--- /dev/null
+// 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;
+};
+
+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;
+}
+
+#define BATCH 48
+#define LOW_WATERMARK 32
+#define HIGH_WATERMARK 96
+/* Assuming the average number of elements per bucket is 64, when all buckets
+ * are used the total memory will be: 64*16*32 + 64*32*32 + 64*64*32 + ... +
+ * 64*4096*32 ~ 20Mbyte
+ */
+
+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_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);
+ free_one(c, llnode);
+ } while (cnt > (HIGH_WATERMARK + LOW_WATERMARK) / 2);
+
+ /* and drain free_llist_extra */
+ llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
+ free_one(c, llnode);
+}
+
+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 < 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, BATCH, NUMA_NO_NODE);
+ else if (cnt > HIGH_WATERMARK)
+ free_bulk(c);
+}
+
+static void notrace irq_work_raise(struct bpf_mem_cache *c)
+{
+ irq_work_queue(&c->refill_work);
+}
+
+static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
+{
+ init_irq_work(&c->refill_work, bpf_mem_refill);
+ /* 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);
+ 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;
+
+ 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);
+ 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);
+ 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 < 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 > 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);
+}
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