kernel/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/cpu.h>
  44 #include <linux/smp.h>
  45
  46 #include <linux/hw_breakpoint.h>
  47
  48 /*
  49  * Constraints data
  50  */
  51
  52 /* Number of pinned cpu breakpoints in a cpu */
  53 static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned);
  54
  55 /* Number of pinned task breakpoints in a cpu */
  56 static DEFINE_PER_CPU(unsigned int, nr_task_bp_pinned[HBP_NUM]);
  57
  58 /* Number of non-pinned cpu/task breakpoints in a cpu */
  59 static DEFINE_PER_CPU(unsigned int, nr_bp_flexible);
  60
  61 /* Gather the number of total pinned and un-pinned bp in a cpuset */
  62 struct bp_busy_slots {
  63         unsigned int pinned;
  64         unsigned int flexible;
  65 };
  66
  67 /* Serialize accesses to the above constraints */
  68 static DEFINE_MUTEX(nr_bp_mutex);
  69
  70 /*
  71  * Report the maximum number of pinned breakpoints a task
  72  * have in this cpu
  73  */
  74 static unsigned int max_task_bp_pinned(int cpu)
  75 {
  76         int i;
  77         unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned, cpu);
  78
  79         for (i = HBP_NUM -1; i >= 0; i--) {
  80                 if (tsk_pinned[i] > 0)
  81                         return i + 1;
  82         }
  83
  84         return 0;
  85 }
  86
  87 static int task_bp_pinned(struct task_struct *tsk)
  88 {
  89         struct perf_event_context *ctx = tsk->perf_event_ctxp;
  90         struct list_head *list;
  91         struct perf_event *bp;
  92         unsigned long flags;
  93         int count = 0;
  94
  95         if (WARN_ONCE(!ctx, "No perf context for this task"))
  96                 return 0;
  97
  98         list = &ctx->event_list;
  99
 100         raw_spin_lock_irqsave(&ctx->lock, flags);
 101
 102         /*
 103          * The current breakpoint counter is not included in the list
 104          * at the open() callback time
 105          */
 106         list_for_each_entry(bp, list, event_entry) {
 107                 if (bp->attr.type == PERF_TYPE_BREAKPOINT)
 108                         count++;
 109         }
 110
 111         raw_spin_unlock_irqrestore(&ctx->lock, flags);
 112
 113         return count;
 114 }
 115
 116 /*
 117  * Report the number of pinned/un-pinned breakpoints we have in
 118  * a given cpu (cpu > -1) or in all of them (cpu = -1).
 119  */
 120 static void
 121 fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp)
 122 {
 123         int cpu = bp->cpu;
 124         struct task_struct *tsk = bp->ctx->task;
 125
 126         if (cpu >= 0) {
 127                 slots->pinned = per_cpu(nr_cpu_bp_pinned, cpu);
 128                 if (!tsk)
 129                         slots->pinned += max_task_bp_pinned(cpu);
 130                 else
 131                         slots->pinned += task_bp_pinned(tsk);
 132                 slots->flexible = per_cpu(nr_bp_flexible, cpu);
 133
 134                 return;
 135         }
 136
 137         for_each_online_cpu(cpu) {
 138                 unsigned int nr;
 139
 140                 nr = per_cpu(nr_cpu_bp_pinned, cpu);
 141                 if (!tsk)
 142                         nr += max_task_bp_pinned(cpu);
 143                 else
 144                         nr += task_bp_pinned(tsk);
 145
 146                 if (nr > slots->pinned)
 147                         slots->pinned = nr;
 148
 149                 nr = per_cpu(nr_bp_flexible, cpu);
 150
 151                 if (nr > slots->flexible)
 152                         slots->flexible = nr;
 153         }
 154 }
 155
 156 /*
 157  * Add a pinned breakpoint for the given task in our constraint table
 158  */
 159 static void toggle_bp_task_slot(struct task_struct *tsk, int cpu, bool enable)
 160 {
 161         unsigned int *tsk_pinned;
 162         int count = 0;
 163
 164         count = task_bp_pinned(tsk);
 165
 166         tsk_pinned = per_cpu(nr_task_bp_pinned, cpu);
 167         if (enable) {
 168                 tsk_pinned[count]++;
 169                 if (count > 0)
 170                         tsk_pinned[count-1]--;
 171         } else {
 172                 tsk_pinned[count]--;
 173                 if (count > 0)
 174                         tsk_pinned[count-1]++;
 175         }
 176 }
 177
 178 /*
 179  * Add/remove the given breakpoint in our constraint table
 180  */
 181 static void toggle_bp_slot(struct perf_event *bp, bool enable)
 182 {
 183         int cpu = bp->cpu;
 184         struct task_struct *tsk = bp->ctx->task;
 185
 186         /* Pinned counter task profiling */
 187         if (tsk) {
 188                 if (cpu >= 0) {
 189                         toggle_bp_task_slot(tsk, cpu, enable);
 190                         return;
 191                 }
 192
 193                 for_each_online_cpu(cpu)
 194                         toggle_bp_task_slot(tsk, cpu, enable);
 195                 return;
 196         }
 197
 198         /* Pinned counter cpu profiling */
 199         if (enable)
 200                 per_cpu(nr_cpu_bp_pinned, bp->cpu)++;
 201         else
 202                 per_cpu(nr_cpu_bp_pinned, bp->cpu)--;
 203 }
 204
 205 /*
 206  * Contraints to check before allowing this new breakpoint counter:
 207  *
 208  *  == Non-pinned counter == (Considered as pinned for now)
 209  *
 210  *   - If attached to a single cpu, check:
 211  *
 212  *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
 213  *           + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
 214  *
 215  *       -> If there are already non-pinned counters in this cpu, it means
 216  *          there is already a free slot for them.
