arch/sh/kernel/hw_breakpoint.c

   1 /*
   2  * arch/sh/kernel/hw_breakpoint.c
   3  *
   4  * Unified kernel/user-space hardware breakpoint facility for the on-chip UBC.
   5  *
   6  * Copyright (C) 2009 - 2010  Paul Mundt
   7  *
   8  * This file is subject to the terms and conditions of the GNU General Public
   9  * License.  See the file "COPYING" in the main directory of this archive
  10  * for more details.
  11  */
  12 #include <linux/init.h>
  13 #include <linux/perf_event.h>
  14 #include <linux/hw_breakpoint.h>
  15 #include <linux/percpu.h>
  16 #include <linux/kallsyms.h>
  17 #include <linux/notifier.h>
  18 #include <linux/kprobes.h>
  19 #include <linux/kdebug.h>
  20 #include <linux/io.h>
  21 #include <linux/clk.h>
  22 #include <asm/hw_breakpoint.h>
  23 #include <asm/mmu_context.h>
  24 #include <asm/ptrace.h>
  25 #include <asm/traps.h>
  26
  27 /*
  28  * Stores the breakpoints currently in use on each breakpoint address
  29  * register for each cpus
  30  */
  31 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
  32
  33 /*
  34  * A dummy placeholder for early accesses until the CPUs get a chance to
  35  * register their UBCs later in the boot process.
  36  */
  37 static struct sh_ubc ubc_dummy = { .num_events = 0 };
  38
  39 static struct sh_ubc *sh_ubc __read_mostly = &ubc_dummy;
  40
  41 /*
  42  * Install a perf counter breakpoint.
  43  *
  44  * We seek a free UBC channel and use it for this breakpoint.
  45  *
  46  * Atomic: we hold the counter->ctx->lock and we only handle variables
  47  * and registers local to this cpu.
  48  */
  49 int arch_install_hw_breakpoint(struct perf_event *bp)
  50 {
  51         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
  52         int i;
  53
  54         for (i = 0; i < sh_ubc->num_events; i++) {
  55                 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
  56
  57                 if (!*slot) {
  58                         *slot = bp;
  59                         break;
  60                 }
  61         }
  62
  63         if (WARN_ONCE(i == sh_ubc->num_events, "Can't find any breakpoint slot"))
  64                 return -EBUSY;
  65
  66         clk_enable(sh_ubc->clk);
  67         sh_ubc->enable(info, i);
  68
  69         return 0;
  70 }
  71
  72 /*
  73  * Uninstall the breakpoint contained in the given counter.
  74  *
  75  * First we search the debug address register it uses and then we disable
  76  * it.
  77  *
  78  * Atomic: we hold the counter->ctx->lock and we only handle variables
  79  * and registers local to this cpu.
  80  */
  81 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
  82 {
  83         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
  84         int i;
  85
  86         for (i = 0; i < sh_ubc->num_events; i++) {
  87                 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
  88
  89                 if (*slot == bp) {
  90                         *slot = NULL;
  91                         break;
  92                 }
  93         }
  94
  95         if (WARN_ONCE(i == sh_ubc->num_events, "Can't find any breakpoint slot"))
  96                 return;
  97
  98         sh_ubc->disable(info, i);
  99         clk_disable(sh_ubc->clk);
 100 }
 101
 102 static int get_hbp_len(u16 hbp_len)
 103 {
 104         unsigned int len_in_bytes = 0;
 105
 106         switch (hbp_len) {
 107         case SH_BREAKPOINT_LEN_1:
 108                 len_in_bytes = 1;
 109                 break;
 110         case SH_BREAKPOINT_LEN_2:
 111                 len_in_bytes = 2;
 112                 break;
 113         case SH_BREAKPOINT_LEN_4:
 114                 len_in_bytes = 4;
 115                 break;
 116         case SH_BREAKPOINT_LEN_8:
 117                 len_in_bytes = 8;
 118                 break;
 119         }
 120         return len_in_bytes;
 121 }
 122
 123 /*
 124  * Check for virtual address in kernel space.
