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1// SPDX-License-Identifier: GPL-2.0
2/* Support for MMIO probes.
3 * Benefit many code from kprobes
4 * (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
5 * 2007 Alexander Eichner
6 * 2008 Pekka Paalanen <pq@iki.fi>
7 */
8
9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11#include <linux/list.h>
12#include <linux/rculist.h>
13#include <linux/spinlock.h>
14#include <linux/hash.h>
15#include <linux/export.h>
16#include <linux/kernel.h>
17#include <linux/uaccess.h>
18#include <linux/ptrace.h>
19#include <linux/preempt.h>
20#include <linux/percpu.h>
21#include <linux/kdebug.h>
22#include <linux/mutex.h>
23#include <linux/io.h>
24#include <linux/slab.h>
25#include <asm/cacheflush.h>
26#include <asm/tlbflush.h>
27#include <linux/errno.h>
28#include <asm/debugreg.h>
29#include <linux/mmiotrace.h>
30
31#define KMMIO_PAGE_HASH_BITS 4
32#define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
33
34struct kmmio_fault_page {
35 struct list_head list;
36 struct kmmio_fault_page *release_next;
37 unsigned long addr; /* the requested address */
38 pteval_t old_presence; /* page presence prior to arming */
39 bool armed;
40
41 /*
42 * Number of times this page has been registered as a part
43 * of a probe. If zero, page is disarmed and this may be freed.
44 * Used only by writers (RCU) and post_kmmio_handler().
45 * Protected by kmmio_lock, when linked into kmmio_page_table.
46 */
47 int count;
48
49 bool scheduled_for_release;
50};
51
52struct kmmio_delayed_release {
53 struct rcu_head rcu;
54 struct kmmio_fault_page *release_list;
55};
56
57struct kmmio_context {
58 struct kmmio_fault_page *fpage;
59 struct kmmio_probe *probe;
60 unsigned long saved_flags;
61 unsigned long addr;
62 int active;
63};
64
65/*
66 * The kmmio_lock is taken in int3 context, which is treated as NMI context.
67 * This causes lockdep to complain about it bein in both NMI and normal
68 * context. Hide it from lockdep, as it should not have any other locks
69 * taken under it, and this is only enabled for debugging mmio anyway.
70 */
71static arch_spinlock_t kmmio_lock = __ARCH_SPIN_LOCK_UNLOCKED;
72
73/* Protected by kmmio_lock */
74unsigned int kmmio_count;
75
76/* Read-protected by RCU, write-protected by kmmio_lock. */
77static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
78static LIST_HEAD(kmmio_probes);
79
80static struct list_head *kmmio_page_list(unsigned long addr)
81{
82 unsigned int l;
83 pte_t *pte = lookup_address(addr, &l);
84
85 if (!pte)
86 return NULL;
87 addr &= page_level_mask(l);
88
89 return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)];
90}
91
92/* Accessed per-cpu */
93static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
94
95/*
96 * this is basically a dynamic stabbing problem:
97 * Could use the existing prio tree code or
98 * Possible better implementations:
99 * The Interval Skip List: A Data Structure for Finding All Intervals That
100 * Overlap a Point (might be simple)
101 * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
102 */
103/* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
104static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
105{
106 struct kmmio_probe *p;
107 list_for_each_entry_rcu(p, &kmmio_probes, list) {
108 if (addr >= p->addr && addr < (p->addr + p->len))
109 return p;
110 }
111 return NULL;
112}
113
114/* You must be holding RCU read lock. */
115static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr)
116{
117 struct list_head *head;
118 struct kmmio_fault_page *f;
119 unsigned int l;
120 pte_t *pte = lookup_address(addr, &l);
121
122 if (!pte)
123 return NULL;
124 addr &= page_level_mask(l);
125 head = kmmio_page_list(addr);
126 list_for_each_entry_rcu(f, head, list) {
127 if (f->addr == addr)
128 return f;
129 }
130 return NULL;
131}
132
133static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
134{
135 pmd_t new_pmd;
136 pmdval_t v = pmd_val(*pmd);
137 if (clear) {
138 *old = v;
139 new_pmd = pmd_mkinvalid(*pmd);
140 } else {
141 /* Presume this has been called with clear==true previously */
142 new_pmd = __pmd(*old);
143 }
144 set_pmd(pmd, new_pmd);
145}
146
147static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
148{
149 pteval_t v = pte_val(*pte);
150 if (clear) {
151 *old = v;
152 /* Nothing should care about address */
153 pte_clear(&init_mm, 0, pte);
154 } else {
155 /* Presume this has been called with clear==true previously */
156 set_pte_atomic(pte, __pte(*old));
157 }
158}
159
160static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
161{
162 unsigned int level;
163 pte_t *pte = lookup_address(f->addr, &level);
164
165 if (!pte) {
166 pr_err("no pte for addr 0x%08lx\n", f->addr);
167 return -1;
168 }
169
170 switch (level) {
171 case PG_LEVEL_2M:
172 clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
173 break;
174 case PG_LEVEL_4K:
175 clear_pte_presence(pte, clear, &f->old_presence);
176 break;
177 default:
178 pr_err("unexpected page level 0x%x.\n", level);
179 return -1;
180 }
181
182 flush_tlb_one_kernel(f->addr);
183 return 0;
184}
185
186/*
187 * Mark the given page as not present. Access to it will trigger a fault.
