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Linux/arch/x86/mm/kmmio.c

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  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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 
 10 #include <linux/list.h>
 11 #include <linux/rculist.h>
 12 #include <linux/spinlock.h>
 13 #include <linux/hash.h>
 14 #include <linux/module.h>
 15 #include <linux/kernel.h>
 16 #include <linux/uaccess.h>
 17 #include <linux/ptrace.h>
 18 #include <linux/preempt.h>
 19 #include <linux/percpu.h>
 20 #include <linux/kdebug.h>
 21 #include <linux/mutex.h>
 22 #include <linux/io.h>
 23 #include <linux/slab.h>
 24 #include <asm/cacheflush.h>
 25 #include <asm/tlbflush.h>
 26 #include <linux/errno.h>
 27 #include <asm/debugreg.h>
 28 #include <linux/mmiotrace.h>
 29 
 30 #define KMMIO_PAGE_HASH_BITS 4
 31 #define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
 32 
 33 struct kmmio_fault_page {
 34         struct list_head list;
 35         struct kmmio_fault_page *release_next;
 36         unsigned long addr; /* the requested address */
 37         pteval_t old_presence; /* page presence prior to arming */
 38         bool armed;
 39 
 40         /*
 41          * Number of times this page has been registered as a part
 42          * of a probe. If zero, page is disarmed and this may be freed.
 43          * Used only by writers (RCU) and post_kmmio_handler().
 44          * Protected by kmmio_lock, when linked into kmmio_page_table.
 45          */
 46         int count;
 47 
 48         bool scheduled_for_release;
 49 };
 50 
 51 struct kmmio_delayed_release {
 52         struct rcu_head rcu;
 53         struct kmmio_fault_page *release_list;
 54 };
 55 
 56 struct kmmio_context {
 57         struct kmmio_fault_page *fpage;
 58         struct kmmio_probe *probe;
 59         unsigned long saved_flags;
 60         unsigned long addr;
 61         int active;
 62 };
 63 
 64 static DEFINE_SPINLOCK(kmmio_lock);
 65 
 66 /* Protected by kmmio_lock */
 67 unsigned int kmmio_count;
 68 
 69 /* Read-protected by RCU, write-protected by kmmio_lock. */
 70 static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
 71 static LIST_HEAD(kmmio_probes);
 72 
 73 static struct list_head *kmmio_page_list(unsigned long addr)
 74 {
 75         unsigned int l;
 76         pte_t *pte = lookup_address(addr, &l);
 77 
 78         if (!pte)
 79                 return NULL;
 80         addr &= page_level_mask(l);
 81 
 82         return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)];
 83 }
 84 
 85 /* Accessed per-cpu */
 86 static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
 87 
 88 /*
 89  * this is basically a dynamic stabbing problem:
 90  * Could use the existing prio tree code or
 91  * Possible better implementations:
 92  * The Interval Skip List: A Data Structure for Finding All Intervals That
 93  * Overlap a Point (might be simple)
 94  * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
 95  */
 96 /* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
 97 static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
 98 {
 99         struct kmmio_probe *p;
100         list_for_each_entry_rcu(p, &kmmio_probes, list) {
101                 if (addr >= p->addr && addr < (p->addr + p->len))
102                         return p;
103         }
104         return NULL;
105 }
106 
107 /* You must be holding RCU read lock. */
108 static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr)
109 {
110         struct list_head *head;
111         struct kmmio_fault_page *f;
112         unsigned int l;
113         pte_t *pte = lookup_address(addr, &l);
114 
115         if (!pte)
116                 return NULL;
117         addr &= page_level_mask(l);
118         head = kmmio_page_list(addr);
119         list_for_each_entry_rcu(f, head, list) {
120                 if (f->addr == addr)
121                         return f;
122         }
123         return NULL;
124 }
125 
126 static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
127 {
128         pmdval_t v = pmd_val(*pmd);
129         if (clear) {
130                 *old = v & _PAGE_PRESENT;
131                 v &= ~_PAGE_PRESENT;
132         } else  /* presume this has been called with clear==true previously */
133                 v |= *old;
134         set_pmd(pmd, __pmd(v));
135 }
136 
137 static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
138 {
