1/*
2 *
3 * Copyright (c) 2009, Microsoft Corporation.
4 *
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms and conditions of the GNU General Public License,
7 * version 2, as published by the Free Software Foundation.
8 *
9 * This program is distributed in the hope it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
12 * more details.
13 *
14 * You should have received a copy of the GNU General Public License along with
15 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
16 * Place - Suite 330, Boston, MA 02111-1307 USA.
17 *
18 * Authors:
19 * Haiyang Zhang <haiyangz@microsoft.com>
20 * Hank Janssen <hjanssen@microsoft.com>
21 * K. Y. Srinivasan <kys@microsoft.com>
22 *
23 */
24#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
25
26#include <linux/kernel.h>
27#include <linux/mm.h>
28#include <linux/hyperv.h>
29#include <linux/uio.h>
30#include <linux/vmalloc.h>
31#include <linux/slab.h>
32#include <linux/prefetch.h>
33
34#include "hyperv_vmbus.h"
35
36#define VMBUS_PKT_TRAILER 8
37
38/*
39 * When we write to the ring buffer, check if the host needs to
40 * be signaled. Here is the details of this protocol:
41 *
42 * 1. The host guarantees that while it is draining the
43 * ring buffer, it will set the interrupt_mask to
44 * indicate it does not need to be interrupted when
45 * new data is placed.
46 *
47 * 2. The host guarantees that it will completely drain
48 * the ring buffer before exiting the read loop. Further,
49 * once the ring buffer is empty, it will clear the
50 * interrupt_mask and re-check to see if new data has
51 * arrived.
52 *
53 * KYS: Oct. 30, 2016:
54 * It looks like Windows hosts have logic to deal with DOS attacks that
55 * can be triggered if it receives interrupts when it is not expecting
56 * the interrupt. The host expects interrupts only when the ring
57 * transitions from empty to non-empty (or full to non full on the guest
58 * to host ring).
59 * So, base the signaling decision solely on the ring state until the
60 * host logic is fixed.
61 */
62
63static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
64{
65 struct hv_ring_buffer_info *rbi = &channel->outbound;
66
67 virt_mb();
68 if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
69 return;
70
71 /* check interrupt_mask before read_index */
72 virt_rmb();
73 /*
74 * This is the only case we need to signal when the
75 * ring transitions from being empty to non-empty.
76 */
77 if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
78 ++channel->intr_out_empty;
79 vmbus_setevent(channel);
80 }
81}
82
83/* Get the next write location for the specified ring buffer. */
84static inline u32
85hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
86{
87 u32 next = ring_info->ring_buffer->write_index;
88
89 return next;
90}
91
92/* Set the next write location for the specified ring buffer. */
93static inline void
94hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
95 u32 next_write_location)
96{
97 ring_info->ring_buffer->write_index = next_write_location;
98}
99
100/* Set the next read location for the specified ring buffer. */
101static inline void
102hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
103 u32 next_read_location)
104{
105 ring_info->ring_buffer->read_index = next_read_location;
106 ring_info->priv_read_index = next_read_location;
107}
108
109/* Get the size of the ring buffer. */
110static inline u32
111hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
112{
113 return ring_info->ring_datasize;
114}
115
116/* Get the read and write indices as u64 of the specified ring buffer. */
117static inline u64
118hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
119{
120 return (u64)ring_info->ring_buffer->write_index << 32;
121}
122
123/*
124 * Helper routine to copy from source to ring buffer.
125 * Assume there is enough room. Handles wrap-around in dest case only!!