188 *
189 * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
190 * protection is ignored here. RCU read lock is assumed held, so the struct
191 * will not disappear unexpectedly. Furthermore, the caller must guarantee,
192 * that double arming the same virtual address (page) cannot occur.
193 *
194 * Double disarming on the other hand is allowed, and may occur when a fault
195 * and mmiotrace shutdown happen simultaneously.
196 */
197static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
198{
199 int ret;
200 WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
201 if (f->armed) {
202 pr_warn("double-arm: addr 0x%08lx, ref %d, old %d\n",
203 f->addr, f->count, !!f->old_presence);
204 }
205 ret = clear_page_presence(f, true);
206 WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"),
207 f->addr);
208 f->armed = true;
209 return ret;
210}
211
212/** Restore the given page to saved presence state. */
213static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
214{
215 int ret = clear_page_presence(f, false);
216 WARN_ONCE(ret < 0,
217 KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr);
218 f->armed = false;
219}
220
221/*
222 * This is being called from do_page_fault().
223 *
224 * We may be in an interrupt or a critical section. Also prefecthing may
225 * trigger a page fault. We may be in the middle of process switch.
226 * We cannot take any locks, because we could be executing especially
227 * within a kmmio critical section.
228 *
229 * Local interrupts are disabled, so preemption cannot happen.
230 * Do not enable interrupts, do not sleep, and watch out for other CPUs.
231 */
232/*
233 * Interrupts are disabled on entry as trap3 is an interrupt gate
234 * and they remain disabled throughout this function.
235 */
236int kmmio_handler(struct pt_regs *regs, unsigned long addr)
237{
238 struct kmmio_context *ctx;
239 struct kmmio_fault_page *faultpage;
240 int ret = 0; /* default to fault not handled */
241 unsigned long page_base = addr;
242 unsigned int l;
243 pte_t *pte = lookup_address(addr, &l);
244 if (!pte)
245 return -EINVAL;
246 page_base &= page_level_mask(l);
247
248 /*
249 * Hold the RCU read lock over single stepping to avoid looking
250 * up the probe and kmmio_fault_page again. The rcu_read_lock_sched()
251 * also disables preemption and prevents process switch during
252 * the single stepping. We can only handle one active kmmio trace
253 * per cpu, so ensure that we finish it before something else
254 * gets to run.
255 */
256 rcu_read_lock_sched_notrace();
257
258 faultpage = get_kmmio_fault_page(page_base);
259 if (!faultpage) {
260 /*
261 * Either this page fault is not caused by kmmio, or
262 * another CPU just pulled the kmmio probe from under
263 * our feet. The latter case should not be possible.
264 */
265 goto no_kmmio;
266 }
267
268 ctx = this_cpu_ptr(&kmmio_ctx);
269 if (ctx->active) {
270 if (page_base == ctx->addr) {
271 /*
272 * A second fault on the same page means some other
273 * condition needs handling by do_page_fault(), the
274 * page really not being present is the most common.
275 */
276 pr_debug("secondary hit for 0x%08lx CPU %d.\n",
277 addr, smp_processor_id());
278
279 if (!faultpage->old_presence)
280 pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
281 addr, smp_processor_id());
282 } else {
283 /*
284 * Prevent overwriting already in-flight context.
285 * This should not happen, let's hope disarming at
286 * least prevents a panic.
287 */
288 pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
289 smp_processor_id(), addr);
290 pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
291 disarm_kmmio_fault_page(faultpage);
292 }
293 goto no_kmmio;
294 }
295 ctx->active++;
296
297 ctx->fpage = faultpage;
298 ctx->probe = get_kmmio_probe(page_base);
299 ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
300 ctx->addr = page_base;
301
302 if (ctx->probe && ctx->probe->pre_handler)
303 ctx->probe->pre_handler(ctx->probe, regs, addr);
304
305 /*
306 * Enable single-stepping and disable interrupts for the faulting
307 * context. Local interrupts must not get enabled during stepping.
