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 /* Set the next read location for the specified ring buffer. */ 88 static inline void 89 hv_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. */ 97 static inline u32 98 hv_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. */ 104 static inline u64 105 hv_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 */ 114 static 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 */ 139 static void 140 hv_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. */ 156 int 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 } 182 EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo); 183 184 /* Initialize a channel's ring buffer info mutex locks */ 185 void 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. */ 192 int 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. */ 241 void 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. */ 250 int hv_ringbuffer_write(struct vmbus_channel *channel, 251 const struct kvec *kv_list, u32 kv_count, 252 u64 requestid) 253 { 254 int i; 255 u32 bytes_avail_towrite; 256 u32 totalbytes_towrite = sizeof(u64); 257 u32 next_write_location; 258 u32 old_write; 259 u64 prev_indices; 260 unsigned long flags; 261 struct hv_ring_buffer_info *outring_info = &channel->outbound; 262 struct vmpacket_descriptor *desc = kv_list[0].iov_base; 263 u64 rqst_id = VMBUS_NO_RQSTOR; 264 265 if (channel->rescind) 266 return -ENODEV; 267 268 for (i = 0; i < kv_count; i++) 269 totalbytes_towrite += kv_list[i].iov_len; 270 271 spin_lock_irqsave(&outring_info->ring_lock, flags); 272 273 bytes_avail_towrite = hv_get_bytes_to_write(outring_info); 274 275 /* 276 * If there is only room for the packet, assume it is full. 277 * Otherwise, the next time around, we think the ring buffer 278 * is empty since the read index == write index. 279 */ 280 if (bytes_avail_towrite <= totalbytes_towrite) { 281 ++channel->out_full_total; 282 283 if (!channel->out_full_flag) { 284 ++channel->out_full_first; 285 channel->out_full_flag = true; 286 } 287 288 spin_unlock_irqrestore(&outring_info->ring_lock, flags); 289 return -EAGAIN; 290 } 291 292 channel->out_full_flag = false; 293 294 /* Write to the ring buffer */ 295 next_write_location = hv_get_next_write_location(outring_info); 296 297 old_write = next_write_location; 298 299 for (i = 0; i < kv_count; i++) { 300 next_write_location = hv_copyto_ringbuffer(outring_info, 301 next_write_location, 302 kv_list[i].iov_base, 303 kv_list[i].iov_len); 304 } 305 306 /* 307 * Allocate the request ID after the data has been copied into the 308 * ring buffer. Once this request ID is allocated, the completion 309 * path could find the data and free it. 310 */ 311 312 if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) { 313 rqst_id = vmbus_next_request_id(&channel->requestor, requestid); 314 if (rqst_id == VMBUS_RQST_ERROR) { 315 spin_unlock_irqrestore(&outring_info->ring_lock, flags); 316 pr_err("No request id available\n"); 317 return -EAGAIN; 318 } 319 } 320 desc = hv_get_ring_buffer(outring_info) + old_write; 321 desc->trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id; 322 323 /* Set previous packet start */ 324 prev_indices = hv_get_ring_bufferindices(outring_info); 325 326 next_write_location = hv_copyto_ringbuffer(outring_info, 327 next_write_location, 328 &prev_indices, 329 sizeof(u64)); 330 331 /* Issue a full memory barrier before updating the write index */ 332 virt_mb(); 333 334 /* Now, update the write location */ 335 hv_set_next_write_location(outring_info, next_write_location); 336 337 338 spin_unlock_irqrestore(&outring_info->ring_lock, flags); 339 340 hv_signal_on_write(old_write, channel); 341 342 if (channel->rescind) { 343 if (rqst_id != VMBUS_NO_RQSTOR) { 344 /* Reclaim request ID to avoid leak of IDs */ 345 vmbus_request_addr(&channel->requestor, rqst_id); 