126 */
127static u32 hv_copyto_ringbuffer(
128 struct hv_ring_buffer_info *ring_info,
129 u32 start_write_offset,
130 const void *src,
131 u32 srclen)
132{
133 void *ring_buffer = hv_get_ring_buffer(ring_info);
134 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
135
136 memcpy(ring_buffer + start_write_offset, src, srclen);
137
138 start_write_offset += srclen;
139 if (start_write_offset >= ring_buffer_size)
140 start_write_offset -= ring_buffer_size;
141
142 return start_write_offset;
143}
144
145/*
146 *
147 * hv_get_ringbuffer_availbytes()
148 *
149 * Get number of bytes available to read and to write to
150 * for the specified ring buffer
151 */
152static void
153hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
154 u32 *read, u32 *write)
155{
156 u32 read_loc, write_loc, dsize;
157
158 /* Capture the read/write indices before they changed */
159 read_loc = READ_ONCE(rbi->ring_buffer->read_index);
160 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
161 dsize = rbi->ring_datasize;
162
163 *write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
164 read_loc - write_loc;
165 *read = dsize - *write;
166}
167
168/* Get various debug metrics for the specified ring buffer. */
169int hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
170 struct hv_ring_buffer_debug_info *debug_info)
171{
172 u32 bytes_avail_towrite;
173 u32 bytes_avail_toread;
174
175 if (!ring_info->ring_buffer)
176 return -EINVAL;
177
178 hv_get_ringbuffer_availbytes(ring_info,
179 &bytes_avail_toread,
180 &bytes_avail_towrite);
181 debug_info->bytes_avail_toread = bytes_avail_toread;
182 debug_info->bytes_avail_towrite = bytes_avail_towrite;
183 debug_info->current_read_index = ring_info->ring_buffer->read_index;
184 debug_info->current_write_index = ring_info->ring_buffer->write_index;
185 debug_info->current_interrupt_mask
186 = ring_info->ring_buffer->interrupt_mask;
187 return 0;
188}
189EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
190
191/* Initialize the ring buffer. */
192int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
193 struct page *pages, u32 page_cnt)
194{
195 int i;
196 struct page **pages_wraparound;
197
198 BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
199
200 memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
201
202 /*
203 * First page holds struct hv_ring_buffer, do wraparound mapping for
204 * the rest.
205 */
206 pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *),
207 GFP_KERNEL);
208 if (!pages_wraparound)
209 return -ENOMEM;
210
211 pages_wraparound[0] = pages;
212 for (i = 0; i < 2 * (page_cnt - 1); i++)
213 pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
214
215 ring_info->ring_buffer = (struct hv_ring_buffer *)
216 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
217
218 kfree(pages_wraparound);
219
220
221 if (!ring_info->ring_buffer)
222 return -ENOMEM;
223
224 ring_info->ring_buffer->read_index =
225 ring_info->ring_buffer->write_index = 0;
226
227 /* Set the feature bit for enabling flow control. */
228 ring_info->ring_buffer->feature_bits.value = 1;
229
230 ring_info->ring_size = page_cnt << PAGE_SHIFT;
231 ring_info->ring_size_div10_reciprocal =
232 reciprocal_value(ring_info->ring_size / 10);
233 ring_info->ring_datasize = ring_info->ring_size -
234 sizeof(struct hv_ring_buffer);
235
236 spin_lock_init(&ring_info->ring_lock);
237
238 return 0;
239}
240
241/* Cleanup the ring buffer. */
242void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
243{
244 vunmap(ring_info->ring_buffer);
245 ring_info->ring_buffer = NULL;
246}
247
248/* Write to the ring buffer. */
249int hv_ringbuffer_write(struct vmbus_channel *channel,
250 const struct kvec *kv_list, u32 kv_count)
251{
252 int i;
253 u32 bytes_avail_towrite;
254 u32 totalbytes_towrite = sizeof(u64);
255 u32 next_write_location;
256 u32 old_write;
257 u64 prev_indices;
258 unsigned long flags;
259 struct hv_ring_buffer_info *outring_info = &channel->outbound;
260
261 if (channel->rescind)
262 return -ENODEV;
263
264 for (i = 0; i < kv_count; i++)
265 totalbytes_towrite += kv_list[i].iov_len;
266
267 spin_lock_irqsave(&outring_info->ring_lock, flags);
268
269 bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
270
271 /*
272 * If there is only room for the packet, assume it is full.
273 * Otherwise, the next time around, we think the ring buffer
274 * is empty since the read index == write index.