308 */
309 regs->flags |= X86_EFLAGS_TF;
310 regs->flags &= ~X86_EFLAGS_IF;
311
312 /* Now we set present bit in PTE and single step. */
313 disarm_kmmio_fault_page(ctx->fpage);
314
315 /*
316 * If another cpu accesses the same page while we are stepping,
317 * the access will not be caught. It will simply succeed and the
318 * only downside is we lose the event. If this becomes a problem,
319 * the user should drop to single cpu before tracing.
320 */
321
322 return 1; /* fault handled */
323
324no_kmmio:
325 rcu_read_unlock_sched_notrace();
326 return ret;
327}
328
329/*
330 * Interrupts are disabled on entry as trap1 is an interrupt gate
331 * and they remain disabled throughout this function.
332 * This must always get called as the pair to kmmio_handler().
333 */
334static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
335{
336 int ret = 0;
337 struct kmmio_context *ctx = this_cpu_ptr(&kmmio_ctx);
338
339 if (!ctx->active) {
340 /*
341 * debug traps without an active context are due to either
342 * something external causing them (f.e. using a debugger while
343 * mmio tracing enabled), or erroneous behaviour
344 */
345 pr_warn("unexpected debug trap on CPU %d.\n", smp_processor_id());
346 goto out;
347 }
348
349 if (ctx->probe && ctx->probe->post_handler)
350 ctx->probe->post_handler(ctx->probe, condition, regs);
351
352 /* Prevent racing against release_kmmio_fault_page(). */
353 arch_spin_lock(&kmmio_lock);
354 if (ctx->fpage->count)
355 arm_kmmio_fault_page(ctx->fpage);
356 arch_spin_unlock(&kmmio_lock);
357
358 regs->flags &= ~X86_EFLAGS_TF;
359 regs->flags |= ctx->saved_flags;
360
361 /* These were acquired in kmmio_handler(). */
362 ctx->active--;
363 BUG_ON(ctx->active);
364 rcu_read_unlock_sched_notrace();
365
366 /*
367 * if somebody else is singlestepping across a probe point, flags
368 * will have TF set, in which case, continue the remaining processing
369 * of do_debug, as if this is not a probe hit.
370 */
371 if (!(regs->flags & X86_EFLAGS_TF))
372 ret = 1;
373out:
374 return ret;
375}
376
377/* You must be holding kmmio_lock. */
378static int add_kmmio_fault_page(unsigned long addr)
379{
380 struct kmmio_fault_page *f;
381
382 f = get_kmmio_fault_page(addr);
383 if (f) {
384 if (!f->count)
385 arm_kmmio_fault_page(f);
386 f->count++;
387 return 0;
388 }
389
390 f = kzalloc(sizeof(*f), GFP_ATOMIC);
391 if (!f)
392 return -1;
393
394 f->count = 1;
395 f->addr = addr;
396
397 if (arm_kmmio_fault_page(f)) {
398 kfree(f);
399 return -1;
400 }
401
402 list_add_rcu(&f->list, kmmio_page_list(f->addr));
403
404 return 0;
405}
406
407/* You must be holding kmmio_lock. */
408static void release_kmmio_fault_page(unsigned long addr,
409 struct kmmio_fault_page **release_list)
410{
411 struct kmmio_fault_page *f;
412
413 f = get_kmmio_fault_page(addr);
414 if (!f)
415 return;
416
417 f->count--;
418 BUG_ON(f->count < 0);
419 if (!f->count) {
420 disarm_kmmio_fault_page(f);
421 if (!f->scheduled_for_release) {
422 f->release_next = *release_list;
423 *release_list = f;
424 f->scheduled_for_release = true;
425 }
426 }
427}
428
429/*
430 * With page-unaligned ioremaps, one or two armed pages may contain
431 * addresses from outside the intended mapping. Events for these addresses
432 * are currently silently dropped. The events may result only from programming
433 * mistakes by accessing addresses before the beginning or past the end of a
434 * mapping.
