1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Performance events callchain code, extracted from core.c:
4 *
5 *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
6 *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
7 *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
8 *  Copyright  ��  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
9 */
10
11#include <linux/perf_event.h>
12#include <linux/slab.h>
13#include <linux/sched/task_stack.h>
14
15#include "internal.h"
16
17struct callchain_cpus_entries {
18	struct rcu_head			rcu_head;
19	struct perf_callchain_entry	*cpu_entries[];
20};
21
22int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
23int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
24
25static inline size_t perf_callchain_entry__sizeof(void)
26{
27	return (sizeof(struct perf_callchain_entry) +
28		sizeof(__u64) * (sysctl_perf_event_max_stack +
29				 sysctl_perf_event_max_contexts_per_stack));
30}
31
32static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
33static atomic_t nr_callchain_events;
34static DEFINE_MUTEX(callchain_mutex);
35static struct callchain_cpus_entries *callchain_cpus_entries;
36
37
38__weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
39				  struct pt_regs *regs)
40{
41}
42
43__weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
44				struct pt_regs *regs)
45{
46}
47
48static void release_callchain_buffers_rcu(struct rcu_head *head)
49{
50	struct callchain_cpus_entries *entries;
51	int cpu;
52
53	entries = container_of(head, struct callchain_cpus_entries, rcu_head);
54
55	for_each_possible_cpu(cpu)
56		kfree(entries->cpu_entries[cpu]);
57
58	kfree(entries);
59}
60
61static void release_callchain_buffers(void)
62{
63	struct callchain_cpus_entries *entries;
64
65	entries = callchain_cpus_entries;
66	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
67	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
68}
69
70static int alloc_callchain_buffers(void)
71{
72	int cpu;
73	int size;
74	struct callchain_cpus_entries *entries;
75
76	/*
77	 * We can't use the percpu allocation API for data that can be
78	 * accessed from NMI. Use a temporary manual per cpu allocation
79	 * until that gets sorted out.
80	 */
81	size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
82
83	entries = kzalloc(size, GFP_KERNEL);
84	if (!entries)
85		return -ENOMEM;
86
87	size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
88
89	for_each_possible_cpu(cpu) {
90		entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
91							 cpu_to_node(cpu));
92		if (!entries->cpu_entries[cpu])
93			goto fail;
94	}
95
96	rcu_assign_pointer(callchain_cpus_entries, entries);
97
98	return 0;
99
100fail:
101	for_each_possible_cpu(cpu)
102		kfree(entries->cpu_entries[cpu]);
103	kfree(entries);
104
105	return -ENOMEM;
106}
107
108int get_callchain_buffers(int event_max_stack)
109{
110	int err = 0;
111	int count;
112
113	mutex_lock(&callchain_mutex);
114
115	count = atomic_inc_return(&nr_callchain_events);
116	if (WARN_ON_ONCE(count < 1)) {
117		err = -EINVAL;
118		goto exit;
119	}
120
121	/*
122	 * If requesting per event more than the global cap,
123	 * return a different error to help userspace figure
124	 * this out.
125	 *
126	 * And also do it here so that we have &callchain_mutex held.
127	 */
128	if (event_max_stack > sysctl_perf_event_max_stack) {
129		err = -EOVERFLOW;
130		goto exit;
131	}
132
133	if (count == 1)
134		err = alloc_callchain_buffers();
135exit:
136	if (err)
137		atomic_dec(&nr_callchain_events);
138
139	mutex_unlock(&callchain_mutex);
140
141	return err;
142}
143
144void put_callchain_buffers(void)
145{
146	if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
147		release_callchain_buffers();
148		mutex_unlock(&callchain_mutex);
149	}
150}
151
152struct perf_callchain_entry *get_callchain_entry(int *rctx)
153{
154	int cpu;
155	struct callchain_cpus_entries *entries;
156
157	*rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
158	if (*rctx == -1)
159		return NULL;
160
161	entries = rcu_dereference(callchain_cpus_entries);
162	if (!entries) {
163		put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
164		return NULL;
165	}
166
167	cpu = smp_processor_id();
168
169	return (((void *)entries->cpu_entries[cpu]) +
170		(*rctx * perf_callchain_entry__sizeof()));
171}
172
173void
174put_callchain_entry(int rctx)
175{
176	put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
177}
178
179struct perf_callchain_entry *
180get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
181		   u32 max_stack, bool crosstask, bool add_mark)
182{
183	struct perf_callchain_entry *entry;
184	struct perf_callchain_entry_ctx ctx;
185	int rctx;
186
187	entry = get_callchain_entry(&rctx);
188	if (!entry)
189		return NULL;
190
191	ctx.entry     = entry;
192	ctx.max_stack = max_stack;
193	ctx.nr	      = entry->nr = init_nr;
194	ctx.contexts       = 0;
195	ctx.contexts_maxed = false;
196
197	if (kernel && !user_mode(regs)) {
198		if (add_mark)
199			perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
200		perf_callchain_kernel(&ctx, regs);
201	}
202
203	if (user) {
204		if (!user_mode(regs)) {
205			if  (current->mm)
206				regs = task_pt_regs(current);
207			else
208				regs = NULL;
209		}
210
211		if (regs) {
212			if (crosstask)
213				goto exit_put;
214
215			if (add_mark)
216				perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
217
218			perf_callchain_user(&ctx, regs);
219		}
220	}
221
222exit_put:
223	put_callchain_entry(rctx);
224
225	return entry;
226}
227
228/*
229 * Used for sysctl_perf_event_max_stack and
230 * sysctl_perf_event_max_contexts_per_stack.
231 */
232int perf_event_max_stack_handler(struct ctl_table *table, int write,
233				 void *buffer, size_t *lenp, loff_t *ppos)
234{
235	int *value = table->data;
236	int new_value = *value, ret;
237	struct ctl_table new_table = *table;
238
239	new_table.data = &new_value;
240	ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
241	if (ret || !write)
242		return ret;
243
244	mutex_lock(&callchain_mutex);
245	if (atomic_read(&nr_callchain_events))
246		ret = -EBUSY;
247	else
248		*value = new_value;
249
250	mutex_unlock(&callchain_mutex);
251
252	return ret;
253}
254