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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
31#include "hyperv_vmbus.h"
32
33void hv_begin_read(struct hv_ring_buffer_info *rbi)
34{
35 rbi->ring_buffer->interrupt_mask = 1;
36 mb();
37}
38
39u32 hv_end_read(struct hv_ring_buffer_info *rbi)
40{
41 u32 read;
42 u32 write;
43
44 rbi->ring_buffer->interrupt_mask = 0;
45 mb();
46
47 /*
48 * Now check to see if the ring buffer is still empty.
49 * If it is not, we raced and we need to process new
50 * incoming messages.
51 */
52 hv_get_ringbuffer_availbytes(rbi, &read, &write);
53
54 return read;
55}
56
57/*
58 * When we write to the ring buffer, check if the host needs to
59 * be signaled. Here is the details of this protocol:
60 *
61 * 1. The host guarantees that while it is draining the
62 * ring buffer, it will set the interrupt_mask to
63 * indicate it does not need to be interrupted when
64 * new data is placed.
65 *
66 * 2. The host guarantees that it will completely drain
67 * the ring buffer before exiting the read loop. Further,
68 * once the ring buffer is empty, it will clear the
69 * interrupt_mask and re-check to see if new data has
70 * arrived.
71 */
72
73static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
74{
75 mb();
76 if (rbi->ring_buffer->interrupt_mask)
77 return false;
78
79 /* check interrupt_mask before read_index */
80 rmb();
81 /*
82 * This is the only case we need to signal when the
83 * ring transitions from being empty to non-empty.
84 */
85 if (old_write == rbi->ring_buffer->read_index)
86 return true;
87
88 return false;
89}
90
91/*
92 * To optimize the flow management on the send-side,
93 * when the sender is blocked because of lack of
94 * sufficient space in the ring buffer, potential the
95 * consumer of the ring buffer can signal the producer.
96 * This is controlled by the following parameters:
97 *
98 * 1. pending_send_sz: This is the size in bytes that the
99 * producer is trying to send.
100 * 2. The feature bit feat_pending_send_sz set to indicate if
101 * the consumer of the ring will signal when the ring
102 * state transitions from being full to a state where
103 * there is room for the producer to send the pending packet.
104 */
105
106static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
107{
108 u32 cur_write_sz;
109 u32 r_size;
110 u32 write_loc;
111 u32 read_loc = rbi->ring_buffer->read_index;
112 u32 pending_sz;
113
114 /*
115 * Issue a full memory barrier before making the signaling decision.
116 * Here is the reason for having this barrier:
117 * If the reading of the pend_sz (in this function)
118 * were to be reordered and read before we commit the new read
119 * index (in the calling function) we could
120 * have a problem. If the host were to set the pending_sz after we
121 * have sampled pending_sz and go to sleep before we commit the
122 * read index, we could miss sending the interrupt. Issue a full
123 * memory barrier to address this.
124 */
125 mb();
126
127 pending_sz = rbi->ring_buffer->pending_send_sz;
128 write_loc = rbi->ring_buffer->write_index;
129 /* If the other end is not blocked on write don't bother. */
130 if (pending_sz == 0)
131 return false;
132
133 r_size = rbi->ring_datasize;
134 cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
135 read_loc - write_loc;
136
137 if (cur_write_sz >= pending_sz)
138 return true;
139
140 return false;
141}
142
143/* Get the next write location for the specified ring buffer. */
144static inline u32
145hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
146{
147 u32 next = ring_info->ring_buffer->write_index;
148
149 return next;
150}
151
152/* Set the next write location for the specified ring buffer. */
153static inline void
154hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
155 u32 next_write_location)
156{
157 ring_info->ring_buffer->write_index = next_write_location;
158}
159
160/* Get the next read location for the specified ring buffer. */
161static inline u32
162hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
163{
164 u32 next = ring_info->ring_buffer->read_index;
165
166 return next;
167}
168
169/*
170 * Get the next read location + offset for the specified ring buffer.
171 * This allows the caller to skip.
