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
  51/*
  52 * Constraints data
  53 */
  54
  55/* Number of pinned cpu breakpoints in a cpu */
  56static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned[TYPE_MAX]);
  57
  58/* Number of pinned task breakpoints in a cpu */
  59static DEFINE_PER_CPU(unsigned int *, nr_task_bp_pinned[TYPE_MAX]);
  60
  61/* Number of non-pinned cpu/task breakpoints in a cpu */
  62static DEFINE_PER_CPU(unsigned int, nr_bp_flexible[TYPE_MAX]);
  63
  64static int nr_slots[TYPE_MAX];
  65
  66/* Keep track of the breakpoints attached to tasks */
  67static LIST_HEAD(bp_task_head);
  68
  69static int constraints_initialized;
  70
  71/* Gather the number of total pinned and un-pinned bp in a cpuset */
  72struct bp_busy_slots {
  73        unsigned int pinned;
  74        unsigned int flexible;
  75};
  76
  77/* Serialize accesses to the above constraints */
  78static DEFINE_MUTEX(nr_bp_mutex);
  79
  80__weak int hw_breakpoint_weight(struct perf_event *bp)
  81{
  82        return 1;
  83}
  84
  85static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
  86{
  87        if (bp->attr.bp_type & HW_BREAKPOINT_RW)
  88                return TYPE_DATA;
  89
  90        return TYPE_INST;
  91}
  92
  93/*
  94 * Report the maximum number of pinned breakpoints a task
  95 * have in this cpu
  96 */
  97static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
  98{
  99        int i;
 100        unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
 101
 102        for (i = nr_slots[type] - 1; i >= 0; i--) {
 103                if (tsk_pinned[i] > 0)
 104                        return i + 1;
 105        }
 106
 107        return 0;
 108}
 109
 110/*
 111 * Count the number of breakpoints of the same type and same task.
 112 * The given event must be not on the list.
 113 */
 114static int task_bp_pinned(struct perf_event *bp, enum bp_type_idx type)
 115{
 116        struct task_struct *tsk = bp->hw.bp_target;
 117        struct perf_event *iter;
 118        int count = 0;
 119
 120        list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
 121                if (iter->hw.bp_target == tsk && find_slot_idx(iter) == type)
 122                        count += hw_breakpoint_weight(iter);
 123        }
 124
 125        return count;
 126}
 127
 128/*
 129 * Report the number of pinned/un-pinned breakpoints we have in
 130 * a given cpu (cpu > -1) or in all of them (cpu = -1).
 131 */
 132static void
 133fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
 134                    enum bp_type_idx type)
 135{
 136        int cpu = bp->cpu;
 137        struct task_struct *tsk = bp->hw.bp_target;
 138
 139        if (cpu >= 0) {
 140                slots->pinned = per_cpu(nr_cpu_bp_pinned[type], cpu);
 141                if (!tsk)
 142                        slots->pinned += max_task_bp_pinned(cpu, type);
 143                else
 144                        slots->pinned += task_bp_pinned(bp, type);
 145                slots->flexible = per_cpu(nr_bp_flexible[type], cpu);
 146
 147                return;
 148        }
 149
 150        for_each_online_cpu(cpu) {
 151                unsigned int nr;
 152
 153                nr = per_cpu(nr_cpu_bp_pinned[type], cpu);
 154                if (!tsk)
 155                        nr += max_task_bp_pinned(cpu, type);
 156                else
 157                        nr += task_bp_pinned(bp, type);
 158
 159                if (nr > slots->pinned)
 160                        slots->pinned = nr;
 161
 162                nr = per_cpu(nr_bp_flexible[type], cpu);
 163
 164                if (nr > slots->flexible)
 165                        slots->flexible = nr;
 166        }
 167}
 168
 169/*
 170 * For now, continue to consider flexible as pinned, until we can
 171 * ensure no flexible event can ever be scheduled before a pinned event
 172 * in a same cpu.
