linux/kernel/bpf/memalloc.c

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bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <linux/mm.h>
#include <linux/llist.h>
#include <linux/bpf.h>
#include <linux/irq_work.h>
#include <linux/bpf_mem_alloc.h>
#include <linux/memcontrol.h>
#include <asm/local.h>
/* Any context (including NMI) BPF specific memory allocator.
*
* Tracing BPF programs can attach to kprobe and fentry. Hence they
* run in unknown context where calling plain kmalloc() might not be safe.
*
* Front-end kmalloc() with per-cpu per-bucket cache of free elements.
* Refill this cache asynchronously from irq_work.
*
* CPU_0 buckets
* 16 32 64 96 128 196 256 512 1024 2048 4096
* ...
* CPU_N buckets
* 16 32 64 96 128 196 256 512 1024 2048 4096
*
* The buckets are prefilled at the start.
* BPF programs always run with migration disabled.
* It's safe to allocate from cache of the current cpu with irqs disabled.
* Free-ing is always done into bucket of the current cpu as well.
* irq_work trims extra free elements from buckets with kfree
* and refills them with kmalloc, so global kmalloc logic takes care
* of freeing objects allocated by one cpu and freed on another.
*
* Every allocated objected is padded with extra 8 bytes that contains
* struct llist_node.
*/
#define LLIST_NODE_SZ sizeof(struct llist_node)
/* similar to kmalloc, but sizeof == 8 bucket is gone */
static u8 size_index[24] __ro_after_init = {
3, /* 8 */
3, /* 16 */
4, /* 24 */
4, /* 32 */
5, /* 40 */
5, /* 48 */
5, /* 56 */
5, /* 64 */
1, /* 72 */
1, /* 80 */
1, /* 88 */
1, /* 96 */
6, /* 104 */
6, /* 112 */
6, /* 120 */
6, /* 128 */
2, /* 136 */
2, /* 144 */
2, /* 152 */
2, /* 160 */
2, /* 168 */
2, /* 176 */
2, /* 184 */
2 /* 192 */
};
static int bpf_mem_cache_idx(size_t size)
{
if (!size || size > 4096)
return -1;
if (size <= 192)
return size_index[(size - 1) / 8] - 1;
return fls(size - 1) - 1;
}
#define NUM_CACHES 11
struct bpf_mem_cache {
/* per-cpu list of free objects of size 'unit_size'.
* All accesses are done with interrupts disabled and 'active' counter
* protection with __llist_add() and __llist_del_first().
*/
struct llist_head free_llist;
local_t active;
/* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
* are sequenced by per-cpu 'active' counter. But unit_free() cannot
* fail. When 'active' is busy the unit_free() will add an object to
* free_llist_extra.
*/
struct llist_head free_llist_extra;
/* kmem_cache != NULL when bpf_mem_alloc was created for specific
* element size.
*/
struct kmem_cache *kmem_cache;
struct irq_work refill_work;
struct obj_cgroup *objcg;
int unit_size;
/* count of objects in free_llist */
int free_cnt;
int low_watermark, high_watermark, batch;
struct rcu_head rcu;
struct llist_head free_by_rcu;
struct llist_head waiting_for_gp;
atomic_t call_rcu_in_progress;
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
};
struct bpf_mem_caches {
struct bpf_mem_cache cache[NUM_CACHES];
};
static struct llist_node notrace *__llist_del_first(struct llist_head *head)
{
struct llist_node *entry, *next;
entry = head->first;
if (!entry)
return NULL;
next = entry->next;
head->first = next;
return entry;
}
static void *__alloc(struct bpf_mem_cache *c, int node)
{
/* Allocate, but don't deplete atomic reserves that typical
* GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
* will allocate from the current numa node which is what we
* want here.
