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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#include <linux/io.h>
21#include <asm/mshyperv.h>
22
23#include "hyperv_vmbus.h"
24
25#define VMBUS_PKT_TRAILER 8
26
27/*
28 * When we write to the ring buffer, check if the host needs to
29 * be signaled. Here is the details of this protocol:
30 *
31 * 1. The host guarantees that while it is draining the
32 * ring buffer, it will set the interrupt_mask to
33 * indicate it does not need to be interrupted when
34 * new data is placed.
35 *
36 * 2. The host guarantees that it will completely drain
37 * the ring buffer before exiting the read loop. Further,
38 * once the ring buffer is empty, it will clear the
39 * interrupt_mask and re-check to see if new data has
40 * arrived.
41 *
42 * KYS: Oct. 30, 2016:
43 * It looks like Windows hosts have logic to deal with DOS attacks that
44 * can be triggered if it receives interrupts when it is not expecting
45 * the interrupt. The host expects interrupts only when the ring
46 * transitions from empty to non-empty (or full to non full on the guest
47 * to host ring).
48 * So, base the signaling decision solely on the ring state until the
49 * host logic is fixed.
50 */
51
52static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
53{
54 struct hv_ring_buffer_info *rbi = &channel->outbound;
55
56 virt_mb();
57 if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
58 return;
59
60 /* check interrupt_mask before read_index */
61 virt_rmb();
62 /*
63 * This is the only case we need to signal when the
64 * ring transitions from being empty to non-empty.
65 */
66 if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
67 ++channel->intr_out_empty;
68 vmbus_setevent(channel);
69 }
70}
71
72/* Get the next write location for the specified ring buffer. */
73static inline u32
74hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
75{
76 u32 next = ring_info->ring_buffer->write_index;
77
78 return next;
79}
80
81/* Set the next write location for the specified ring buffer. */
82static inline void
83hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
84 u32 next_write_location)
85{
86 ring_info->ring_buffer->write_index = next_write_location;
87}
88
89/* Get the size of the ring buffer. */
90static inline u32
91hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
92{
93 return ring_info->ring_datasize;
94}
95
96/* Get the read and write indices as u64 of the specified ring buffer. */
97static inline u64
98hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
99{
100 return (u64)ring_info->ring_buffer->write_index << 32;
101}
102
103/*
104 * Helper routine to copy from source to ring buffer.
105 * Assume there is enough room. Handles wrap-around in dest case only!!
106 */
107static u32 hv_copyto_ringbuffer(
108 struct hv_ring_buffer_info *ring_info,
109 u32 start_write_offset,
110 const void *src,
111 u32 srclen)
112{
113 void *ring_buffer = hv_get_ring_buffer(ring_info);
114 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
115
116 memcpy(ring_buffer + start_write_offset, src, srclen);
117
118 start_write_offset += srclen;
119 if (start_write_offset >= ring_buffer_size)
120 start_write_offset -= ring_buffer_size;
121
122 return start_write_offset;
123}
124
125/*
126 *
127 * hv_get_ringbuffer_availbytes()
128 *
129 * Get number of bytes available to read and to write to
130 * for the specified ring buffer
131 */
132static void
133hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
134 u32 *read, u32 *write)
135{
136 u32 read_loc, write_loc, dsize;
137
138 /* Capture the read/write indices before they changed */
139 read_loc = READ_ONCE(rbi->ring_buffer->read_index);
140 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
141 dsize = rbi->ring_datasize;
142
143 *write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
144 read_loc - write_loc;
145 *read = dsize - *write;
146}
147
148/* Get various debug metrics for the specified ring buffer. */
149int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
150 struct hv_ring_buffer_debug_info *debug_info)
151{
152 u32 bytes_avail_towrite;
153 u32 bytes_avail_toread;
154
155 mutex_lock(&ring_info->ring_buffer_mutex);
156
157 if (!ring_info->ring_buffer) {
158 mutex_unlock(&ring_info->ring_buffer_mutex);
159 return -EINVAL;
160 }
161
162 hv_get_ringbuffer_availbytes(ring_info,
163 &bytes_avail_toread,
164 &bytes_avail_towrite);
165 debug_info->bytes_avail_toread = bytes_avail_toread;
166 debug_info->bytes_avail_towrite = bytes_avail_towrite;
167 debug_info->current_read_index = ring_info->ring_buffer->read_index;
168 debug_info->current_write_index = ring_info->ring_buffer->write_index;
169 debug_info->current_interrupt_mask
170 = ring_info->ring_buffer->interrupt_mask;
171 mutex_unlock(&ring_info->ring_buffer_mutex);
172
173 return 0;
174}
175EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
176
177/* Initialize a channel's ring buffer info mutex locks */
178void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
179{
180 mutex_init(&channel->inbound.ring_buffer_mutex);
181 mutex_init(&channel->outbound.ring_buffer_mutex);
182}
183
184/* Initialize the ring buffer. */
185int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
186 struct page *pages, u32 page_cnt, u32 max_pkt_size)
187{
188 struct page **pages_wraparound;
189 int i;
190
191 BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
192
193 /*
194 * First page holds struct hv_ring_buffer, do wraparound mapping for
195 * the rest.
