1 files changed, 649 insertions, 0 deletions

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
new file mode 100644
index 000000000..ace303a22
--- /dev/null
+++ b/kernel/bpf/memalloc.c
@@ -0,0 +1,649 @@
+// 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) - 2;
+}
+
+#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 | __GFP_ZERO, 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.
+	 *
+	 * Except for waiting_for_gp list, there are no concurrent operations
+	 * on these lists, so it is safe to use __llist_del_all().
+	 */
+	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);
+			/*
+			 * refill_work may be unfinished for PREEMPT_RT kernel
+			 * in which irq work is invoked in a per-CPU RT thread.
+			 * It is also possible for kernel with
+			 * arch_irq_work_has_interrupt() being false and irq
+			 * work is invoked in timer interrupt. So waiting for
+			 * the completion of irq work to ease the handling of
+			 * concurrency.
+			 */
+			irq_work_sync(&c->refill_work);
+			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];
+				irq_work_sync(&c->refill_work);
+				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);
+}