 173 */
 174static void
 175fetch_this_slot(struct bp_busy_slots *slots, int weight)
 176{
 177        slots->pinned += weight;
 178}
 179
 180/*
 181 * Add a pinned breakpoint for the given task in our constraint table
 182 */
 183static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
 184                                enum bp_type_idx type, int weight)
 185{
 186        unsigned int *tsk_pinned;
 187        int old_count = 0;
 188        int old_idx = 0;
 189        int idx = 0;
 190
 191        old_count = task_bp_pinned(bp, type);
 192        old_idx = old_count - 1;
 193        idx = old_idx + weight;
 194
 195        /* tsk_pinned[n] is the number of tasks having n breakpoints */
 196        tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
 197        if (enable) {
 198                tsk_pinned[idx]++;
 199                if (old_count > 0)
 200                        tsk_pinned[old_idx]--;
 201        } else {
 202                tsk_pinned[idx]--;
 203                if (old_count > 0)
 204                        tsk_pinned[old_idx]++;
 205        }
 206}
 207
 208/*
 209 * Add/remove the given breakpoint in our constraint table
 210 */
 211static void
 212toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 213               int weight)
 214{
 215        int cpu = bp->cpu;
 216        struct task_struct *tsk = bp->hw.bp_target;
 217
 218        /* Pinned counter cpu profiling */
 219        if (!tsk) {
 220
 221                if (enable)
 222                        per_cpu(nr_cpu_bp_pinned[type], bp->cpu) += weight;
 223                else
 224                        per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
 225                return;
 226        }
 227
 228        /* Pinned counter task profiling */
 229
 230        if (!enable)
 231                list_del(&bp->hw.bp_list);
 232
 233        if (cpu >= 0) {
 234                toggle_bp_task_slot(bp, cpu, enable, type, weight);
 235        } else {
 236                for_each_online_cpu(cpu)
 237                        toggle_bp_task_slot(bp, cpu, enable, type, weight);
 238        }
 239
 240        if (enable)
 241                list_add_tail(&bp->hw.bp_list, &bp_task_head);
 242}
 243
 244/*
 245 * Function to perform processor-specific cleanup during unregistration
 246 */
 247__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
 248{
 249        /*
 250         * A weak stub function here for those archs that don't define
 251         * it inside arch/.../kernel/hw_breakpoint.c
 252         */
 253}
 254
 255/*
 256 * Contraints to check before allowing this new breakpoint counter:
 257 *
 258 *  == Non-pinned counter == (Considered as pinned for now)
 259 *
 260 *   - If attached to a single cpu, check:
 261 *
 262 *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
 263 *           + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
 264 *
 265 *       -> If there are already non-pinned counters in this cpu, it means
 266 *          there is already a free slot for them.
 267 *          Otherwise, we check that the maximum number of per task
 268 *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 269 *          (for this cpu) doesn't cover every registers.
 270 *
 271 *   - If attached to every cpus, check:
 272 *
 273 *       (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
 274 *           + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
 275 *
 276 *       -> This is roughly the same, except we check the number of per cpu
 277 *          bp for every cpu and we keep the max one. Same for the per tasks
 278 *          breakpoints.
 279 *
 280 *
 281 * == Pinned counter ==
 282 *
 283 *   - If attached to a single cpu, check:
 284 *
 285 *       ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
 286 *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
 287 *
 288 *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
 289 *          one register at least (or they will never be fed).
 290 *
 291 *   - If attached to every cpus, check:
 292 *
 293 *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
 294 *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
 295 */
 296static int __reserve_bp_slot(struct perf_event *bp)
 297{
 298        struct bp_busy_slots slots = {0};
 299        enum bp_type_idx type;
 300        int weight;
 301
 302        /* We couldn't initialize breakpoint constraints on boot */
 303        if (!constraints_initialized)
 304                return -ENOMEM;
 305
 306        /* Basic checks */
 307        if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
 308            bp->attr.bp_type == HW_BREAKPOINT_INVALID)
 309                return -EINVAL;
 310
 311        type = find_slot_idx(bp);
 312        weight = hw_breakpoint_weight(bp);
 313
 314        fetch_bp_busy_slots(&slots, bp, type);
 315        /*
 316         * Simulate the addition of this breakpoint to the constraints
 317         * and see the result.
