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 int reserve_bp_slot(struct perf_event *bp)
 247 {
 248         struct bp_busy_slots slots = {0};
 249         int ret = 0;
 250
 251         mutex_lock(&nr_bp_mutex);
 252
 253         fetch_bp_busy_slots(&slots, bp);
 254
 255         /* Flexible counters need to keep at least one slot */
 256         if (slots.pinned + (!!slots.flexible) == HBP_NUM) {
 257                 ret = -ENOSPC;
 258                 goto end;
 259         }
 260
 261         toggle_bp_slot(bp, true);
 262
 263 end:
 264         mutex_unlock(&nr_bp_mutex);
 265
 266         return ret;
 267 }
 268
 269 void release_bp_slot(struct perf_event *bp)
 270 {
 271         mutex_lock(&nr_bp_mutex);
 272
 273         toggle_bp_slot(bp, false);
 274
 275         mutex_unlock(&nr_bp_mutex);
 276 }
 277
 278
 279 int register_perf_hw_breakpoint(struct perf_event *bp)
 280 {
 281         int ret;
 282
 283         ret = reserve_bp_slot(bp);
 284         if (ret)
 285                 return ret;
 286
 287         /*
 288          * Ptrace breakpoints can be temporary perf events only
 289          * meant to reserve a slot. In this case, it is created disabled and
 290          * we don't want to check the params right now (as we put a null addr)
 291          * But perf tools create events as disabled and we want to check
 292          * the params for them.
 293          * This is a quick hack that will be removed soon, once we remove
 294          * the tmp breakpoints from ptrace
 295          */
 296         if (!bp->attr.disabled || !bp->overflow_handler)
 297                 ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
 298
 299         return ret;
 300 }
 301
 302 /**
 303  * register_user_hw_breakpoint - register a hardware breakpoint for user space
 304  * @attr: breakpoint attributes
 305  * @triggered: callback to trigger when we hit the breakpoint
 306  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 307  */
 308 struct perf_event *
 309 register_user_hw_breakpoint(struct perf_event_attr *attr,
 310                             perf_overflow_handler_t triggered,
 311                             struct task_struct *tsk)
 312 {
 313         return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
 314 }
 315 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 316
 317 /**
 318  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 319  * @bp: the breakpoint structure to modify
 320  * @attr: new breakpoint attributes
 321  * @triggered: callback to trigger when we hit the breakpoint
 322  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 323  */
 324 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 325 {
 326         u64 old_addr = bp->attr.bp_addr;
 327         int old_type = bp->attr.bp_type;
 328         int old_len = bp->attr.bp_len;
 329         int err = 0;
 330
 331         perf_event_disable(bp);
 332
 333         bp->attr.bp_addr = attr->bp_addr;
 334         bp->attr.bp_type = attr->bp_type;
 335         bp->attr.bp_len = attr->bp_len;
 336
 337         if (attr->disabled)
 338                 goto end;
 339
 340         err = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
 341         if (!err)
 342                 perf_event_enable(bp);
 343
 344         if (err) {
 345                 bp->attr.bp_addr = old_addr;
 346                 bp->attr.bp_type = old_type;
 347                 bp->attr.bp_len = old_len;
 348                 if (!bp->attr.disabled)
 349                         perf_event_enable(bp);
 350
 351                 return err;
 352         }
 353
 354 end:
 355         bp->attr.disabled = attr->disabled;
 356
 357         return 0;
 358 }
 359 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 360
 361 /**
 362  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 363  * @bp: the breakpoint structure to unregister
 364  */
 365 void unregister_hw_breakpoint(struct perf_event *bp)
 366 {
 367         if (!bp)
 368                 return;
 369         perf_event_release_kernel(bp);
 370 }
 371 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 372
 373 /**
 374  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 375  * @attr: breakpoint attributes
 376  * @triggered: callback to trigger when we hit the breakpoint
 377  *
 378  * @return a set of per_cpu pointers to perf events
 379  */
 380 struct perf_event **
 381 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 382                             perf_overflow_handler_t triggered)
 383 {
 384         struct perf_event **cpu_events, **pevent, *bp;
 385         long err;
 386         int cpu;
 387
 388         cpu_events = alloc_percpu(typeof(*cpu_events));
 389         if (!cpu_events)
 390                 return ERR_PTR(-ENOMEM);
 391
 392         get_online_cpus();
 393         for_each_online_cpu(cpu) {
 394                 pevent = per_cpu_ptr(cpu_events, cpu);
 395                 bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
 396
 397                 *pevent = bp;
 398
 399                 if (IS_ERR(bp)) {
 400                         err = PTR_ERR(bp);
 401                         goto fail;
 402                 }
 403         }
 404         put_online_cpus();
 405
 406         return cpu_events;
 407
 408 fail:
 409         for_each_online_cpu(cpu) {
 410                 pevent = per_cpu_ptr(cpu_events, cpu);
 411                 if (IS_ERR(*pevent))
 412                         break;
 413                 unregister_hw_breakpoint(*pevent);
 414         }
 415         put_online_cpus();
 416
 417         free_percpu(cpu_events);
 418         return ERR_PTR(err);
 419 }
 420 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 421
 422 /**
 423  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 424  * @cpu_events: the per cpu set of events to unregister
 425  */
 426 void unregister_wide_hw_breakpoint(struct perf_event **cpu_events)
 427 {
 428         int cpu;
 429         struct perf_event **pevent;
 430
 431         for_each_possible_cpu(cpu) {
 432                 pevent = per_cpu_ptr(cpu_events, cpu);
 433                 unregister_hw_breakpoint(*pevent);
 434         }
 435         free_percpu(cpu_events);
 436 }
 437 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 438
 439 static struct notifier_block hw_breakpoint_exceptions_nb = {
 440         .notifier_call = hw_breakpoint_exceptions_notify,
 441         /* we need to be notified first */
 442         .priority = 0x7fffffff
 443 };
 444
 445 static int __init init_hw_breakpoint(void)
 446 {
 447         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 448 }
 449 core_initcall(init_hw_breakpoint);
 450
 451
 452 struct pmu perf_ops_bp = {
 453         .enable         = arch_install_hw_breakpoint,
 454         .disable        = arch_uninstall_hw_breakpoint,
 455         .read           = hw_breakpoint_pmu_read,
 456         .unthrottle     = hw_breakpoint_pmu_unthrottle
 457 };