summaryrefslogtreecommitdiffstats
path: root/sys/net/bpf_zerocopy.c
blob: 7a3e6cd5fd9db279cbb6f190480065270b36ab7c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
/*-
 * Copyright (c) 2007 Seccuris Inc.
 * All rights reserved.
 *
 * This sofware was developed by Robert N. M. Watson under contract to
 * Seccuris Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_bpf.h"

#include <sys/param.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sf_buf.h>
#include <sys/socket.h>
#include <sys/uio.h>

#include <machine/atomic.h>

#include <net/if.h>
#include <net/bpf.h>
#include <net/bpf_zerocopy.h>
#include <net/bpfdesc.h>

#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>

/*
 * Zero-copy buffer scheme for BPF: user space "donates" two buffers, which
 * are mapped into the kernel address space using sf_bufs and used directly
 * by BPF.  Memory is wired since page faults cannot be tolerated in the
 * contexts where the buffers are copied to (locks held, interrupt context,
 * etc).  Access to shared memory buffers is synchronized using a header on
 * each buffer, allowing the number of system calls to go to zero as BPF
 * reaches saturation (buffers filled as fast as they can be drained by the
 * user process).  Full details of the protocol for communicating between the
 * user process and BPF may be found in bpf(4).
 */

/*
 * Maximum number of pages per buffer.  Since all BPF devices use two, the
 * maximum per device is 2*BPF_MAX_PAGES.  Resource limits on the number of
 * sf_bufs may be an issue, so do not set this too high.  On older systems,
 * kernel address space limits may also be an issue.
 */
#define	BPF_MAX_PAGES	512

/*
 * struct zbuf describes a memory buffer loaned by a user process to the
 * kernel.  We represent this as a series of pages managed using an array of
 * sf_bufs.  Even though the memory is contiguous in user space, it may not
 * be mapped contiguously in the kernel (i.e., a set of physically
 * non-contiguous pages in the direct map region) so we must implement
 * scatter-gather copying.  One significant mitigating factor is that on
 * systems with a direct memory map, we can avoid TLB misses.
 *
 * At the front of the shared memory region is a bpf_zbuf_header, which
 * contains shared control data to allow user space and the kernel to
 * synchronize; this is included in zb_size, but not bpf_bufsize, so that BPF
 * knows that the space is not available.
 */
struct zbuf {
	vm_offset_t	 zb_uaddr;	/* User address at time of setup. */
	size_t		 zb_size;	/* Size of buffer, incl. header. */
	u_int		 zb_numpages;	/* Number of pages. */
	int		 zb_flags;	/* Flags on zbuf. */
	struct sf_buf	**zb_pages;	/* Pages themselves. */
	struct bpf_zbuf_header	*zb_header;	/* Shared header. */
};

/*
 * When a buffer has been assigned to userspace, flag it as such, as the
 * buffer may remain in the store position as a result of the user process
 * not yet having acknowledged the buffer in the hold position yet.
 */
#define	ZBUF_FLAG_ASSIGNED	0x00000001	/* Set when owned by user. */

/*
 * Release a page we've previously wired.
 */
static void
zbuf_page_free(vm_page_t pp)
{

	vm_page_lock(pp);
	vm_page_unwire(pp, 0);
	if (pp->wire_count == 0 && pp->object == NULL)
		vm_page_free(pp);
	vm_page_unlock(pp);
}

/*
 * Free an sf_buf with attached page.
 */
static void
zbuf_sfbuf_free(struct sf_buf *sf)
{
	vm_page_t pp;

	pp = sf_buf_page(sf);
	sf_buf_free(sf);
	zbuf_page_free(pp);
}

/*
 * Free a zbuf, including its page array, sbufs, and pages.  Allow partially
 * allocated zbufs to be freed so that it may be used even during a zbuf
 * setup.
 */
static void
zbuf_free(struct zbuf *zb)
{
	int i;

	for (i = 0; i < zb->zb_numpages; i++) {
		if (zb->zb_pages[i] != NULL)
			zbuf_sfbuf_free(zb->zb_pages[i]);
	}
	free(zb->zb_pages, M_BPF);
	free(zb, M_BPF);
}

/*
 * Given a user pointer to a page of user memory, return an sf_buf for the
 * page.  Because we may be requesting quite a few sf_bufs, prefer failure to
 * deadlock and use SFB_NOWAIT.
 */
static struct sf_buf *
zbuf_sfbuf_get(struct vm_map *map, vm_offset_t uaddr)
{
	struct sf_buf *sf;
	vm_page_t pp;

	if (vm_fault_quick_hold_pages(map, uaddr, PAGE_SIZE, VM_PROT_READ |
	    VM_PROT_WRITE, &pp, 1) < 0)
		return (NULL);
	vm_page_lock(pp);
	vm_page_wire(pp);
	vm_page_unhold(pp);
	vm_page_unlock(pp);
	sf = sf_buf_alloc(pp, SFB_NOWAIT);
	if (sf == NULL) {
		zbuf_page_free(pp);
		return (NULL);
	}
	return (sf);
}