*/
gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
if (c->kmem_cache)
return kmem_cache_alloc_node(c->kmem_cache, flags, node);
return kmalloc_node(c->unit_size, flags, node);
}
static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
{
#ifdef CONFIG_MEMCG_KMEM
if (c->objcg)
return get_mem_cgroup_from_objcg(c->objcg);
#endif
#ifdef CONFIG_MEMCG
return root_mem_cgroup;
#else
return NULL;
#endif
}
/* Mostly runs from irq_work except __init phase. */
static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
{
struct mem_cgroup *memcg = NULL, *old_memcg;
unsigned long flags;
void *obj;
int i;
memcg = get_memcg(c);
old_memcg = set_active_memcg(memcg);
for (i = 0; i < cnt; i++) {
obj = __alloc(c, node);
if (!obj)
break;
if (IS_ENABLED(CONFIG_PREEMPT_RT))
/* In RT irq_work runs in per-cpu kthread, so disable
* interrupts to avoid preemption and interrupts and
* reduce the chance of bpf prog executing on this cpu
* when active counter is busy.
*/
local_irq_save(flags);
/* alloc_bulk runs from irq_work which will not preempt a bpf
* program that does unit_alloc/unit_free since IRQs are
* disabled there. There is no race to increment 'active'
* counter. It protects free_llist from corruption in case NMI
* bpf prog preempted this loop.
*/
WARN_ON_ONCE(local_inc_return(&c->active) != 1);
__llist_add(obj, &c->free_llist);
c->free_cnt++;
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
}
set_active_memcg(old_memcg);
mem_cgroup_put(memcg);
}
static void free_one(struct bpf_mem_cache *c, void *obj)
{
if (c->kmem_cache)
kmem_cache_free(c->kmem_cache, obj);
else
kfree(obj);
}
static void __free_rcu(struct rcu_head *head)
{
struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
struct llist_node *pos, *t;
llist_for_each_safe(pos, t, llnode)
free_one(c, pos);
atomic_set(&c->call_rcu_in_progress, 0);
}
static void enque_to_free(struct bpf_mem_cache *c, void *obj)
{
struct llist_node *llnode = obj;
/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
* Nothing races to add to free_by_rcu list.
*/
__llist_add(llnode, &c->free_by_rcu);
}
static void do_call_rcu(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
if (atomic_xchg(&c->call_rcu_in_progress, 1))
return;
WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
/* There is no concurrent __llist_add(waiting_for_gp) access.
* It doesn't race with llist_del_all either.
* But there could be two concurrent llist_del_all(waiting_for_gp):
* from __free_rcu() and from drain_mem_cache().
*/
__llist_add(llnode, &c->waiting_for_gp);
call_rcu(&c->rcu, __free_rcu);
}
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
static void free_bulk(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
unsigned long flags;
int cnt;
do {
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_save(flags);
WARN_ON_ONCE(local_inc_return(&c->active) != 1);
llnode = __llist_del_first(&c->free_llist);
if (llnode)
cnt = --c->free_cnt;
else
cnt = 0;
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
enque_to_free(c, llnode);
} while (cnt > (c->high_watermark + c->low_watermark) / 2);
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
/* and drain free_llist_extra */
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
enque_to_free(c, llnode);
do_call_rcu(c);
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
}
static void bpf_mem_refill(struct irq_work *work)
{
struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
int cnt;
/* Racy access to free_cnt. It doesn't need to be 100% accurate */
cnt = c->free_cnt;
if (cnt < c->low_watermark)
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
/* irq_work runs on this cpu and kmalloc will allocate
* from the current numa node which is what we want here.
*/
alloc_bulk(c, c->batch, NUMA_NO_NODE);
else if (cnt > c->high_watermark)
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
free_bulk(c);
}
static void notrace irq_work_raise(struct bpf_mem_cache *c)
{
irq_work_queue(&c->refill_work);
}
/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
* the freelist cache will be elem_size * 64 (or less) on each cpu.
*
* For bpf programs that don't have statically known allocation sizes and
* assuming (low_mark + high_mark) / 2 as an average number of elements per
* bucket and all buckets are used the total amount of memory in freelists
* on each cpu will be:
* 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
* == ~ 116 Kbyte using below heuristic.
* Initialized, but unused bpf allocator (not bpf map specific one) will
* consume ~ 11 Kbyte per cpu.
