linux/kernel/events/hw_breakpoint.c
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   1/*
   2 * This program is free software; you can redistribute it and/or modify
   3 * it under the terms of the GNU General Public License as published by
   4 * the Free Software Foundation; either version 2 of the License, or
   5 * (at your option) any later version.
   6 *
   7 * This program is distributed in the hope that it will be useful,
   8 * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10 * GNU General Public License for more details.
  11 *
  12 * You should have received a copy of the GNU General Public License
  13 * along with this program; if not, write to the Free Software
  14 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  15 *
  16 * Copyright (C) 2007 Alan Stern
  17 * Copyright (C) IBM Corporation, 2009
  18 * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
  19 *
  20 * Thanks to Ingo Molnar for his many suggestions.
  21 *
  22 * Authors: Alan Stern <stern@rowland.harvard.edu>
  23 *          K.Prasad <prasad@linux.vnet.ibm.com>
  24 *          Frederic Weisbecker <fweisbec@gmail.com>
  25 */
  26
  27/*
  28 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
  29 * using the CPU's debug registers.
  30 * This file contains the arch-independent routines.
  31 */
  32
  33#include <linux/irqflags.h>
  34#include <linux/kallsyms.h>
  35#include <linux/notifier.h>
  36#include <linux/kprobes.h>
  37#include <linux/kdebug.h>
  38#include <linux/kernel.h>
  39#include <linux/module.h>
  40#include <linux/percpu.h>
  41#include <linux/sched.h>
  42#include <linux/init.h>
  43#include <linux/slab.h>
  44#include <linux/list.h>
  45#include <linux/cpu.h>
  46#include <linux/smp.h>
  47
  48#include <linux/hw_breakpoint.h>
  49/*
  50 * Constraints data
  51 */
  52struct bp_cpuinfo {
  53        /* Number of pinned cpu breakpoints in a cpu */
  54        unsigned int    cpu_pinned;
  55        /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */
  56        unsigned int    *tsk_pinned;
  57        /* Number of non-pinned cpu/task breakpoints in a cpu */
  58        unsigned int    flexible; /* XXX: placeholder, see fetch_this_slot() */
  59};
  60
  61static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
  62static int nr_slots[TYPE_MAX];
  63
  64static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
  65{
  66        return per_cpu_ptr(bp_cpuinfo + type, cpu);
  67}
  68
  69/* Keep track of the breakpoints attached to tasks */
  70static LIST_HEAD(bp_task_head);
  71
  72static int constraints_initialized;
  73
  74/* Gather the number of total pinned and un-pinned bp in a cpuset */
  75struct bp_busy_slots {
  76        unsigned int pinned;
  77        unsigned int flexible;
  78};
  79
  80/* Serialize accesses to the above constraints */
  81static DEFINE_MUTEX(nr_bp_mutex);
  82
  83__weak int hw_breakpoint_weight(struct perf_event *bp)
  84{
  85        return 1;
  86}
  87
  88static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
  89{
  90        if (bp->attr.bp_type & HW_BREAKPOINT_RW)
  91                return TYPE_DATA;
  92
  93        return TYPE_INST;
  94}
  95
  96/*
  97 * Report the maximum number of pinned breakpoints a task
  98 * have in this cpu
  99 */
 100static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
 101{
 102        unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
 103        int i;
 104
 105        for (i = nr_slots[type] - 1; i >= 0; i--) {
 106                if (tsk_pinned[i] > 0)
 107                        return i + 1;
 108        }
 109
 110        return 0;
 111}
 112
 113/*
 114 * Count the number of breakpoints of the same type and same task.
 115 * The given event must be not on the list.
