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-rw-r--r--arch/x86/mm/kmmio.c510
1 files changed, 510 insertions, 0 deletions
diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
new file mode 100644
index 000000000000..93d82038af4b
--- /dev/null
+++ b/arch/x86/mm/kmmio.c
@@ -0,0 +1,510 @@
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
31struct 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
44struct kmmio_delayed_release {
45 struct rcu_head rcu;
46 struct kmmio_fault_page *release_list;
47};
48
49struct 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
57static DEFINE_SPINLOCK(kmmio_lock);
58
59/* Protected by kmmio_lock */
60unsigned int kmmio_count;
61
62/* Read-protected by RCU, write-protected by kmmio_lock. */
63static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
64static LIST_HEAD(kmmio_probes);
65
66static 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 */
72static 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. */
83static 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. */
94static 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
108static 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. */
150static 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. */
156static 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 */
176int 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
259no_kmmio_ctx:
260 put_cpu_var(kmmio_ctx);
261no_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 */
272static 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;
304out:
305 put_cpu_var(kmmio_ctx);
306 return ret;
307}
308
309/* You must be holding kmmio_lock. */
310static 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. */
337static 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 */
363int 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 }
382out:
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}
391EXPORT_SYMBOL(register_kmmio_probe);
392
393static 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
409static 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 */
445void 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}
485EXPORT_SYMBOL(unregister_kmmio_probe);
486
487static 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
499static struct notifier_block nb_die = {
500 .notifier_call = kmmio_die_notifier
501};
502
503static 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}
510fs_initcall(init_kmmio); /* should be before device_initcall() */