 318         */
 319        fetch_this_slot(&slots, weight);
 320
 321        /* Flexible counters need to keep at least one slot */
 322        if (slots.pinned + (!!slots.flexible) > nr_slots[type])
 323                return -ENOSPC;
 324
 325        toggle_bp_slot(bp, true, type, weight);
 326
 327        return 0;
 328}
 329
 330int reserve_bp_slot(struct perf_event *bp)
 331{
 332        int ret;
 333
 334        mutex_lock(&nr_bp_mutex);
 335
 336        ret = __reserve_bp_slot(bp);
 337
 338        mutex_unlock(&nr_bp_mutex);
 339
 340        return ret;
 341}
 342
 343static void __release_bp_slot(struct perf_event *bp)
 344{
 345        enum bp_type_idx type;
 346        int weight;
 347
 348        type = find_slot_idx(bp);
 349        weight = hw_breakpoint_weight(bp);
 350        toggle_bp_slot(bp, false, type, weight);
 351}
 352
 353void release_bp_slot(struct perf_event *bp)
 354{
 355        mutex_lock(&nr_bp_mutex);
 356
 357        arch_unregister_hw_breakpoint(bp);
 358        __release_bp_slot(bp);
 359
 360        mutex_unlock(&nr_bp_mutex);
 361}
 362
 363/*
 364 * Allow the kernel debugger to reserve breakpoint slots without
 365 * taking a lock using the dbg_* variant of for the reserve and
 366 * release breakpoint slots.
 367 */
 368int dbg_reserve_bp_slot(struct perf_event *bp)
 369{
 370        if (mutex_is_locked(&nr_bp_mutex))
 371                return -1;
 372
 373        return __reserve_bp_slot(bp);
 374}
 375
 376int dbg_release_bp_slot(struct perf_event *bp)
 377{
 378        if (mutex_is_locked(&nr_bp_mutex))
 379                return -1;
 380
 381        __release_bp_slot(bp);
 382
 383        return 0;
 384}
 385
 386static int validate_hw_breakpoint(struct perf_event *bp)
 387{
 388        int ret;
 389
 390        ret = arch_validate_hwbkpt_settings(bp);
 391        if (ret)
 392                return ret;
 393
 394        if (arch_check_bp_in_kernelspace(bp)) {
 395                if (bp->attr.exclude_kernel)
 396                        return -EINVAL;
 397                /*
 398                 * Don't let unprivileged users set a breakpoint in the trap
 399                 * path to avoid trap recursion attacks.
 400                 */
 401                if (!capable(CAP_SYS_ADMIN))
 402                        return -EPERM;
 403        }
 404
 405        return 0;
 406}
 407
 408int register_perf_hw_breakpoint(struct perf_event *bp)
 409{
 410        int ret;
 411
 412        ret = reserve_bp_slot(bp);
 413        if (ret)
 414                return ret;
 415
 416        ret = validate_hw_breakpoint(bp);
 417
 418        /* if arch_validate_hwbkpt_settings() fails then release bp slot */
 419        if (ret)
 420                release_bp_slot(bp);
 421
 422        return ret;
 423}
 424
 425/**
 426 * register_user_hw_breakpoint - register a hardware breakpoint for user space
 427 * @attr: breakpoint attributes
 428 * @triggered: callback to trigger when we hit the breakpoint
 429 * @tsk: pointer to 'task_struct' of the process to which the address belongs
 430 */
 431struct perf_event *
 432register_user_hw_breakpoint(struct perf_event_attr *attr,
 433                            perf_overflow_handler_t triggered,
 434                            void *context,
 435                            struct task_struct *tsk)
 436{
 437        return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
 438                                                context);
 439}
 440EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 441
 442/**
 443 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 444 * @bp: the breakpoint structure to modify
 445 * @attr: new breakpoint attributes
 446 * @triggered: callback to trigger when we hit the breakpoint
 447 * @tsk: pointer to 'task_struct' of the process to which the address belongs
 448 */
 449int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 450{
 451        u64 old_addr = bp->attr.bp_addr;
 452        u64 old_len = bp->attr.bp_len;
 453        int old_type = bp->attr.bp_type;
 454        int err = 0;
 455
 456        /*
 457         * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 458         * will not be possible to raise IPIs that invoke __perf_event_disable.
