drivers/hv/ring_buffer.c

   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
  50 static 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. */
  71 static inline u32
  72 hv_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. */
  80 static inline void
  81 hv_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 /* Get the size of the ring buffer. */
  88 static inline u32
  89 hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
  90 {
  91         return ring_info->ring_datasize;
  92 }
  93
  94 /* Get the read and write indices as u64 of the specified ring buffer. */
  95 static inline u64
  96 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
  97 {
  98         return (u64)ring_info->ring_buffer->write_index << 32;
  99 }
 100
 101 /*
 102  * Helper routine to copy from source to ring buffer.
 103  * Assume there is enough room. Handles wrap-around in dest case only!!
 104  */
 105 static u32 hv_copyto_ringbuffer(
 106         struct hv_ring_buffer_info      *ring_info,
 107         u32                             start_write_offset,
 108         const void                      *src,
 109         u32                             srclen)
 110 {
 111         void *ring_buffer = hv_get_ring_buffer(ring_info);
 112         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 113
 114         memcpy(ring_buffer + start_write_offset, src, srclen);
 115
 116         start_write_offset += srclen;
 117         if (start_write_offset >= ring_buffer_size)
 118                 start_write_offset -= ring_buffer_size;
 119
 120         return start_write_offset;
 121 }
 122
 123 /*
 124  *
 125  * hv_get_ringbuffer_availbytes()
 126  *
 127  * Get number of bytes available to read and to write to
 128  * for the specified ring buffer
 129  */
 130 static void
 131 hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
 132                              u32 *read, u32 *write)
 133 {
 134         u32 read_loc, write_loc, dsize;
 135
 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;
 140
 141         *write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
 142                 read_loc - write_loc;
 143         *read = dsize - *write;
 144 }
 145
 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)
 149 {
 150         u32 bytes_avail_towrite;
 151         u32 bytes_avail_toread;
 152
 153         mutex_lock(&ring_info->ring_buffer_mutex);
 154
 155         if (!ring_info->ring_buffer) {
 156                 mutex_unlock(&ring_info->ring_buffer_mutex);
 157                 return -EINVAL;
 158         }
 159
 160         hv_get_ringbuffer_availbytes(ring_info,
 161                                      &bytes_avail_toread,
 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);
 170
 171         return 0;
 172 }
 173 EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
 174
 175 /* Initialize a channel's ring buffer info mutex locks */
 176 void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
 177 {
 178         mutex_init(&channel->inbound.ring_buffer_mutex);
 179         mutex_init(&channel->outbound.ring_buffer_mutex);
 180 }
 181
 182 /* Initialize the ring buffer. */
 183 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 184                        struct page *pages, u32 page_cnt)
 185 {
 186         int i;
 187         struct page **pages_wraparound;
 188
 189         BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
 190
 191         /*
 192          * First page holds struct hv_ring_buffer, do wraparound mapping for
 193          * the rest.
 194          */
 195         pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *),
 196                                    GFP_KERNEL);
 197         if (!pages_wraparound)
 198                 return -ENOMEM;
 199
 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];
 203
 204         ring_info->ring_buffer = (struct hv_ring_buffer *)
 205                 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
 206
 207         kfree(pages_wraparound);
 208
 209
 210         if (!ring_info->ring_buffer)
 211                 return -ENOMEM;
 212
 213         ring_info->ring_buffer->read_index =
 214                 ring_info->ring_buffer->write_index = 0;
 215
 216         /* Set the feature bit for enabling flow control. */
 217         ring_info->ring_buffer->feature_bits.value = 1;
 218
 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;
 225
 226         spin_lock_init(&ring_info->ring_lock);
 227
 228         return 0;
 229 }
 230
 231 /* Cleanup the ring buffer. */
 232 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 233 {
 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);
 238 }
 239
 240 /* Write to the ring buffer. */
 241 int hv_ringbuffer_write(struct vmbus_channel *channel,
 242                         const struct kvec *kv_list, u32 kv_count,
 243                         u64 requestid)
 244 {
 245         int i;
 246         u32 bytes_avail_towrite;
 247         u32 totalbytes_towrite = sizeof(u64);
 248         u32 next_write_location;
 249         u32 old_write;
 250         u64 prev_indices;
 251         unsigned long flags;
 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;
 255
 256         if (channel->rescind)
 257                 return -ENODEV;
 258
 259         for (i = 0; i < kv_count; i++)
 260                 totalbytes_towrite += kv_list[i].iov_len;
 261
 262         spin_lock_irqsave(&outring_info->ring_lock, flags);
 263
 264         bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
 265
 266         /*
 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.