275 */
276 if (bytes_avail_towrite <= totalbytes_towrite) {
277 ++channel->out_full_total;
278
279 if (!channel->out_full_flag) {
280 ++channel->out_full_first;
281 channel->out_full_flag = true;
282 }
283
284 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
285 return -EAGAIN;
286 }
287
288 channel->out_full_flag = false;
289
290 /* Write to the ring buffer */
291 next_write_location = hv_get_next_write_location(outring_info);
292
293 old_write = next_write_location;
294
295 for (i = 0; i < kv_count; i++) {
296 next_write_location = hv_copyto_ringbuffer(outring_info,
297 next_write_location,
298 kv_list[i].iov_base,
299 kv_list[i].iov_len);
300 }
301
302 /* Set previous packet start */
303 prev_indices = hv_get_ring_bufferindices(outring_info);
304
305 next_write_location = hv_copyto_ringbuffer(outring_info,
306 next_write_location,
307 &prev_indices,
308 sizeof(u64));
309
310 /* Issue a full memory barrier before updating the write index */
311 virt_mb();
312
313 /* Now, update the write location */
314 hv_set_next_write_location(outring_info, next_write_location);
315
316
317 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
318
319 hv_signal_on_write(old_write, channel);
320
321 if (channel->rescind)
322 return -ENODEV;
323
324 return 0;
325}
326
327int hv_ringbuffer_read(struct vmbus_channel *channel,
328 void *buffer, u32 buflen, u32 *buffer_actual_len,
329 u64 *requestid, bool raw)
330{
331 struct vmpacket_descriptor *desc;
332 u32 packetlen, offset;
333
334 if (unlikely(buflen == 0))
335 return -EINVAL;
336
337 *buffer_actual_len = 0;
338 *requestid = 0;
339
340 /* Make sure there is something to read */
341 desc = hv_pkt_iter_first(channel);
342 if (desc == NULL) {
343 /*
344 * No error is set when there is even no header, drivers are
345 * supposed to analyze buffer_actual_len.
346 */
347 return 0;
348 }
349
350 offset = raw ? 0 : (desc->offset8 << 3);
351 packetlen = (desc->len8 << 3) - offset;
352 *buffer_actual_len = packetlen;
353 *requestid = desc->trans_id;
354
355 if (unlikely(packetlen > buflen))
356 return -ENOBUFS;
357
358 /* since ring is double mapped, only one copy is necessary */
359 memcpy(buffer, (const char *)desc + offset, packetlen);
360
361 /* Advance ring index to next packet descriptor */
362 __hv_pkt_iter_next(channel, desc);
363
364 /* Notify host of update */
365 hv_pkt_iter_close(channel);
366
367 return 0;
368}
369
370/*
371 * Determine number of bytes available in ring buffer after
372 * the current iterator (priv_read_index) location.
373 *
374 * This is similar to hv_get_bytes_to_read but with private
375 * read index instead.
376 */
377static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
378{
379 u32 priv_read_loc = rbi->priv_read_index;
380 u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
381
382 if (write_loc >= priv_read_loc)
383 return write_loc - priv_read_loc;
384 else
385 return (rbi->ring_datasize - priv_read_loc) + write_loc;
386}
387
388/*
389 * Get first vmbus packet from ring buffer after read_index
390 *
391 * If ring buffer is empty, returns NULL and no other action needed.
392 */
393struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
394{
395 struct hv_ring_buffer_info *rbi = &channel->inbound;
396 struct vmpacket_descriptor *desc;
397
398 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
399 return NULL;
400
401 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
402 if (desc)
403 prefetch((char *)desc + (desc->len8 << 3));
404
405 return desc;
406}
407EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
408
409/*
410 * Get next vmbus packet from ring buffer.
411 *
412 * Advances the current location (priv_read_index) and checks for more
413 * data. If the end of the ring buffer is reached, then return NULL.