435 */
436int register_kmmio_probe(struct kmmio_probe *p)
437{
438 unsigned long flags;
439 int ret = 0;
440 unsigned long size = 0;
441 unsigned long addr = p->addr & PAGE_MASK;
442 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
443 unsigned int l;
444 pte_t *pte;
445
446 local_irq_save(flags);
447 arch_spin_lock(&kmmio_lock);
448 if (get_kmmio_probe(addr)) {
449 ret = -EEXIST;
450 goto out;
451 }
452
453 pte = lookup_address(addr, &l);
454 if (!pte) {
455 ret = -EINVAL;
456 goto out;
457 }
458
459 kmmio_count++;
460 list_add_rcu(&p->list, &kmmio_probes);
461 while (size < size_lim) {
462 if (add_kmmio_fault_page(addr + size))
463 pr_err("Unable to set page fault.\n");
464 size += page_level_size(l);
465 }
466out:
467 arch_spin_unlock(&kmmio_lock);
468 local_irq_restore(flags);
469
470 /*
471 * XXX: What should I do here?
472 * Here was a call to global_flush_tlb(), but it does not exist
473 * anymore. It seems it's not needed after all.
474 */
475 return ret;
476}
477EXPORT_SYMBOL(register_kmmio_probe);
478
479static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
480{
481 struct kmmio_delayed_release *dr = container_of(
482 head,
483 struct kmmio_delayed_release,
484 rcu);
485 struct kmmio_fault_page *f = dr->release_list;
486 while (f) {
487 struct kmmio_fault_page *next = f->release_next;
488 BUG_ON(f->count);
489 kfree(f);
490 f = next;
491 }
492 kfree(dr);
493}
494
495static void remove_kmmio_fault_pages(struct rcu_head *head)
496{
497 struct kmmio_delayed_release *dr =
498 container_of(head, struct kmmio_delayed_release, rcu);
499 struct kmmio_fault_page *f = dr->release_list;
500 struct kmmio_fault_page **prevp = &dr->release_list;
501 unsigned long flags;
502
503 local_irq_save(flags);
504 arch_spin_lock(&kmmio_lock);
505 while (f) {
506 if (!f->count) {
507 list_del_rcu(&f->list);
508 prevp = &f->release_next;
509 } else {
510 *prevp = f->release_next;
511 f->release_next = NULL;
512 f->scheduled_for_release = false;
513 }
514 f = *prevp;
515 }
516 arch_spin_unlock(&kmmio_lock);
517 local_irq_restore(flags);
518
519 /* This is the real RCU destroy call. */
520 call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
521}
522
523/*
524 * Remove a kmmio probe. You have to synchronize_rcu() before you can be
525 * sure that the callbacks will not be called anymore. Only after that
526 * you may actually release your struct kmmio_probe.
527 *
528 * Unregistering a kmmio fault page has three steps:
529 * 1. release_kmmio_fault_page()
530 * Disarm the page, wait a grace period to let all faults finish.
531 * 2. remove_kmmio_fault_pages()
532 * Remove the pages from kmmio_page_table.
533 * 3. rcu_free_kmmio_fault_pages()
534 * Actually free the kmmio_fault_page structs as with RCU.
535 */
536void unregister_kmmio_probe(struct kmmio_probe *p)
537{
538 unsigned long flags;
539 unsigned long size = 0;
540 unsigned long addr = p->addr & PAGE_MASK;
541 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
542 struct kmmio_fault_page *release_list = NULL;
543 struct kmmio_delayed_release *drelease;
544 unsigned int l;
545 pte_t *pte;
546
547 pte = lookup_address(addr, &l);
548 if (!pte)
549 return;
550
551 local_irq_save(flags);
552 arch_spin_lock(&kmmio_lock);
553 while (size < size_lim) {
554 release_kmmio_fault_page(addr + size, &release_list);
555 size += page_level_size(l);
556 }
557 list_del_rcu(&p->list);
558 kmmio_count--;
559 arch_spin_unlock(&kmmio_lock);
560 local_irq_restore(flags);
561
562 if (!release_list)
563 return;
564
565 drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
566 if (!drelease) {
567 pr_crit("leaking kmmio_fault_page objects.\n");
568 return;
569 }
570 drelease->release_list = release_list;
571
572 /*
573 * This is not really RCU here. We have just disarmed a set of
574 * pages so that they cannot trigger page faults anymore. However,
575 * we cannot remove the pages from kmmio_page_table,
576 * because a probe hit might be in flight on another CPU. The
577 * pages are collected into a list, and they will be removed from
578 * kmmio_page_table when it is certain that no probe hit related to
579 * these pages can be in flight. RCU grace period sounds like a
580 * good choice.
581 *
582 * If we removed the pages too early, kmmio page fault handler might
583 * not find the respective kmmio_fault_page and determine it's not
584 * a kmmio fault, when it actually is. This would lead to madness.
