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