414 */
415struct vmpacket_descriptor *
416__hv_pkt_iter_next(struct vmbus_channel *channel,
417 const struct vmpacket_descriptor *desc)
418{
419 struct hv_ring_buffer_info *rbi = &channel->inbound;
420 u32 packetlen = desc->len8 << 3;
421 u32 dsize = rbi->ring_datasize;
422
423 /* bump offset to next potential packet */
424 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
425 if (rbi->priv_read_index >= dsize)
426 rbi->priv_read_index -= dsize;
427
428 /* more data? */
429 return hv_pkt_iter_first(channel);
430}
431EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
432
433/* How many bytes were read in this iterator cycle */
434static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
435 u32 start_read_index)
436{
437 if (rbi->priv_read_index >= start_read_index)
438 return rbi->priv_read_index - start_read_index;
439 else
440 return rbi->ring_datasize - start_read_index +
441 rbi->priv_read_index;
442}
443
444/*
445 * Update host ring buffer after iterating over packets. If the host has
446 * stopped queuing new entries because it found the ring buffer full, and
447 * sufficient space is being freed up, signal the host. But be careful to
448 * only signal the host when necessary, both for performance reasons and
449 * because Hyper-V protects itself by throttling guests that signal
450 * inappropriately.
451 *
452 * Determining when to signal is tricky. There are three key data inputs
453 * that must be handled in this order to avoid race conditions:
454 *
455 * 1. Update the read_index
456 * 2. Read the pending_send_sz
457 * 3. Read the current write_index
458 *
459 * The interrupt_mask is not used to determine when to signal. The
460 * interrupt_mask is used only on the guest->host ring buffer when
461 * sending requests to the host. The host does not use it on the host->
462 * guest ring buffer to indicate whether it should be signaled.
463 */
464void hv_pkt_iter_close(struct vmbus_channel *channel)
465{
466 struct hv_ring_buffer_info *rbi = &channel->inbound;
467 u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
468
469 /*
470 * Make sure all reads are done before we update the read index since
471 * the writer may start writing to the read area once the read index
472 * is updated.
473 */
474 virt_rmb();
475 start_read_index = rbi->ring_buffer->read_index;
476 rbi->ring_buffer->read_index = rbi->priv_read_index;
477
478 /*
479 * Older versions of Hyper-V (before WS2102 and Win8) do not
480 * implement pending_send_sz and simply poll if the host->guest
481 * ring buffer is full. No signaling is needed or expected.
482 */
483 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
484 return;
485
486 /*
487 * Issue a full memory barrier before making the signaling decision.
488 * If reading pending_send_sz were to be reordered and happen
489 * before we commit the new read_index, a race could occur. If the
490 * host were to set the pending_send_sz after we have sampled
491 * pending_send_sz, and the ring buffer blocks before we commit the
492 * read index, we could miss sending the interrupt. Issue a full
493 * memory barrier to address this.
494 */
495 virt_mb();
496
497 /*
498 * If the pending_send_sz is zero, then the ring buffer is not
499 * blocked and there is no need to signal. This is far by the
500 * most common case, so exit quickly for best performance.
501 */
502 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
503 if (!pending_sz)
504 return;
505
506 /*
507 * Ensure the read of write_index in hv_get_bytes_to_write()
508 * happens after the read of pending_send_sz.
509 */
510 virt_rmb();
511 curr_write_sz = hv_get_bytes_to_write(rbi);
512 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
513
514 /*
515 * We want to signal the host only if we're transitioning
516 * from a "not enough free space" state to a "enough free
517 * space" state. For example, it's possible that this function
518 * could run and free up enough space to signal the host, and then
519 * run again and free up additional space before the host has a
520 * chance to clear the pending_send_sz. The 2nd invocation would
521 * be a null transition from "enough free space" to "enough free
522 * space", which doesn't warrant a signal.
523 *
524 * Exactly filling the ring buffer is treated as "not enough
525 * space". The ring buffer always must have at least one byte
526 * empty so the empty and full conditions are distinguishable.
527 * hv_get_bytes_to_write() doesn't fully tell the truth in
528 * this regard.
529 *
530 * So first check if we were in the "enough free space" state
531 * before we began the iteration. If so, the host was not
532 * blocked, and there's no need to signal.
533 */
534 if (curr_write_sz - bytes_read > pending_sz)
535 return;
536
537 /*
538 * Similarly, if the new state is "not enough space", then
539 * there's no need to signal.
540 */
541 if (curr_write_sz <= pending_sz)
542 return;
543
544 ++channel->intr_in_full;
545 vmbus_setevent(channel);
546}
547EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
548