arch/x86/mm/kmmio.c

   1 /* Support for MMIO probes.
   2  * Benfit many code from kprobes
   3  * (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
   4  *     2007 Alexander Eichner
   5  *     2008 Pekka Paalanen <pq@iki.fi>
   6  */
   7
   8 #include <linux/list.h>
   9 #include <linux/rculist.h>
  10 #include <linux/spinlock.h>
  11 #include <linux/hash.h>
  12 #include <linux/init.h>
  13 #include <linux/module.h>
  14 #include <linux/kernel.h>
  15 #include <linux/uaccess.h>
  16 #include <linux/ptrace.h>
  17 #include <linux/preempt.h>
  18 #include <linux/percpu.h>
  19 #include <linux/kdebug.h>
  20 #include <linux/mutex.h>
  21 #include <linux/io.h>
  22 #include <asm/cacheflush.h>
  23 #include <asm/tlbflush.h>
  24 #include <linux/errno.h>
  25 #include <asm/debugreg.h>
  26 #include <linux/mmiotrace.h>
  27
  28 #define KMMIO_PAGE_HASH_BITS 4
  29 #define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
  30
  31 struct kmmio_fault_page {
  32         struct list_head list;
  33         struct kmmio_fault_page *release_next;
  34         unsigned long page; /* location of the fault page */
  35
  36         /*
  37          * Number of times this page has been registered as a part
  38          * of a probe. If zero, page is disarmed and this may be freed.
  39          * Used only by writers (RCU).
  40          */
  41         int count;
  42 };
  43
  44 struct kmmio_delayed_release {
  45         struct rcu_head rcu;
  46         struct kmmio_fault_page *release_list;
  47 };
  48
  49 struct kmmio_context {
  50         struct kmmio_fault_page *fpage;
  51         struct kmmio_probe *probe;
  52         unsigned long saved_flags;
  53         unsigned long addr;
  54         int active;
  55 };
  56
  57 static DEFINE_SPINLOCK(kmmio_lock);
  58
  59 /* Protected by kmmio_lock */
  60 unsigned int kmmio_count;
  61
  62 /* Read-protected by RCU, write-protected by kmmio_lock. */
  63 static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
  64 static LIST_HEAD(kmmio_probes);
  65
  66 static struct list_head *kmmio_page_list(unsigned long page)
  67 {
  68         return &kmmio_page_table[hash_long(page, KMMIO_PAGE_HASH_BITS)];
  69 }
  70
  71 /* Accessed per-cpu */
  72 static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
  73
  74 /*
  75  * this is basically a dynamic stabbing problem:
  76  * Could use the existing prio tree code or
  77  * Possible better implementations:
  78  * The Interval Skip List: A Data Structure for Finding All Intervals That
  79  * Overlap a Point (might be simple)
  80  * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
  81  */
  82 /* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
  83 static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
  84 {
  85         struct kmmio_probe *p;
  86         list_for_each_entry_rcu(p, &kmmio_probes, list) {
  87                 if (addr >= p->addr && addr <= (p->addr + p->len))
  88                         return p;
  89         }
  90         return NULL;
  91 }
  92
  93 /* You must be holding RCU read lock. */
  94 static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
  95 {
  96         struct list_head *head;
  97         struct kmmio_fault_page *p;
  98
  99         page &= PAGE_MASK;
 100         head = kmmio_page_list(page);
 101         list_for_each_entry_rcu(p, head, list) {
 102                 if (p->page == page)
 103                         return p;
 104         }
 105         return NULL;
 106 }
 107
 108 static void set_page_present(unsigned long addr, bool present,
 109                                                         unsigned int *pglevel)
 110 {
 111         pteval_t pteval;
 112         pmdval_t pmdval;
 113         unsigned int level;
 114         pmd_t *pmd;
 115         pte_t *pte = lookup_address(addr, &level);
 116
 117         if (!pte) {
 118                 pr_err("kmmio: no pte for page 0x%08lx\n", addr);
 119                 return;
 120         }
 121
 122         if (pglevel)
 123                 *pglevel = level;
 124
 125         switch (level) {
 126         case PG_LEVEL_2M:
 127                 pmd = (pmd_t *)pte;
 128                 pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
 129                 if (present)
 130                         pmdval |= _PAGE_PRESENT;
 131                 set_pmd(pmd, __pmd(pmdval));
 132                 break;
 133
 134         case PG_LEVEL_4K:
 135                 pteval = pte_val(*pte) & ~_PAGE_PRESENT;
 136                 if (present)
 137                         pteval |= _PAGE_PRESENT;
 138                 set_pte_atomic(pte, __pte(pteval));
 139                 break;
 140
 141         default:
 142                 pr_err("kmmio: unexpected page level 0x%x.\n", level);
 143                 return;
 144         }
 145
 146         __flush_tlb_one(addr);
 147 }
 148
 149 /** Mark the given page as not present. Access to it will trigger a fault. */
 150 static void arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
 151 {
 152         set_page_present(page & PAGE_MASK, false, pglevel);
 153 }
 154
 155 /** Mark the given page as present. */
 156 static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
 157 {
 158         set_page_present(page & PAGE_MASK, true, pglevel);
 159 }
 160
 161 /*
 162  * This is being called from do_page_fault().