172 */
173static inline u32
174hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
175 u32 offset)
176{
177 u32 next = ring_info->ring_buffer->read_index;
178
179 next += offset;
180 next %= ring_info->ring_datasize;
181
182 return next;
183}
184
185/* Set the next read location for the specified ring buffer. */
186static inline void
187hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
188 u32 next_read_location)
189{
190 ring_info->ring_buffer->read_index = next_read_location;
191}
192
193
194/* Get the start of the ring buffer. */
195static inline void *
196hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
197{
198 return (void *)ring_info->ring_buffer->buffer;
199}
200
201
202/* Get the size of the ring buffer. */
203static inline u32
204hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
205{
206 return ring_info->ring_datasize;
207}
208
209/* Get the read and write indices as u64 of the specified ring buffer. */
210static inline u64
211hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
212{
213 return (u64)ring_info->ring_buffer->write_index << 32;
214}
215
216/*
217 * Helper routine to copy to source from ring buffer.
218 * Assume there is enough room. Handles wrap-around in src case only!!
219 */
220static u32 hv_copyfrom_ringbuffer(
221 struct hv_ring_buffer_info *ring_info,
222 void *dest,
223 u32 destlen,
224 u32 start_read_offset)
225{
226 void *ring_buffer = hv_get_ring_buffer(ring_info);
227 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
228
229 u32 frag_len;
230
231 /* wrap-around detected at the src */
232 if (destlen > ring_buffer_size - start_read_offset) {
233 frag_len = ring_buffer_size - start_read_offset;
234
235 memcpy(dest, ring_buffer + start_read_offset, frag_len);
236 memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
237 } else
238
239 memcpy(dest, ring_buffer + start_read_offset, destlen);
240
241
242 start_read_offset += destlen;
243 start_read_offset %= ring_buffer_size;
244
245 return start_read_offset;
246}
247
248
249/*
250 * Helper routine to copy from source to ring buffer.
251 * Assume there is enough room. Handles wrap-around in dest case only!!
252 */
253static u32 hv_copyto_ringbuffer(
254 struct hv_ring_buffer_info *ring_info,
255 u32 start_write_offset,
256 void *src,
257 u32 srclen)
258{
259 void *ring_buffer = hv_get_ring_buffer(ring_info);
260 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
261 u32 frag_len;
262
263 /* wrap-around detected! */
264 if (srclen > ring_buffer_size - start_write_offset) {
265 frag_len = ring_buffer_size - start_write_offset;
266 memcpy(ring_buffer + start_write_offset, src, frag_len);
267 memcpy(ring_buffer, src + frag_len, srclen - frag_len);
268 } else
269 memcpy(ring_buffer + start_write_offset, src, srclen);
270
271 start_write_offset += srclen;
272 start_write_offset %= ring_buffer_size;
273
274 return start_write_offset;
275}
276
277/* Get various debug metrics for the specified ring buffer. */
278void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
279 struct hv_ring_buffer_debug_info *debug_info)
280{
281 u32 bytes_avail_towrite;
282 u32 bytes_avail_toread;
283
284 if (ring_info->ring_buffer) {
285 hv_get_ringbuffer_availbytes(ring_info,
286 &bytes_avail_toread,
287 &bytes_avail_towrite);
288
289 debug_info->bytes_avail_toread = bytes_avail_toread;
290 debug_info->bytes_avail_towrite = bytes_avail_towrite;
291 debug_info->current_read_index =
292 ring_info->ring_buffer->read_index;
293 debug_info->current_write_index =
294 ring_info->ring_buffer->write_index;
295 debug_info->current_interrupt_mask =
296 ring_info->ring_buffer->interrupt_mask;
297 }
298}
299
300/* Initialize the ring buffer. */
301int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
302 void *buffer, u32 buflen)
303{
304 if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
305 return -EINVAL;
306
307 memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
308
309 ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
310 ring_info->ring_buffer->read_index =
311 ring_info->ring_buffer->write_index = 0;
312
313 /* Set the feature bit for enabling flow control. */
314 ring_info->ring_buffer->feature_bits.value = 1;
315
316 ring_info->ring_size = buflen;
317 ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
318
319 spin_lock_init(&ring_info->ring_lock);
320
321 return 0;
322}
323
324/* Cleanup the ring buffer. */
325void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
326{
327}
328
329/* Write to the ring buffer. */
330int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
331 struct kvec *kv_list, u32 kv_count, bool *signal, bool lock)
332{
333 int i = 0;
334 u32 bytes_avail_towrite;
335 u32 bytes_avail_toread;
336 u32 totalbytes_towrite = 0;
337
338 u32 next_write_location;
339 u32 old_write;
340 u64 prev_indices = 0;
341 unsigned long flags = 0;
342
343 for (i = 0; i < kv_count; i++)
344 totalbytes_towrite += kv_list[i].iov_len;
345
346 totalbytes_towrite += sizeof(u64);
347
348 if (lock)
349 spin_lock_irqsave(&outring_info->ring_lock, flags);
350
351 hv_get_ringbuffer_availbytes(outring_info,
352 &bytes_avail_toread,
353 &bytes_avail_towrite);
354
355 /*
356 * If there is only room for the packet, assume it is full.