139         pteval_t v = pte_val(*pte);
140         if (clear) {
141                 *old = v & _PAGE_PRESENT;
142                 v &= ~_PAGE_PRESENT;
143         } else  /* presume this has been called with clear==true previously */
144                 v |= *old;
145         set_pte_atomic(pte, __pte(v));
146 }
147 
148 static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
149 {
150         unsigned int level;
151         pte_t *pte = lookup_address(f->addr, &level);
152 
153         if (!pte) {
154                 pr_err("no pte for addr 0x%08lx\n", f->addr);
155                 return -1;
156         }
157 
158         switch (level) {
159         case PG_LEVEL_2M:
160                 clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
161                 break;
162         case PG_LEVEL_4K:
163                 clear_pte_presence(pte, clear, &f->old_presence);
164                 break;
165         default:
166                 pr_err("unexpected page level 0x%x.\n", level);
167                 return -1;
168         }
169 
170         __flush_tlb_one(f->addr);
171         return 0;
172 }
173 
174 /*
175  * Mark the given page as not present. Access to it will trigger a fault.
176  *
177  * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
178  * protection is ignored here. RCU read lock is assumed held, so the struct
179  * will not disappear unexpectedly. Furthermore, the caller must guarantee,
180  * that double arming the same virtual address (page) cannot occur.
181  *
182  * Double disarming on the other hand is allowed, and may occur when a fault
183  * and mmiotrace shutdown happen simultaneously.
184  */
185 static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
186 {
187         int ret;
188         WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
189         if (f->armed) {
190                 pr_warning("double-arm: addr 0x%08lx, ref %d, old %d\n",
191                            f->addr, f->count, !!f->old_presence);
192         }
193         ret = clear_page_presence(f, true);
194         WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"),
195                   f->addr);
196         f->armed = true;
197         return ret;
198 }
199 
200 /** Restore the given page to saved presence state. */
201 static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
202 {
203         int ret = clear_page_presence(f, false);
204         WARN_ONCE(ret < 0,
205                         KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr);
206         f->armed = false;
207 }
208 
209 /*
210  * This is being called from do_page_fault().
211  *
212  * We may be in an interrupt or a critical section. Also prefecthing may
213  * trigger a page fault. We may be in the middle of process switch.
214  * We cannot take any locks, because we could be executing especially
215  * within a kmmio critical section.
216  *
217  * Local interrupts are disabled, so preemption cannot happen.
218  * Do not enable interrupts, do not sleep, and watch out for other CPUs.
219  */
220 /*
221  * Interrupts are disabled on entry as trap3 is an interrupt gate
222  * and they remain disabled throughout this function.
223  */
224 int kmmio_handler(struct pt_regs *regs, unsigned long addr)
225 {
226         struct kmmio_context *ctx;
227         struct kmmio_fault_page *faultpage;
228         int ret = 0; /* default to fault not handled */
229         unsigned long page_base = addr;
230         unsigned int l;
231         pte_t *pte = lookup_address(addr, &l);
232         if (!pte)
233                 return -EINVAL;
234         page_base &= page_level_mask(l);
235 
236         /*
237          * Preemption is now disabled to prevent process switch during
238          * single stepping. We can only handle one active kmmio trace
239          * per cpu, so ensure that we finish it before something else
240          * gets to run. We also hold the RCU read lock over single
241          * stepping to avoid looking up the probe and kmmio_fault_page
242          * again.
243          */
244         preempt_disable();
245         rcu_read_lock();
246 
247         faultpage = get_kmmio_fault_page(page_base);
248         if (!faultpage) {
249                 /*
250                  * Either this page fault is not caused by kmmio, or
251                  * another CPU just pulled the kmmio probe from under
252                  * our feet. The latter case should not be possible.