/*
 * Create a zbuf describing a range of user address space memory.  Validate
 * page alignment, size requirements, etc.
 */
static int
zbuf_setup(struct thread *td, vm_offset_t uaddr, size_t len,
    struct zbuf **zbp)
{
	struct zbuf *zb;
	struct vm_map *map;
	int error, i;

	*zbp = NULL;

	/*
	 * User address must be page-aligned.
	 */
	if (uaddr & PAGE_MASK)
		return (EINVAL);

	/*
	 * Length must be an integer number of full pages.
	 */
	if (len & PAGE_MASK)
		return (EINVAL);

	/*
	 * Length must not exceed per-buffer resource limit.
	 */
	if ((len / PAGE_SIZE) > BPF_MAX_PAGES)
		return (EINVAL);

	/*
	 * Allocate the buffer and set up each page with is own sf_buf.
	 */
	error = 0;
	zb = malloc(sizeof(*zb), M_BPF, M_ZERO | M_WAITOK);
	zb->zb_uaddr = uaddr;
	zb->zb_size = len;
	zb->zb_numpages = len / PAGE_SIZE;
	zb->zb_pages = malloc(sizeof(struct sf_buf *) *
	    zb->zb_numpages, M_BPF, M_ZERO | M_WAITOK);
	map = &td->td_proc->p_vmspace->vm_map;
	for (i = 0; i < zb->zb_numpages; i++) {
		zb->zb_pages[i] = zbuf_sfbuf_get(map,
		    uaddr + (i * PAGE_SIZE));
		if (zb->zb_pages[i] == NULL) {
			error = EFAULT;
			goto error;
		}
	}
	zb->zb_header =
	    (struct bpf_zbuf_header *)sf_buf_kva(zb->zb_pages[0]);
	bzero(zb->zb_header, sizeof(*zb->zb_header));
	*zbp = zb;
	return (0);

error:
	zbuf_free(zb);
	return (error);
}

/*
 * Copy bytes from a source into the specified zbuf.  The caller is
 * responsible for performing bounds checking, etc.
 */
void
bpf_zerocopy_append_bytes(struct bpf_d *d, caddr_t buf, u_int offset,
    void *src, u_int len)
{
	u_int count, page, poffset;
	u_char *src_bytes;
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_append_bytes: not in zbuf mode"));
	KASSERT(buf != NULL, ("bpf_zerocopy_append_bytes: NULL buf"));

	src_bytes = (u_char *)src;
	zb = (struct zbuf *)buf;

	KASSERT((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0,
	    ("bpf_zerocopy_append_bytes: ZBUF_FLAG_ASSIGNED"));

	/*
	 * Scatter-gather copy to user pages mapped into kernel address space
	 * using sf_bufs: copy up to a page at a time.
	 */
	offset += sizeof(struct bpf_zbuf_header);
	page = offset / PAGE_SIZE;
	poffset = offset % PAGE_SIZE;
	while (len > 0) {
		KASSERT(page < zb->zb_numpages, ("bpf_zerocopy_append_bytes:"
		   " page overflow (%d p %d np)\n", page, zb->zb_numpages));

		count = min(len, PAGE_SIZE - poffset);
		bcopy(src_bytes, ((u_char *)sf_buf_kva(zb->zb_pages[page])) +
		    poffset, count);
		poffset += count;
		if (poffset == PAGE_SIZE) {
			poffset = 0;
			page++;
		}
		KASSERT(poffset < PAGE_SIZE,
		    ("bpf_zerocopy_append_bytes: page offset overflow (%d)",
		    poffset));
		len -= count;
		src_bytes += count;
	}
}

/*
 * Copy bytes from an mbuf chain to the specified zbuf: copying will be
 * scatter-gather both from mbufs, which may be fragmented over memory, and
 * to pages, which may not be contiguously mapped in kernel address space.
 * As with bpf_zerocopy_append_bytes(), the caller is responsible for
 * checking that this will not exceed the buffer limit.
 */
void
bpf_zerocopy_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset,
    void *src, u_int len)
{
	u_int count, moffset, page, poffset;
	const struct mbuf *m;
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_append_mbuf not in zbuf mode"));
	KASSERT(buf != NULL, ("bpf_zerocopy_append_mbuf: NULL buf"));

	m = (struct mbuf *)src;
	zb = (struct zbuf *)buf;