* Typical case will be between 11K and 116K closer to 11K.
* bpf progs can and should share bpf_mem_cache when possible.
*/
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
{
init_irq_work(&c->refill_work, bpf_mem_refill);
if (c->unit_size <= 256) {
c->low_watermark = 32;
c->high_watermark = 96;
} else {
/* When page_size == 4k, order-0 cache will have low_mark == 2
* and high_mark == 6 with batch alloc of 3 individual pages at
* a time.
* 8k allocs and above low == 1, high == 3, batch == 1.
*/
c->low_watermark = max(32 * 256 / c->unit_size, 1);
c->high_watermark = max(96 * 256 / c->unit_size, 3);
}
c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
/* To avoid consuming memory assume that 1st run of bpf
* prog won't be doing more than 4 map_update_elem from
* irq disabled region
*/
alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu));
}
/* When size != 0 create kmem_cache and bpf_mem_cache for each cpu.
* This is typical bpf hash map use case when all elements have equal size.
*
* When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
* kmalloc/kfree. Max allocation size is 4096 in this case.
* This is bpf_dynptr and bpf_kptr use case.
*/
int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
{
static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
struct bpf_mem_caches *cc, __percpu *pcc;
struct bpf_mem_cache *c, __percpu *pc;
struct kmem_cache *kmem_cache;
struct obj_cgroup *objcg = NULL;
char buf[32];
int cpu, i;
if (size) {
pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
if (!pc)
return -ENOMEM;
size += LLIST_NODE_SZ; /* room for llist_node */
snprintf(buf, sizeof(buf), "bpf-%u", size);
kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
if (!kmem_cache) {
free_percpu(pc);
return -ENOMEM;
}
#ifdef CONFIG_MEMCG_KMEM
objcg = get_obj_cgroup_from_current();
#endif
for_each_possible_cpu(cpu) {
c = per_cpu_ptr(pc, cpu);
c->kmem_cache = kmem_cache;
c->unit_size = size;
c->objcg = objcg;
prefill_mem_cache(c, cpu);
}
ma->cache = pc;
return 0;
}
pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
if (!pcc)
return -ENOMEM;
#ifdef CONFIG_MEMCG_KMEM
objcg = get_obj_cgroup_from_current();
#endif
for_each_possible_cpu(cpu) {
cc = per_cpu_ptr(pcc, cpu);
for (i = 0; i < NUM_CACHES; i++) {
c = &cc->cache[i];
c->unit_size = sizes[i];
c->objcg = objcg;
prefill_mem_cache(c, cpu);
}
}
ma->caches = pcc;
return 0;
}
static void drain_mem_cache(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
/* The caller has done rcu_barrier() and no progs are using this
* bpf_mem_cache, but htab_map_free() called bpf_mem_cache_free() for
* all remaining elements and they can be in free_by_rcu or in
* waiting_for_gp lists, so drain those lists now.
*/
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
free_one(c, llnode);
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
free_one(c, llnode);
}
void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
{
struct bpf_mem_caches *cc;
struct bpf_mem_cache *c;
int cpu, i;
if (ma->cache) {
for_each_possible_cpu(cpu) {
c = per_cpu_ptr(ma->cache, cpu);
drain_mem_cache(c);
}
/* kmem_cache and memcg are the same across cpus */
kmem_cache_destroy(c->kmem_cache);
if (c->objcg)
obj_cgroup_put(c->objcg);
/* c->waiting_for_gp list was drained, but __free_rcu might
* still execute. Wait for it now before we free 'c'.
*/
rcu_barrier();
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
free_percpu(ma->cache);
ma->cache = NULL;
}
if (ma->caches) {
for_each_possible_cpu(cpu) {
cc = per_cpu_ptr(ma->caches, cpu);
for (i = 0; i < NUM_CACHES; i++) {
c = &cc->cache[i];
drain_mem_cache(c);
}
}
if (c->objcg)
obj_cgroup_put(c->objcg);
rcu_barrier();
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
free_percpu(ma->caches);
ma->caches = NULL;
}
}
/* notrace is necessary here and in other functions to make sure
* bpf programs cannot attach to them and cause llist corruptions.
