1 // SPDX-License-Identifier: GPL-2.0-only
4 * Copyright (c) 2009, Microsoft Corporation.
7 * Haiyang Zhang <haiyangz@microsoft.com>
8 * Hank Janssen <hjanssen@microsoft.com>
9 * K. Y. Srinivasan <kys@microsoft.com>
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13 #include <linux/kernel.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>
21 #include "hyperv_vmbus.h"
23 #define VMBUS_PKT_TRAILER 8
26 * When we write to the ring buffer, check if the host needs to
27 * be signaled. Here is the details of this protocol:
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
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
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
46 * So, base the signaling decision solely on the ring state until the
47 * host logic is fixed.
50 static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
52 struct hv_ring_buffer_info *rbi = &channel->outbound;
55 if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
58 /* check interrupt_mask before read_index */
61 * This is the only case we need to signal when the
62 * ring transitions from being empty to non-empty.
64 if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
65 ++channel->intr_out_empty;
66 vmbus_setevent(channel);
70 /* Get the next write location for the specified ring buffer. */
72 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
74 u32 next = ring_info->ring_buffer->write_index;
79 /* Set the next write location for the specified ring buffer. */
81 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
82 u32 next_write_location)
84 ring_info->ring_buffer->write_index = next_write_location;
87 /* Get the size of the ring buffer. */
89 hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
91 return ring_info->ring_datasize;
94 /* Get the read and write indices as u64 of the specified ring buffer. */
96 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
98 return (u64)ring_info->ring_buffer->write_index << 32;
102 * Helper routine to copy from source to ring buffer.
103 * Assume there is enough room. Handles wrap-around in dest case only!!
105 static u32 hv_copyto_ringbuffer(
106 struct hv_ring_buffer_info *ring_info,
107 u32 start_write_offset,
111 void *ring_buffer = hv_get_ring_buffer(ring_info);
112 u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
114 memcpy(ring_buffer + start_write_offset, src, srclen);
116 start_write_offset += srclen;
117 if (start_write_offset >= ring_buffer_size)
118 start_write_offset -= ring_buffer_size;
120 return start_write_offset;
125 * hv_get_ringbuffer_availbytes()
127 * Get number of bytes available to read and to write to
128 * for the specified ring buffer
131 hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
132 u32 *read, u32 *write)
134 u32 read_loc, write_loc, dsize;
136 /* Capture the read/write indices before they changed */
137 read_loc = READ_ONCE(rbi->ring_buffer->read_index);
138 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
139 dsize = rbi->ring_datasize;
141 *write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
142 read_loc - write_loc;
143 *read = dsize - *write;
146 /* Get various debug metrics for the specified ring buffer. */
147 int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
148 struct hv_ring_buffer_debug_info *debug_info)
150 u32 bytes_avail_towrite;
151 u32 bytes_avail_toread;
153 mutex_lock(&ring_info->ring_buffer_mutex);
155 if (!ring_info->ring_buffer) {
156 mutex_unlock(&ring_info->ring_buffer_mutex);
160 hv_get_ringbuffer_availbytes(ring_info,
162 &bytes_avail_towrite);
163 debug_info->bytes_avail_toread = bytes_avail_toread;
164 debug_info->bytes_avail_towrite = bytes_avail_towrite;
165 debug_info->current_read_index = ring_info->ring_buffer->read_index;
166 debug_info->current_write_index = ring_info->ring_buffer->write_index;
167 debug_info->current_interrupt_mask
168 = ring_info->ring_buffer->interrupt_mask;
169 mutex_unlock(&ring_info->ring_buffer_mutex);
173 EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
175 /* Initialize a channel's ring buffer info mutex locks */
176 void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
178 mutex_init(&channel->inbound.ring_buffer_mutex);
179 mutex_init(&channel->outbound.ring_buffer_mutex);
182 /* Initialize the ring buffer. */
183 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
184 struct page *pages, u32 page_cnt)
187 struct page **pages_wraparound;
189 BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
192 * First page holds struct hv_ring_buffer, do wraparound mapping for
195 pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *),
197 if (!pages_wraparound)
200 pages_wraparound[0] = pages;
201 for (i = 0; i < 2 * (page_cnt - 1); i++)
202 pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
204 ring_info->ring_buffer = (struct hv_ring_buffer *)
205 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
