
value, htab->map.value_size);
if (!onallcpus) {
memcpy(this_cpu_ptr(pptr), value, size);
} else {
int off = 0, cpu;
size = round_up(size, 8);
for_each_possible_cpu(cpu) {
bpf_long_memcpy(per_cpu_ptr(pptr, cpu),
value + off, size);
off += size;
}
}
} else {
l_new = alloc_htab_elem(htab, key, value, key_size,
hash, true);
hash, true, onallcpus);
if (!l_new) {
ret = -ENOMEM;
goto err;
@ -455,6 +479,12 @@ static int htab_percpu_map_update_elem(struct bpf_map *map, void *key,
return ret;
}
static int htab_percpu_map_update_elem(struct bpf_map *map, void *key,
void *value, u64 map_flags)
{
return __htab_percpu_map_update_elem(map, key, value, map_flags, false);
}
/* Called from syscall or from eBPF program */
static int htab_map_delete_elem(struct bpf_map *map, void *key)
{
@ -557,6 +587,41 @@ static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
return NULL;
}
int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value)
{
struct htab_elem *l;
void __percpu *pptr;
int ret = -ENOENT;
int cpu, off = 0;
u32 size;
/* per_cpu areas are zero-filled and bpf programs can only
* access 'value_size' of them, so copying rounded areas
* will not leak any kernel data
*/
size = round_up(map->value_size, 8);
rcu_read_lock();
l = __htab_map_lookup_elem(map, key);
if (!l)
goto out;
pptr = htab_elem_get_ptr(l, map->key_size);
for_each_possible_cpu(cpu) {
bpf_long_memcpy(value + off,
per_cpu_ptr(pptr, cpu), size);
off += size;
}
ret = 0;
out:
rcu_read_unlock();
return ret;
}
int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,
u64 map_flags)
{
return __htab_percpu_map_update_elem(map, key, value, map_flags, true);
}
static const struct bpf_map_ops htab_percpu_ops = {
.map_alloc = htab_map_alloc,
.map_free = htab_map_free,

57
kernel/bpf/syscall.c
View File

@ -239,6 +239,7 @@ static int map_lookup_elem(union bpf_attr *attr)
int ufd = attr->map_fd;
struct bpf_map *map;
void *key, *value, *ptr;
u32 value_size;
struct fd f;
int err;
@ -259,23 +260,35 @@ static int map_lookup_elem(union bpf_attr *attr)
if (copy_from_user(key, ukey, map->key_size) != 0)
goto free_key;
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
value_size = round_up(map->value_size, 8) * num_possible_cpus();
else
value_size = map->value_size;
err = -ENOMEM;
value = kmalloc(map->value_size, GFP_USER | __GFP_NOWARN);
value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
if (!value)
goto free_key;
rcu_read_lock();
ptr = map->ops->map_lookup_elem(map, key);
if (ptr)
memcpy(value, ptr, map->value_size);
rcu_read_unlock();
if (map->map_type == BPF_MAP_TYPE_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);
} else {
rcu_read_lock();
ptr = map->ops->map_lookup_elem(map, key);
if (ptr)
memcpy(value, ptr, value_size);
rcu_read_unlock();
err = ptr ? 0 : -ENOENT;
}
err = -ENOENT;
if (!ptr)
if (err)
goto free_value;
err = -EFAULT;
if (copy_to_user(uvalue, value, map->value_size) != 0)
if (copy_to_user(uvalue, value, value_size) != 0)
goto free_value;
err = 0;
@ -298,6 +311,7 @@ static int map_update_elem(union bpf_attr *attr)
int ufd = attr->map_fd;
struct bpf_map *map;
void *key, *value;
u32 value_size;
struct fd f;
int err;
@ -318,21 +332,30 @@ static int map_update_elem(union bpf_attr *attr)
if (copy_from_user(key, ukey, map->key_size) != 0)
goto free_key;
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
value_size = round_up(map->value_size, 8) * num_possible_cpus();
else
value_size = map->value_size;
err = -ENOMEM;
value = kmalloc(map->value_size, GFP_USER | __GFP_NOWARN);
value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
if (!value)
goto free_key;
err = -EFAULT;
if (copy_from_user(value, uvalue, map->value_size) != 0)
if (copy_from_user(value, uvalue, value_size) != 0)
goto free_value;
/* eBPF program that use maps are running under rcu_read_lock(),
* therefore all map accessors rely on this fact, so do the same here
*/
rcu_read_lock();
err = map->ops->map_update_elem(map, key, value, attr->flags);
rcu_read_unlock();
if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH) {
err = bpf_percpu_hash_update(map, key, value, attr->flags);
} else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
err = bpf_percpu_array_update(map, key, value, attr->flags);
} else {
rcu_read_lock();
err = map->ops->map_update_elem(map, key, value, attr->flags);
rcu_read_unlock();
}
free_value:
kfree(value);