357 * Otherwise, the next time around, we think the ring buffer
358 * is empty since the read index == write index.
359 */
360 if (bytes_avail_towrite <= totalbytes_towrite) {
361 if (lock)
362 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
363 return -EAGAIN;
364 }
365
366 /* Write to the ring buffer */
367 next_write_location = hv_get_next_write_location(outring_info);
368
369 old_write = next_write_location;
370
371 for (i = 0; i < kv_count; i++) {
372 next_write_location = hv_copyto_ringbuffer(outring_info,
373 next_write_location,
374 kv_list[i].iov_base,
375 kv_list[i].iov_len);
376 }
377
378 /* Set previous packet start */
379 prev_indices = hv_get_ring_bufferindices(outring_info);
380
381 next_write_location = hv_copyto_ringbuffer(outring_info,
382 next_write_location,
383 &prev_indices,
384 sizeof(u64));
385
386 /* Issue a full memory barrier before updating the write index */
387 mb();
388
389 /* Now, update the write location */
390 hv_set_next_write_location(outring_info, next_write_location);
391
392
393 if (lock)
394 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
395
396 *signal = hv_need_to_signal(old_write, outring_info);
397 return 0;
398}
399
400int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
401 void *buffer, u32 buflen, u32 *buffer_actual_len,
402 u64 *requestid, bool *signal, bool raw)
403{
404 u32 bytes_avail_towrite;
405 u32 bytes_avail_toread;
406 u32 next_read_location = 0;
407 u64 prev_indices = 0;
408 struct vmpacket_descriptor desc;
409 u32 offset;
410 u32 packetlen;
411 int ret = 0;
412
413 if (buflen <= 0)
414 return -EINVAL;
415
416
417 *buffer_actual_len = 0;
418 *requestid = 0;
419
420 hv_get_ringbuffer_availbytes(inring_info,
421 &bytes_avail_toread,
422 &bytes_avail_towrite);
423
424 /* Make sure there is something to read */
425 if (bytes_avail_toread < sizeof(desc)) {
426 /*
427 * No error is set when there is even no header, drivers are
428 * supposed to analyze buffer_actual_len.
429 */
430 return ret;
431 }
432
433 next_read_location = hv_get_next_read_location(inring_info);
434 next_read_location = hv_copyfrom_ringbuffer(inring_info, &desc,
435 sizeof(desc),
436 next_read_location);
437
438 offset = raw ? 0 : (desc.offset8 << 3);
439 packetlen = (desc.len8 << 3) - offset;
440 *buffer_actual_len = packetlen;
441 *requestid = desc.trans_id;
442
443 if (bytes_avail_toread < packetlen + offset)
444 return -EAGAIN;
445
446 if (packetlen > buflen)
447 return -ENOBUFS;
448
449 next_read_location =
450 hv_get_next_readlocation_withoffset(inring_info, offset);
451
452 next_read_location = hv_copyfrom_ringbuffer(inring_info,
453 buffer,
454 packetlen,
455 next_read_location);
456
457 next_read_location = hv_copyfrom_ringbuffer(inring_info,
458 &prev_indices,
459 sizeof(u64),
460 next_read_location);
461
462 /*
463 * Make sure all reads are done before we update the read index since
464 * the writer may start writing to the read area once the read index
465 * is updated.
466 */
467 mb();
468
469 /* Update the read index */
470 hv_set_next_read_location(inring_info, next_read_location);
471
472 *signal = hv_need_to_signal_on_read(inring_info);
473
474 return ret;
475}
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *
4 * Copyright (c) 2009, Microsoft Corporation.