 116 */
 117static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
 118{
 119        struct task_struct *tsk = bp->hw.target;
 120        struct perf_event *iter;
 121        int count = 0;
 122
 123        list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
 124                if (iter->hw.target == tsk &&
 125                    find_slot_idx(iter) == type &&
 126                    (iter->cpu < 0 || cpu == iter->cpu))
 127                        count += hw_breakpoint_weight(iter);
 128        }
 129
 130        return count;
 131}
 132
 133static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
 134{
 135        if (bp->cpu >= 0)
 136                return cpumask_of(bp->cpu);
 137        return cpu_possible_mask;
 138}
 139
 140/*
 141 * Report the number of pinned/un-pinned breakpoints we have in
 142 * a given cpu (cpu > -1) or in all of them (cpu = -1).
 143 */
 144static void
 145fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
 146                    enum bp_type_idx type)
 147{
 148        const struct cpumask *cpumask = cpumask_of_bp(bp);
 149        int cpu;
 150
 151        for_each_cpu(cpu, cpumask) {
 152                struct bp_cpuinfo *info = get_bp_info(cpu, type);
 153                int nr;
 154
 155                nr = info->cpu_pinned;
 156                if (!bp->hw.target)
 157                        nr += max_task_bp_pinned(cpu, type);
 158                else
 159                        nr += task_bp_pinned(cpu, bp, type);
 160
 161                if (nr > slots->pinned)
 162                        slots->pinned = nr;
 163
 164                nr = info->flexible;
 165                if (nr > slots->flexible)
 166                        slots->flexible = nr;
 167        }
 168}
 169
 170/*
 171 * For now, continue to consider flexible as pinned, until we can
 172 * ensure no flexible event can ever be scheduled before a pinned event
 173 * in a same cpu.
 174 */
 175static void
 176fetch_this_slot(struct bp_busy_slots *slots, int weight)
 177{
 178        slots->pinned += weight;
 179}
 180
 181/*
 182 * Add a pinned breakpoint for the given task in our constraint table
 183 */
 184static void toggle_bp_task_slot(struct perf_event *bp, int cpu,
 185                                enum bp_type_idx type, int weight)
 186{
 187        unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
 188        int old_idx, new_idx;
 189
 190        old_idx = task_bp_pinned(cpu, bp, type) - 1;
 191        new_idx = old_idx + weight;
 192
 193        if (old_idx >= 0)
 194                tsk_pinned[old_idx]--;
 195        if (new_idx >= 0)
 196                tsk_pinned[new_idx]++;
 197}
 198
 199/*
 200 * Add/remove the given breakpoint in our constraint table
 201 */
 202static void
 203toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 204               int weight)
 205{
 206        const struct cpumask *cpumask = cpumask_of_bp(bp);
 207        int cpu;
 208
 209        if (!enable)
 210                weight = -weight;
 211
 212        /* Pinned counter cpu profiling */
 213        if (!bp->hw.target) {
 214                get_bp_info(bp->cpu, type)->cpu_pinned += weight;
 215                return;
 216        }
 217
 218        /* Pinned counter task profiling */
 219        for_each_cpu(cpu, cpumask)
 220                toggle_bp_task_slot(bp, cpu, type, weight);
 221
 222        if (enable)
 223                list_add_tail(&bp->hw.bp_list, &bp_task_head);
 224        else
 225                list_del(&bp->hw.bp_list);
 226}
 227
 228/*
 229 * Function to perform processor-specific cleanup during unregistration
 230 */
 231__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
 232{
 233        /*
 234         * A weak stub function here for those archs that don't define
 235         * it inside arch/.../kernel/hw_breakpoint.c
 236         */
 237}
 238
 239/*
 240 * Contraints to check before allowing this new breakpoint counter:
 241 *
 242 *  == Non-pinned counter == (Considered as pinned for now)
 243 *
 244 *   - If attached to a single cpu, check:
 245 *
 246 *       (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
 247 *           + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
 248 *
 249 *       -> If there are already non-pinned counters in this cpu, it means
 250 *          there is already a free slot for them.
 251 *          Otherwise, we check that the maximum number of per task
 252 *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 253 *          (for this cpu) doesn't cover every registers.
 254 *
 255 *   - If attached to every cpus, check:
 256 *
 257 *       (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
 258 *           + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
 259 *
 260 *       -> This is roughly the same, except we check the number of per cpu
 261 *          bp for every cpu and we keep the max one. Same for the per tasks
 262 *          breakpoints.
