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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Tty buffer allocation management
4 */
5
6#include <linux/types.h>
7#include <linux/errno.h>
8#include <linux/minmax.h>
9#include <linux/tty.h>
10#include <linux/tty_buffer.h>
11#include <linux/tty_driver.h>
12#include <linux/tty_flip.h>
13#include <linux/timer.h>
14#include <linux/string.h>
15#include <linux/slab.h>
16#include <linux/sched.h>
17#include <linux/wait.h>
18#include <linux/bitops.h>
19#include <linux/delay.h>
20#include <linux/module.h>
21#include <linux/ratelimit.h>
22#include "tty.h"
23
24#define MIN_TTYB_SIZE 256
25#define TTYB_ALIGN_MASK 0xff
26
27/*
28 * Byte threshold to limit memory consumption for flip buffers.
29 * The actual memory limit is > 2x this amount.
30 */
31#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
32
33/*
34 * We default to dicing tty buffer allocations to this many characters
35 * in order to avoid multiple page allocations. We know the size of
36 * tty_buffer itself but it must also be taken into account that the
37 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
38 * logic this must match.
39 */
40
41#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
42
43/**
44 * tty_buffer_lock_exclusive - gain exclusive access to buffer
45 * @port: tty port owning the flip buffer
46 *
47 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
48 * the buffer work and any pending flush from using the flip buffer. Data can
49 * continue to be added concurrently to the flip buffer from the driver side.
50 *
51 * See also tty_buffer_unlock_exclusive().
52 */
53void tty_buffer_lock_exclusive(struct tty_port *port)
54{
55 struct tty_bufhead *buf = &port->buf;
56
57 atomic_inc(&buf->priority);
58 mutex_lock(&buf->lock);
59}
60EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
61
62static bool tty_buffer_queue_work(struct tty_bufhead *buf)
63{
64 struct workqueue_struct *flip_wq = READ_ONCE(buf->flip_wq);
65
66 return queue_work(flip_wq ?: system_dfl_wq, &buf->work);
67}
68
69/**
70 * tty_buffer_unlock_exclusive - release exclusive access
71 * @port: tty port owning the flip buffer
72 *
73 * The buffer work is restarted if there is data in the flip buffer.
74 *
75 * See also tty_buffer_lock_exclusive().
76 */
77void tty_buffer_unlock_exclusive(struct tty_port *port)
78{
79 struct tty_bufhead *buf = &port->buf;
80 bool restart = buf->head->commit != buf->head->read;
81
82 atomic_dec(&buf->priority);
83 mutex_unlock(&buf->lock);
84
85 if (restart)
86 tty_buffer_queue_work(buf);
87}
88EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
89
90/**
91 * tty_buffer_space_avail - return unused buffer space
92 * @port: tty port owning the flip buffer
93 *
94 * Returns: the # of bytes which can be written by the driver without reaching
95 * the buffer limit.
96 *
97 * Note: this does not guarantee that memory is available to write the returned
98 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
99 * guarantee is required).
100 */
101unsigned int tty_buffer_space_avail(struct tty_port *port)
102{
103 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
104
105 return max(space, 0);
106}
107EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
108
109static void tty_buffer_reset(struct tty_buffer *p, size_t size)
110{
111 p->used = 0;
112 p->size = size;
113 p->next = NULL;
114 p->commit = 0;
115 p->lookahead = 0;
116 p->read = 0;
117 p->flags = true;
118}
119
120/**
121 * tty_buffer_free_all - free buffers used by a tty
122 * @port: tty port to free from
123 *
124 * Remove all the buffers pending on a tty whether queued with data or in the
125 * free ring. Must be called when the tty is no longer in use.
126 */
127void tty_buffer_free_all(struct tty_port *port)
128{
129 struct tty_bufhead *buf = &port->buf;
130 struct tty_buffer *p, *next;
131 struct llist_node *llist;
132 unsigned int freed = 0;
133 int still_used;
134
135 while ((p = buf->head) != NULL) {
136 buf->head = p->next;
137 freed += p->size;
138 if (p->size > 0)
139 kfree(p);
140 }
141 llist = llist_del_all(&buf->free);
142 llist_for_each_entry_safe(p, next, llist, free)
143 kfree(p);
144
145 tty_buffer_reset(&buf->sentinel, 0);
146 buf->head = &buf->sentinel;
147 buf->tail = &buf->sentinel;
148
149 still_used = atomic_xchg(&buf->mem_used, 0);
150 WARN(still_used != freed, "we still have not freed %d bytes!",
151 still_used - freed);
152}
153
154/**
155 * tty_buffer_alloc - allocate a tty buffer
156 * @port: tty port
157 * @size: desired size (characters)
158 *
159 * Allocate a new tty buffer to hold the desired number of characters. We
160 * round our buffers off in 256 character chunks to get better allocation
161 * behaviour.
