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Linux/arch/um/kernel/irq.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * Copyright (C) 2017 - Cambridge Greys Ltd
  4  * Copyright (C) 2011 - 2014 Cisco Systems Inc
  5  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  6  * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
  7  *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
  8  */
  9 
 10 #include <linux/cpumask.h>
 11 #include <linux/hardirq.h>
 12 #include <linux/interrupt.h>
 13 #include <linux/kernel_stat.h>
 14 #include <linux/module.h>
 15 #include <linux/sched.h>
 16 #include <linux/seq_file.h>
 17 #include <linux/slab.h>
 18 #include <as-layout.h>
 19 #include <kern_util.h>
 20 #include <os.h>
 21 #include <irq_user.h>
 22 
 23 
 24 extern void free_irqs(void);
 25 
 26 /* When epoll triggers we do not know why it did so
 27  * we can also have different IRQs for read and write.
 28  * This is why we keep a small irq_fd array for each fd -
 29  * one entry per IRQ type
 30  */
 31 
 32 struct irq_entry {
 33         struct irq_entry *next;
 34         int fd;
 35         struct irq_fd *irq_array[MAX_IRQ_TYPE + 1];
 36 };
 37 
 38 static struct irq_entry *active_fds;
 39 
 40 static DEFINE_SPINLOCK(irq_lock);
 41 
 42 static void irq_io_loop(struct irq_fd *irq, struct uml_pt_regs *regs)
 43 {
 44 /*
 45  * irq->active guards against reentry
 46  * irq->pending accumulates pending requests
 47  * if pending is raised the irq_handler is re-run
 48  * until pending is cleared
 49  */
 50         if (irq->active) {
 51                 irq->active = false;
 52                 do {
 53                         irq->pending = false;
 54                         do_IRQ(irq->irq, regs);
 55                 } while (irq->pending && (!irq->purge));
 56                 if (!irq->purge)
 57                         irq->active = true;
 58         } else {
 59                 irq->pending = true;
 60         }
 61 }
 62 
 63 void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 64 {
 65         struct irq_entry *irq_entry;
 66         struct irq_fd *irq;
 67 
 68         int n, i, j;
 69 
 70         while (1) {
 71                 /* This is now lockless - epoll keeps back-referencesto the irqs
 72                  * which have trigger it so there is no need to walk the irq
 73                  * list and lock it every time. We avoid locking by turning off
 74                  * IO for a specific fd by executing os_del_epoll_fd(fd) before
 75                  * we do any changes to the actual data structures
 76                  */
 77                 n = os_waiting_for_events_epoll();
 78 
 79                 if (n <= 0) {
 80                         if (n == -EINTR)
 81                                 continue;
 82                         else
 83                                 break;
 84                 }
 85 
 86                 for (i = 0; i < n ; i++) {
 87                         /* Epoll back reference is the entry with 3 irq_fd
 88                          * leaves - one for each irq type.
 89                          */
 90                         irq_entry = (struct irq_entry *)
 91                                 os_epoll_get_data_pointer(i);
 92                         for (j = 0; j < MAX_IRQ_TYPE ; j++) {
 93                                 irq = irq_entry->irq_array[j];
 94                                 if (irq == NULL)
 95                                         continue;
 96                                 if (os_epoll_triggered(i, irq->events) > 0)
 97                                         irq_io_loop(irq, regs);
 98                                 if (irq->purge) {
 99                                         irq_entry->irq_array[j] = NULL;
100                                         kfree(irq);
101                                 }
102                         }
103                 }
104         }
105 
106         free_irqs();
107 }
108 
109 static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
110 {
111         int i;
112         int events = 0;
113         struct irq_fd *irq;
114 
115         for (i = 0; i < MAX_IRQ_TYPE ; i++) {
116                 irq = irq_entry->irq_array[i];
117                 if (irq != NULL)
118                         events = irq->events | events;
119         }
120         if (events > 0) {
121         /* os_add_epoll will call os_mod_epoll if this already exists */
122                 return os_add_epoll_fd(events, irq_entry->fd, irq_entry);
123         }
124         /* No events - delete */
125         return os_del_epoll_fd(irq_entry->fd);
126 }
127 
128 
129 
130 static int activate_fd(int irq, int fd, int type, void *dev_id)
131 {
132         struct irq_fd *new_fd;
133         struct irq_entry *irq_entry;
134         int i, err, events;
135         unsigned long flags;
136 
137         err = os_set_fd_async(fd);
138         if (err < 0)
139                 goto out;
140 
141         spin_lock_irqsave(&irq_lock, flags);
142 
143         /* Check if we have an entry for this fd */
144 
145         err = -EBUSY;
146         for (irq_entry = active_fds;
147                 irq_entry != NULL; irq_entry = irq_entry->next) {
148                 if (irq_entry->fd == fd)
149                         break;
150         }
151 
152         if (irq_entry == NULL) {
153                 /* This needs to be atomic as it may be called from an
154                  * IRQ context.