 163  *
 164  * We may be in an interrupt or a critical section. Also prefecthing may
 165  * trigger a page fault. We may be in the middle of process switch.
 166  * We cannot take any locks, because we could be executing especially
 167  * within a kmmio critical section.
 168  *
 169  * Local interrupts are disabled, so preemption cannot happen.
 170  * Do not enable interrupts, do not sleep, and watch out for other CPUs.
 171  */
 172 /*
 173  * Interrupts are disabled on entry as trap3 is an interrupt gate
 174  * and they remain disabled thorough out this function.
 175  */
 176 int kmmio_handler(struct pt_regs *regs, unsigned long addr)
 177 {
 178         struct kmmio_context *ctx;
 179         struct kmmio_fault_page *faultpage;
 180         int ret = 0; /* default to fault not handled */
 181
 182         /*
 183          * Preemption is now disabled to prevent process switch during
 184          * single stepping. We can only handle one active kmmio trace
 185          * per cpu, so ensure that we finish it before something else
 186          * gets to run. We also hold the RCU read lock over single
 187          * stepping to avoid looking up the probe and kmmio_fault_page
 188          * again.
 189          */
 190         preempt_disable();
 191         rcu_read_lock();
 192
 193         faultpage = get_kmmio_fault_page(addr);
 194         if (!faultpage) {
 195                 /*
 196                  * Either this page fault is not caused by kmmio, or
 197                  * another CPU just pulled the kmmio probe from under
 198                  * our feet. The latter case should not be possible.
 199                  */
 200                 goto no_kmmio;
 201         }
 202
 203         ctx = &get_cpu_var(kmmio_ctx);
 204         if (ctx->active) {
 205                 disarm_kmmio_fault_page(faultpage->page, NULL);
 206                 if (addr == ctx->addr) {
 207                         /*
 208                          * On SMP we sometimes get recursive probe hits on the
 209                          * same address. Context is already saved, fall out.
 210                          */
 211                         pr_debug("kmmio: duplicate probe hit on CPU %d, for "
 212                                                 "address 0x%08lx.\n",
 213                                                 smp_processor_id(), addr);
 214                         ret = 1;
 215                         goto no_kmmio_ctx;
 216                 }
 217                 /*
 218                  * Prevent overwriting already in-flight context.
 219                  * This should not happen, let's hope disarming at least
 220                  * prevents a panic.
 221                  */
 222                 pr_emerg("kmmio: recursive probe hit on CPU %d, "
 223                                         "for address 0x%08lx. Ignoring.\n",
 224                                         smp_processor_id(), addr);
 225                 pr_emerg("kmmio: previous hit was at 0x%08lx.\n",
 226                                         ctx->addr);
 227                 goto no_kmmio_ctx;
 228         }
 229         ctx->active++;
 230
 231         ctx->fpage = faultpage;
 232         ctx->probe = get_kmmio_probe(addr);
 233         ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
 234         ctx->addr = addr;
 235
 236         if (ctx->probe && ctx->probe->pre_handler)
 237                 ctx->probe->pre_handler(ctx->probe, regs, addr);
 238
 239         /*
 240          * Enable single-stepping and disable interrupts for the faulting
 241          * context. Local interrupts must not get enabled during stepping.
 242          */
 243         regs->flags |= X86_EFLAGS_TF;
 244         regs->flags &= ~X86_EFLAGS_IF;
 245
 246         /* Now we set present bit in PTE and single step. */
 247         disarm_kmmio_fault_page(ctx->fpage->page, NULL);
 248
 249         /*
 250          * If another cpu accesses the same page while we are stepping,
 251          * the access will not be caught. It will simply succeed and the
 252          * only downside is we lose the event. If this becomes a problem,
 253          * the user should drop to single cpu before tracing.