585 */
586 call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
587}
588EXPORT_SYMBOL(unregister_kmmio_probe);
589
590static int
591kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
592{
593 struct die_args *arg = args;
594 unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
595
596 if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
597 if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
598 /*
599 * Reset the BS bit in dr6 (pointed by args->err) to
600 * denote completion of processing
601 */
602 *dr6_p &= ~DR_STEP;
603 return NOTIFY_STOP;
604 }
605
606 return NOTIFY_DONE;
607}
608
609static struct notifier_block nb_die = {
610 .notifier_call = kmmio_die_notifier
611};
612
613int kmmio_init(void)
614{
615 int i;
616
617 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
618 INIT_LIST_HEAD(&kmmio_page_table[i]);
619
620 return register_die_notifier(&nb_die);
621}
622
623void kmmio_cleanup(void)
624{
625 int i;
626
627 unregister_die_notifier(&nb_die);
628 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
629 WARN_ONCE(!list_empty(&kmmio_page_table[i]),
630 KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
631 }
632}
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/init.h>
15#include <linux/module.h>
16#include <linux/kernel.h>
17#include <linux/uaccess.h>
18#include <linux/ptrace.h>
19#include <linux/preempt.h>
20#include <linux/percpu.h>
21#include <linux/kdebug.h>
22#include <linux/mutex.h>
23#include <linux/io.h>
24#include <linux/slab.h>
25#include <asm/cacheflush.h>
26#include <asm/tlbflush.h>
27#include <linux/errno.h>
28#include <asm/debugreg.h>
29#include <linux/mmiotrace.h>
30
31#define KMMIO_PAGE_HASH_BITS 4
32#define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
33
34struct kmmio_fault_page {
35 struct list_head list;
36 struct kmmio_fault_page *release_next;
37 unsigned long page; /* location of the fault page */
38 pteval_t old_presence; /* page presence prior to arming */
39 bool armed;
40
41 /*
42 * Number of times this page has been registered as a part
43 * of a probe. If zero, page is disarmed and this may be freed.
44 * Used only by writers (RCU) and post_kmmio_handler().
45 * Protected by kmmio_lock, when linked into kmmio_page_table.
46 */
47 int count;
48
49 bool scheduled_for_release;
50};
51
52struct kmmio_delayed_release {
53 struct rcu_head rcu;
54 struct kmmio_fault_page *release_list;
55};
56
57struct kmmio_context {
58 struct kmmio_fault_page *fpage;
59 struct kmmio_probe *probe;
60 unsigned long saved_flags;
61 unsigned long addr;
62 int active;
63};
64
65static DEFINE_SPINLOCK(kmmio_lock);
66
67/* Protected by kmmio_lock */
68unsigned int kmmio_count;
69
70/* Read-protected by RCU, write-protected by kmmio_lock. */
71static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
72static LIST_HEAD(kmmio_probes);
73
74static struct list_head *kmmio_page_list(unsigned long page)
75{
76 return &kmmio_page_table[hash_long(page, KMMIO_PAGE_HASH_BITS)];
77}
78
79/* Accessed per-cpu */
80static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
81
82/*
83 * this is basically a dynamic stabbing problem:
84 * Could use the existing prio tree code or
85 * Possible better implementations:
86 * The Interval Skip List: A Data Structure for Finding All Intervals That
87 * Overlap a Point (might be simple)
88 * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
89 */
90/* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
91static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
92{
93 struct kmmio_probe *p;
94 list_for_each_entry_rcu(p, &kmmio_probes, list) {
95 if (addr >= p->addr && addr < (p->addr + p->len))
96 return p;
97 }
98 return NULL;
99}
100
101/* You must be holding RCU read lock. */
102static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
103{
104 struct list_head *head;
105 struct kmmio_fault_page *f;
106
107 page &= PAGE_MASK;
108 head = kmmio_page_list(page);
109 list_for_each_entry_rcu(f, head, list) {
110 if (f->page == page)
111 return f;
112 }
113 return NULL;
114}
115
116static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
117{
118 pmdval_t v = pmd_val(*pmd);
119 if (clear) {
120 *old = v & _PAGE_PRESENT;
121 v &= ~_PAGE_PRESENT;
122 } else /* presume this has been called with clear==true previously */
123 v |= *old;
124 set_pmd(pmd, __pmd(v));
125}
126
127static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
128{
129 pteval_t v = pte_val(*pte);
130 if (clear) {
131 *old = v & _PAGE_PRESENT;
132 v &= ~_PAGE_PRESENT;
133 } else /* presume this has been called with clear==true previously */
134 v |= *old;
135 set_pte_atomic(pte, __pte(v));
136}
137
138static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
139{
140 unsigned int level;
141 pte_t *pte = lookup_address(f->page, &level);
142
143 if (!pte) {
144 pr_err("no pte for page 0x%08lx\n", f->page);
145 return -1;
146 }
147
148 switch (level) {
149 case PG_LEVEL_2M:
150 clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
151 break;
152 case PG_LEVEL_4K:
153 clear_pte_presence(pte, clear, &f->old_presence);
154 break;
155 default:
156 pr_err("unexpected page level 0x%x.\n", level);
157 return -1;
158 }
159
160 __flush_tlb_one(f->page);
161 return 0;
162}
163
164/*
165 * Mark the given page as not present. Access to it will trigger a fault.