155                  */
156                 irq_entry = kmalloc(sizeof(struct irq_entry), GFP_ATOMIC);
157                 if (irq_entry == NULL) {
158                         printk(KERN_ERR
159                                 "Failed to allocate new IRQ entry\n");
160                         goto out_unlock;
161                 }
162                 irq_entry->fd = fd;
163                 for (i = 0; i < MAX_IRQ_TYPE; i++)
164                         irq_entry->irq_array[i] = NULL;
165                 irq_entry->next = active_fds;
166                 active_fds = irq_entry;
167         }
168 
169         /* Check if we are trying to re-register an interrupt for a
170          * particular fd
171          */
172 
173         if (irq_entry->irq_array[type] != NULL) {
174                 printk(KERN_ERR
175                         "Trying to reregister IRQ %d FD %d TYPE %d ID %p\n",
176                         irq, fd, type, dev_id
177                 );
178                 goto out_unlock;
179         } else {
180                 /* New entry for this fd */
181 
182                 err = -ENOMEM;
183                 new_fd = kmalloc(sizeof(struct irq_fd), GFP_ATOMIC);
184                 if (new_fd == NULL)
185                         goto out_unlock;
186 
187                 events = os_event_mask(type);
188 
189                 *new_fd = ((struct irq_fd) {
190                         .id             = dev_id,
191                         .irq            = irq,
192                         .type           = type,
193                         .events         = events,
194                         .active         = true,
195                         .pending        = false,
196                         .purge          = false
197                 });
198                 /* Turn off any IO on this fd - allows us to
199                  * avoid locking the IRQ loop
200                  */
201                 os_del_epoll_fd(irq_entry->fd);
202                 irq_entry->irq_array[type] = new_fd;
203         }
204 
205         /* Turn back IO on with the correct (new) IO event mask */
206         assign_epoll_events_to_irq(irq_entry);
207         spin_unlock_irqrestore(&irq_lock, flags);
208         maybe_sigio_broken(fd, (type != IRQ_NONE));
209 
210         return 0;
211 out_unlock:
212         spin_unlock_irqrestore(&irq_lock, flags);
213 out:
214         return err;
215 }
216 
217 /*
218  * Walk the IRQ list and dispose of any unused entries.
219  * Should be done under irq_lock.
220  */
221 
222 static void garbage_collect_irq_entries(void)
223 {
224         int i;
225         bool reap;
226         struct irq_entry *walk;
227         struct irq_entry *previous = NULL;
228         struct irq_entry *to_free;
229 
230         if (active_fds == NULL)
231                 return;
232         walk = active_fds;
233         while (walk != NULL) {
234                 reap = true;
235                 for (i = 0; i < MAX_IRQ_TYPE ; i++) {
236                         if (walk->irq_array[i] != NULL) {
237                                 reap = false;
238                                 break;
239                         }
240                 }
241                 if (reap) {
242                         if (previous == NULL)
243                                 active_fds = walk->next;
244                         else
245                                 previous->next = walk->next;
246                         to_free = walk;
247                 } else {
248                         to_free = NULL;
249                 }
250                 walk = walk->next;
251                 kfree(to_free);
252         }
253 }
254 
255 /*
256  * Walk the IRQ list and get the descriptor for our FD
257  */
258 
259 static struct irq_entry *get_irq_entry_by_fd(int fd)
260 {
261         struct irq_entry *walk = active_fds;
262 
263         while (walk != NULL) {
264                 if (walk->fd == fd)
265                         return walk;
266                 walk = walk->next;
267         }
268         return NULL;
269 }
270 
271 
272 /*
273  * Walk the IRQ list and dispose of an entry for a specific
274  * device, fd and number. Note - if sharing an IRQ for read
275  * and writefor the same FD it will be disposed in either case.
276  * If this behaviour is undesirable use different IRQ ids.