253                  */
254                 goto no_kmmio;
255         }
256 
257         ctx = &get_cpu_var(kmmio_ctx);
258         if (ctx->active) {
259                 if (page_base == ctx->addr) {
260                         /*
261                          * A second fault on the same page means some other
262                          * condition needs handling by do_page_fault(), the
263                          * page really not being present is the most common.
264                          */
265                         pr_debug("secondary hit for 0x%08lx CPU %d.\n",
266                                  addr, smp_processor_id());
267 
268                         if (!faultpage->old_presence)
269                                 pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
270                                         addr, smp_processor_id());
271                 } else {
272                         /*
273                          * Prevent overwriting already in-flight context.
274                          * This should not happen, let's hope disarming at
275                          * least prevents a panic.
276                          */
277                         pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
278                                  smp_processor_id(), addr);
279                         pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
280                         disarm_kmmio_fault_page(faultpage);
281                 }
282                 goto no_kmmio_ctx;
283         }
284         ctx->active++;
285 
286         ctx->fpage = faultpage;
287         ctx->probe = get_kmmio_probe(page_base);
288         ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
289         ctx->addr = page_base;
290 
291         if (ctx->probe && ctx->probe->pre_handler)
292                 ctx->probe->pre_handler(ctx->probe, regs, addr);
293 
294         /*
295          * Enable single-stepping and disable interrupts for the faulting
296          * context. Local interrupts must not get enabled during stepping.
297          */
298         regs->flags |= X86_EFLAGS_TF;
299         regs->flags &= ~X86_EFLAGS_IF;
300 
301         /* Now we set present bit in PTE and single step. */
302         disarm_kmmio_fault_page(ctx->fpage);
303 
304         /*
305          * If another cpu accesses the same page while we are stepping,
306          * the access will not be caught. It will simply succeed and the
307          * only downside is we lose the event. If this becomes a problem,
308          * the user should drop to single cpu before tracing.
309          */
310 
311         put_cpu_var(kmmio_ctx);
312         return 1; /* fault handled */
313 
314 no_kmmio_ctx:
315         put_cpu_var(kmmio_ctx);
316 no_kmmio:
317         rcu_read_unlock();
318         preempt_enable_no_resched();
319         return ret;
320 }
321 
322 /*
323  * Interrupts are disabled on entry as trap1 is an interrupt gate
324  * and they remain disabled throughout this function.
325  * This must always get called as the pair to kmmio_handler().
326  */
327 static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
328 {
329         int ret = 0;
330         struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
331 
332         if (!ctx->active) {
333                 /*
334                  * debug traps without an active context are due to either
335                  * something external causing them (f.e. using a debugger while
336                  * mmio tracing enabled), or erroneous behaviour
337                  */
338                 pr_warning("unexpected debug trap on CPU %d.\n",
339                            smp_processor_id());
340                 goto out;
341         }
342 
343         if (ctx->probe && ctx->probe->post_handler)
344                 ctx->probe->post_handler(ctx->probe, condition, regs);
345 
346         /* Prevent racing against release_kmmio_fault_page(). */
347         spin_lock(&kmmio_lock);
348         if (ctx->fpage->count)
349                 arm_kmmio_fault_page(ctx->fpage);
350         spin_unlock(&kmmio_lock);
351 
352         regs->flags &= ~X86_EFLAGS_TF;
353         regs->flags |= ctx->saved_flags;
354 
355         /* These were acquired in kmmio_handler(). */
356         ctx->active--;
357         BUG_ON(ctx->active);
358         rcu_read_unlock();
359         preempt_enable_no_resched();
360 
361         /*
362          * if somebody else is singlestepping across a probe point, flags
363          * will have TF set, in which case, continue the remaining processing
364          * of do_debug, as if this is not a probe hit.