 263 *
 264 *
 265 * == Pinned counter ==
 266 *
 267 *   - If attached to a single cpu, check:
 268 *
 269 *       ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
 270 *            + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
 271 *
 272 *       -> Same checks as before. But now the info->flexible, if any, must keep
 273 *          one register at least (or they will never be fed).
 274 *
 275 *   - If attached to every cpus, check:
 276 *
 277 *       ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
 278 *            + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
 279 */
 280static int __reserve_bp_slot(struct perf_event *bp)
 281{
 282        struct bp_busy_slots slots = {0};
 283        enum bp_type_idx type;
 284        int weight;
 285
 286        /* We couldn't initialize breakpoint constraints on boot */
 287        if (!constraints_initialized)
 288                return -ENOMEM;
 289
 290        /* Basic checks */
 291        if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
 292            bp->attr.bp_type == HW_BREAKPOINT_INVALID)
 293                return -EINVAL;
 294
 295        type = find_slot_idx(bp);
 296        weight = hw_breakpoint_weight(bp);
 297
 298        fetch_bp_busy_slots(&slots, bp, type);
 299        /*
 300         * Simulate the addition of this breakpoint to the constraints
 301         * and see the result.
 302         */
 303        fetch_this_slot(&slots, weight);
 304
 305        /* Flexible counters need to keep at least one slot */
 306        if (slots.pinned + (!!slots.flexible) > nr_slots[type])
 307                return -ENOSPC;
 308
 309        toggle_bp_slot(bp, true, type, weight);
 310
 311        return 0;
 312}
 313
 314int reserve_bp_slot(struct perf_event *bp)
 315{
 316        int ret;
 317
 318        mutex_lock(&nr_bp_mutex);
 319
 320        ret = __reserve_bp_slot(bp);
 321
 322        mutex_unlock(&nr_bp_mutex);
 323
 324        return ret;
 325}
 326
 327static void __release_bp_slot(struct perf_event *bp)
 328{
 329        enum bp_type_idx type;
 330        int weight;
 331
 332        type = find_slot_idx(bp);
 333        weight = hw_breakpoint_weight(bp);
 334        toggle_bp_slot(bp, false, type, weight);
 335}
 336
 337void release_bp_slot(struct perf_event *bp)
 338{
 339        mutex_lock(&nr_bp_mutex);
 340
 341        arch_unregister_hw_breakpoint(bp);
 342        __release_bp_slot(bp);
 343
 344        mutex_unlock(&nr_bp_mutex);
 345}
 346
 347/*
 348 * Allow the kernel debugger to reserve breakpoint slots without
 349 * taking a lock using the dbg_* variant of for the reserve and
 350 * release breakpoint slots.
 351 */
 352int dbg_reserve_bp_slot(struct perf_event *bp)
 353{
 354        if (mutex_is_locked(&nr_bp_mutex))
 355                return -1;
 356
 357        return __reserve_bp_slot(bp);
 358}
 359
 360int dbg_release_bp_slot(struct perf_event *bp)
 361{
 362        if (mutex_is_locked(&nr_bp_mutex))
 363                return -1;
 364
 365        __release_bp_slot(bp);
 366
 367        return 0;
 368}
 369
 370static int validate_hw_breakpoint(struct perf_event *bp)
 371{
 372        int ret;
 373
 374        ret = arch_validate_hwbkpt_settings(bp);
 375        if (ret)
 376                return ret;
 377
 378        if (arch_check_bp_in_kernelspace(bp)) {
 379                if (bp->attr.exclude_kernel)
 380                        return -EINVAL;
 381                /*
 382                 * Don't let unprivileged users set a breakpoint in the trap
 383                 * path to avoid trap recursion attacks.