196 */
197 pages_wraparound = kcalloc(page_cnt * 2 - 1,
198 sizeof(struct page *),
199 GFP_KERNEL);
200 if (!pages_wraparound)
201 return -ENOMEM;
202
203 pages_wraparound[0] = pages;
204 for (i = 0; i < 2 * (page_cnt - 1); i++)
205 pages_wraparound[i + 1] =
206 &pages[i % (page_cnt - 1) + 1];
207
208 ring_info->ring_buffer = (struct hv_ring_buffer *)
209 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP,
210 pgprot_decrypted(PAGE_KERNEL));
211
212 kfree(pages_wraparound);
213 if (!ring_info->ring_buffer)
214 return -ENOMEM;
215
216 /*
217 * Ensure the header page is zero'ed since
218 * encryption status may have changed.
219 */
220 memset(ring_info->ring_buffer, 0, HV_HYP_PAGE_SIZE);
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 /* Initialize buffer that holds copies of incoming packets */
236 if (max_pkt_size) {
237 ring_info->pkt_buffer = kzalloc(max_pkt_size, GFP_KERNEL);
238 if (!ring_info->pkt_buffer)
239 return -ENOMEM;
240 ring_info->pkt_buffer_size = max_pkt_size;
241 }
242
243 spin_lock_init(&ring_info->ring_lock);
244
245 return 0;
246}
247
248/* Cleanup the ring buffer. */
249void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
250{
251 mutex_lock(&ring_info->ring_buffer_mutex);
252 vunmap(ring_info->ring_buffer);
253 ring_info->ring_buffer = NULL;
254 mutex_unlock(&ring_info->ring_buffer_mutex);
255
256 kfree(ring_info->pkt_buffer);
257 ring_info->pkt_buffer = NULL;
258 ring_info->pkt_buffer_size = 0;
259}
260
261/*
262 * Check if the ring buffer spinlock is available to take or not; used on
263 * atomic contexts, like panic path (see the Hyper-V framebuffer driver).
264 */
265
266bool hv_ringbuffer_spinlock_busy(struct vmbus_channel *channel)
267{
268 struct hv_ring_buffer_info *rinfo = &channel->outbound;
269
270 return spin_is_locked(&rinfo->ring_lock);
271}
272EXPORT_SYMBOL_GPL(hv_ringbuffer_spinlock_busy);
273
274/* Write to the ring buffer. */
275int hv_ringbuffer_write(struct vmbus_channel *channel,
276 const struct kvec *kv_list, u32 kv_count,
277 u64 requestid, u64 *trans_id)
278{
279 int i;
280 u32 bytes_avail_towrite;
281 u32 totalbytes_towrite = sizeof(u64);
282 u32 next_write_location;
283 u32 old_write;
284 u64 prev_indices;
285 unsigned long flags;
286 struct hv_ring_buffer_info *outring_info = &channel->outbound;
287 struct vmpacket_descriptor *desc = kv_list[0].iov_base;
288 u64 __trans_id, rqst_id = VMBUS_NO_RQSTOR;
289
290 if (channel->rescind)
291 return -ENODEV;
292
293 for (i = 0; i < kv_count; i++)
294 totalbytes_towrite += kv_list[i].iov_len;
295
296 spin_lock_irqsave(&outring_info->ring_lock, flags);
297
298 bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
299
300 /*
301 * If there is only room for the packet, assume it is full.