277  */
278 
279 #define IGNORE_IRQ 1
280 #define IGNORE_DEV (1<<1)
281 
282 static void do_free_by_irq_and_dev(
283         struct irq_entry *irq_entry,
284         unsigned int irq,
285         void *dev,
286         int flags
287 )
288 {
289         int i;
290         struct irq_fd *to_free;
291 
292         for (i = 0; i < MAX_IRQ_TYPE ; i++) {
293                 if (irq_entry->irq_array[i] != NULL) {
294                         if (
295                         ((flags & IGNORE_IRQ) ||
296                                 (irq_entry->irq_array[i]->irq == irq)) &&
297                         ((flags & IGNORE_DEV) ||
298                                 (irq_entry->irq_array[i]->id == dev))
299                         ) {
300                                 /* Turn off any IO on this fd - allows us to
301                                  * avoid locking the IRQ loop
302                                  */
303                                 os_del_epoll_fd(irq_entry->fd);
304                                 to_free = irq_entry->irq_array[i];
305                                 irq_entry->irq_array[i] = NULL;
306                                 assign_epoll_events_to_irq(irq_entry);
307                                 if (to_free->active)
308                                         to_free->purge = true;
309                                 else
310                                         kfree(to_free);
311                         }
312                 }
313         }
314 }
315 
316 void free_irq_by_fd(int fd)
317 {
318         struct irq_entry *to_free;
319         unsigned long flags;
320 
321         spin_lock_irqsave(&irq_lock, flags);
322         to_free = get_irq_entry_by_fd(fd);
323         if (to_free != NULL) {
324                 do_free_by_irq_and_dev(
325                         to_free,
326                         -1,
327                         NULL,
328                         IGNORE_IRQ | IGNORE_DEV
329                 );
330         }
331         garbage_collect_irq_entries();
332         spin_unlock_irqrestore(&irq_lock, flags);
333 }
334 EXPORT_SYMBOL(free_irq_by_fd);
335 
336 static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
337 {
338         struct irq_entry *to_free;
339         unsigned long flags;
340 
341         spin_lock_irqsave(&irq_lock, flags);
342         to_free = active_fds;
343         while (to_free != NULL) {
344                 do_free_by_irq_and_dev(
345                         to_free,
346                         irq,
347                         dev,
348                         0
349                 );
350                 to_free = to_free->next;
351         }
352         garbage_collect_irq_entries();
353         spin_unlock_irqrestore(&irq_lock, flags);
354 }
355 
356 
357 void deactivate_fd(int fd, int irqnum)
358 {
359         struct irq_entry *to_free;
360         unsigned long flags;
361 
362         os_del_epoll_fd(fd);
363         spin_lock_irqsave(&irq_lock, flags);
364         to_free = get_irq_entry_by_fd(fd);
365         if (to_free != NULL) {
366                 do_free_by_irq_and_dev(
367                         to_free,
368                         irqnum,
369                         NULL,
370                         IGNORE_DEV
371                 );
372         }
373         garbage_collect_irq_entries();
374         spin_unlock_irqrestore(&irq_lock, flags);
375         ignore_sigio_fd(fd);
376 }
377 EXPORT_SYMBOL(deactivate_fd);
378 
379 /*
380  * Called just before shutdown in order to provide a clean exec
381  * environment in case the system is rebooting.  No locking because
382  * that would cause a pointless shutdown hang if something hadn't
383  * released the lock.
384  */
385 int deactivate_all_fds(void)
386 {
387         struct irq_entry *to_free;
388 
389         /* Stop IO. The IRQ loop has no lock so this is our
390          * only way of making sure we are safe to dispose
391          * of all IRQ handlers
392          */
393         os_set_ioignore();
394         to_free = active_fds;
395         while (to_free != NULL) {
396                 do_free_by_irq_and_dev(
397                         to_free,
398                         -1,
399                         NULL,
400                         IGNORE_IRQ | IGNORE_DEV
401                 );
402                 to_free = to_free->next;
403         }
404         /* don't garbage collect - we can no longer call kfree() here */
405         os_close_epoll_fd();
406         return 0;
407 }
408 
409 /*
410  * do_IRQ handles all normal device IRQs (the special
411  * SMP cross-CPU interrupts have their own specific
412  * handlers).
413  */
414 unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
415 {
416         struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
417         irq_enter();
418         generic_handle_irq(irq);
419         irq_exit();
420         set_irq_regs(old_regs);
421         return 1;
422 }
423 
424 void um_free_irq(unsigned int irq, void *dev)
425 {
426         free_irq_by_irq_and_dev(irq, dev);
427         free_irq(irq, dev);
428 }
429 EXPORT_SYMBOL(um_free_irq);
430 
431 int um_request_irq(unsigned int irq, int fd, int type,
432                    irq_handler_t handler,
433                    unsigned long irqflags, const char * devname,
434                    void *dev_id)
435 {
436         int err;
437 
438         if (fd != -1) {
439                 err = activate_fd(irq, fd, type, dev_id);
440                 if (err)
441                         return err;
442         }
443 
444         return request_irq(irq, handler, irqflags, devname, dev_id);
445 }
446 
447 EXPORT_SYMBOL(um_request_irq);
448 
449 /*
450  * irq_chip must define at least enable/disable and ack when
451  * the edge handler is used.