365          */
366         if (!(regs->flags & X86_EFLAGS_TF))
367                 ret = 1;
368 out:
369         put_cpu_var(kmmio_ctx);
370         return ret;
371 }
372 
373 /* You must be holding kmmio_lock. */
374 static int add_kmmio_fault_page(unsigned long addr)
375 {
376         struct kmmio_fault_page *f;
377 
378         f = get_kmmio_fault_page(addr);
379         if (f) {
380                 if (!f->count)
381                         arm_kmmio_fault_page(f);
382                 f->count++;
383                 return 0;
384         }
385 
386         f = kzalloc(sizeof(*f), GFP_ATOMIC);
387         if (!f)
388                 return -1;
389 
390         f->count = 1;
391         f->addr = addr;
392 
393         if (arm_kmmio_fault_page(f)) {
394                 kfree(f);
395                 return -1;
396         }
397 
398         list_add_rcu(&f->list, kmmio_page_list(f->addr));
399 
400         return 0;
401 }
402 
403 /* You must be holding kmmio_lock. */
404 static void release_kmmio_fault_page(unsigned long addr,
405                                 struct kmmio_fault_page **release_list)
406 {
407         struct kmmio_fault_page *f;
408 
409         f = get_kmmio_fault_page(addr);
410         if (!f)
411                 return;
412 
413         f->count--;
414         BUG_ON(f->count < 0);
415         if (!f->count) {
416                 disarm_kmmio_fault_page(f);
417                 if (!f->scheduled_for_release) {
418                         f->release_next = *release_list;
419                         *release_list = f;
420                         f->scheduled_for_release = true;
421                 }
422         }
423 }
424 
425 /*
426  * With page-unaligned ioremaps, one or two armed pages may contain
427  * addresses from outside the intended mapping. Events for these addresses
428  * are currently silently dropped. The events may result only from programming
429  * mistakes by accessing addresses before the beginning or past the end of a
430  * mapping.
431  */
432 int register_kmmio_probe(struct kmmio_probe *p)
433 {
434         unsigned long flags;
435         int ret = 0;
436         unsigned long size = 0;
437         unsigned long addr = p->addr & PAGE_MASK;
438         const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
439         unsigned int l;
440         pte_t *pte;
441 
442         spin_lock_irqsave(&kmmio_lock, flags);
443         if (get_kmmio_probe(addr)) {
444                 ret = -EEXIST;
445                 goto out;
446         }
447 
448         pte = lookup_address(addr, &l);
449         if (!pte) {
450                 ret = -EINVAL;
451                 goto out;
452         }
453 
454         kmmio_count++;
455         list_add_rcu(&p->list, &kmmio_probes);
456         while (size < size_lim) {
457                 if (add_kmmio_fault_page(addr + size))
458                         pr_err("Unable to set page fault.\n");
459                 size += page_level_size(l);
460         }
461 out:
462         spin_unlock_irqrestore(&kmmio_lock, flags);
463         /*
464          * XXX: What should I do here?
465          * Here was a call to global_flush_tlb(), but it does not exist
466          * anymore. It seems it's not needed after all.
467          */
468         return ret;
469 }
470 EXPORT_SYMBOL(register_kmmio_probe);
471 
472 static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
473 {
474         struct kmmio_delayed_release *dr = container_of(
475                                                 head,
476                                                 struct kmmio_delayed_release,
477                                                 rcu);
478         struct kmmio_fault_page *f = dr->release_list;
479         while (f) {
480                 struct kmmio_fault_page *next = f->release_next;
481                 BUG_ON(f->count);
482                 kfree(f);
483                 f = next;
484         }
485         kfree(dr);
486 }
487 
488 static void remove_kmmio_fault_pages(struct rcu_head *head)
489 {
490         struct kmmio_delayed_release *dr =
491                 container_of(head, struct kmmio_delayed_release, rcu);
492         struct kmmio_fault_page *f = dr->release_list;
493         struct kmmio_fault_page **prevp = &dr->release_list;
494         unsigned long flags;
495 
496         spin_lock_irqsave(&kmmio_lock, flags);
497         while (f) {
498                 if (!f->count) {
499                         list_del_rcu(&f->list);
500                         prevp = &f->release_next;
501                 } else {
502                         *prevp = f->release_next;
503                         f->release_next = NULL;
504                         f->scheduled_for_release = false;
505                 }
506                 f = *prevp;
507         }
508         spin_unlock_irqrestore(&kmmio_lock, flags);
509 
510         /* This is the real RCU destroy call. */
511         call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
512 }
513 
514 /*
515  * Remove a kmmio probe. You have to synchronize_rcu() before you can be
516  * sure that the callbacks will not be called anymore. Only after that
517  * you may actually release your struct kmmio_probe.