166 *
167 * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
168 * protection is ignored here. RCU read lock is assumed held, so the struct
169 * will not disappear unexpectedly. Furthermore, the caller must guarantee,
170 * that double arming the same virtual address (page) cannot occur.
171 *
172 * Double disarming on the other hand is allowed, and may occur when a fault
173 * and mmiotrace shutdown happen simultaneously.
174 */
175static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
176{
177 int ret;
178 WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
179 if (f->armed) {
180 pr_warning("double-arm: page 0x%08lx, ref %d, old %d\n",
181 f->page, f->count, !!f->old_presence);
182 }
183 ret = clear_page_presence(f, true);
184 WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming 0x%08lx failed.\n"),
185 f->page);
186 f->armed = true;
187 return ret;
188}
189
190/** Restore the given page to saved presence state. */
191static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
192{
193 int ret = clear_page_presence(f, false);
194 WARN_ONCE(ret < 0,
195 KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
196 f->armed = false;
197}
198
199/*
200 * This is being called from do_page_fault().
201 *
202 * We may be in an interrupt or a critical section. Also prefecthing may
203 * trigger a page fault. We may be in the middle of process switch.
204 * We cannot take any locks, because we could be executing especially
205 * within a kmmio critical section.
206 *
207 * Local interrupts are disabled, so preemption cannot happen.
208 * Do not enable interrupts, do not sleep, and watch out for other CPUs.
209 */
210/*
211 * Interrupts are disabled on entry as trap3 is an interrupt gate
212 * and they remain disabled throughout this function.
213 */
214int kmmio_handler(struct pt_regs *regs, unsigned long addr)
215{
216 struct kmmio_context *ctx;
217 struct kmmio_fault_page *faultpage;
218 int ret = 0; /* default to fault not handled */
219
220 /*
221 * Preemption is now disabled to prevent process switch during
222 * single stepping. We can only handle one active kmmio trace
223 * per cpu, so ensure that we finish it before something else
224 * gets to run. We also hold the RCU read lock over single
225 * stepping to avoid looking up the probe and kmmio_fault_page
226 * again.
227 */
228 preempt_disable();
229 rcu_read_lock();
230
231 faultpage = get_kmmio_fault_page(addr);
232 if (!faultpage) {
233 /*
234 * Either this page fault is not caused by kmmio, or
235 * another CPU just pulled the kmmio probe from under
236 * our feet. The latter case should not be possible.
237 */
238 goto no_kmmio;
239 }
240
241 ctx = &get_cpu_var(kmmio_ctx);
242 if (ctx->active) {
243 if (addr == ctx->addr) {
244 /*
245 * A second fault on the same page means some other
246 * condition needs handling by do_page_fault(), the
247 * page really not being present is the most common.
248 */
249 pr_debug("secondary hit for 0x%08lx CPU %d.\n",
250 addr, smp_processor_id());
251
252 if (!faultpage->old_presence)
253 pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
254 addr, smp_processor_id());
255 } else {
256 /*
257 * Prevent overwriting already in-flight context.
258 * This should not happen, let's hope disarming at
259 * least prevents a panic.
260 */
261 pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
262 smp_processor_id(), addr);
263 pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
264 disarm_kmmio_fault_page(faultpage);
265 }
266 goto no_kmmio_ctx;
267 }
268 ctx->active++;
269
270 ctx->fpage = faultpage;
271 ctx->probe = get_kmmio_probe(addr);
272 ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
273 ctx->addr = addr;
274
275 if (ctx->probe && ctx->probe->pre_handler)
276 ctx->probe->pre_handler(ctx->probe, regs, addr);
277
278 /*
279 * Enable single-stepping and disable interrupts for the faulting
280 * context. Local interrupts must not get enabled during stepping.
281 */
282 regs->flags |= X86_EFLAGS_TF;
283 regs->flags &= ~X86_EFLAGS_IF;
284
285 /* Now we set present bit in PTE and single step. */
286 disarm_kmmio_fault_page(ctx->fpage);
287
288 /*
289 * If another cpu accesses the same page while we are stepping,
290 * the access will not be caught. It will simply succeed and the
291 * only downside is we lose the event. If this becomes a problem,
292 * the user should drop to single cpu before tracing.