452  */
453 static void dummy(struct irq_data *d)
454 {
455 }
456 
457 /* This is used for everything else than the timer. */
458 static struct irq_chip normal_irq_type = {
459         .name = "SIGIO",
460         .irq_disable = dummy,
461         .irq_enable = dummy,
462         .irq_ack = dummy,
463         .irq_mask = dummy,
464         .irq_unmask = dummy,
465 };
466 
467 static struct irq_chip SIGVTALRM_irq_type = {
468         .name = "SIGVTALRM",
469         .irq_disable = dummy,
470         .irq_enable = dummy,
471         .irq_ack = dummy,
472         .irq_mask = dummy,
473         .irq_unmask = dummy,
474 };
475 
476 void __init init_IRQ(void)
477 {
478         int i;
479 
480         irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);
481 
482 
483         for (i = 1; i <= LAST_IRQ; i++)
484                 irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
485         /* Initialize EPOLL Loop */
486         os_setup_epoll();
487 }
488 
489 /*
490  * IRQ stack entry and exit:
491  *
492  * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
493  * and switch over to the IRQ stack after some preparation.  We use
494  * sigaltstack to receive signals on a separate stack from the start.
495  * These two functions make sure the rest of the kernel won't be too
496  * upset by being on a different stack.  The IRQ stack has a
497  * thread_info structure at the bottom so that current et al continue
498  * to work.
499  *
500  * to_irq_stack copies the current task's thread_info to the IRQ stack
501  * thread_info and sets the tasks's stack to point to the IRQ stack.
502  *
503  * from_irq_stack copies the thread_info struct back (flags may have
504  * been modified) and resets the task's stack pointer.
505  *
506  * Tricky bits -
507  *
508  * What happens when two signals race each other?  UML doesn't block
509  * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
510  * could arrive while a previous one is still setting up the
511  * thread_info.
512  *
513  * There are three cases -
514  *     The first interrupt on the stack - sets up the thread_info and
515  * handles the interrupt
516  *     A nested interrupt interrupting the copying of the thread_info -
517  * can't handle the interrupt, as the stack is in an unknown state
518  *     A nested interrupt not interrupting the copying of the
519  * thread_info - doesn't do any setup, just handles the interrupt
520  *
521  * The first job is to figure out whether we interrupted stack setup.
522  * This is done by xchging the signal mask with thread_info->pending.
523  * If the value that comes back is zero, then there is no setup in
524  * progress, and the interrupt can be handled.  If the value is
525  * non-zero, then there is stack setup in progress.  In order to have
526  * the interrupt handled, we leave our signal in the mask, and it will
527  * be handled by the upper handler after it has set up the stack.
528  *
529  * Next is to figure out whether we are the outer handler or a nested
530  * one.  As part of setting up the stack, thread_info->real_thread is
531  * set to non-NULL (and is reset to NULL on exit).  This is the
532  * nesting indicator.  If it is non-NULL, then the stack is already
533  * set up and the handler can run.
534  */
535 
536 static unsigned long pending_mask;
537 
538 unsigned long to_irq_stack(unsigned long *mask_out)
539 {
540         struct thread_info *ti;
541         unsigned long mask, old;
542         int nested;
543 
544         mask = xchg(&pending_mask, *mask_out);
545         if (mask != 0) {
546                 /*
547                  * If any interrupts come in at this point, we want to
548                  * make sure that their bits aren't lost by our
549                  * putting our bit in.  So, this loop accumulates bits
550                  * until xchg returns the same value that we put in.
551                  * When that happens, there were no new interrupts,
552                  * and pending_mask contains a bit for each interrupt
553                  * that came in.
554                  */
555                 old = *mask_out;
556                 do {
557                         old |= mask;
558                         mask = xchg(&pending_mask, old);
559                 } while (mask != old);
560                 return 1;
561         }
562 
563         ti = current_thread_info();
564         nested = (ti->real_thread != NULL);
565         if (!nested) {
566                 struct task_struct *task;
567                 struct thread_info *tti;
568 
569                 task = cpu_tasks[ti->cpu].task;
570                 tti = task_thread_info(task);
571 
572                 *ti = *tti;
573                 ti->real_thread = tti;
574                 task->stack = ti;
575         }
576 
577         mask = xchg(&pending_mask, 0);
578         *mask_out |= mask | nested;
579         return 0;
580 }
581 
582 unsigned long from_irq_stack(int nested)
583 {
584         struct thread_info *ti, *to;
585         unsigned long mask;
586 
587         ti = current_thread_info();
588 
589         pending_mask = 1;
590 
591         to = ti->real_thread;
592         current->stack = to;
593         ti->real_thread = NULL;
594         *to = *ti;
595 
596         mask = xchg(&pending_mask, 0);
597         return mask & ~1;
598 }
599 
600 

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