 217  *          Otherwise, we check that the maximum number of per task
 218  *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 219  *          (for this cpu) doesn't cover every registers.
 220  *
 221  *   - If attached to every cpus, check:
 222  *
 223  *       (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
 224  *           + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
 225  *
 226  *       -> This is roughly the same, except we check the number of per cpu
 227  *          bp for every cpu and we keep the max one. Same for the per tasks
 228  *          breakpoints.
 229  *
 230  *
 231  * == Pinned counter ==
 232  *
 233  *   - If attached to a single cpu, check:
 234  *
 235  *       ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
 236  *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
 237  *
 238  *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
 239  *          one register at least (or they will never be fed).
 240  *
 241  *   - If attached to every cpus, check:
 242  *
 243  *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
 244  *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
 245  */
 246 static int __reserve_bp_slot(struct perf_event *bp)
 247 {
 248         struct bp_busy_slots slots = {0};
 249
 250         fetch_bp_busy_slots(&slots, bp);
 251
 252         /* Flexible counters need to keep at least one slot */
 253         if (slots.pinned + (!!slots.flexible) == HBP_NUM)
 254                 return -ENOSPC;
 255
 256         toggle_bp_slot(bp, true);
 257
 258         return 0;
 259 }
 260
 261 int reserve_bp_slot(struct perf_event *bp)
 262 {
 263         int ret;
 264
 265         mutex_lock(&nr_bp_mutex);
 266
 267         ret = __reserve_bp_slot(bp);
 268
 269         mutex_unlock(&nr_bp_mutex);
 270
 271         return ret;
 272 }
 273
 274 static void __release_bp_slot(struct perf_event *bp)
 275 {
 276         toggle_bp_slot(bp, false);
 277 }
 278
 279 void release_bp_slot(struct perf_event *bp)
 280 {
 281         mutex_lock(&nr_bp_mutex);
 282
 283         __release_bp_slot(bp);
 284
 285         mutex_unlock(&nr_bp_mutex);
 286 }
 287
 288 /*
 289  * Allow the kernel debugger to reserve breakpoint slots without
 290  * taking a lock using the dbg_* variant of for the reserve and
 291  * release breakpoint slots.
 292  */
 293 int dbg_reserve_bp_slot(struct perf_event *bp)
 294 {
 295         if (mutex_is_locked(&nr_bp_mutex))
 296                 return -1;
 297
 298         return __reserve_bp_slot(bp);
 299 }
 300
 301 int dbg_release_bp_slot(struct perf_event *bp)
 302 {
 303         if (mutex_is_locked(&nr_bp_mutex))
 304                 return -1;
 305
 306         __release_bp_slot(bp);
 307
 308         return 0;
 309 }
 310
 311 int register_perf_hw_breakpoint(struct perf_event *bp)
 312 {
 313         int ret;
 314
 315         ret = reserve_bp_slot(bp);
 316         if (ret)
 317                 return ret;
 318
 319         /*
 320          * Ptrace breakpoints can be temporary perf events only
 321          * meant to reserve a slot. In this case, it is created disabled and
 322          * we don't want to check the params right now (as we put a null addr)
 323          * But perf tools create events as disabled and we want to check
 324          * the params for them.