5 *
6 * Authors:
7 * Haiyang Zhang <haiyangz@microsoft.com>
8 * Hank Janssen <hjanssen@microsoft.com>
9 * K. Y. Srinivasan <kys@microsoft.com>
10 */
11#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12
13#include <linux/kernel.h>
14#include <linux/mm.h>
15#include <linux/hyperv.h>
16#include <linux/uio.h>
17#include <linux/vmalloc.h>
18#include <linux/slab.h>
19#include <linux/prefetch.h>
20
21#include "hyperv_vmbus.h"
22
23#define VMBUS_PKT_TRAILER 8
24
25/*
26 * When we write to the ring buffer, check if the host needs to
27 * be signaled. Here is the details of this protocol:
28 *
29 * 1. The host guarantees that while it is draining the
30 * ring buffer, it will set the interrupt_mask to
31 * indicate it does not need to be interrupted when
32 * new data is placed.
33 *
34 * 2. The host guarantees that it will completely drain
35 * the ring buffer before exiting the read loop. Further,
36 * once the ring buffer is empty, it will clear the
37 * interrupt_mask and re-check to see if new data has
38 * arrived.
39 *
40 * KYS: Oct. 30, 2016:
41 * It looks like Windows hosts have logic to deal with DOS attacks that
42 * can be triggered if it receives interrupts when it is not expecting
43 * the interrupt. The host expects interrupts only when the ring
44 * transitions from empty to non-empty (or full to non full on the guest
45 * to host ring).
46 * So, base the signaling decision solely on the ring state until the
47 * host logic is fixed.
48 */
49
50static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
51{
52 struct hv_ring_buffer_info *rbi = &channel->outbound;
53
54 virt_mb();
55 if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
56 return;
57
58 /* check interrupt_mask before read_index */
59 virt_rmb();
60 /*
61 * This is the only case we need to signal when the
62 * ring transitions from being empty to non-empty.
63 */
64 if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
65 ++channel->intr_out_empty;
66 vmbus_setevent(channel);
67 }
68}
69
70/* Get the next write location for the specified ring buffer. */
71static inline u32
72hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
73{
74 u32 next = ring_info->ring_buffer->write_index;
75
76 return next;
77}
78
79/* Set the next write location for the specified ring buffer. */
80static inline void
81hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
82 u32 next_write_location)
83{
84 ring_info->ring_buffer->write_index = next_write_location;
85}
86
87/* Set the next read location for the specified ring buffer. */
88static inline void
89hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
90 u32 next_read_location)
91{
92 ring_info->ring_buffer->read_index = next_read_location;
93 ring_info->priv_read_index = next_read_location;
94}
95
96/* Get the size of the ring buffer. */
97static inline u32
98hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
99{
100 return ring_info->ring_datasize;
101}
102
103/* Get the read and write indices as u64 of the specified ring buffer. */
104static inline u64
105hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
106{
107 return (u64)ring_info->ring_buffer->write_index << 32;
108}
109
110/*
111 * Helper routine to copy from source to ring buffer.
112 * Assume there is enough room. Handles wrap-around in dest case only!!