162 *
163 * Returns: %NULL if out of memory or the allocation would exceed the per
164 * device queue.
165 */
166static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
167{
168 struct llist_node *free;
169 struct tty_buffer *p;
170
171 /* Round the buffer size out */
172 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
173
174 if (size <= MIN_TTYB_SIZE) {
175 free = llist_del_first(&port->buf.free);
176 if (free) {
177 p = llist_entry(free, struct tty_buffer, free);
178 goto found;
179 }
180 }
181
182 /* Should possibly check if this fails for the largest buffer we
183 * have queued and recycle that ?
184 */
185 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
186 return NULL;
187 p = kmalloc_flex(*p, data, 2 * size, GFP_ATOMIC | __GFP_NOWARN);
188 if (p == NULL)
189 return NULL;
190
191found:
192 tty_buffer_reset(p, size);
193 atomic_add(size, &port->buf.mem_used);
194 return p;
195}
196
197/**
198 * tty_buffer_free - free a tty buffer
199 * @port: tty port owning the buffer
200 * @b: the buffer to free
201 *
202 * Free a tty buffer, or add it to the free list according to our internal
203 * strategy.
204 */
205static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
206{
207 struct tty_bufhead *buf = &port->buf;
208
209 /* Dumb strategy for now - should keep some stats */
210 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
211
212 if (b->size > MIN_TTYB_SIZE)
213 kfree(b);
214 else if (b->size > 0)
215 llist_add(&b->free, &buf->free);
216}
217
218/**
219 * tty_buffer_flush - flush full tty buffers
220 * @tty: tty to flush
221 * @ld: optional ldisc ptr (must be referenced)
222 *
223 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
224 * ldisc input buffer.
225 *
226 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
227 */
228void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
229{
230 struct tty_port *port = tty->port;
231 struct tty_bufhead *buf = &port->buf;
232 struct tty_buffer *next;
233
234 atomic_inc(&buf->priority);
235
236 mutex_lock(&buf->lock);
237 /* paired w/ release in __tty_buffer_request_room; ensures there are
238 * no pending memory accesses to the freed buffer
239 */
240 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
241 tty_buffer_free(port, buf->head);
242 buf->head = next;
243 }
244 buf->head->read = buf->head->commit;
245 buf->head->lookahead = buf->head->read;
246
247 if (ld && ld->ops->flush_buffer)
248 ld->ops->flush_buffer(tty);
249
250 atomic_dec(&buf->priority);
251 mutex_unlock(&buf->lock);
252}
253
254/**
255 * __tty_buffer_request_room - grow tty buffer if needed
256 * @port: tty port
257 * @size: size desired
258 * @flags: buffer has to store flags along character data
259 *
260 * Make at least @size bytes of linear space available for the tty buffer.
261 *
262 * Will change over to a new buffer if the current buffer is encoded as
263 * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
264 * buffer.
265 *
266 * Returns: the size we managed to find.
267 */
268static int __tty_buffer_request_room(struct tty_port *port, size_t size,
269 bool flags)
270{
271 struct tty_bufhead *buf = &port->buf;
272 struct tty_buffer *n, *b = buf->tail;
273 size_t left = (b->flags ? 1 : 2) * b->size - b->used;
274 bool change = !b->flags && flags;
275
276 if (!change && left >= size)
277 return size;
278
279 /* This is the slow path - looking for new buffers to use */
280 n = tty_buffer_alloc(port, size);
281 if (n == NULL)
282 return change ? 0 : left;
283
284 n->flags = flags;
285 buf->tail = n;
286 /*
287 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
288 * ensures they see all buffer data.
289 */
290 smp_store_release(&b->commit, b->used);
291 /*
292 * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
293 * ensures the latest commit value can be read before the head
294 * is advanced to the next buffer.