302 * Otherwise, the next time around, we think the ring buffer
303 * is empty since the read index == write index.
304 */
305 if (bytes_avail_towrite <= totalbytes_towrite) {
306 ++channel->out_full_total;
307
308 if (!channel->out_full_flag) {
309 ++channel->out_full_first;
310 channel->out_full_flag = true;
311 }
312
313 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
314 return -EAGAIN;
315 }
316
317 channel->out_full_flag = false;
318
319 /* Write to the ring buffer */
320 next_write_location = hv_get_next_write_location(outring_info);
321
322 old_write = next_write_location;
323
324 for (i = 0; i < kv_count; i++) {
325 next_write_location = hv_copyto_ringbuffer(outring_info,
326 next_write_location,
327 kv_list[i].iov_base,
328 kv_list[i].iov_len);
329 }
330
331 /*
332 * Allocate the request ID after the data has been copied into the
333 * ring buffer. Once this request ID is allocated, the completion
334 * path could find the data and free it.
335 */
336
337 if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) {
338 if (channel->next_request_id_callback != NULL) {
339 rqst_id = channel->next_request_id_callback(channel, requestid);
340 if (rqst_id == VMBUS_RQST_ERROR) {
341 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
342 return -EAGAIN;
343 }
344 }
345 }
346 desc = hv_get_ring_buffer(outring_info) + old_write;
347 __trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id;
348 /*
349 * Ensure the compiler doesn't generate code that reads the value of
350 * the transaction ID from the ring buffer, which is shared with the
351 * Hyper-V host and subject to being changed at any time.
352 */
353 WRITE_ONCE(desc->trans_id, __trans_id);
354 if (trans_id)
355 *trans_id = __trans_id;
356
357 /* Set previous packet start */
358 prev_indices = hv_get_ring_bufferindices(outring_info);
359
360 next_write_location = hv_copyto_ringbuffer(outring_info,
361 next_write_location,
362 &prev_indices,
363 sizeof(u64));
364
365 /* Issue a full memory barrier before updating the write index */
366 virt_mb();
367
368 /* Now, update the write location */
369 hv_set_next_write_location(outring_info, next_write_location);
370
371
372 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
373
374 hv_signal_on_write(old_write, channel);
375
376 if (channel->rescind) {
377 if (rqst_id != VMBUS_NO_RQSTOR) {
378 /* Reclaim request ID to avoid leak of IDs */
379 if (channel->request_addr_callback != NULL)
380 channel->request_addr_callback(channel, rqst_id);
381 }
382 return -ENODEV;
383 }
384
385 return 0;
386}
387
388int hv_ringbuffer_read(struct vmbus_channel *channel,
389 void *buffer, u32 buflen, u32 *buffer_actual_len,
390 u64 *requestid, bool raw)
391{
392 struct vmpacket_descriptor *desc;
393 u32 packetlen, offset;
394
395 if (unlikely(buflen == 0))
396 return -EINVAL;
397
398 *buffer_actual_len = 0;
399 *requestid = 0;
400
401 /* Make sure there is something to read */
402 desc = hv_pkt_iter_first(channel);
403 if (desc == NULL) {
404 /*
405 * No error is set when there is even no header, drivers are
406 * supposed to analyze buffer_actual_len.
407 */
408 return 0;
409 }
410
411 offset = raw ? 0 : (desc->offset8 << 3);
412 packetlen = (desc->len8 << 3) - offset;
413 *buffer_actual_len = packetlen;
414 *requestid = desc->trans_id;
415
416 if (unlikely(packetlen > buflen))
417 return -ENOBUFS;
418
419 /* since ring is double mapped, only one copy is necessary */
420 memcpy(buffer, (const char *)desc + offset, packetlen);
421
422 /* Advance ring index to next packet descriptor */
423 __hv_pkt_iter_next(channel, desc);
424
425 /* Notify host of update */
426 hv_pkt_iter_close(channel);
427
428 return 0;
429}
430
431/*
432 * Determine number of bytes available in ring buffer after
433 * the current iterator (priv_read_index) location.
434 *
435 * This is similar to hv_get_bytes_to_read but with private
436 * read index instead.