113 */
114static u32 hv_copyto_ringbuffer(
115 struct hv_ring_buffer_info *ring_info,
116 u32 start_write_offset,
117 const void *src,
118 u32 srclen)
119{
120 void *ring_buffer = hv_get_ring_buffer(ring_info);
121 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
122
123 memcpy(ring_buffer + start_write_offset, src, srclen);
124
125 start_write_offset += srclen;
126 if (start_write_offset >= ring_buffer_size)
127 start_write_offset -= ring_buffer_size;
128
129 return start_write_offset;
130}
131
132/*
133 *
134 * hv_get_ringbuffer_availbytes()
135 *
136 * Get number of bytes available to read and to write to
137 * for the specified ring buffer
138 */
139static void
140hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
141 u32 *read, u32 *write)
142{
143 u32 read_loc, write_loc, dsize;
144
145 /* Capture the read/write indices before they changed */
146 read_loc = READ_ONCE(rbi->ring_buffer->read_index);
147 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
148 dsize = rbi->ring_datasize;
149
150 *write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
151 read_loc - write_loc;
152 *read = dsize - *write;
153}
154
155/* Get various debug metrics for the specified ring buffer. */
156int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
157 struct hv_ring_buffer_debug_info *debug_info)
158{
159 u32 bytes_avail_towrite;
160 u32 bytes_avail_toread;
161
162 mutex_lock(&ring_info->ring_buffer_mutex);
163
164 if (!ring_info->ring_buffer) {
165 mutex_unlock(&ring_info->ring_buffer_mutex);
166 return -EINVAL;
167 }
168
169 hv_get_ringbuffer_availbytes(ring_info,
170 &bytes_avail_toread,
171 &bytes_avail_towrite);
172 debug_info->bytes_avail_toread = bytes_avail_toread;
173 debug_info->bytes_avail_towrite = bytes_avail_towrite;
174 debug_info->current_read_index = ring_info->ring_buffer->read_index;
175 debug_info->current_write_index = ring_info->ring_buffer->write_index;
176 debug_info->current_interrupt_mask
177 = ring_info->ring_buffer->interrupt_mask;
178 mutex_unlock(&ring_info->ring_buffer_mutex);
179
180 return 0;
181}
182EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
183
184/* Initialize a channel's ring buffer info mutex locks */
185void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
186{
187 mutex_init(&channel->inbound.ring_buffer_mutex);
188 mutex_init(&channel->outbound.ring_buffer_mutex);
189}
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 /*
201 * First page holds struct hv_ring_buffer, do wraparound mapping for
202 * the rest.
203 */
204 pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *),
205 GFP_KERNEL);
206 if (!pages_wraparound)
207 return -ENOMEM;
208
209 pages_wraparound[0] = pages;
210 for (i = 0; i < 2 * (page_cnt - 1); i++)
211 pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
212
213 ring_info->ring_buffer = (struct hv_ring_buffer *)
214 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
215
216 kfree(pages_wraparound);
217
218
219 if (!ring_info->ring_buffer)
220 return -ENOMEM;
221
222 ring_info->ring_buffer->read_index =
223 ring_info->ring_buffer->write_index = 0;
224
225 /* Set the feature bit for enabling flow control. */
226 ring_info->ring_buffer->feature_bits.value = 1;
227
228 ring_info->ring_size = page_cnt << PAGE_SHIFT;
229 ring_info->ring_size_div10_reciprocal =
230 reciprocal_value(ring_info->ring_size / 10);
231 ring_info->ring_datasize = ring_info->ring_size -
232 sizeof(struct hv_ring_buffer);
233 ring_info->priv_read_index = 0;
234
235 spin_lock_init(&ring_info->ring_lock);
236
237 return 0;
238}
239
240/* Cleanup the ring buffer. */
241void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
242{
243 mutex_lock(&ring_info->ring_buffer_mutex);
244 vunmap(ring_info->ring_buffer);
245 ring_info->ring_buffer = NULL;
246 mutex_unlock(&ring_info->ring_buffer_mutex);
247}
248
249/* Write to the ring buffer. */
250int hv_ringbuffer_write(struct vmbus_channel *channel,
251 const struct kvec *kv_list, u32 kv_count)
252{
253 int i;
254 u32 bytes_avail_towrite;
255 u32 totalbytes_towrite = sizeof(u64);
256 u32 next_write_location;
257 u32 old_write;
258 u64 prev_indices;
259 unsigned long flags;
260 struct hv_ring_buffer_info *outring_info = &channel->outbound;
261
262 if (channel->rescind)
263 return -ENODEV;
264
265 for (i = 0; i < kv_count; i++)
266 totalbytes_towrite += kv_list[i].iov_len;
267
268 spin_lock_irqsave(&outring_info->ring_lock, flags);
269
270 bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
271
272 /*
273 * If there is only room for the packet, assume it is full.
274 * Otherwise, the next time around, we think the ring buffer
275 * is empty since the read index == write index.