 384                 */
 385                if (!capable(CAP_SYS_ADMIN))
 386                        return -EPERM;
 387        }
 388
 389        return 0;
 390}
 391
 392int register_perf_hw_breakpoint(struct perf_event *bp)
 393{
 394        int ret;
 395
 396        ret = reserve_bp_slot(bp);
 397        if (ret)
 398                return ret;
 399
 400        ret = validate_hw_breakpoint(bp);
 401
 402        /* if arch_validate_hwbkpt_settings() fails then release bp slot */
 403        if (ret)
 404                release_bp_slot(bp);
 405
 406        return ret;
 407}
 408
 409/**
 410 * register_user_hw_breakpoint - register a hardware breakpoint for user space
 411 * @attr: breakpoint attributes
 412 * @triggered: callback to trigger when we hit the breakpoint
 413 * @tsk: pointer to 'task_struct' of the process to which the address belongs
 414 */
 415struct perf_event *
 416register_user_hw_breakpoint(struct perf_event_attr *attr,
 417                            perf_overflow_handler_t triggered,
 418                            void *context,
 419                            struct task_struct *tsk)
 420{
 421        return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
 422                                                context);
 423}
 424EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 425
 426/**
 427 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 428 * @bp: the breakpoint structure to modify
 429 * @attr: new breakpoint attributes
 430 * @triggered: callback to trigger when we hit the breakpoint
 431 * @tsk: pointer to 'task_struct' of the process to which the address belongs
 432 */
 433int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 434{
 435        u64 old_addr = bp->attr.bp_addr;
 436        u64 old_len = bp->attr.bp_len;
 437        int old_type = bp->attr.bp_type;
 438        int err = 0;
 439
 440        /*
 441         * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 442         * will not be possible to raise IPIs that invoke __perf_event_disable.
 443         * So call the function directly after making sure we are targeting the
 444         * current task.
 445         */
 446        if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
 447                perf_event_disable_local(bp);
 448        else
 449                perf_event_disable(bp);
 450
 451        bp->attr.bp_addr = attr->bp_addr;
 452        bp->attr.bp_type = attr->bp_type;
 453        bp->attr.bp_len = attr->bp_len;
 454
 455        if (attr->disabled)
 456                goto end;
 457
 458        err = validate_hw_breakpoint(bp);
 459        if (!err)
 460                perf_event_enable(bp);
 461
 462        if (err) {
 463                bp->attr.bp_addr = old_addr;
 464                bp->attr.bp_type = old_type;
 465                bp->attr.bp_len = old_len;
 466                if (!bp->attr.disabled)
 467                        perf_event_enable(bp);
 468
 469                return err;
 470        }
 471
 472end:
 473        bp->attr.disabled = attr->disabled;
 474
 475        return 0;
 476}
 477EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 478
 479/**
 480 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 481 * @bp: the breakpoint structure to unregister
 482 */
 483void unregister_hw_breakpoint(struct perf_event *bp)
 484{
 485        if (!bp)
 486                return;
 487        perf_event_release_kernel(bp);
 488}
 489EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 490
 491/**
 492 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 493 * @attr: breakpoint attributes
 494 * @triggered: callback to trigger when we hit the breakpoint
 495 *
 496 * @return a set of per_cpu pointers to perf events
 497 */
 498struct perf_event * __percpu *
 499register_wide_hw_breakpoint(struct perf_event_attr *attr,
 500                            perf_overflow_handler_t triggered,
 501                            void *context)
 502{
 503        struct perf_event * __percpu *cpu_events, *bp;
 504        long err = 0;
 505        int cpu;
 506
 507        cpu_events = alloc_percpu(typeof(*cpu_events));
 508        if (!cpu_events)
 509                return (void __percpu __force *)ERR_PTR(-ENOMEM);
 510
 511        get_online_cpus();
 512        for_each_online_cpu(cpu) {
 513                bp = perf_event_create_kernel_counter(attr, cpu, NULL,