 254          */
 255
 256         put_cpu_var(kmmio_ctx);
 257         return 1; /* fault handled */
 258
 259 no_kmmio_ctx:
 260         put_cpu_var(kmmio_ctx);
 261 no_kmmio:
 262         rcu_read_unlock();
 263         preempt_enable_no_resched();
 264         return ret;
 265 }
 266
 267 /*
 268  * Interrupts are disabled on entry as trap1 is an interrupt gate
 269  * and they remain disabled thorough out this function.
 270  * This must always get called as the pair to kmmio_handler().
 271  */
 272 static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
 273 {
 274         int ret = 0;
 275         struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
 276
 277         if (!ctx->active) {
 278                 pr_debug("kmmio: spurious debug trap on CPU %d.\n",
 279                                                         smp_processor_id());
 280                 goto out;
 281         }
 282
 283         if (ctx->probe && ctx->probe->post_handler)
 284                 ctx->probe->post_handler(ctx->probe, condition, regs);
 285
 286         arm_kmmio_fault_page(ctx->fpage->page, NULL);
 287
 288         regs->flags &= ~X86_EFLAGS_TF;
 289         regs->flags |= ctx->saved_flags;
 290
 291         /* These were acquired in kmmio_handler(). */
 292         ctx->active--;
 293         BUG_ON(ctx->active);
 294         rcu_read_unlock();
 295         preempt_enable_no_resched();
 296
 297         /*
 298          * if somebody else is singlestepping across a probe point, flags
 299          * will have TF set, in which case, continue the remaining processing
 300          * of do_debug, as if this is not a probe hit.
 301          */
 302         if (!(regs->flags & X86_EFLAGS_TF))
 303                 ret = 1;
 304 out:
 305         put_cpu_var(kmmio_ctx);
 306         return ret;
 307 }
 308
 309 /* You must be holding kmmio_lock. */
 310 static int add_kmmio_fault_page(unsigned long page)
 311 {
 312         struct kmmio_fault_page *f;
 313
 314         page &= PAGE_MASK;
 315         f = get_kmmio_fault_page(page);
 316         if (f) {
 317                 if (!f->count)
 318                         arm_kmmio_fault_page(f->page, NULL);
 319                 f->count++;
 320                 return 0;
 321         }
 322
 323         f = kmalloc(sizeof(*f), GFP_ATOMIC);
 324         if (!f)
 325                 return -1;
 326
 327         f->count = 1;
 328         f->page = page;
 329         list_add_rcu(&f->list, kmmio_page_list(f->page));
 330
 331         arm_kmmio_fault_page(f->page, NULL);
 332
 333         return 0;
 334 }
 335
 336 /* You must be holding kmmio_lock. */
 337 static void release_kmmio_fault_page(unsigned long page,
 338                                 struct kmmio_fault_page **release_list)
 339 {
 340         struct kmmio_fault_page *f;
 341
 342         page &= PAGE_MASK;
 343         f = get_kmmio_fault_page(page);
 344         if (!f)
 345                 return;
 346
 347         f->count--;
 348         BUG_ON(f->count < 0);
 349         if (!f->count) {
 350                 disarm_kmmio_fault_page(f->page, NULL);
 351                 f->release_next = *release_list;
 352                 *release_list = f;
 353         }
 354 }
 355
 356 /*
 357  * With page-unaligned ioremaps, one or two armed pages may contain
 358  * addresses from outside the intended mapping. Events for these addresses
 359  * are currently silently dropped. The events may result only from programming
 360  * mistakes by accessing addresses before the beginning or past the end of a
 361  * mapping.
 362  */
 363 int register_kmmio_probe(struct kmmio_probe *p)
 364 {
 365         unsigned long flags;
 366         int ret = 0;
 367         unsigned long size = 0;
 368         const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
 369
 370         spin_lock_irqsave(&kmmio_lock, flags);
 371         if (get_kmmio_probe(p->addr)) {
 372                 ret = -EEXIST;
 373                 goto out;
 374         }
 375         kmmio_count++;
 376         list_add_rcu(&p->list, &kmmio_probes);
 377         while (size < size_lim) {
 378                 if (add_kmmio_fault_page(p->addr + size))
 379                         pr_err("kmmio: Unable to set page fault.\n");
 380                 size += PAGE_SIZE;
 381         }
 382 out:
 383         spin_unlock_irqrestore(&kmmio_lock, flags);
 384         /*
 385          * XXX: What should I do here?
 386          * Here was a call to global_flush_tlb(), but it does not exist
 387          * anymore. It seems it's not needed after all.
