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 /* Get various debug metrics for the specified ring buffer. */
 144 void hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
 145                                  struct hv_ring_buffer_debug_info *debug_info)
 146 {
 147         u32 bytes_avail_towrite;
 148         u32 bytes_avail_toread;
 149
 150         if (ring_info->ring_buffer) {
 151                 hv_get_ringbuffer_availbytes(ring_info,
 152                                         &bytes_avail_toread,
 153                                         &bytes_avail_towrite);
 154
 155                 debug_info->bytes_avail_toread = bytes_avail_toread;
 156                 debug_info->bytes_avail_towrite = bytes_avail_towrite;
 157                 debug_info->current_read_index =
 158                         ring_info->ring_buffer->read_index;
 159                 debug_info->current_write_index =
 160                         ring_info->ring_buffer->write_index;
 161                 debug_info->current_interrupt_mask =
 162                         ring_info->ring_buffer->interrupt_mask;
 163         }
 164 }
 165 EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
 166
 167 /* Initialize the ring buffer. */
 168 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 169                        struct page *pages, u32 page_cnt)
 170 {
 171         int i;
 172         struct page **pages_wraparound;
 173
 174         BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
 175
 176         memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
 177
 178         /*
 179          * First page holds struct hv_ring_buffer, do wraparound mapping for
 180          * the rest.
 181          */
 182         pages_wraparound = kzalloc(sizeof(struct page *) * (page_cnt * 2 - 1),
 183                                    GFP_KERNEL);
 184         if (!pages_wraparound)
 185                 return -ENOMEM;
 186
 187         pages_wraparound[0] = pages;
 188         for (i = 0; i < 2 * (page_cnt - 1); i++)
 189                 pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
 190
 191         ring_info->ring_buffer = (struct hv_ring_buffer *)
 192                 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
 193
 194         kfree(pages_wraparound);
 195
 196
 197         if (!ring_info->ring_buffer)
 198                 return -ENOMEM;
 199
 200         ring_info->ring_buffer->read_index =
 201                 ring_info->ring_buffer->write_index = 0;
 202
 203         /* Set the feature bit for enabling flow control. */
 204         ring_info->ring_buffer->feature_bits.value = 1;
 205
 206         ring_info->ring_size = page_cnt << PAGE_SHIFT;
 207         ring_info->ring_datasize = ring_info->ring_size -
 208                 sizeof(struct hv_ring_buffer);
 209
 210         spin_lock_init(&ring_info->ring_lock);
 211
 212         return 0;
 213 }
 214
 215 /* Cleanup the ring buffer. */
 216 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 217 {
 218         vunmap(ring_info->ring_buffer);
 219 }
 220
 221 /* Write to the ring buffer. */
 222 int hv_ringbuffer_write(struct vmbus_channel *channel,
 223                         const struct kvec *kv_list, u32 kv_count)
 224 {
 225         int i;
 226         u32 bytes_avail_towrite;
 227         u32 totalbytes_towrite = sizeof(u64);
 228         u32 next_write_location;
 229         u32 old_write;
 230         u64 prev_indices;
 231         unsigned long flags;
 232         struct hv_ring_buffer_info *outring_info = &channel->outbound;
 233
 234         if (channel->rescind)
 235                 return -ENODEV;
 236
 237         for (i = 0; i < kv_count; i++)
 238                 totalbytes_towrite += kv_list[i].iov_len;
 239
 240         spin_lock_irqsave(&outring_info->ring_lock, flags);
 241
 242         bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
 243
 244         /*
 245          * If there is only room for the packet, assume it is full.
 246          * Otherwise, the next time around, we think the ring buffer
 247          * is empty since the read index == write index.
 248          */
 249         if (bytes_avail_towrite <= totalbytes_towrite) {
 250                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 251                 return -EAGAIN;
 252         }
 253
 254         /* Write to the ring buffer */
 255         next_write_location = hv_get_next_write_location(outring_info);
 256
 257         old_write = next_write_location;
 258
 259         for (i = 0; i < kv_count; i++) {
 260                 next_write_location = hv_copyto_ringbuffer(outring_info,
 261                                                      next_write_location,
 262                                                      kv_list[i].iov_base,
 263                                                      kv_list[i].iov_len);
 264         }
 265
 266         /* Set previous packet start */
 267         prev_indices = hv_get_ring_bufferindices(outring_info);
 268
 269         next_write_location = hv_copyto_ringbuffer(outring_info,
 270                                              next_write_location,
 271                                              &prev_indices,
 272                                              sizeof(u64));
 273
 274         /* Issue a full memory barrier before updating the write index */
 275         virt_mb();
 276
 277         /* Now, update the write location */
 278         hv_set_next_write_location(outring_info, next_write_location);
 279
 280
 281         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 282
 283         hv_signal_on_write(old_write, channel);
 284
 285         if (channel->rescind)
 286                 return -ENODEV;
 287
 288         return 0;
 289 }
 290
 291 int hv_ringbuffer_read(struct vmbus_channel *channel,
 292                        void *buffer, u32 buflen, u32 *buffer_actual_len,
 293                        u64 *requestid, bool raw)
 294 {
 295         struct vmpacket_descriptor *desc;
 296         u32 packetlen, offset;
 297
 298         if (unlikely(buflen == 0))
 299                 return -EINVAL;
 300
 301         *buffer_actual_len = 0;
 302         *requestid = 0;
 303
 304         /* Make sure there is something to read */
 305         desc = hv_pkt_iter_first(channel);
 306         if (desc == NULL) {
 307                 /*
 308                  * No error is set when there is even no header, drivers are
 309                  * supposed to analyze buffer_actual_len.