*/
static void notrace *unit_alloc(struct bpf_mem_cache *c)
{
struct llist_node *llnode = NULL;
unsigned long flags;
int cnt = 0;
/* Disable irqs to prevent the following race for majority of prog types:
* prog_A
* bpf_mem_alloc
* preemption or irq -> prog_B
* bpf_mem_alloc
*
* but prog_B could be a perf_event NMI prog.
* Use per-cpu 'active' counter to order free_list access between
* unit_alloc/unit_free/bpf_mem_refill.
*/
local_irq_save(flags);
if (local_inc_return(&c->active) == 1) {
llnode = __llist_del_first(&c->free_llist);
if (llnode)
cnt = --c->free_cnt;
}
local_dec(&c->active);
local_irq_restore(flags);
WARN_ON(cnt < 0);
if (cnt < c->low_watermark)
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
irq_work_raise(c);
return llnode;
}
/* Though 'ptr' object could have been allocated on a different cpu
* add it to the free_llist of the current cpu.
* Let kfree() logic deal with it when it's later called from irq_work.
*/
static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
{
struct llist_node *llnode = ptr - LLIST_NODE_SZ;
unsigned long flags;
int cnt = 0;
BUILD_BUG_ON(LLIST_NODE_SZ > 8);
local_irq_save(flags);
if (local_inc_return(&c->active) == 1) {
__llist_add(llnode, &c->free_llist);
cnt = ++c->free_cnt;
} else {
/* unit_free() cannot fail. Therefore add an object to atomic
* llist. free_bulk() will drain it. Though free_llist_extra is
* a per-cpu list we have to use atomic llist_add here, since
* it also can be interrupted by bpf nmi prog that does another
* unit_free() into the same free_llist_extra.
*/
llist_add(llnode, &c->free_llist_extra);
}
local_dec(&c->active);
local_irq_restore(flags);
if (cnt > c->high_watermark)
bpf: Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with minimal per-cpu cache of free elements. Refill this cache asynchronously from irq_work. BPF programs always run with migration disabled. It's safe to allocate from cache of the current cpu with irqs disabled. Free-ing is always done into bucket of the current cpu as well. irq_work trims extra free elements from buckets with kfree and refills them with kmalloc, so global kmalloc logic takes care of freeing objects allocated by one cpu and freed on another. struct bpf_mem_alloc supports two modes: - When size != 0 create kmem_cache and bpf_mem_cache for each cpu. This is typical bpf hash map use case when all elements have equal size. - When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on kmalloc/kfree. Max allocation size is 4096 in this case. This is bpf_dynptr and bpf_kptr use case. bpf_mem_alloc/bpf_mem_free are bpf specific 'wrappers' of kmalloc/kfree. bpf_mem_cache_alloc/bpf_mem_cache_free are 'wrappers' of kmem_cache_alloc/kmem_cache_free. The allocators are NMI-safe from bpf programs only. They are not NMI-safe in general. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-2-alexei.starovoitov@gmail.com
2022-09-03 05:10:43 +08:00
/* free few objects from current cpu into global kmalloc pool */
irq_work_raise(c);
}
/* Called from BPF program or from sys_bpf syscall.
* In both cases migration is disabled.
*/
void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
{
int idx;
void *ret;
if (!size)
return ZERO_SIZE_PTR;
idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
if (idx < 0)
return NULL;
ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
return !ret ? NULL : ret + LLIST_NODE_SZ;
}
void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
{
int idx;
if (!ptr)
return;
idx = bpf_mem_cache_idx(__ksize(ptr - LLIST_NODE_SZ));
if (idx < 0)
return;
unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}
void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
{
void *ret;
ret = unit_alloc(this_cpu_ptr(ma->cache));
return !ret ? NULL : ret + LLIST_NODE_SZ;
}
void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
{
if (!ptr)
return;
unit_free(this_cpu_ptr(ma->cache), ptr);
}