276 */
277 if (bytes_avail_towrite <= totalbytes_towrite) {
278 ++channel->out_full_total;
279
280 if (!channel->out_full_flag) {
281 ++channel->out_full_first;
282 channel->out_full_flag = true;
283 }
284
285 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
286 return -EAGAIN;
287 }
288
289 channel->out_full_flag = false;
290
291 /* Write to the ring buffer */
292 next_write_location = hv_get_next_write_location(outring_info);
293
294 old_write = next_write_location;
295
296 for (i = 0; i < kv_count; i++) {
297 next_write_location = hv_copyto_ringbuffer(outring_info,
298 next_write_location,
299 kv_list[i].iov_base,
300 kv_list[i].iov_len);
301 }
302
303 /* Set previous packet start */
304 prev_indices = hv_get_ring_bufferindices(outring_info);
305
306 next_write_location = hv_copyto_ringbuffer(outring_info,
307 next_write_location,
308 &prev_indices,
309 sizeof(u64));
310
311 /* Issue a full memory barrier before updating the write index */
312 virt_mb();
313
314 /* Now, update the write location */
315 hv_set_next_write_location(outring_info, next_write_location);
316
317
318 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
319
320 hv_signal_on_write(old_write, channel);
321
322 if (channel->rescind)
323 return -ENODEV;
324
325 return 0;
326}
327
328int hv_ringbuffer_read(struct vmbus_channel *channel,
329 void *buffer, u32 buflen, u32 *buffer_actual_len,
330 u64 *requestid, bool raw)
331{
332 struct vmpacket_descriptor *desc;
333 u32 packetlen, offset;
334
335 if (unlikely(buflen == 0))
336 return -EINVAL;
337
338 *buffer_actual_len = 0;
339 *requestid = 0;
340
341 /* Make sure there is something to read */
342 desc = hv_pkt_iter_first(channel);
343 if (desc == NULL) {
344 /*
345 * No error is set when there is even no header, drivers are
346 * supposed to analyze buffer_actual_len.
347 */
348 return 0;
349 }
350
351 offset = raw ? 0 : (desc->offset8 << 3);
352 packetlen = (desc->len8 << 3) - offset;
353 *buffer_actual_len = packetlen;
354 *requestid = desc->trans_id;
355
356 if (unlikely(packetlen > buflen))
357 return -ENOBUFS;
358
359 /* since ring is double mapped, only one copy is necessary */
360 memcpy(buffer, (const char *)desc + offset, packetlen);
361
362 /* Advance ring index to next packet descriptor */
363 __hv_pkt_iter_next(channel, desc);
364
365 /* Notify host of update */
366 hv_pkt_iter_close(channel);
367
368 return 0;
369}
370
371/*
372 * Determine number of bytes available in ring buffer after
373 * the current iterator (priv_read_index) location.
374 *
375 * This is similar to hv_get_bytes_to_read but with private
376 * read index instead.
377 */
378static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
379{
380 u32 priv_read_loc = rbi->priv_read_index;
381 u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
382
383 if (write_loc >= priv_read_loc)
384 return write_loc - priv_read_loc;
385 else
386 return (rbi->ring_datasize - priv_read_loc) + write_loc;
387}
388
389/*
390 * Get first vmbus packet from ring buffer after read_index
391 *
392 * If ring buffer is empty, returns NULL and no other action needed.
393 */
394struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
395{
396 struct hv_ring_buffer_info *rbi = &channel->inbound;
397 struct vmpacket_descriptor *desc;
398
399 hv_debug_delay_test(channel, MESSAGE_DELAY);
400 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
401 return NULL;
402
403 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
404 if (desc)
405 prefetch((char *)desc + (desc->len8 << 3));
406
407 return desc;
408}
409EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
410
411/*
412 * Get next vmbus packet from ring buffer.
413 *
414 * Advances the current location (priv_read_index) and checks for more
415 * data. If the end of the ring buffer is reached, then return NULL.