 459         * So call the function directly after making sure we are targeting the
 460         * current task.
 461         */
 462        if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
 463                __perf_event_disable(bp);
 464        else
 465                perf_event_disable(bp);
 466
 467        bp->attr.bp_addr = attr->bp_addr;
 468        bp->attr.bp_type = attr->bp_type;
 469        bp->attr.bp_len = attr->bp_len;
 470
 471        if (attr->disabled)
 472                goto end;
 473
 474        err = validate_hw_breakpoint(bp);
 475        if (!err)
 476                perf_event_enable(bp);
 477
 478        if (err) {
 479                bp->attr.bp_addr = old_addr;
 480                bp->attr.bp_type = old_type;
 481                bp->attr.bp_len = old_len;
 482                if (!bp->attr.disabled)
 483                        perf_event_enable(bp);
 484
 485                return err;
 486        }
 487
 488end:
 489        bp->attr.disabled = attr->disabled;
 490
 491        return 0;
 492}
 493EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 494
 495/**
 496 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 497 * @bp: the breakpoint structure to unregister
 498 */
 499void unregister_hw_breakpoint(struct perf_event *bp)
 500{
 501        if (!bp)
 502                return;
 503        perf_event_release_kernel(bp);
 504}
 505EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 506
 507/**
 508 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 509 * @attr: breakpoint attributes
 510 * @triggered: callback to trigger when we hit the breakpoint
 511 *
 512 * @return a set of per_cpu pointers to perf events
 513 */
 514struct perf_event * __percpu *
 515register_wide_hw_breakpoint(struct perf_event_attr *attr,
 516                            perf_overflow_handler_t triggered,
 517                            void *context)
 518{
 519        struct perf_event * __percpu *cpu_events, **pevent, *bp;
 520        long err;
 521        int cpu;
 522
 523        cpu_events = alloc_percpu(typeof(*cpu_events));
 524        if (!cpu_events)
 525                return (void __percpu __force *)ERR_PTR(-ENOMEM);
 526
 527        get_online_cpus();
 528        for_each_online_cpu(cpu) {
 529                pevent = per_cpu_ptr(cpu_events, cpu);
 530                bp = perf_event_create_kernel_counter(attr, cpu, NULL,
 531                                                      triggered, context);
 532
 533                *pevent = bp;
 534
 535                if (IS_ERR(bp)) {
 536                        err = PTR_ERR(bp);
 537                        goto fail;
 538                }
 539        }
 540        put_online_cpus();
 541
 542        return cpu_events;
 543
 544fail:
 545        for_each_online_cpu(cpu) {
 546                pevent = per_cpu_ptr(cpu_events, cpu);
 547                if (IS_ERR(*pevent))
 548                        break;
 549                unregister_hw_breakpoint(*pevent);
 550        }
 551        put_online_cpus();
 552
 553        free_percpu(cpu_events);
 554        return (void __percpu __force *)ERR_PTR(err);
 555}
 556EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 557
 558/**
 559 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 560 * @cpu_events: the per cpu set of events to unregister
 561 */
 562void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 563{
 564        int cpu;
 565        struct perf_event **pevent;
 566
 567        for_each_possible_cpu(cpu) {
 568                pevent = per_cpu_ptr(cpu_events, cpu);