207 kfree(pages_wraparound);
210 if (!ring_info->ring_buffer)
213 ring_info->ring_buffer->read_index =
214 ring_info->ring_buffer->write_index = 0;
216 /* Set the feature bit for enabling flow control. */
217 ring_info->ring_buffer->feature_bits.value = 1;
219 ring_info->ring_size = page_cnt << PAGE_SHIFT;
220 ring_info->ring_size_div10_reciprocal =
221 reciprocal_value(ring_info->ring_size / 10);
222 ring_info->ring_datasize = ring_info->ring_size -
223 sizeof(struct hv_ring_buffer);
224 ring_info->priv_read_index = 0;
226 spin_lock_init(&ring_info->ring_lock);
231 /* Cleanup the ring buffer. */
232 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
234 mutex_lock(&ring_info->ring_buffer_mutex);
235 vunmap(ring_info->ring_buffer);
236 ring_info->ring_buffer = NULL;
237 mutex_unlock(&ring_info->ring_buffer_mutex);
240 /* Write to the ring buffer. */
241 int hv_ringbuffer_write(struct vmbus_channel *channel,
242 const struct kvec *kv_list, u32 kv_count,
246 u32 bytes_avail_towrite;
247 u32 totalbytes_towrite = sizeof(u64);
248 u32 next_write_location;
252 struct hv_ring_buffer_info *outring_info = &channel->outbound;
253 struct vmpacket_descriptor *desc = kv_list[0].iov_base;
254 u64 rqst_id = VMBUS_NO_RQSTOR;
256 if (channel->rescind)
259 for (i = 0; i < kv_count; i++)
260 totalbytes_towrite += kv_list[i].iov_len;
262 spin_lock_irqsave(&outring_info->ring_lock, flags);
264 bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
267 * If there is only room for the packet, assume it is full.
268 * Otherwise, the next time around, we think the ring buffer
269 * is empty since the read index == write index.
271 if (bytes_avail_towrite <= totalbytes_towrite) {
272 ++channel->out_full_total;
274 if (!channel->out_full_flag) {
275 ++channel->out_full_first;
276 channel->out_full_flag = true;
279 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
283 channel->out_full_flag = false;
285 /* Write to the ring buffer */
286 next_write_location = hv_get_next_write_location(outring_info);
288 old_write = next_write_location;
290 for (i = 0; i < kv_count; i++) {
291 next_write_location = hv_copyto_ringbuffer(outring_info,
298 * Allocate the request ID after the data has been copied into the
299 * ring buffer. Once this request ID is allocated, the completion
300 * path could find the data and free it.
303 if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) {
304 rqst_id = vmbus_next_request_id(&channel->requestor, requestid);
305 if (rqst_id == VMBUS_RQST_ERROR) {
306 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
310 desc = hv_get_ring_buffer(outring_info) + old_write;
311 desc->trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id;
313 /* Set previous packet start */
314 prev_indices = hv_get_ring_bufferindices(outring_info);
316 next_write_location = hv_copyto_ringbuffer(outring_info,
321 /* Issue a full memory barrier before updating the write index */
324 /* Now, update the write location */
325 hv_set_next_write_location(outring_info, next_write_location);
328 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
330 hv_signal_on_write(old_write, channel);
332 if (channel->rescind) {
333 if (rqst_id != VMBUS_NO_RQSTOR) {
334 /* Reclaim request ID to avoid leak of IDs */
335 vmbus_request_addr(&channel->requestor, rqst_id);
343 int hv_ringbuffer_read(struct vmbus_channel *channel,
344 void *buffer, u32 buflen, u32 *buffer_actual_len,
345 u64 *requestid, bool raw)
347 struct vmpacket_descriptor *desc;
348 u32 packetlen, offset;
350 if (unlikely(buflen == 0))
353 *buffer_actual_len = 0;
356 /* Make sure there is something to read */
357 desc = hv_pkt_iter_first(channel);
360 * No error is set when there is even no header, drivers are
361 * supposed to analyze buffer_actual_len.
366 offset = raw ? 0 : (desc->offset8 << 3);
367 packetlen = (desc->len8 << 3) - offset;
368 *buffer_actual_len = packetlen;
369 *requestid = desc->trans_id;
371 if (unlikely(packetlen > buflen))
374 /* since ring is double mapped, only one copy is necessary */
375 memcpy(buffer, (const char *)desc + offset, packetlen);
377 /* Advance ring index to next packet descriptor */
378 __hv_pkt_iter_next(channel, desc);
380 /* Notify host of update */
381 hv_pkt_iter_close(channel);
387 * Determine number of bytes available in ring buffer after
388 * the current iterator (priv_read_index) location.
390 * This is similar to hv_get_bytes_to_read but with private
391 * read index instead.
393 static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
395 u32 priv_read_loc = rbi->priv_read_index;
396 u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
398 if (write_loc >= priv_read_loc)
399 return write_loc - priv_read_loc;
401 return (rbi->ring_datasize - priv_read_loc) + write_loc;
405 * Get first vmbus packet from ring buffer after read_index
407 * If ring buffer is empty, returns NULL and no other action needed.