293 */
294
295 put_cpu_var(kmmio_ctx);
296 return 1; /* fault handled */
297
298no_kmmio_ctx:
299 put_cpu_var(kmmio_ctx);
300no_kmmio:
301 rcu_read_unlock();
302 preempt_enable_no_resched();
303 return ret;
304}
305
306/*
307 * Interrupts are disabled on entry as trap1 is an interrupt gate
308 * and they remain disabled throughout this function.
309 * This must always get called as the pair to kmmio_handler().
310 */
311static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
312{
313 int ret = 0;
314 struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
315
316 if (!ctx->active) {
317 /*
318 * debug traps without an active context are due to either
319 * something external causing them (f.e. using a debugger while
320 * mmio tracing enabled), or erroneous behaviour
321 */
322 pr_warning("unexpected debug trap on CPU %d.\n",
323 smp_processor_id());
324 goto out;
325 }
326
327 if (ctx->probe && ctx->probe->post_handler)
328 ctx->probe->post_handler(ctx->probe, condition, regs);
329
330 /* Prevent racing against release_kmmio_fault_page(). */
331 spin_lock(&kmmio_lock);
332 if (ctx->fpage->count)
333 arm_kmmio_fault_page(ctx->fpage);
334 spin_unlock(&kmmio_lock);
335
336 regs->flags &= ~X86_EFLAGS_TF;
337 regs->flags |= ctx->saved_flags;
338
339 /* These were acquired in kmmio_handler(). */
340 ctx->active--;
341 BUG_ON(ctx->active);
342 rcu_read_unlock();
343 preempt_enable_no_resched();
344
345 /*
346 * if somebody else is singlestepping across a probe point, flags
347 * will have TF set, in which case, continue the remaining processing
348 * of do_debug, as if this is not a probe hit.
349 */
350 if (!(regs->flags & X86_EFLAGS_TF))
351 ret = 1;
352out:
353 put_cpu_var(kmmio_ctx);
354 return ret;
355}
356
357/* You must be holding kmmio_lock. */
358static int add_kmmio_fault_page(unsigned long page)
359{
360 struct kmmio_fault_page *f;
361
362 page &= PAGE_MASK;
363 f = get_kmmio_fault_page(page);
364 if (f) {
365 if (!f->count)
366 arm_kmmio_fault_page(f);
367 f->count++;
368 return 0;
369 }
370
371 f = kzalloc(sizeof(*f), GFP_ATOMIC);
372 if (!f)
373 return -1;
374
375 f->count = 1;
376 f->page = page;
377
378 if (arm_kmmio_fault_page(f)) {
379 kfree(f);
380 return -1;
381 }
382
383 list_add_rcu(&f->list, kmmio_page_list(f->page));
384
385 return 0;
386}
387
388/* You must be holding kmmio_lock. */
389static void release_kmmio_fault_page(unsigned long page,
390 struct kmmio_fault_page **release_list)
391{
392 struct kmmio_fault_page *f;
393
394 page &= PAGE_MASK;
395 f = get_kmmio_fault_page(page);
396 if (!f)
397 return;
398
399 f->count--;
400 BUG_ON(f->count < 0);
401 if (!f->count) {
402 disarm_kmmio_fault_page(f);
403 if (!f->scheduled_for_release) {
404 f->release_next = *release_list;
405 *release_list = f;
406 f->scheduled_for_release = true;
407 }
408 }
409}
410
411/*
412 * With page-unaligned ioremaps, one or two armed pages may contain
413 * addresses from outside the intended mapping. Events for these addresses
414 * are currently silently dropped. The events may result only from programming
415 * mistakes by accessing addresses before the beginning or past the end of a
416 * mapping.
417 */
418int register_kmmio_probe(struct kmmio_probe *p)
419{
420 unsigned long flags;
421 int ret = 0;
422 unsigned long size = 0;
423 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
424
425 spin_lock_irqsave(&kmmio_lock, flags);
426 if (get_kmmio_probe(p->addr)) {
427 ret = -EEXIST;
428 goto out;
429 }
430 kmmio_count++;
431 list_add_rcu(&p->list, &kmmio_probes);
432 while (size < size_lim) {
433 if (add_kmmio_fault_page(p->addr + size))
434 pr_err("Unable to set page fault.\n");
435 size += PAGE_SIZE;
436 }
437out:
438 spin_unlock_irqrestore(&kmmio_lock, flags);
439 /*
440 * XXX: What should I do here?