437 */
438static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
439{
440 u32 priv_read_loc = rbi->priv_read_index;
441 u32 write_loc;
442
443 /*
444 * The Hyper-V host writes the packet data, then uses
445 * store_release() to update the write_index. Use load_acquire()
446 * here to prevent loads of the packet data from being re-ordered
447 * before the read of the write_index and potentially getting
448 * stale data.
449 */
450 write_loc = virt_load_acquire(&rbi->ring_buffer->write_index);
451
452 if (write_loc >= priv_read_loc)
453 return write_loc - priv_read_loc;
454 else
455 return (rbi->ring_datasize - priv_read_loc) + write_loc;
456}
457
458/*
459 * Get first vmbus packet from ring buffer after read_index
460 *
461 * If ring buffer is empty, returns NULL and no other action needed.
462 */
463struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
464{
465 struct hv_ring_buffer_info *rbi = &channel->inbound;
466 struct vmpacket_descriptor *desc, *desc_copy;
467 u32 bytes_avail, pkt_len, pkt_offset;
468
469 hv_debug_delay_test(channel, MESSAGE_DELAY);
470
471 bytes_avail = hv_pkt_iter_avail(rbi);
472 if (bytes_avail < sizeof(struct vmpacket_descriptor))
473 return NULL;
474 bytes_avail = min(rbi->pkt_buffer_size, bytes_avail);
475
476 desc = (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi->priv_read_index);
477
478 /*
479 * Ensure the compiler does not use references to incoming Hyper-V values (which
480 * could change at any moment) when reading local variables later in the code
481 */
482 pkt_len = READ_ONCE(desc->len8) << 3;
483 pkt_offset = READ_ONCE(desc->offset8) << 3;
484
485 /*
486 * If pkt_len is invalid, set it to the smaller of hv_pkt_iter_avail() and
487 * rbi->pkt_buffer_size
488 */
489 if (pkt_len < sizeof(struct vmpacket_descriptor) || pkt_len > bytes_avail)
490 pkt_len = bytes_avail;
491
492 /*
493 * If pkt_offset is invalid, arbitrarily set it to
494 * the size of vmpacket_descriptor
495 */
496 if (pkt_offset < sizeof(struct vmpacket_descriptor) || pkt_offset > pkt_len)
497 pkt_offset = sizeof(struct vmpacket_descriptor);
498
499 /* Copy the Hyper-V packet out of the ring buffer */
500 desc_copy = (struct vmpacket_descriptor *)rbi->pkt_buffer;
501 memcpy(desc_copy, desc, pkt_len);
502
503 /*
504 * Hyper-V could still change len8 and offset8 after the earlier read.
505 * Ensure that desc_copy has legal values for len8 and offset8 that
506 * are consistent with the copy we just made
507 */
508 desc_copy->len8 = pkt_len >> 3;
509 desc_copy->offset8 = pkt_offset >> 3;
510
511 return desc_copy;
512}
513EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
514
515/*
516 * Get next vmbus packet from ring buffer.
517 *
518 * Advances the current location (priv_read_index) and checks for more
519 * data. If the end of the ring buffer is reached, then return NULL.
520 */
521struct vmpacket_descriptor *
522__hv_pkt_iter_next(struct vmbus_channel *channel,
523 const struct vmpacket_descriptor *desc)
524{
525 struct hv_ring_buffer_info *rbi = &channel->inbound;
526 u32 packetlen = desc->len8 << 3;
527 u32 dsize = rbi->ring_datasize;
528
529 hv_debug_delay_test(channel, MESSAGE_DELAY);
530 /* bump offset to next potential packet */
531 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
532 if (rbi->priv_read_index >= dsize)
533 rbi->priv_read_index -= dsize;
534
535 /* more data? */
536 return hv_pkt_iter_first(channel);
537}
538EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
539
540/* How many bytes were read in this iterator cycle */
541static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
542 u32 start_read_index)
543{
544 if (rbi->priv_read_index >= start_read_index)
545 return rbi->priv_read_index - start_read_index;
546 else
547 return rbi->ring_datasize - start_read_index +
548 rbi->priv_read_index;
549}
550
551/*
552 * Update host ring buffer after iterating over packets. If the host has
553 * stopped queuing new entries because it found the ring buffer full, and
554 * sufficient space is being freed up, signal the host. But be careful to
555 * only signal the host when necessary, both for performance reasons and
556 * because Hyper-V protects itself by throttling guests that signal
557 * inappropriately.