 310                  */
 311                 return 0;
 312         }
 313
 314         offset = raw ? 0 : (desc->offset8 << 3);
 315         packetlen = (desc->len8 << 3) - offset;
 316         *buffer_actual_len = packetlen;
 317         *requestid = desc->trans_id;
 318
 319         if (unlikely(packetlen > buflen))
 320                 return -ENOBUFS;
 321
 322         /* since ring is double mapped, only one copy is necessary */
 323         memcpy(buffer, (const char *)desc + offset, packetlen);
 324
 325         /* Advance ring index to next packet descriptor */
 326         __hv_pkt_iter_next(channel, desc);
 327
 328         /* Notify host of update */
 329         hv_pkt_iter_close(channel);
 330
 331         return 0;
 332 }
 333
 334 /*
 335  * Determine number of bytes available in ring buffer after
 336  * the current iterator (priv_read_index) location.
 337  *
 338  * This is similar to hv_get_bytes_to_read but with private
 339  * read index instead.
 340  */
 341 static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
 342 {
 343         u32 priv_read_loc = rbi->priv_read_index;
 344         u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
 345
 346         if (write_loc >= priv_read_loc)
 347                 return write_loc - priv_read_loc;
 348         else
 349                 return (rbi->ring_datasize - priv_read_loc) + write_loc;
 350 }
 351
 352 /*
 353  * Get first vmbus packet from ring buffer after read_index
 354  *
 355  * If ring buffer is empty, returns NULL and no other action needed.
 356  */
 357 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
 358 {
 359         struct hv_ring_buffer_info *rbi = &channel->inbound;
 360         struct vmpacket_descriptor *desc;
 361
 362         if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
 363                 return NULL;
 364
 365         desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
 366         if (desc)
 367                 prefetch((char *)desc + (desc->len8 << 3));
 368
 369         return desc;
 370 }
 371 EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
 372
 373 /*
 374  * Get next vmbus packet from ring buffer.
 375  *
 376  * Advances the current location (priv_read_index) and checks for more
 377  * data. If the end of the ring buffer is reached, then return NULL.
 378  */
 379 struct vmpacket_descriptor *
 380 __hv_pkt_iter_next(struct vmbus_channel *channel,
 381                    const struct vmpacket_descriptor *desc)
 382 {
 383         struct hv_ring_buffer_info *rbi = &channel->inbound;
 384         u32 packetlen = desc->len8 << 3;
 385         u32 dsize = rbi->ring_datasize;
 386
 387         /* bump offset to next potential packet */
 388         rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
 389         if (rbi->priv_read_index >= dsize)
 390                 rbi->priv_read_index -= dsize;
 391
 392         /* more data? */
 393         return hv_pkt_iter_first(channel);
 394 }
 395 EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
 396
 397 /*
 398  * Update host ring buffer after iterating over packets.
 399  */
 400 void hv_pkt_iter_close(struct vmbus_channel *channel)
 401 {
 402         struct hv_ring_buffer_info *rbi = &channel->inbound;
 403         u32 orig_write_sz = hv_get_bytes_to_write(rbi);
 404
 405         /*
 406          * Make sure all reads are done before we update the read index since
 407          * the writer may start writing to the read area once the read index
 408          * is updated.
 409          */
 410         virt_rmb();
 411         rbi->ring_buffer->read_index = rbi->priv_read_index;
 412
 413         /*
 414          * Issue a full memory barrier before making the signaling decision.
 415          * Here is the reason for having this barrier:
 416          * If the reading of the pend_sz (in this function)
 417          * were to be reordered and read before we commit the new read
 418          * index (in the calling function)  we could
 419          * have a problem. If the host were to set the pending_sz after we
 420          * have sampled pending_sz and go to sleep before we commit the
 421          * read index, we could miss sending the interrupt. Issue a full
 422          * memory barrier to address this.
 423          */
 424         virt_mb();
 425
 426         /* If host has disabled notifications then skip */
 427         if (rbi->ring_buffer->interrupt_mask)
 428                 return;
 429
 430         if (rbi->ring_buffer->feature_bits.feat_pending_send_sz) {
 431                 u32 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
 432
 433                 /*
 434                  * If there was space before we began iteration,
 435                  * then host was not blocked. Also handles case where
 436                  * pending_sz is zero then host has nothing pending
 437                  * and does not need to be signaled.
 438                  */
 439                 if (orig_write_sz > pending_sz)
 440                         return;
 441
 442                 /* If pending write will not fit, don't give false hope. */
 443                 if (hv_get_bytes_to_write(rbi) < pending_sz)
 444                         return;
 445         }
 446
 447         vmbus_setevent(channel);
 448 }
 449 EXPORT_SYMBOL_GPL(hv_pkt_iter_close);