295 */
296 smp_store_release(&b->next, n);
297
298 return size;
299}
300
301int tty_buffer_request_room(struct tty_port *port, size_t size)
302{
303 return __tty_buffer_request_room(port, size, true);
304}
305EXPORT_SYMBOL_GPL(tty_buffer_request_room);
306
307size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
308 const u8 *flags, bool mutable_flags,
309 size_t size)
310{
311 bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
312 size_t copied = 0;
313
314 do {
315 size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
316 size_t space = __tty_buffer_request_room(port, goal, need_flags);
317 struct tty_buffer *tb = port->buf.tail;
318
319 if (unlikely(space == 0))
320 break;
321
322 memcpy(char_buf_ptr(tb, tb->used), chars, space);
323
324 if (mutable_flags) {
325 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
326 flags += space;
327 } else if (tb->flags) {
328 memset(flag_buf_ptr(tb, tb->used), flags[0], space);
329 } else {
330 /* tb->flags should be available once requested */
331 WARN_ON_ONCE(need_flags);
332 }
333
334 tb->used += space;
335 copied += space;
336 chars += space;
337
338 /* There is a small chance that we need to split the data over
339 * several buffers. If this is the case we must loop.
340 */
341 } while (unlikely(size > copied));
342
343 return copied;
344}
345EXPORT_SYMBOL(__tty_insert_flip_string_flags);
346
347/**
348 * tty_prepare_flip_string - make room for characters
349 * @port: tty port
350 * @chars: return pointer for character write area
351 * @size: desired size
352 *
353 * Prepare a block of space in the buffer for data.
354 *
355 * This is used for drivers that need their own block copy routines into the
356 * buffer. There is no guarantee the buffer is a DMA target!
357 *
358 * Returns: the length available and buffer pointer (@chars) to the space which
359 * is now allocated and accounted for as ready for normal characters.
360 */
361size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
362{
363 size_t space = __tty_buffer_request_room(port, size, false);
364
365 if (likely(space)) {
366 struct tty_buffer *tb = port->buf.tail;
367
368 *chars = char_buf_ptr(tb, tb->used);
369 if (tb->flags)
370 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
371 tb->used += space;
372 }
373
374 return space;
375}
376EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
377
378/**
379 * tty_ldisc_receive_buf - forward data to line discipline
380 * @ld: line discipline to process input
381 * @p: char buffer
382 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
383 * @count: number of bytes to process
384 *
385 * Callers other than flush_to_ldisc() need to exclude the kworker from
386 * concurrent use of the line discipline, see paste_selection().
387 *
388 * Returns: the number of bytes processed.
389 */
390size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
391 size_t count)
392{
393 if (ld->ops->receive_buf2)
394 count = ld->ops->receive_buf2(ld->tty, p, f, count);
395 else {
396 count = min_t(size_t, count, ld->tty->receive_room);
397 if (count && ld->ops->receive_buf)
398 ld->ops->receive_buf(ld->tty, p, f, count);
399 }
400 return count;
401}
402EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
403
404static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
405{
406 head->lookahead = max(head->lookahead, head->read);
407
408 while (head) {
409 struct tty_buffer *next;
410 unsigned int count;
411
412 /*
413 * Paired w/ release in __tty_buffer_request_room();
414 * ensures commit value read is not stale if the head
415 * is advancing to the next buffer.
416 */
417 next = smp_load_acquire(&head->next);
418 /*
419 * Paired w/ release in __tty_buffer_request_room() or in
420 * tty_buffer_flush(); ensures we see the committed buffer data.
421 */
422 count = smp_load_acquire(&head->commit) - head->lookahead;
423 if (!count) {
424 head = next;
425 continue;
426 }
427
428 if (port->client_ops->lookahead_buf) {
429 u8 *p, *f = NULL;
430
431 p = char_buf_ptr(head, head->lookahead);
432 if (head->flags)
433 f = flag_buf_ptr(head, head->lookahead);
434
435 port->client_ops->lookahead_buf(port, p, f, count);
436 }
437
438 head->lookahead += count;
439 }
440}
441
442static size_t
443receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
444{
445 u8 *p = char_buf_ptr(head, head->read);
446 const u8 *f = NULL;
447 size_t n;
448
449 if (head->flags)
450 f = flag_buf_ptr(head, head->read);
451
452 n = port->client_ops->receive_buf(port, p, f, count);
453 if (n > 0)
454 memset(p, 0, n);
455 return n;
456}
457
458/**
459 * flush_to_ldisc - flush data from buffer to ldisc
460 * @work: tty structure passed from work queue.
461 *
462 * This routine is called out of the software interrupt to flush data from the
463 * buffer chain to the line discipline.
464 *
465 * The receive_buf() method is single threaded for each tty instance.