346 } 347 return -ENODEV; 348 } 349 350 return 0; 351 } 352 353 int hv_ringbuffer_read(struct vmbus_channel *channel, 354 void *buffer, u32 buflen, u32 *buffer_actual_len, 355 u64 *requestid, bool raw) 356 { 357 struct vmpacket_descriptor *desc; 358 u32 packetlen, offset; 359 360 if (unlikely(buflen == 0)) 361 return -EINVAL; 362 363 *buffer_actual_len = 0; 364 *requestid = 0; 365 366 /* Make sure there is something to read */ 367 desc = hv_pkt_iter_first(channel); 368 if (desc == NULL) { 369 /* 370 * No error is set when there is even no header, drivers are 371 * supposed to analyze buffer_actual_len. 372 */ 373 return 0; 374 } 375 376 offset = raw ? 0 : (desc->offset8 << 3); 377 packetlen = (desc->len8 << 3) - offset; 378 *buffer_actual_len = packetlen; 379 *requestid = desc->trans_id; 380 381 if (unlikely(packetlen > buflen)) 382 return -ENOBUFS; 383 384 /* since ring is double mapped, only one copy is necessary */ 385 memcpy(buffer, (const char *)desc + offset, packetlen); 386 387 /* Advance ring index to next packet descriptor */ 388 __hv_pkt_iter_next(channel, desc); 389 390 /* Notify host of update */ 391 hv_pkt_iter_close(channel); 392 393 return 0; 394 } 395 396 /* 397 * Determine number of bytes available in ring buffer after 398 * the current iterator (priv_read_index) location. 399 * 400 * This is similar to hv_get_bytes_to_read but with private 401 * read index instead. 402 */ 403 static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi) 404 { 405 u32 priv_read_loc = rbi->priv_read_index; 406 u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index); 407 408 if (write_loc >= priv_read_loc) 409 return write_loc - priv_read_loc; 410 else 411 return (rbi->ring_datasize - priv_read_loc) + write_loc; 412 } 413 414 /* 415 * Get first vmbus packet from ring buffer after read_index 416 * 417 * If ring buffer is empty, returns NULL and no other action needed. 418 */ 419 struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel) 420 { 421 struct hv_ring_buffer_info *rbi = &channel->inbound; 422 struct vmpacket_descriptor *desc; 423 424 hv_debug_delay_test(channel, MESSAGE_DELAY); 425 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor)) 426 return NULL; 427 428 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index; 429 if (desc) 430 prefetch((char *)desc + (desc->len8 << 3)); 431 432 return desc; 433 } 434 EXPORT_SYMBOL_GPL(hv_pkt_iter_first); 435 436 /* 437 * Get next vmbus packet from ring buffer. 438 * 439 * Advances the current location (priv_read_index) and checks for more 440 * data. If the end of the ring buffer is reached, then return NULL. 441 */ 442 struct vmpacket_descriptor * 443 __hv_pkt_iter_next(struct vmbus_channel *channel, 444 const struct vmpacket_descriptor *desc) 445 { 446 struct hv_ring_buffer_info *rbi = &channel->inbound; 447 u32 packetlen = desc->len8 << 3; 448 u32 dsize = rbi->ring_datasize; 449 450 hv_debug_delay_test(channel, MESSAGE_DELAY); 451 /* bump offset to next potential packet */ 452 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER; 453 if (rbi->priv_read_index >= dsize) 454 rbi->priv_read_index -= dsize; 455 456 /* more data? */ 457 return hv_pkt_iter_first(channel); 458 } 459 EXPORT_SYMBOL_GPL(__hv_pkt_iter_next); 460 461 /* How many bytes were read in this iterator cycle */ 462 static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi, 463 u32 start_read_index) 464 { 465 if (rbi->priv_read_index >= start_read_index) 466 return rbi->priv_read_index - start_read_index; 467 else 468 return rbi->ring_datasize - start_read_index + 469 rbi->priv_read_index; 470 } 471 472 /* 473 * Update host ring buffer after iterating over packets. If the host has 474 * stopped queuing new entries because it found the ring buffer full, and 475 * sufficient space is being freed up, signal the host. But be careful to 476 * only signal the host when necessary, both for performance reasons and 477 * because Hyper-V protects itself by throttling guests that signal 478 * inappropriately. 