	KASSERT((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0,
	    ("bpf_zerocopy_append_mbuf: ZBUF_FLAG_ASSIGNED"));

	/*
	 * Scatter gather both from an mbuf chain and to a user page set
	 * mapped into kernel address space using sf_bufs.  If we're lucky,
	 * each mbuf requires one copy operation, but if page alignment and
	 * mbuf alignment work out less well, we'll be doing two copies per
	 * mbuf.
	 */
	offset += sizeof(struct bpf_zbuf_header);
	page = offset / PAGE_SIZE;
	poffset = offset % PAGE_SIZE;
	moffset = 0;
	while (len > 0) {
		KASSERT(page < zb->zb_numpages,
		    ("bpf_zerocopy_append_mbuf: page overflow (%d p %d "
		    "np)\n", page, zb->zb_numpages));
		KASSERT(m != NULL,
		    ("bpf_zerocopy_append_mbuf: end of mbuf chain"));

		count = min(m->m_len - moffset, len);
		count = min(count, PAGE_SIZE - poffset);
		bcopy(mtod(m, u_char *) + moffset,
		    ((u_char *)sf_buf_kva(zb->zb_pages[page])) + poffset,
		    count);
		poffset += count;
		if (poffset == PAGE_SIZE) {
			poffset = 0;
			page++;
		}
		KASSERT(poffset < PAGE_SIZE,
		    ("bpf_zerocopy_append_mbuf: page offset overflow (%d)",
		    poffset));
		moffset += count;
		if (moffset == m->m_len) {
			m = m->m_next;
			moffset = 0;
		}
		len -= count;
	}
}

/*
 * Notification from the BPF framework that a buffer in the store position is
 * rejecting packets and may be considered full.  We mark the buffer as
 * immutable and assign to userspace so that it is immediately available for
 * the user process to access.
 */
void
bpf_zerocopy_buffull(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_buffull: not in zbuf mode"));

	zb = (struct zbuf *)d->bd_sbuf;
	KASSERT(zb != NULL, ("bpf_zerocopy_buffull: zb == NULL"));

	if ((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0) {
		zb->zb_flags |= ZBUF_FLAG_ASSIGNED;
		zb->zb_header->bzh_kernel_len = d->bd_slen;
		atomic_add_rel_int(&zb->zb_header->bzh_kernel_gen, 1);
	}
}

/*
 * Notification from the BPF framework that a buffer has moved into the held
 * slot on a descriptor.  Zero-copy BPF will update the shared page to let
 * the user process know and flag the buffer as assigned if it hasn't already
 * been marked assigned due to filling while it was in the store position.
 *
 * Note: identical logic as in bpf_zerocopy_buffull(), except that we operate
 * on bd_hbuf and bd_hlen.
 */
void
bpf_zerocopy_bufheld(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_bufheld: not in zbuf mode"));

	zb = (struct zbuf *)d->bd_hbuf;
	KASSERT(zb != NULL, ("bpf_zerocopy_bufheld: zb == NULL"));

	if ((zb->zb_flags & ZBUF_FLAG_ASSIGNED) == 0) {
		zb->zb_flags |= ZBUF_FLAG_ASSIGNED;
		zb->zb_header->bzh_kernel_len = d->bd_hlen;
		atomic_add_rel_int(&zb->zb_header->bzh_kernel_gen, 1);
	}
}

/*
 * Notification from the BPF framework that the free buffer has been been
 * rotated out of the held position to the free position.  This happens when
 * the user acknowledges the held buffer.
 */
void
bpf_zerocopy_buf_reclaimed(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_reclaim_buf: not in zbuf mode"));

	KASSERT(d->bd_fbuf != NULL,
	    ("bpf_zerocopy_buf_reclaimed: NULL free buf"));
	zb = (struct zbuf *)d->bd_fbuf;
	zb->zb_flags &= ~ZBUF_FLAG_ASSIGNED;
}

/*
 * Query from the BPF framework regarding whether the buffer currently in the
 * held position can be moved to the free position, which can be indicated by
 * the user process making their generation number equal to the kernel
 * generation number.
 */
int
bpf_zerocopy_canfreebuf(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_canfreebuf: not in zbuf mode"));

	zb = (struct zbuf *)d->bd_hbuf;
	if (zb == NULL)
		return (0);
	if (zb->zb_header->bzh_kernel_gen ==
	    atomic_load_acq_int(&zb->zb_header->bzh_user_gen))
		return (1);
	return (0);
}