 514                                                      triggered, context);
 515                if (IS_ERR(bp)) {
 516                        err = PTR_ERR(bp);
 517                        break;
 518                }
 519
 520                per_cpu(*cpu_events, cpu) = bp;
 521        }
 522        put_online_cpus();
 523
 524        if (likely(!err))
 525                return cpu_events;
 526
 527        unregister_wide_hw_breakpoint(cpu_events);
 528        return (void __percpu __force *)ERR_PTR(err);
 529}
 530EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 531
 532/**
 533 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 534 * @cpu_events: the per cpu set of events to unregister
 535 */
 536void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 537{
 538        int cpu;
 539
 540        for_each_possible_cpu(cpu)
 541                unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
 542
 543        free_percpu(cpu_events);
 544}
 545EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 546
 547static struct notifier_block hw_breakpoint_exceptions_nb = {
 548        .notifier_call = hw_breakpoint_exceptions_notify,
 549        /* we need to be notified first */
 550        .priority = 0x7fffffff
 551};
 552
 553static void bp_perf_event_destroy(struct perf_event *event)
 554{
 555        release_bp_slot(event);
 556}
 557
 558static int hw_breakpoint_event_init(struct perf_event *bp)
 559{
 560        int err;
 561
 562        if (bp->attr.type != PERF_TYPE_BREAKPOINT)
 563                return -ENOENT;
 564
 565        /*
 566         * no branch sampling for breakpoint events
 567         */
 568        if (has_branch_stack(bp))
 569                return -EOPNOTSUPP;
 570
 571        err = register_perf_hw_breakpoint(bp);
 572        if (err)
 573                return err;
 574
 575        bp->destroy = bp_perf_event_destroy;
 576
 577        return 0;
 578}
 579
 580static int hw_breakpoint_add(struct perf_event *bp, int flags)
 581{
 582        if (!(flags & PERF_EF_START))
 583                bp->hw.state = PERF_HES_STOPPED;
 584
 585        if (is_sampling_event(bp)) {
 586                bp->hw.last_period = bp->hw.sample_period;
 587                perf_swevent_set_period(bp);
 588        }
 589
 590        return arch_install_hw_breakpoint(bp);
 591}
 592
 593static void hw_breakpoint_del(struct perf_event *bp, int flags)
 594{
 595        arch_uninstall_hw_breakpoint(bp);
 596}
 597
 598static void hw_breakpoint_start(struct perf_event *bp, int flags)
 599{
 600        bp->hw.state = 0;
 601}
 602
 603static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 604{
 605        bp->hw.state = PERF_HES_STOPPED;
 606}
 607
 608static struct pmu perf_breakpoint = {
 609        .task_ctx_nr    = perf_sw_context, /* could eventually get its own */
 610
 611        .event_init     = hw_breakpoint_event_init,
 612        .add            = hw_breakpoint_add,
 613        .del            = hw_breakpoint_del,
 614        .start          = hw_breakpoint_start,
 615        .stop           = hw_breakpoint_stop,
 616        .read           = hw_breakpoint_pmu_read,
 617};
 618
 619int __init init_hw_breakpoint(void)
 620{
 621        int cpu, err_cpu;
 622        int i;
 623
 624        for (i = 0; i < TYPE_MAX; i++)
 625                nr_slots[i] = hw_breakpoint_slots(i);
 626
 627        for_each_possible_cpu(cpu) {
 628                for (i = 0; i < TYPE_MAX; i++) {
 629                        struct bp_cpuinfo *info = get_bp_info(cpu, i);
 630
 631                        info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
 632                                                        GFP_KERNEL);
 633                        if (!info->tsk_pinned)
 634                                goto err_alloc;
 635                }
 636        }
 637
 638        constraints_initialized = 1;
 639
 640        perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
 641
 642        return register_die_notifier(&hw_breakpoint_exceptions_nb);
 643
 644 err_alloc:
 645        for_each_possible_cpu(err_cpu) {
 646                for (i = 0; i < TYPE_MAX; i++)
 647                        kfree(get_bp_info(err_cpu, i)->tsk_pinned);
 648                if (err_cpu == cpu)
 649                        break;
 650        }
 651
 652        return -ENOMEM;
 653}
 654
 655
 656