466 *
467 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
468 */
469static void flush_to_ldisc(struct work_struct *work)
470{
471 struct tty_port *port = container_of(work, struct tty_port, buf.work);
472 struct tty_bufhead *buf = &port->buf;
473
474 mutex_lock(&buf->lock);
475
476 while (1) {
477 struct tty_buffer *head = buf->head;
478 struct tty_buffer *next;
479 size_t count, rcvd;
480
481 /* Ldisc or user is trying to gain exclusive access */
482 if (atomic_read(&buf->priority))
483 break;
484
485 /* paired w/ release in __tty_buffer_request_room();
486 * ensures commit value read is not stale if the head
487 * is advancing to the next buffer
488 */
489 next = smp_load_acquire(&head->next);
490 /* paired w/ release in __tty_buffer_request_room() or in
491 * tty_buffer_flush(); ensures we see the committed buffer data
492 */
493 count = smp_load_acquire(&head->commit) - head->read;
494 if (!count) {
495 if (next == NULL)
496 break;
497 buf->head = next;
498 tty_buffer_free(port, head);
499 continue;
500 }
501
502 rcvd = receive_buf(port, head, count);
503 head->read += rcvd;
504 if (rcvd < count)
505 lookahead_bufs(port, head);
506 if (!rcvd)
507 break;
508
509 cond_resched();
510 }
511
512 mutex_unlock(&buf->lock);
513
514}
515
516static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
517{
518 /*
519 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
520 * buffer data.
521 */
522 smp_store_release(&tail->commit, tail->used);
523}
524
525/**
526 * tty_flip_buffer_push - push terminal buffers
527 * @port: tty port to push
528 *
529 * Queue a push of the terminal flip buffers to the line discipline. Can be
530 * called from IRQ/atomic context.
531 *
532 * In the event of the queue being busy for flipping the work will be held off
533 * and retried later.
534 */
535void tty_flip_buffer_push(struct tty_port *port)
536{
537 struct tty_bufhead *buf = &port->buf;
538
539 tty_flip_buffer_commit(buf->tail);
540 tty_buffer_queue_work(buf);
541}
542EXPORT_SYMBOL(tty_flip_buffer_push);
543
544/**
545 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
546 * push
547 * @port: tty port
548 * @chars: characters
549 * @size: size
550 *
551 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
552 * with the exception of properly holding the @port->lock.
553 *
554 * To be used only internally (by pty currently).
555 *
556 * Returns: the number added.
557 */
558int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
559 const u8 *chars, size_t size)
560{
561 struct tty_bufhead *buf = &port->buf;
562 unsigned long flags;
563
564 spin_lock_irqsave(&port->lock, flags);
565 size = tty_insert_flip_string(port, chars, size);
566 if (size)
567 tty_flip_buffer_commit(buf->tail);
568 spin_unlock_irqrestore(&port->lock, flags);
569
570 tty_buffer_queue_work(buf);
571
572 return size;
573}
574
575/**
576 * tty_buffer_init - prepare a tty buffer structure
577 * @port: tty port to initialise
578 *
579 * Set up the initial state of the buffer management for a tty device. Must be
580 * called before the other tty buffer functions are used.
581 */
582void tty_buffer_init(struct tty_port *port)
583{
584 struct tty_bufhead *buf = &port->buf;
585
586 mutex_init(&buf->lock);
587 tty_buffer_reset(&buf->sentinel, 0);
588 buf->head = &buf->sentinel;
589 buf->tail = &buf->sentinel;
590 init_llist_head(&buf->free);
591 atomic_set(&buf->mem_used, 0);
592 atomic_set(&buf->priority, 0);
593 INIT_WORK(&buf->work, flush_to_ldisc);
594 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
595}
596
597/**
598 * tty_buffer_set_limit - change the tty buffer memory limit
599 * @port: tty port to change
600 * @limit: memory limit to set
601 *
602 * Change the tty buffer memory limit.
603 *
604 * Must be called before the other tty buffer functions are used.
605 */
606int tty_buffer_set_limit(struct tty_port *port, int limit)
607{
608 if (limit < MIN_TTYB_SIZE)
609 return -EINVAL;
610 port->buf.mem_limit = limit;
611 return 0;
612}
613EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
614
615/* slave ptys can claim nested buffer lock when handling BRK and INTR */
616void tty_buffer_set_lock_subclass(struct tty_port *port)
617{
618 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
619}
620
621bool tty_buffer_restart_work(struct tty_port *port)
622{
623 return tty_buffer_queue_work(&port->buf);
624}
625
626bool tty_buffer_cancel_work(struct tty_port *port)
627{
628 return cancel_work_sync(&port->buf.work);
629}
630
631void tty_buffer_flush_work(struct tty_port *port)
632{
633 flush_work(&port->buf.work);
634}