kernel/events/hw_breakpoint.c

   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  */
  52 struct 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
  61 static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
  62 static int nr_slots[TYPE_MAX];
  63
  64 static 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 */
  70 static LIST_HEAD(bp_task_head);
  71
  72 static int constraints_initialized;
  73
  74 /* Gather the number of total pinned and un-pinned bp in a cpuset */
  75 struct bp_busy_slots {
  76         unsigned int pinned;
  77         unsigned int flexible;
  78 };
  79
  80 /* Serialize accesses to the above constraints */
  81 static DEFINE_MUTEX(nr_bp_mutex);
  82
  83 __weak int hw_breakpoint_weight(struct perf_event *bp)
  84 {
  85         return 1;
  86 }
  87
  88 static 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  */
 100 static 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  */
 117 static 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
 133 static 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  */
 144 static void
 145 fetch_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  */
 175 static void
 176 fetch_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  */
 184 static 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  */
 202 static void
 203 toggle_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  */
 280 static 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
 314 int 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
 327 static 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
 337 void 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  */
 352 int 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
 360 int 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
 370 static 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
 392 int 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  */
 415 struct perf_event *
 416 register_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 }
 424 EXPORT_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  */
 431 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 432 {
 433         /*
 434          * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 435          * will not be possible to raise IPIs that invoke __perf_event_disable.
 436          * So call the function directly after making sure we are targeting the
 437          * current task.
 438          */
 439         if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
 440                 __perf_event_disable(bp);
 441         else
 442                 perf_event_disable(bp);
 443
 444         bp->attr.bp_addr = attr->bp_addr;
 445         bp->attr.bp_type = attr->bp_type;
 446         bp->attr.bp_len = attr->bp_len;
 447         bp->attr.disabled = 1;
 448
 449         if (!attr->disabled) {
 450                 int err = validate_hw_breakpoint(bp);
 451
 452                 if (err)
 453                         return err;
 454
 455                 perf_event_enable(bp);
 456                 bp->attr.disabled = 0;
 457         }
 458
 459         return 0;
 460 }
 461 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 462
 463 /**
 464  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 465  * @bp: the breakpoint structure to unregister
 466  */
 467 void unregister_hw_breakpoint(struct perf_event *bp)
 468 {
 469         if (!bp)
 470                 return;
 471         perf_event_release_kernel(bp);
 472 }
 473 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 474
 475 /**
 476  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 477  * @attr: breakpoint attributes
 478  * @triggered: callback to trigger when we hit the breakpoint
 479  *
 480  * @return a set of per_cpu pointers to perf events
 481  */
 482 struct perf_event * __percpu *
 483 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 484                             perf_overflow_handler_t triggered,
 485                             void *context)
 486 {
 487         struct perf_event * __percpu *cpu_events, *bp;
 488         long err = 0;
 489         int cpu;
 490
 491         cpu_events = alloc_percpu(typeof(*cpu_events));
 492         if (!cpu_events)
 493                 return (void __percpu __force *)ERR_PTR(-ENOMEM);
 494
 495         get_online_cpus();
 496         for_each_online_cpu(cpu) {
 497                 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
 498                                                       triggered, context);
 499                 if (IS_ERR(bp)) {
 500                         err = PTR_ERR(bp);
 501                         break;
 502                 }
 503
 504                 per_cpu(*cpu_events, cpu) = bp;
 505         }
 506         put_online_cpus();
 507
 508         if (likely(!err))
 509                 return cpu_events;
 510
 511         unregister_wide_hw_breakpoint(cpu_events);
 512         return (void __percpu __force *)ERR_PTR(err);
 513 }
 514 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 515
 516 /**
 517  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 518  * @cpu_events: the per cpu set of events to unregister
 519  */
 520 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 521 {
 522         int cpu;
 523
 524         for_each_possible_cpu(cpu)
 525                 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
 526
 527         free_percpu(cpu_events);
 528 }
 529 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 530
 531 static struct notifier_block hw_breakpoint_exceptions_nb = {
 532         .notifier_call = hw_breakpoint_exceptions_notify,
 533         /* we need to be notified first */
 534         .priority = 0x7fffffff
 535 };
 536
 537 static void bp_perf_event_destroy(struct perf_event *event)
 538 {
 539         release_bp_slot(event);
 540 }
 541
 542 static int hw_breakpoint_event_init(struct perf_event *bp)
 543 {
 544         int err;
 545
 546         if (bp->attr.type != PERF_TYPE_BREAKPOINT)
 547                 return -ENOENT;
 548
 549         /*
 550          * no branch sampling for breakpoint events
 551          */
 552         if (has_branch_stack(bp))
 553                 return -EOPNOTSUPP;
 554
 555         err = register_perf_hw_breakpoint(bp);
 556         if (err)
 557                 return err;
 558
 559         bp->destroy = bp_perf_event_destroy;
 560
 561         return 0;
 562 }
 563
 564 static int hw_breakpoint_add(struct perf_event *bp, int flags)
 565 {
 566         if (!(flags & PERF_EF_START))
 567                 bp->hw.state = PERF_HES_STOPPED;
 568
 569         if (is_sampling_event(bp)) {
 570                 bp->hw.last_period = bp->hw.sample_period;
 571                 perf_swevent_set_period(bp);
 572         }
 573
 574         return arch_install_hw_breakpoint(bp);
 575 }
 576
 577 static void hw_breakpoint_del(struct perf_event *bp, int flags)
 578 {
 579         arch_uninstall_hw_breakpoint(bp);
 580 }
 581
 582 static void hw_breakpoint_start(struct perf_event *bp, int flags)
 583 {
 584         bp->hw.state = 0;
 585 }
 586
 587 static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 588 {
 589         bp->hw.state = PERF_HES_STOPPED;
 590 }
 591
 592 static struct pmu perf_breakpoint = {
 593         .task_ctx_nr    = perf_sw_context, /* could eventually get its own */
 594
 595         .event_init     = hw_breakpoint_event_init,
 596         .add            = hw_breakpoint_add,
 597         .del            = hw_breakpoint_del,
 598         .start          = hw_breakpoint_start,
 599         .stop           = hw_breakpoint_stop,
 600         .read           = hw_breakpoint_pmu_read,
 601 };
 602
 603 int __init init_hw_breakpoint(void)
 604 {
 605         int cpu, err_cpu;
 606         int i;
 607
 608         for (i = 0; i < TYPE_MAX; i++)
 609                 nr_slots[i] = hw_breakpoint_slots(i);
 610
 611         for_each_possible_cpu(cpu) {
 612                 for (i = 0; i < TYPE_MAX; i++) {
 613                         struct bp_cpuinfo *info = get_bp_info(cpu, i);
 614
 615                         info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
 616                                                         GFP_KERNEL);
 617                         if (!info->tsk_pinned)
 618                                 goto err_alloc;
 619                 }
 620         }
 621
 622         constraints_initialized = 1;
 623
 624         perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
 625
 626         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 627
 628  err_alloc:
 629         for_each_possible_cpu(err_cpu) {
 630                 for (i = 0; i < TYPE_MAX; i++)
 631                         kfree(get_bp_info(err_cpu, i)->tsk_pinned);
 632                 if (err_cpu == cpu)
 633                         break;
 634         }
 635
 636         return -ENOMEM;
 637 }
 638
 639