416 */
417struct vmpacket_descriptor *
418__hv_pkt_iter_next(struct vmbus_channel *channel,
419 const struct vmpacket_descriptor *desc)
420{
421 struct hv_ring_buffer_info *rbi = &channel->inbound;
422 u32 packetlen = desc->len8 << 3;
423 u32 dsize = rbi->ring_datasize;
424
425 hv_debug_delay_test(channel, MESSAGE_DELAY);
426 /* bump offset to next potential packet */
427 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
428 if (rbi->priv_read_index >= dsize)
429 rbi->priv_read_index -= dsize;
430
431 /* more data? */
432 return hv_pkt_iter_first(channel);
433}
434EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
435
436/* How many bytes were read in this iterator cycle */
437static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
438 u32 start_read_index)
439{
440 if (rbi->priv_read_index >= start_read_index)
441 return rbi->priv_read_index - start_read_index;
442 else
443 return rbi->ring_datasize - start_read_index +
444 rbi->priv_read_index;
445}
446
447/*
448 * Update host ring buffer after iterating over packets. If the host has
449 * stopped queuing new entries because it found the ring buffer full, and
450 * sufficient space is being freed up, signal the host. But be careful to
451 * only signal the host when necessary, both for performance reasons and
452 * because Hyper-V protects itself by throttling guests that signal
453 * inappropriately.
454 *
455 * Determining when to signal is tricky. There are three key data inputs
456 * that must be handled in this order to avoid race conditions:
457 *
458 * 1. Update the read_index
459 * 2. Read the pending_send_sz
460 * 3. Read the current write_index
461 *
462 * The interrupt_mask is not used to determine when to signal. The
463 * interrupt_mask is used only on the guest->host ring buffer when
464 * sending requests to the host. The host does not use it on the host->
465 * guest ring buffer to indicate whether it should be signaled.
466 */
467void hv_pkt_iter_close(struct vmbus_channel *channel)
468{
469 struct hv_ring_buffer_info *rbi = &channel->inbound;
470 u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
471
472 /*
473 * Make sure all reads are done before we update the read index since
474 * the writer may start writing to the read area once the read index
475 * is updated.
476 */
477 virt_rmb();
478 start_read_index = rbi->ring_buffer->read_index;
479 rbi->ring_buffer->read_index = rbi->priv_read_index;
480
481 /*
482 * Older versions of Hyper-V (before WS2102 and Win8) do not
483 * implement pending_send_sz and simply poll if the host->guest
484 * ring buffer is full. No signaling is needed or expected.
485 */
486 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
487 return;
488
489 /*
490 * Issue a full memory barrier before making the signaling decision.
491 * If reading pending_send_sz were to be reordered and happen
492 * before we commit the new read_index, a race could occur. If the
493 * host were to set the pending_send_sz after we have sampled
494 * pending_send_sz, and the ring buffer blocks before we commit the
495 * read index, we could miss sending the interrupt. Issue a full
496 * memory barrier to address this.
497 */
498 virt_mb();
499
500 /*
501 * If the pending_send_sz is zero, then the ring buffer is not
502 * blocked and there is no need to signal. This is far by the
503 * most common case, so exit quickly for best performance.
504 */
505 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
506 if (!pending_sz)
507 return;
508
509 /*
510 * Ensure the read of write_index in hv_get_bytes_to_write()
511 * happens after the read of pending_send_sz.
512 */
513 virt_rmb();
514 curr_write_sz = hv_get_bytes_to_write(rbi);
515 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
516
517 /*
518 * We want to signal the host only if we're transitioning
519 * from a "not enough free space" state to a "enough free
520 * space" state. For example, it's possible that this function
521 * could run and free up enough space to signal the host, and then
522 * run again and free up additional space before the host has a
523 * chance to clear the pending_send_sz. The 2nd invocation would
524 * be a null transition from "enough free space" to "enough free
525 * space", which doesn't warrant a signal.
526 *
527 * Exactly filling the ring buffer is treated as "not enough
528 * space". The ring buffer always must have at least one byte
529 * empty so the empty and full conditions are distinguishable.
530 * hv_get_bytes_to_write() doesn't fully tell the truth in
531 * this regard.
532 *
533 * So first check if we were in the "enough free space" state
534 * before we began the iteration. If so, the host was not
535 * blocked, and there's no need to signal.
536 */
537 if (curr_write_sz - bytes_read > pending_sz)
538 return;
539
540 /*
541 * Similarly, if the new state is "not enough space", then
542 * there's no need to signal.
543 */
544 if (curr_write_sz <= pending_sz)
545 return;
546
547 ++channel->intr_in_full;
548 vmbus_setevent(channel);
549}
550EXPORT_SYMBOL_GPL(hv_pkt_iter_close);