 569                unregister_hw_breakpoint(*pevent);
 570        }
 571        free_percpu(cpu_events);
 572}
 573EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 574
 575static struct notifier_block hw_breakpoint_exceptions_nb = {
 576        .notifier_call = hw_breakpoint_exceptions_notify,
 577        /* we need to be notified first */
 578        .priority = 0x7fffffff
 579};
 580
 581static void bp_perf_event_destroy(struct perf_event *event)
 582{
 583        release_bp_slot(event);
 584}
 585
 586static int hw_breakpoint_event_init(struct perf_event *bp)
 587{
 588        int err;
 589
 590        if (bp->attr.type != PERF_TYPE_BREAKPOINT)
 591                return -ENOENT;
 592
 593        /*
 594         * no branch sampling for breakpoint events
 595         */
 596        if (has_branch_stack(bp))
 597                return -EOPNOTSUPP;
 598
 599        err = register_perf_hw_breakpoint(bp);
 600        if (err)
 601                return err;
 602
 603        bp->destroy = bp_perf_event_destroy;
 604
 605        return 0;
 606}
 607
 608static int hw_breakpoint_add(struct perf_event *bp, int flags)
 609{
 610        if (!(flags & PERF_EF_START))
 611                bp->hw.state = PERF_HES_STOPPED;
 612
 613        return arch_install_hw_breakpoint(bp);
 614}
 615
 616static void hw_breakpoint_del(struct perf_event *bp, int flags)
 617{
 618        arch_uninstall_hw_breakpoint(bp);
 619}
 620
 621static void hw_breakpoint_start(struct perf_event *bp, int flags)
 622{
 623        bp->hw.state = 0;
 624}
 625
 626static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 627{
 628        bp->hw.state = PERF_HES_STOPPED;
 629}
 630
 631static int hw_breakpoint_event_idx(struct perf_event *bp)
 632{
 633        return 0;
 634}
 635
 636static struct pmu perf_breakpoint = {
 637        .task_ctx_nr    = perf_sw_context, /* could eventually get its own */
 638
 639        .event_init     = hw_breakpoint_event_init,
 640        .add            = hw_breakpoint_add,
 641        .del            = hw_breakpoint_del,
 642        .start          = hw_breakpoint_start,
 643        .stop           = hw_breakpoint_stop,
 644        .read           = hw_breakpoint_pmu_read,
 645
 646        .event_idx      = hw_breakpoint_event_idx,
 647};
 648
 649int __init init_hw_breakpoint(void)
 650{
 651        unsigned int **task_bp_pinned;
 652        int cpu, err_cpu;
 653        int i;
 654
 655        for (i = 0; i < TYPE_MAX; i++)
 656                nr_slots[i] = hw_breakpoint_slots(i);
 657
 658        for_each_possible_cpu(cpu) {
 659                for (i = 0; i < TYPE_MAX; i++) {
 660                        task_bp_pinned = &per_cpu(nr_task_bp_pinned[i], cpu);
 661                        *task_bp_pinned = kzalloc(sizeof(int) * nr_slots[i],
 662                                                  GFP_KERNEL);
 663                        if (!*task_bp_pinned)
 664                                goto err_alloc;
 665                }
 666        }
 667
 668        constraints_initialized = 1;
 669
 670        perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
 671
 672        return register_die_notifier(&hw_breakpoint_exceptions_nb);
 673
 674 err_alloc:
 675        for_each_possible_cpu(err_cpu) {
 676                for (i = 0; i < TYPE_MAX; i++)
 677                        kfree(per_cpu(nr_task_bp_pinned[i], cpu));
 678                if (err_cpu == cpu)
 679                        break;
 680        }
 681
 682        return -ENOMEM;
 683}
 684
 685
 686
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