518  *
519  * Unregistering a kmmio fault page has three steps:
520  * 1. release_kmmio_fault_page()
521  *    Disarm the page, wait a grace period to let all faults finish.
522  * 2. remove_kmmio_fault_pages()
523  *    Remove the pages from kmmio_page_table.
524  * 3. rcu_free_kmmio_fault_pages()
525  *    Actually free the kmmio_fault_page structs as with RCU.
526  */
527 void unregister_kmmio_probe(struct kmmio_probe *p)
528 {
529         unsigned long flags;
530         unsigned long size = 0;
531         unsigned long addr = p->addr & PAGE_MASK;
532         const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
533         struct kmmio_fault_page *release_list = NULL;
534         struct kmmio_delayed_release *drelease;
535         unsigned int l;
536         pte_t *pte;
537 
538         pte = lookup_address(addr, &l);
539         if (!pte)
540                 return;
541 
542         spin_lock_irqsave(&kmmio_lock, flags);
543         while (size < size_lim) {
544                 release_kmmio_fault_page(addr + size, &release_list);
545                 size += page_level_size(l);
546         }
547         list_del_rcu(&p->list);
548         kmmio_count--;
549         spin_unlock_irqrestore(&kmmio_lock, flags);
550 
551         if (!release_list)
552                 return;
553 
554         drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
555         if (!drelease) {
556                 pr_crit("leaking kmmio_fault_page objects.\n");
557                 return;
558         }
559         drelease->release_list = release_list;
560 
561         /*
562          * This is not really RCU here. We have just disarmed a set of
563          * pages so that they cannot trigger page faults anymore. However,
564          * we cannot remove the pages from kmmio_page_table,
565          * because a probe hit might be in flight on another CPU. The
566          * pages are collected into a list, and they will be removed from
567          * kmmio_page_table when it is certain that no probe hit related to
568          * these pages can be in flight. RCU grace period sounds like a
569          * good choice.
570          *
571          * If we removed the pages too early, kmmio page fault handler might
572          * not find the respective kmmio_fault_page and determine it's not
573          * a kmmio fault, when it actually is. This would lead to madness.
574          */
575         call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
576 }
577 EXPORT_SYMBOL(unregister_kmmio_probe);
578 
579 static int
580 kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
581 {
582         struct die_args *arg = args;
583         unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
584 
585         if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
586                 if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
587                         /*
588                          * Reset the BS bit in dr6 (pointed by args->err) to
589                          * denote completion of processing
590                          */
591                         *dr6_p &= ~DR_STEP;
592                         return NOTIFY_STOP;
593                 }
594 
595         return NOTIFY_DONE;
596 }
597 
598 static struct notifier_block nb_die = {
599         .notifier_call = kmmio_die_notifier
600 };
601 
602 int kmmio_init(void)
603 {
604         int i;
605 
606         for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
607                 INIT_LIST_HEAD(&kmmio_page_table[i]);
608 
609         return register_die_notifier(&nb_die);
610 }
611 
612 void kmmio_cleanup(void)
613 {
614         int i;
615 
616         unregister_die_notifier(&nb_die);
617         for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
618                 WARN_ONCE(!list_empty(&kmmio_page_table[i]),
619                         KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
620         }
621 }
622 

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