drivers/hv/ring_buffer.c

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