 325          * This is a quick hack that will be removed soon, once we remove
 326          * the tmp breakpoints from ptrace
 327          */
 328         if (!bp->attr.disabled || !bp->overflow_handler)
 329                 ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
 330
 331         /* if arch_validate_hwbkpt_settings() fails then release bp slot */
 332         if (ret)
 333                 release_bp_slot(bp);
 334
 335         return ret;
 336 }
 337
 338 /**
 339  * register_user_hw_breakpoint - register a hardware breakpoint for user space
 340  * @attr: breakpoint attributes
 341  * @triggered: callback to trigger when we hit the breakpoint
 342  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 343  */
 344 struct perf_event *
 345 register_user_hw_breakpoint(struct perf_event_attr *attr,
 346                             perf_overflow_handler_t triggered,
 347                             struct task_struct *tsk)
 348 {
 349         return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
 350 }
 351 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 352
 353 /**
 354  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 355  * @bp: the breakpoint structure to modify
 356  * @attr: new breakpoint attributes
 357  * @triggered: callback to trigger when we hit the breakpoint
 358  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 359  */
 360 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 361 {
 362         u64 old_addr = bp->attr.bp_addr;
 363         u64 old_len = bp->attr.bp_len;
 364         int old_type = bp->attr.bp_type;
 365         int err = 0;
 366
 367         perf_event_disable(bp);
 368
 369         bp->attr.bp_addr = attr->bp_addr;
 370         bp->attr.bp_type = attr->bp_type;
 371         bp->attr.bp_len = attr->bp_len;
 372
 373         if (attr->disabled)
 374                 goto end;
 375
 376         err = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
 377         if (!err)
 378                 perf_event_enable(bp);
 379
 380         if (err) {
 381                 bp->attr.bp_addr = old_addr;
 382                 bp->attr.bp_type = old_type;
 383                 bp->attr.bp_len = old_len;
 384                 if (!bp->attr.disabled)
 385                         perf_event_enable(bp);
 386
 387                 return err;
 388         }
 389
 390 end:
 391         bp->attr.disabled = attr->disabled;
 392
 393         return 0;
 394 }
 395 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 396
 397 /**
 398  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 399  * @bp: the breakpoint structure to unregister
 400  */
 401 void unregister_hw_breakpoint(struct perf_event *bp)
 402 {
 403         if (!bp)
 404                 return;
 405         perf_event_release_kernel(bp);
 406 }
 407 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 408
 409 /**
 410  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 411  * @attr: breakpoint attributes
 412  * @triggered: callback to trigger when we hit the breakpoint
 413  *
 414  * @return a set of per_cpu pointers to perf events
 415  */
 416 struct perf_event * __percpu *
 417 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 418                             perf_overflow_handler_t triggered)
 419 {
 420         struct perf_event * __percpu *cpu_events, **pevent, *bp;
 421         long err;
 422         int cpu;
 423
 424         cpu_events = alloc_percpu(typeof(*cpu_events));
 425         if (!cpu_events)
 426                 return (void __percpu __force *)ERR_PTR(-ENOMEM);
 427
 428         get_online_cpus();
 429         for_each_online_cpu(cpu) {
 430                 pevent = per_cpu_ptr(cpu_events, cpu);
 431                 bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
 432
 433                 *pevent = bp;
 434
 435                 if (IS_ERR(bp)) {
 436                         err = PTR_ERR(bp);
 437                         goto fail;
 438                 }
 439         }
 440         put_online_cpus();
 441
 442         return cpu_events;
 443
 444 fail:
 445         for_each_online_cpu(cpu) {
 446                 pevent = per_cpu_ptr(cpu_events, cpu);
 447                 if (IS_ERR(*pevent))
 448                         break;
 449                 unregister_hw_breakpoint(*pevent);
 450         }
 451         put_online_cpus();
 452
 453         free_percpu(cpu_events);
 454         return (void __percpu __force *)ERR_PTR(err);
 455 }
 456 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 457
 458 /**
 459  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 460  * @cpu_events: the per cpu set of events to unregister
 461  */
 462 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 463 {
 464         int cpu;
 465         struct perf_event **pevent;
 466
 467         for_each_possible_cpu(cpu) {
 468                 pevent = per_cpu_ptr(cpu_events, cpu);
 469                 unregister_hw_breakpoint(*pevent);
 470         }
 471         free_percpu(cpu_events);
 472 }
 473 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 474
 475 static struct notifier_block hw_breakpoint_exceptions_nb = {
 476         .notifier_call = hw_breakpoint_exceptions_notify,
 477         /* we need to be notified first */
 478         .priority = 0x7fffffff
 479 };
 480
 481 static int __init init_hw_breakpoint(void)
 482 {
 483         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 484 }
 485 core_initcall(init_hw_breakpoint);
 486
 487
 488 struct pmu perf_ops_bp = {
 489         .enable         = arch_install_hw_breakpoint,
 490         .disable        = arch_uninstall_hw_breakpoint,
 491         .read           = hw_breakpoint_pmu_read,
 492 };