409 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
411 struct hv_ring_buffer_info *rbi = &channel->inbound;
412 struct vmpacket_descriptor *desc;
414 hv_debug_delay_test(channel, MESSAGE_DELAY);
415 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
418 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
420 prefetch((char *)desc + (desc->len8 << 3));
424 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
427 * Get next vmbus packet from ring buffer.
429 * Advances the current location (priv_read_index) and checks for more
430 * data. If the end of the ring buffer is reached, then return NULL.
432 struct vmpacket_descriptor *
433 __hv_pkt_iter_next(struct vmbus_channel *channel,
434 const struct vmpacket_descriptor *desc)
436 struct hv_ring_buffer_info *rbi = &channel->inbound;
437 u32 packetlen = desc->len8 << 3;
438 u32 dsize = rbi->ring_datasize;
440 hv_debug_delay_test(channel, MESSAGE_DELAY);
441 /* bump offset to next potential packet */
442 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
443 if (rbi->priv_read_index >= dsize)
444 rbi->priv_read_index -= dsize;
447 return hv_pkt_iter_first(channel);
449 EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
451 /* How many bytes were read in this iterator cycle */
452 static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
453 u32 start_read_index)
455 if (rbi->priv_read_index >= start_read_index)
456 return rbi->priv_read_index - start_read_index;
458 return rbi->ring_datasize - start_read_index +
459 rbi->priv_read_index;
463 * Update host ring buffer after iterating over packets. If the host has
464 * stopped queuing new entries because it found the ring buffer full, and
465 * sufficient space is being freed up, signal the host. But be careful to
466 * only signal the host when necessary, both for performance reasons and
467 * because Hyper-V protects itself by throttling guests that signal
470 * Determining when to signal is tricky. There are three key data inputs
471 * that must be handled in this order to avoid race conditions:
473 * 1. Update the read_index
474 * 2. Read the pending_send_sz
475 * 3. Read the current write_index
477 * The interrupt_mask is not used to determine when to signal. The
478 * interrupt_mask is used only on the guest->host ring buffer when
479 * sending requests to the host. The host does not use it on the host->
480 * guest ring buffer to indicate whether it should be signaled.
482 void hv_pkt_iter_close(struct vmbus_channel *channel)
484 struct hv_ring_buffer_info *rbi = &channel->inbound;
485 u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
488 * Make sure all reads are done before we update the read index since
489 * the writer may start writing to the read area once the read index
493 start_read_index = rbi->ring_buffer->read_index;
494 rbi->ring_buffer->read_index = rbi->priv_read_index;
497 * Older versions of Hyper-V (before WS2102 and Win8) do not
498 * implement pending_send_sz and simply poll if the host->guest
499 * ring buffer is full. No signaling is needed or expected.
501 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
505 * Issue a full memory barrier before making the signaling decision.
506 * If reading pending_send_sz were to be reordered and happen
507 * before we commit the new read_index, a race could occur. If the
508 * host were to set the pending_send_sz after we have sampled
509 * pending_send_sz, and the ring buffer blocks before we commit the
510 * read index, we could miss sending the interrupt. Issue a full
511 * memory barrier to address this.
516 * If the pending_send_sz is zero, then the ring buffer is not
517 * blocked and there is no need to signal. This is far by the
518 * most common case, so exit quickly for best performance.
520 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
525 * Ensure the read of write_index in hv_get_bytes_to_write()
526 * happens after the read of pending_send_sz.
529 curr_write_sz = hv_get_bytes_to_write(rbi);
530 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
533 * We want to signal the host only if we're transitioning
534 * from a "not enough free space" state to a "enough free
535 * space" state. For example, it's possible that this function
536 * could run and free up enough space to signal the host, and then
537 * run again and free up additional space before the host has a
538 * chance to clear the pending_send_sz. The 2nd invocation would
539 * be a null transition from "enough free space" to "enough free
540 * space", which doesn't warrant a signal.
542 * Exactly filling the ring buffer is treated as "not enough
543 * space". The ring buffer always must have at least one byte
544 * empty so the empty and full conditions are distinguishable.
545 * hv_get_bytes_to_write() doesn't fully tell the truth in
548 * So first check if we were in the "enough free space" state
549 * before we began the iteration. If so, the host was not
550 * blocked, and there's no need to signal.
552 if (curr_write_sz - bytes_read > pending_sz)
556 * Similarly, if the new state is "not enough space", then
557 * there's no need to signal.
559 if (curr_write_sz <= pending_sz)
562 ++channel->intr_in_full;
563 vmbus_setevent(channel);
565 EXPORT_SYMBOL_GPL(hv_pkt_iter_close);