558 *
559 * Determining when to signal is tricky. There are three key data inputs
560 * that must be handled in this order to avoid race conditions:
561 *
562 * 1. Update the read_index
563 * 2. Read the pending_send_sz
564 * 3. Read the current write_index
565 *
566 * The interrupt_mask is not used to determine when to signal. The
567 * interrupt_mask is used only on the guest->host ring buffer when
568 * sending requests to the host. The host does not use it on the host->
569 * guest ring buffer to indicate whether it should be signaled.
570 */
571void hv_pkt_iter_close(struct vmbus_channel *channel)
572{
573 struct hv_ring_buffer_info *rbi = &channel->inbound;
574 u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
575
576 /*
577 * Make sure all reads are done before we update the read index since
578 * the writer may start writing to the read area once the read index
579 * is updated.
580 */
581 virt_rmb();
582 start_read_index = rbi->ring_buffer->read_index;
583 rbi->ring_buffer->read_index = rbi->priv_read_index;
584
585 /*
586 * Older versions of Hyper-V (before WS2102 and Win8) do not
587 * implement pending_send_sz and simply poll if the host->guest
588 * ring buffer is full. No signaling is needed or expected.
589 */
590 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
591 return;
592
593 /*
594 * Issue a full memory barrier before making the signaling decision.
595 * If reading pending_send_sz were to be reordered and happen
596 * before we commit the new read_index, a race could occur. If the
597 * host were to set the pending_send_sz after we have sampled
598 * pending_send_sz, and the ring buffer blocks before we commit the
599 * read index, we could miss sending the interrupt. Issue a full
600 * memory barrier to address this.
601 */
602 virt_mb();
603
604 /*
605 * If the pending_send_sz is zero, then the ring buffer is not
606 * blocked and there is no need to signal. This is far by the
607 * most common case, so exit quickly for best performance.
608 */
609 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
610 if (!pending_sz)
611 return;
612
613 /*
614 * Ensure the read of write_index in hv_get_bytes_to_write()
615 * happens after the read of pending_send_sz.
616 */
617 virt_rmb();
618 curr_write_sz = hv_get_bytes_to_write(rbi);
619 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
620
621 /*
622 * We want to signal the host only if we're transitioning
623 * from a "not enough free space" state to a "enough free
624 * space" state. For example, it's possible that this function
625 * could run and free up enough space to signal the host, and then
626 * run again and free up additional space before the host has a
627 * chance to clear the pending_send_sz. The 2nd invocation would
628 * be a null transition from "enough free space" to "enough free
629 * space", which doesn't warrant a signal.
630 *
631 * Exactly filling the ring buffer is treated as "not enough
632 * space". The ring buffer always must have at least one byte
633 * empty so the empty and full conditions are distinguishable.
634 * hv_get_bytes_to_write() doesn't fully tell the truth in
635 * this regard.
636 *
637 * So first check if we were in the "enough free space" state
638 * before we began the iteration. If so, the host was not
639 * blocked, and there's no need to signal.
640 */
641 if (curr_write_sz - bytes_read > pending_sz)
642 return;
643
644 /*
645 * Similarly, if the new state is "not enough space", then
646 * there's no need to signal.
647 */
648 if (curr_write_sz <= pending_sz)
649 return;
650
651 ++channel->intr_in_full;
652 vmbus_setevent(channel);
653}
654EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
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 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
400 return NULL;
401
402 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
403 if (desc)
404 prefetch((char *)desc + (desc->len8 << 3));
405
406 return desc;
407}
408EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
409
410/*
411 * Get next vmbus packet from ring buffer.
412 *
413 * Advances the current location (priv_read_index) and checks for more
414 * data. If the end of the ring buffer is reached, then return NULL.