/*
 * Query from the BPF framework as to whether or not the buffer current in
 * the store position can actually be written to.  This may return false if
 * the store buffer is assigned to userspace before the hold buffer is
 * acknowledged.
 */
int
bpf_zerocopy_canwritebuf(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_canwritebuf: not in zbuf mode"));

	zb = (struct zbuf *)d->bd_sbuf;
	KASSERT(zb != NULL, ("bpf_zerocopy_canwritebuf: bd_sbuf NULL"));

	if (zb->zb_flags & ZBUF_FLAG_ASSIGNED)
		return (0);
	return (1);
}

/*
 * Free zero copy buffers at request of descriptor.
 */
void
bpf_zerocopy_free(struct bpf_d *d)
{
	struct zbuf *zb;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_free: not in zbuf mode"));

	zb = (struct zbuf *)d->bd_sbuf;
	if (zb != NULL)
		zbuf_free(zb);
	zb = (struct zbuf *)d->bd_hbuf;
	if (zb != NULL)
		zbuf_free(zb);
	zb = (struct zbuf *)d->bd_fbuf;
	if (zb != NULL)
		zbuf_free(zb);
}

/*
 * Ioctl to return the maximum buffer size.
 */
int
bpf_zerocopy_ioctl_getzmax(struct thread *td, struct bpf_d *d, size_t *i)
{

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_ioctl_getzmax: not in zbuf mode"));

	*i = BPF_MAX_PAGES * PAGE_SIZE;
	return (0);
}

/*
 * Ioctl to force rotation of the two buffers, if there's any data available.
 * This can be used by user space to implement timeouts when waiting for a
 * buffer to fill.
 */
int
bpf_zerocopy_ioctl_rotzbuf(struct thread *td, struct bpf_d *d,
    struct bpf_zbuf *bz)
{
	struct zbuf *bzh;

	bzero(bz, sizeof(*bz));
	BPFD_LOCK(d);
	if (d->bd_hbuf == NULL && d->bd_slen != 0) {
		ROTATE_BUFFERS(d);
		bzh = (struct zbuf *)d->bd_hbuf;
		bz->bz_bufa = (void *)bzh->zb_uaddr;
		bz->bz_buflen = d->bd_hlen;
	}
	BPFD_UNLOCK(d);
	return (0);
}

/*
 * Ioctl to configure zero-copy buffers -- may be done only once.
 */
int
bpf_zerocopy_ioctl_setzbuf(struct thread *td, struct bpf_d *d,
    struct bpf_zbuf *bz)
{
	struct zbuf *zba, *zbb;
	int error;

	KASSERT(d->bd_bufmode == BPF_BUFMODE_ZBUF,
	    ("bpf_zerocopy_ioctl_setzbuf: not in zbuf mode"));

	/*
	 * Must set both buffers.  Cannot clear them.
	 */
	if (bz->bz_bufa == NULL || bz->bz_bufb == NULL)
		return (EINVAL);

	/*
	 * Buffers must have a size greater than 0.  Alignment and other size
	 * validity checking is done in zbuf_setup().
	 */
	if (bz->bz_buflen == 0)
		return (EINVAL);

	/*
	 * Allocate new buffers.
	 */
	error = zbuf_setup(td, (vm_offset_t)bz->bz_bufa, bz->bz_buflen,
	    &zba);
	if (error)
		return (error);
	error = zbuf_setup(td, (vm_offset_t)bz->bz_bufb, bz->bz_buflen,
	    &zbb);
	if (error) {
		zbuf_free(zba);
		return (error);
	}

	/*
	 * We only allow buffers to be installed once, so atomically check
	 * that no buffers are currently installed and install new buffers.
	 */
	BPFD_LOCK(d);
	if (d->bd_hbuf != NULL || d->bd_sbuf != NULL || d->bd_fbuf != NULL ||
	    d->bd_bif != NULL) {
		BPFD_UNLOCK(d);
		zbuf_free(zba);
		zbuf_free(zbb);
		return (EINVAL);
	}

	/*
	 * Point BPF descriptor at buffers; initialize sbuf as zba so that
	 * it is always filled first in the sequence, per bpf(4).
	 */
	d->bd_fbuf = (caddr_t)zbb;
	d->bd_sbuf = (caddr_t)zba;
	d->bd_slen = 0;
	d->bd_hlen = 0;

	/*
	 * We expose only the space left in the buffer after the size of the
	 * shared management region.
	 */
	d->bd_bufsize = bz->bz_buflen - sizeof(struct bpf_zbuf_header);
	BPFD_UNLOCK(d);
	return (0);
}
OpenPOWER on IntegriCloud