 125  */
 126 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 127 {
 128         unsigned int len;
 129         unsigned long va;
 130         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 131
 132         va = info->address;
 133         len = get_hbp_len(info->len);
 134
 135         return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
 136 }
 137
 138 int arch_bp_generic_fields(int sh_len, int sh_type,
 139                            int *gen_len, int *gen_type)
 140 {
 141         /* Len */
 142         switch (sh_len) {
 143         case SH_BREAKPOINT_LEN_1:
 144                 *gen_len = HW_BREAKPOINT_LEN_1;
 145                 break;
 146         case SH_BREAKPOINT_LEN_2:
 147                 *gen_len = HW_BREAKPOINT_LEN_2;
 148                 break;
 149         case SH_BREAKPOINT_LEN_4:
 150                 *gen_len = HW_BREAKPOINT_LEN_4;
 151                 break;
 152         case SH_BREAKPOINT_LEN_8:
 153                 *gen_len = HW_BREAKPOINT_LEN_8;
 154                 break;
 155         default:
 156                 return -EINVAL;
 157         }
 158
 159         /* Type */
 160         switch (sh_type) {
 161         case SH_BREAKPOINT_READ:
 162                 *gen_type = HW_BREAKPOINT_R;
 163         case SH_BREAKPOINT_WRITE:
 164                 *gen_type = HW_BREAKPOINT_W;
 165                 break;
 166         case SH_BREAKPOINT_RW:
 167                 *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
 168                 break;
 169         default:
 170                 return -EINVAL;
 171         }
 172
 173         return 0;
 174 }
 175
 176 static int arch_build_bp_info(struct perf_event *bp)
 177 {
 178         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 179
 180         info->address = bp->attr.bp_addr;
 181
 182         /* Len */
 183         switch (bp->attr.bp_len) {
 184         case HW_BREAKPOINT_LEN_1:
 185                 info->len = SH_BREAKPOINT_LEN_1;
 186                 break;
 187         case HW_BREAKPOINT_LEN_2:
 188                 info->len = SH_BREAKPOINT_LEN_2;
 189                 break;
 190         case HW_BREAKPOINT_LEN_4:
 191                 info->len = SH_BREAKPOINT_LEN_4;
 192                 break;
 193         case HW_BREAKPOINT_LEN_8:
 194                 info->len = SH_BREAKPOINT_LEN_8;
 195                 break;
 196         default:
 197                 return -EINVAL;
 198         }
 199
 200         /* Type */
 201         switch (bp->attr.bp_type) {
 202         case HW_BREAKPOINT_R:
 203                 info->type = SH_BREAKPOINT_READ;
 204                 break;
 205         case HW_BREAKPOINT_W:
 206                 info->type = SH_BREAKPOINT_WRITE;
 207                 break;
 208         case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
 209                 info->type = SH_BREAKPOINT_RW;
 210                 break;
 211         default:
 212                 return -EINVAL;
 213         }
 214
 215         return 0;
 216 }
 217
 218 /*
 219  * Validate the arch-specific HW Breakpoint register settings
 220  */
 221 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 222 {
 223         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 224         unsigned int align;
 225         int ret;
 226
 227         ret = arch_build_bp_info(bp);
 228         if (ret)
 229                 return ret;
 230
 231         ret = -EINVAL;
 232
 233         switch (info->len) {
 234         case SH_BREAKPOINT_LEN_1:
 235                 align = 0;
 236                 break;
 237         case SH_BREAKPOINT_LEN_2:
 238                 align = 1;
 239                 break;
 240         case SH_BREAKPOINT_LEN_4:
 241                 align = 3;
 242                 break;
 243         case SH_BREAKPOINT_LEN_8:
 244                 align = 7;
 245                 break;
 246         default:
 247                 return ret;
 248         }
 249
 250         /*
 251          * For kernel-addresses, either the address or symbol name can be
 252          * specified.
 253          */
 254         if (info->name)
 255                 info->address = (unsigned long)kallsyms_lookup_name(info->name);
 256
 257         /*
 258          * Check that the low-order bits of the address are appropriate
 259          * for the alignment implied by len.
 260          */
 261         if (info->address & align)
 262                 return -EINVAL;
 263
 264         return 0;
 265 }
 266
 267 /*
 268  * Release the user breakpoints used by ptrace
 269  */
 270 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 271 {
 272         int i;
 273         struct thread_struct *t = &tsk->thread;
 274
 275         for (i = 0; i < sh_ubc->num_events; i++) {
 276                 unregister_hw_breakpoint(t->ptrace_bps[i]);
 277                 t->ptrace_bps[i] = NULL;
 278         }
 279 }
 280
 281 static int __kprobes hw_breakpoint_handler(struct die_args *args)
 282 {
 283         int cpu, i, rc = NOTIFY_STOP;
 284         struct perf_event *bp;
 285         unsigned int cmf, resume_mask;
 286
 287         /*
 288          * Do an early return if none of the channels triggered.