415 */
416struct vmpacket_descriptor *
417__hv_pkt_iter_next(struct vmbus_channel *channel,
418 const struct vmpacket_descriptor *desc)
419{
420 struct hv_ring_buffer_info *rbi = &channel->inbound;
421 u32 packetlen = desc->len8 << 3;
422 u32 dsize = rbi->ring_datasize;
423
424 /* bump offset to next potential packet */
425 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
426 if (rbi->priv_read_index >= dsize)
427 rbi->priv_read_index -= dsize;
428
429 /* more data? */
430 return hv_pkt_iter_first(channel);
431}
432EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
433
434/* How many bytes were read in this iterator cycle */
435static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
436 u32 start_read_index)
437{
438 if (rbi->priv_read_index >= start_read_index)
439 return rbi->priv_read_index - start_read_index;
440 else
441 return rbi->ring_datasize - start_read_index +
442 rbi->priv_read_index;
443}
444
445/*
446 * Update host ring buffer after iterating over packets. If the host has
447 * stopped queuing new entries because it found the ring buffer full, and
448 * sufficient space is being freed up, signal the host. But be careful to
449 * only signal the host when necessary, both for performance reasons and
450 * because Hyper-V protects itself by throttling guests that signal
451 * inappropriately.
452 *
453 * Determining when to signal is tricky. There are three key data inputs
454 * that must be handled in this order to avoid race conditions:
455 *
456 * 1. Update the read_index
457 * 2. Read the pending_send_sz
458 * 3. Read the current write_index
459 *
460 * The interrupt_mask is not used to determine when to signal. The
461 * interrupt_mask is used only on the guest->host ring buffer when
462 * sending requests to the host. The host does not use it on the host->
463 * guest ring buffer to indicate whether it should be signaled.
464 */
465void hv_pkt_iter_close(struct vmbus_channel *channel)
466{
467 struct hv_ring_buffer_info *rbi = &channel->inbound;
468 u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
469
470 /*
471 * Make sure all reads are done before we update the read index since
472 * the writer may start writing to the read area once the read index
473 * is updated.
474 */
475 virt_rmb();
476 start_read_index = rbi->ring_buffer->read_index;
477 rbi->ring_buffer->read_index = rbi->priv_read_index;
478
479 /*
480 * Older versions of Hyper-V (before WS2102 and Win8) do not
481 * implement pending_send_sz and simply poll if the host->guest
482 * ring buffer is full. No signaling is needed or expected.
483 */
484 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
485 return;
486
487 /*
488 * Issue a full memory barrier before making the signaling decision.
489 * If reading pending_send_sz were to be reordered and happen
490 * before we commit the new read_index, a race could occur. If the
491 * host were to set the pending_send_sz after we have sampled
492 * pending_send_sz, and the ring buffer blocks before we commit the
493 * read index, we could miss sending the interrupt. Issue a full
494 * memory barrier to address this.
495 */
496 virt_mb();
497
498 /*
499 * If the pending_send_sz is zero, then the ring buffer is not
500 * blocked and there is no need to signal. This is far by the
501 * most common case, so exit quickly for best performance.
502 */
503 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
504 if (!pending_sz)
505 return;
506
507 /*
508 * Ensure the read of write_index in hv_get_bytes_to_write()
509 * happens after the read of pending_send_sz.
510 */
511 virt_rmb();
512 curr_write_sz = hv_get_bytes_to_write(rbi);
513 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
514
515 /*
516 * We want to signal the host only if we're transitioning
517 * from a "not enough free space" state to a "enough free
518 * space" state. For example, it's possible that this function
519 * could run and free up enough space to signal the host, and then
520 * run again and free up additional space before the host has a
521 * chance to clear the pending_send_sz. The 2nd invocation would
522 * be a null transition from "enough free space" to "enough free
523 * space", which doesn't warrant a signal.
524 *
525 * Exactly filling the ring buffer is treated as "not enough
526 * space". The ring buffer always must have at least one byte
527 * empty so the empty and full conditions are distinguishable.
528 * hv_get_bytes_to_write() doesn't fully tell the truth in
529 * this regard.
530 *
531 * So first check if we were in the "enough free space" state
532 * before we began the iteration. If so, the host was not
533 * blocked, and there's no need to signal.
534 */
535 if (curr_write_sz - bytes_read > pending_sz)
536 return;
537
538 /*
539 * Similarly, if the new state is "not enough space", then
540 * there's no need to signal.
541 */
542 if (curr_write_sz <= pending_sz)
543 return;
544
545 ++channel->intr_in_full;
546 vmbus_setevent(channel);
547}
548EXPORT_SYMBOL_GPL(hv_pkt_iter_close);