 270          */
 271         if (bytes_avail_towrite <= totalbytes_towrite) {
 272                 ++channel->out_full_total;
 273
 274                 if (!channel->out_full_flag) {
 275                         ++channel->out_full_first;
 276                         channel->out_full_flag = true;
 277                 }
 278
 279                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 280                 return -EAGAIN;
 281         }
 282
 283         channel->out_full_flag = false;
 284
 285         /* Write to the ring buffer */
 286         next_write_location = hv_get_next_write_location(outring_info);
 287
 288         old_write = next_write_location;
 289
 290         for (i = 0; i < kv_count; i++) {
 291                 next_write_location = hv_copyto_ringbuffer(outring_info,
 292                                                      next_write_location,
 293                                                      kv_list[i].iov_base,
 294                                                      kv_list[i].iov_len);
 295         }
 296
 297         /*
 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.
 301          */
 302
 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);
 307                         return -EAGAIN;
 308                 }
 309         }
 310         desc = hv_get_ring_buffer(outring_info) + old_write;
 311         desc->trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id;
 312
 313         /* Set previous packet start */
 314         prev_indices = hv_get_ring_bufferindices(outring_info);
 315
 316         next_write_location = hv_copyto_ringbuffer(outring_info,
 317                                              next_write_location,
 318                                              &prev_indices,
 319                                              sizeof(u64));
 320
 321         /* Issue a full memory barrier before updating the write index */
 322         virt_mb();
 323
 324         /* Now, update the write location */
 325         hv_set_next_write_location(outring_info, next_write_location);
 326
 327
 328         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 329
 330         hv_signal_on_write(old_write, channel);
 331
 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);
 336                 }
 337                 return -ENODEV;
 338         }
 339
 340         return 0;
 341 }
 342
 343 int hv_ringbuffer_read(struct vmbus_channel *channel,
 344                        void *buffer, u32 buflen, u32 *buffer_actual_len,
 345                        u64 *requestid, bool raw)
 346 {
 347         struct vmpacket_descriptor *desc;
 348         u32 packetlen, offset;
 349
 350         if (unlikely(buflen == 0))
 351                 return -EINVAL;
 352
 353         *buffer_actual_len = 0;
 354         *requestid = 0;
 355
 356         /* Make sure there is something to read */
 357         desc = hv_pkt_iter_first(channel);
 358         if (desc == NULL) {
 359                 /*
 360                  * No error is set when there is even no header, drivers are
 361                  * supposed to analyze buffer_actual_len.
 362                  */
 363                 return 0;
 364         }
 365
 366         offset = raw ? 0 : (desc->offset8 << 3);
 367         packetlen = (desc->len8 << 3) - offset;
 368         *buffer_actual_len = packetlen;
 369         *requestid = desc->trans_id;
 370
 371         if (unlikely(packetlen > buflen))
 372                 return -ENOBUFS;
 373
 374         /* since ring is double mapped, only one copy is necessary */
 375         memcpy(buffer, (const char *)desc + offset, packetlen);
 376
 377         /* Advance ring index to next packet descriptor */
 378         __hv_pkt_iter_next(channel, desc);
 379
 380         /* Notify host of update */
 381         hv_pkt_iter_close(channel);
 382
 383         return 0;
 384 }
 385
 386 /*
 387  * Determine number of bytes available in ring buffer after
 388  * the current iterator (priv_read_index) location.