479 * 480 * Determining when to signal is tricky. There are three key data inputs 481 * that must be handled in this order to avoid race conditions: 482 * 483 * 1. Update the read_index 484 * 2. Read the pending_send_sz 485 * 3. Read the current write_index 486 * 487 * The interrupt_mask is not used to determine when to signal. The 488 * interrupt_mask is used only on the guest->host ring buffer when 489 * sending requests to the host. The host does not use it on the host-> 490 * guest ring buffer to indicate whether it should be signaled. 491 */ 492 void hv_pkt_iter_close(struct vmbus_channel *channel) 493 { 494 struct hv_ring_buffer_info *rbi = &channel->inbound; 495 u32 curr_write_sz, pending_sz, bytes_read, start_read_index; 496 497 /* 498 * Make sure all reads are done before we update the read index since 499 * the writer may start writing to the read area once the read index 500 * is updated. 501 */ 502 virt_rmb(); 503 start_read_index = rbi->ring_buffer->read_index; 504 rbi->ring_buffer->read_index = rbi->priv_read_index; 505 506 /* 507 * Older versions of Hyper-V (before WS2102 and Win8) do not 508 * implement pending_send_sz and simply poll if the host->guest 509 * ring buffer is full. No signaling is needed or expected. 510 */ 511 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz) 512 return; 513 514 /* 515 * Issue a full memory barrier before making the signaling decision. 516 * If reading pending_send_sz were to be reordered and happen 517 * before we commit the new read_index, a race could occur. If the 518 * host were to set the pending_send_sz after we have sampled 519 * pending_send_sz, and the ring buffer blocks before we commit the 520 * read index, we could miss sending the interrupt. Issue a full 521 * memory barrier to address this. 522 */ 523 virt_mb(); 524 525 /* 526 * If the pending_send_sz is zero, then the ring buffer is not 527 * blocked and there is no need to signal. This is far by the 528 * most common case, so exit quickly for best performance. 529 */ 530 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz); 531 if (!pending_sz) 532 return; 533 534 /* 535 * Ensure the read of write_index in hv_get_bytes_to_write() 536 * happens after the read of pending_send_sz. 537 */ 538 virt_rmb(); 539 curr_write_sz = hv_get_bytes_to_write(rbi); 540 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index); 541 542 /* 543 * We want to signal the host only if we're transitioning 544 * from a "not enough free space" state to a "enough free 545 * space" state. For example, it's possible that this function 546 * could run and free up enough space to signal the host, and then 547 * run again and free up additional space before the host has a 548 * chance to clear the pending_send_sz. The 2nd invocation would 549 * be a null transition from "enough free space" to "enough free 550 * space", which doesn't warrant a signal. 551 * 552 * Exactly filling the ring buffer is treated as "not enough 553 * space". The ring buffer always must have at least one byte 554 * empty so the empty and full conditions are distinguishable. 555 * hv_get_bytes_to_write() doesn't fully tell the truth in 556 * this regard. 557 * 558 * So first check if we were in the "enough free space" state 559 * before we began the iteration. If so, the host was not 560 * blocked, and there's no need to signal. 561 */ 562 if (curr_write_sz - bytes_read > pending_sz) 563 return; 564 565 /* 566 * Similarly, if the new state is "not enough space", then 567 * there's no need to signal. 568 */ 569 if (curr_write_sz <= pending_sz) 570 return; 571 572 ++channel->intr_in_full; 573 vmbus_setevent(channel); 574 } 575 EXPORT_SYMBOL_GPL(hv_pkt_iter_close); 576