 388          */
 389         return ret;
 390 }
 391 EXPORT_SYMBOL(register_kmmio_probe);
 392
 393 static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
 394 {
 395         struct kmmio_delayed_release *dr = container_of(
 396                                                 head,
 397                                                 struct kmmio_delayed_release,
 398                                                 rcu);
 399         struct kmmio_fault_page *p = dr->release_list;
 400         while (p) {
 401                 struct kmmio_fault_page *next = p->release_next;
 402                 BUG_ON(p->count);
 403                 kfree(p);
 404                 p = next;
 405         }
 406         kfree(dr);
 407 }
 408
 409 static void remove_kmmio_fault_pages(struct rcu_head *head)
 410 {
 411         struct kmmio_delayed_release *dr = container_of(
 412                                                 head,
 413                                                 struct kmmio_delayed_release,
 414                                                 rcu);
 415         struct kmmio_fault_page *p = dr->release_list;
 416         struct kmmio_fault_page **prevp = &dr->release_list;
 417         unsigned long flags;
 418         spin_lock_irqsave(&kmmio_lock, flags);
 419         while (p) {
 420                 if (!p->count)
 421                         list_del_rcu(&p->list);
 422                 else
 423                         *prevp = p->release_next;
 424                 prevp = &p->release_next;
 425                 p = p->release_next;
 426         }
 427         spin_unlock_irqrestore(&kmmio_lock, flags);
 428         /* This is the real RCU destroy call. */
 429         call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
 430 }
 431
 432 /*
 433  * Remove a kmmio probe. You have to synchronize_rcu() before you can be
 434  * sure that the callbacks will not be called anymore. Only after that
 435  * you may actually release your struct kmmio_probe.
 436  *
 437  * Unregistering a kmmio fault page has three steps:
 438  * 1. release_kmmio_fault_page()
 439  *    Disarm the page, wait a grace period to let all faults finish.
 440  * 2. remove_kmmio_fault_pages()
 441  *    Remove the pages from kmmio_page_table.
 442  * 3. rcu_free_kmmio_fault_pages()
 443  *    Actally free the kmmio_fault_page structs as with RCU.
 444  */
 445 void unregister_kmmio_probe(struct kmmio_probe *p)
 446 {
 447         unsigned long flags;
 448         unsigned long size = 0;
 449         const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
 450         struct kmmio_fault_page *release_list = NULL;
 451         struct kmmio_delayed_release *drelease;
 452
 453         spin_lock_irqsave(&kmmio_lock, flags);
 454         while (size < size_lim) {
 455                 release_kmmio_fault_page(p->addr + size, &release_list);
 456                 size += PAGE_SIZE;
 457         }
 458         list_del_rcu(&p->list);
 459         kmmio_count--;
 460         spin_unlock_irqrestore(&kmmio_lock, flags);
 461
 462         drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
 463         if (!drelease) {
 464                 pr_crit("kmmio: leaking kmmio_fault_page objects.\n");
 465                 return;
 466         }
 467         drelease->release_list = release_list;
 468
 469         /*
 470          * This is not really RCU here. We have just disarmed a set of
 471          * pages so that they cannot trigger page faults anymore. However,
 472          * we cannot remove the pages from kmmio_page_table,
 473          * because a probe hit might be in flight on another CPU. The
 474          * pages are collected into a list, and they will be removed from
 475          * kmmio_page_table when it is certain that no probe hit related to
 476          * these pages can be in flight. RCU grace period sounds like a
 477          * good choice.
 478          *
 479          * If we removed the pages too early, kmmio page fault handler might
 480          * not find the respective kmmio_fault_page and determine it's not
 481          * a kmmio fault, when it actually is. This would lead to madness.
 482          */
 483         call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
 484 }
 485 EXPORT_SYMBOL(unregister_kmmio_probe);
 486
 487 static int kmmio_die_notifier(struct notifier_block *nb, unsigned long val,
 488                                                                 void *args)
 489 {
 490         struct die_args *arg = args;
 491
 492         if (val == DIE_DEBUG && (arg->err & DR_STEP))
 493                 if (post_kmmio_handler(arg->err, arg->regs) == 1)
 494                         return NOTIFY_STOP;
 495
 496         return NOTIFY_DONE;
 497 }
 498
 499 static struct notifier_block nb_die = {
 500         .notifier_call = kmmio_die_notifier
 501 };
 502
 503 static int __init init_kmmio(void)
 504 {
 505         int i;
 506         for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
 507                 INIT_LIST_HEAD(&kmmio_page_table[i]);
 508         return register_die_notifier(&nb_die);
 509 }
 510 fs_initcall(init_kmmio); /* should be before device_initcall() */