 389  *
 390  * This is similar to hv_get_bytes_to_read but with private
 391  * read index instead.
 392  */
 393 static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
 394 {
 395         u32 priv_read_loc = rbi->priv_read_index;
 396         u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
 397
 398         if (write_loc >= priv_read_loc)
 399                 return write_loc - priv_read_loc;
 400         else
 401                 return (rbi->ring_datasize - priv_read_loc) + write_loc;
 402 }
 403
 404 /*
 405  * Get first vmbus packet from ring buffer after read_index
 406  *
 407  * If ring buffer is empty, returns NULL and no other action needed.
 408  */
 409 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
 410 {
 411         struct hv_ring_buffer_info *rbi = &channel->inbound;
 412         struct vmpacket_descriptor *desc;
 413
 414         hv_debug_delay_test(channel, MESSAGE_DELAY);
 415         if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
 416                 return NULL;
 417
 418         desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
 419         if (desc)
 420                 prefetch((char *)desc + (desc->len8 << 3));
 421
 422         return desc;
 423 }
 424 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
 425
 426 /*
 427  * Get next vmbus packet from ring buffer.
 428  *
 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.
 431  */
 432 struct vmpacket_descriptor *
 433 __hv_pkt_iter_next(struct vmbus_channel *channel,
 434                    const struct vmpacket_descriptor *desc)
 435 {
 436         struct hv_ring_buffer_info *rbi = &channel->inbound;
 437         u32 packetlen = desc->len8 << 3;
 438         u32 dsize = rbi->ring_datasize;
 439
 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;
 445
 446         /* more data? */
 447         return hv_pkt_iter_first(channel);
 448 }
 449 EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
 450
 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)
 454 {
 455         if (rbi->priv_read_index >= start_read_index)
 456                 return rbi->priv_read_index - start_read_index;
 457         else
 458                 return rbi->ring_datasize - start_read_index +
 459                         rbi->priv_read_index;
 460 }
 461
 462 /*
 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
 468  * inappropriately.
 469  *
 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:
 472  *
 473  * 1. Update the read_index
 474  * 2. Read the pending_send_sz
 475  * 3. Read the current write_index
 476  *
 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.
 481  */
 482 void hv_pkt_iter_close(struct vmbus_channel *channel)
 483 {
 484         struct hv_ring_buffer_info *rbi = &channel->inbound;
 485         u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
 486
 487         /*
 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
 490          * is updated.
 491          */
 492         virt_rmb();
 493         start_read_index = rbi->ring_buffer->read_index;
 494         rbi->ring_buffer->read_index = rbi->priv_read_index;
 495
 496         /*
 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.
 500          */
 501         if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
 502                 return;
 503
 504         /*
 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.
 512          */
 513         virt_mb();
 514
 515         /*
 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.
 519          */
 520         pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
 521         if (!pending_sz)
 522                 return;
 523
 524         /*
 525          * Ensure the read of write_index in hv_get_bytes_to_write()
 526          * happens after the read of pending_send_sz.
 527          */
 528         virt_rmb();
 529         curr_write_sz = hv_get_bytes_to_write(rbi);
 530         bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
 531
 532         /*
 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.
 541          *
 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
 546          * this regard.
 547          *
 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.
 551          */
 552         if (curr_write_sz - bytes_read > pending_sz)
 553                 return;
 554
 555         /*
 556          * Similarly, if the new state is "not enough space", then
 557          * there's no need to signal.
 558          */
 559         if (curr_write_sz <= pending_sz)
 560                 return;
 561
 562         ++channel->intr_in_full;
 563         vmbus_setevent(channel);
 564 }
 565 EXPORT_SYMBOL_GPL(hv_pkt_iter_close);