441 * Here was a call to global_flush_tlb(), but it does not exist
442 * anymore. It seems it's not needed after all.
443 */
444 return ret;
445}
446EXPORT_SYMBOL(register_kmmio_probe);
447
448static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
449{
450 struct kmmio_delayed_release *dr = container_of(
451 head,
452 struct kmmio_delayed_release,
453 rcu);
454 struct kmmio_fault_page *f = dr->release_list;
455 while (f) {
456 struct kmmio_fault_page *next = f->release_next;
457 BUG_ON(f->count);
458 kfree(f);
459 f = next;
460 }
461 kfree(dr);
462}
463
464static void remove_kmmio_fault_pages(struct rcu_head *head)
465{
466 struct kmmio_delayed_release *dr =
467 container_of(head, struct kmmio_delayed_release, rcu);
468 struct kmmio_fault_page *f = dr->release_list;
469 struct kmmio_fault_page **prevp = &dr->release_list;
470 unsigned long flags;
471
472 spin_lock_irqsave(&kmmio_lock, flags);
473 while (f) {
474 if (!f->count) {
475 list_del_rcu(&f->list);
476 prevp = &f->release_next;
477 } else {
478 *prevp = f->release_next;
479 f->release_next = NULL;
480 f->scheduled_for_release = false;
481 }
482 f = *prevp;
483 }
484 spin_unlock_irqrestore(&kmmio_lock, flags);
485
486 /* This is the real RCU destroy call. */
487 call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
488}
489
490/*
491 * Remove a kmmio probe. You have to synchronize_rcu() before you can be
492 * sure that the callbacks will not be called anymore. Only after that
493 * you may actually release your struct kmmio_probe.
494 *
495 * Unregistering a kmmio fault page has three steps:
496 * 1. release_kmmio_fault_page()
497 * Disarm the page, wait a grace period to let all faults finish.
498 * 2. remove_kmmio_fault_pages()
499 * Remove the pages from kmmio_page_table.
500 * 3. rcu_free_kmmio_fault_pages()
501 * Actually free the kmmio_fault_page structs as with RCU.
502 */
503void unregister_kmmio_probe(struct kmmio_probe *p)
504{
505 unsigned long flags;
506 unsigned long size = 0;
507 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
508 struct kmmio_fault_page *release_list = NULL;
509 struct kmmio_delayed_release *drelease;
510
511 spin_lock_irqsave(&kmmio_lock, flags);
512 while (size < size_lim) {
513 release_kmmio_fault_page(p->addr + size, &release_list);
514 size += PAGE_SIZE;
515 }
516 list_del_rcu(&p->list);
517 kmmio_count--;
518 spin_unlock_irqrestore(&kmmio_lock, flags);
519
520 if (!release_list)
521 return;
522
523 drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
524 if (!drelease) {
525 pr_crit("leaking kmmio_fault_page objects.\n");
526 return;
527 }
528 drelease->release_list = release_list;
529
530 /*
531 * This is not really RCU here. We have just disarmed a set of
532 * pages so that they cannot trigger page faults anymore. However,
533 * we cannot remove the pages from kmmio_page_table,
534 * because a probe hit might be in flight on another CPU. The
535 * pages are collected into a list, and they will be removed from
536 * kmmio_page_table when it is certain that no probe hit related to
537 * these pages can be in flight. RCU grace period sounds like a
538 * good choice.
539 *
540 * If we removed the pages too early, kmmio page fault handler might
541 * not find the respective kmmio_fault_page and determine it's not
542 * a kmmio fault, when it actually is. This would lead to madness.
543 */
544 call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
545}
546EXPORT_SYMBOL(unregister_kmmio_probe);
547
548static int
549kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
550{
551 struct die_args *arg = args;
552 unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
553
554 if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
555 if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
556 /*
557 * Reset the BS bit in dr6 (pointed by args->err) to
558 * denote completion of processing
559 */
560 *dr6_p &= ~DR_STEP;
561 return NOTIFY_STOP;
562 }
563
564 return NOTIFY_DONE;
565}
566
567static struct notifier_block nb_die = {
568 .notifier_call = kmmio_die_notifier
569};
570
571int kmmio_init(void)
572{
573 int i;
574
575 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
576 INIT_LIST_HEAD(&kmmio_page_table[i]);
577
578 return register_die_notifier(&nb_die);
579}
580
581void kmmio_cleanup(void)
582{
583 int i;
584
585 unregister_die_notifier(&nb_die);
586 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
587 WARN_ONCE(!list_empty(&kmmio_page_table[i]),
588 KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
589 }
590}