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-rw-r--r--kernel/bpf/memalloc.c635
1 files changed, 635 insertions, 0 deletions
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
new file mode 100644
index 000000000000..5f83be1d2018
--- /dev/null
+++ b/kernel/bpf/memalloc.c
@@ -0,0 +1,635 @@
+// 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;
+
+ 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;
+ int percpu_size;
+
+ struct rcu_head rcu;
+ struct llist_head free_by_rcu;
+ struct llist_head waiting_for_gp;
+ atomic_t call_rcu_in_progress;
+};
+
+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->percpu_size) {
+ void **obj = kmalloc_node(c->percpu_size, flags, node);
+ void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
+
+ if (!obj || !pptr) {
+ free_percpu(pptr);
+ kfree(obj);
+ return NULL;
+ }
+ obj[1] = pptr;
+ return obj;
+ }
+
+ 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->percpu_size) {
+ free_percpu(((void **)obj)[1]);
+ kfree(obj);
+ return;
+ }
+
+ 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 __free_rcu_tasks_trace(struct rcu_head *head)
+{
+ struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
+
+ call_rcu(&c->rcu, __free_rcu);
+}
+
+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);
+ /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
+ * Then use call_rcu() to wait for normal progs to finish
+ * and finally do free_one() on each element.
+ */
+ call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
+}
+
+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);
+ if (llnode)
+ enque_to_free(c, llnode);
+ } while (cnt > (c->high_watermark + c->low_watermark) / 2);
+
+ /* 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);
+}
+
+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)
+ /* 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)
+ 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.
+ */
+
+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);
+
+ /* 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 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, bool percpu)
+{
+ 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 obj_cgroup *objcg = NULL;
+ int cpu, i, unit_size, percpu_size = 0;
+
+ if (size) {
+ pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
+ if (!pc)
+ return -ENOMEM;
+
+ if (percpu)
+ /* room for llist_node and per-cpu pointer */
+ percpu_size = LLIST_NODE_SZ + sizeof(void *);
+ else
+ size += LLIST_NODE_SZ; /* room for llist_node */
+ unit_size = size;
+
+#ifdef CONFIG_MEMCG_KMEM
+ objcg = get_obj_cgroup_from_current();
+#endif
+ for_each_possible_cpu(cpu) {
+ c = per_cpu_ptr(pc, cpu);
+ c->unit_size = unit_size;
+ c->objcg = objcg;
+ c->percpu_size = percpu_size;
+ prefill_mem_cache(c, cpu);
+ }
+ ma->cache = pc;
+ return 0;
+ }
+
+ /* size == 0 && percpu is an invalid combination */
+ if (WARN_ON_ONCE(percpu))
+ return -EINVAL;
+
+ 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;
+
+ /* 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);
+ 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);
+}
+
+static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
+{
+ free_percpu(ma->cache);
+ free_percpu(ma->caches);
+ ma->cache = NULL;
+ ma->caches = NULL;
+}
+
+static void free_mem_alloc(struct bpf_mem_alloc *ma)
+{
+ /* waiting_for_gp lists was drained, but __free_rcu might
+ * still execute. Wait for it now before we freeing percpu caches.
+ */
+ rcu_barrier_tasks_trace();
+ rcu_barrier();
+ free_mem_alloc_no_barrier(ma);
+}
+
+static void free_mem_alloc_deferred(struct work_struct *work)
+{
+ struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work);
+
+ free_mem_alloc(ma);
+ kfree(ma);
+}
+
+static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
+{
+ struct bpf_mem_alloc *copy;
+
+ if (!rcu_in_progress) {
+ /* Fast path. No callbacks are pending, hence no need to do
+ * rcu_barrier-s.
+ */
+ free_mem_alloc_no_barrier(ma);
+ return;
+ }
+
+ copy = kmalloc(sizeof(*ma), GFP_KERNEL);
+ if (!copy) {
+ /* Slow path with inline barrier-s */
+ free_mem_alloc(ma);
+ return;
+ }
+
+ /* Defer barriers into worker to let the rest of map memory to be freed */
+ copy->cache = ma->cache;
+ ma->cache = NULL;
+ copy->caches = ma->caches;
+ ma->caches = NULL;
+ INIT_WORK(&copy->work, free_mem_alloc_deferred);
+ queue_work(system_unbound_wq, &copy->work);
+}
+
+void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
+{
+ struct bpf_mem_caches *cc;
+ struct bpf_mem_cache *c;
+ int cpu, i, rcu_in_progress;
+
+ if (ma->cache) {
+ rcu_in_progress = 0;
+ for_each_possible_cpu(cpu) {
+ c = per_cpu_ptr(ma->cache, cpu);
+ drain_mem_cache(c);
+ rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
+ }
+ /* objcg is the same across cpus */
+ if (c->objcg)
+ obj_cgroup_put(c->objcg);
+ destroy_mem_alloc(ma, rcu_in_progress);
+ }
+ if (ma->caches) {
+ rcu_in_progress = 0;
+ 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);
+ rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
+ }
+ }
+ if (c->objcg)
+ obj_cgroup_put(c->objcg);
+ destroy_mem_alloc(ma, rcu_in_progress);
+ }
+}
+
+/* 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)
+ 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)
+ /* 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);
+}