 289          */
 290         cmf = sh_ubc->triggered_mask();
 291         if (unlikely(!cmf))
 292                 return NOTIFY_DONE;
 293
 294         /*
 295          * By default, resume all of the active channels.
 296          */
 297         resume_mask = sh_ubc->active_mask();
 298
 299         /*
 300          * Disable breakpoints during exception handling.
 301          */
 302         sh_ubc->disable_all();
 303
 304         cpu = get_cpu();
 305         for (i = 0; i < sh_ubc->num_events; i++) {
 306                 unsigned long event_mask = (1 << i);
 307
 308                 if (likely(!(cmf & event_mask)))
 309                         continue;
 310
 311                 /*
 312                  * The counter may be concurrently released but that can only
 313                  * occur from a call_rcu() path. We can then safely fetch
 314                  * the breakpoint, use its callback, touch its counter
 315                  * while we are in an rcu_read_lock() path.
 316                  */
 317                 rcu_read_lock();
 318
 319                 bp = per_cpu(bp_per_reg[i], cpu);
 320                 if (bp)
 321                         rc = NOTIFY_DONE;
 322
 323                 /*
 324                  * Reset the condition match flag to denote completion of
 325                  * exception handling.
 326                  */
 327                 sh_ubc->clear_triggered_mask(event_mask);
 328
 329                 /*
 330                  * bp can be NULL due to concurrent perf counter
 331                  * removing.
 332                  */
 333                 if (!bp) {
 334                         rcu_read_unlock();
 335                         break;
 336                 }
 337
 338                 /*
 339                  * Don't restore the channel if the breakpoint is from
 340                  * ptrace, as it always operates in one-shot mode.
 341                  */
 342                 if (bp->overflow_handler == ptrace_triggered)
 343                         resume_mask &= ~(1 << i);
 344
 345                 perf_bp_event(bp, args->regs);
 346
 347                 /* Deliver the signal to userspace */
 348                 if (!arch_check_bp_in_kernelspace(bp)) {
 349                         siginfo_t info;
 350
 351                         info.si_signo = args->signr;
 352                         info.si_errno = notifier_to_errno(rc);
 353                         info.si_code = TRAP_HWBKPT;
 354
 355                         force_sig_info(args->signr, &info, current);
 356                 }
 357
 358                 rcu_read_unlock();
 359         }
 360
 361         if (cmf == 0)
 362                 rc = NOTIFY_DONE;
 363
 364         sh_ubc->enable_all(resume_mask);
 365
 366         put_cpu();
 367
 368         return rc;
 369 }
 370
 371 BUILD_TRAP_HANDLER(breakpoint)
 372 {
 373         unsigned long ex = lookup_exception_vector();
 374         TRAP_HANDLER_DECL;
 375
 376         notify_die(DIE_BREAKPOINT, "breakpoint", regs, 0, ex, SIGTRAP);
 377 }
 378
 379 /*
 380  * Handle debug exception notifications.
 381  */
 382 int __kprobes hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 383                                     unsigned long val, void *data)
 384 {
 385         struct die_args *args = data;
 386
 387         if (val != DIE_BREAKPOINT)
 388                 return NOTIFY_DONE;
 389
 390         /*
 391          * If the breakpoint hasn't been triggered by the UBC, it's
 392          * probably from a debugger, so don't do anything more here.
 393          *
 394          * This also permits the UBC interface clock to remain off for
 395          * non-UBC breakpoints, as we don't need to check the triggered
 396          * or active channel masks.
 397          */
 398         if (args->trapnr != sh_ubc->trap_nr)
 399                 return NOTIFY_DONE;
 400
 401         return hw_breakpoint_handler(data);
 402 }
 403
 404 void hw_breakpoint_pmu_read(struct perf_event *bp)
 405 {
 406         /* TODO */
 407 }
 408
 409 int register_sh_ubc(struct sh_ubc *ubc)
 410 {
 411         /* Bail if it's already assigned */
 412         if (sh_ubc != &ubc_dummy)
 413                 return -EBUSY;
 414         sh_ubc = ubc;
 415
 416         pr_info("HW Breakpoints: %s UBC support registered\n", ubc->name);
 417
 418         WARN_ON(ubc->num_events > HBP_NUM);
 419
 420         return 0;
 421 }