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 50static 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. */ 71static inline u32 72hv_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. */ 80static inline void 81hv_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. */ 88static inline void 89hv_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. */ 97static inline u32 98hv_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. */ 104static inline u64 105hv_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 */ 114static 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 */ 139static void 140hv_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. */ 156int 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} 182EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo); 183 184/* Initialize a channel's ring buffer info mutex locks */ 185void 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. */ 192int 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. */ 241void 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/* 250 * Check if the ring buffer spinlock is available to take or not; used on 251 * atomic contexts, like panic path (see the Hyper-V framebuffer driver). 252 */ 253 254bool hv_ringbuffer_spinlock_busy(struct vmbus_channel *channel) 255{ 256 struct hv_ring_buffer_info *rinfo = &channel->outbound; 257 258 return spin_is_locked(&rinfo->ring_lock); 259} 260EXPORT_SYMBOL_GPL(hv_ringbuffer_spinlock_busy); 261 262/* Write to the ring buffer. */ 263int hv_ringbuffer_write(struct vmbus_channel *channel, 264 const struct kvec *kv_list, u32 kv_count) 265{ 266 int i; 267 u32 bytes_avail_towrite; 268 u32 totalbytes_towrite = sizeof(u64); 269 u32 next_write_location; 270 u32 old_write; 271 u64 prev_indices; 272 unsigned long flags; 273 struct hv_ring_buffer_info *outring_info = &channel->outbound; 274 275 if (channel->rescind) 276 return -ENODEV; 277 278 for (i = 0; i < kv_count; i++) 279 totalbytes_towrite += kv_list[i].iov_len; 280 281 spin_lock_irqsave(&outring_info->ring_lock, flags); 282 283 bytes_avail_towrite = hv_get_bytes_to_write(outring_info); 284 285 /* 286 * If there is only room for the packet, assume it is full. 287 * Otherwise, the next time around, we think the ring buffer 288 * is empty since the read index == write index. 289 */ 290 if (bytes_avail_towrite <= totalbytes_towrite) { 291 ++channel->out_full_total; 292 293 if (!channel->out_full_flag) { 294 ++channel->out_full_first; 295 channel->out_full_flag = true; 296 } 297 298 spin_unlock_irqrestore(&outring_info->ring_lock, flags); 299 return -EAGAIN; 300 } 301 302 channel->out_full_flag = false; 303 304 /* Write to the ring buffer */ 305 next_write_location = hv_get_next_write_location(outring_info); 306 307 old_write = next_write_location; 308 309 for (i = 0; i < kv_count; i++) { 310 next_write_location = hv_copyto_ringbuffer(outring_info, 311 next_write_location, 312 kv_list[i].iov_base, 313 kv_list[i].iov_len); 314 } 315 316 /* Set previous packet start */ 317 prev_indices = hv_get_ring_bufferindices(outring_info); 318 319 next_write_location = hv_copyto_ringbuffer(outring_info, 320 next_write_location, 321 &prev_indices, 322 sizeof(u64)); 323 324 /* Issue a full memory barrier before updating the write index */ 325 virt_mb(); 326 327 /* Now, update the write location */ 328 hv_set_next_write_location(outring_info, next_write_location); 329 330 331 spin_unlock_irqrestore(&outring_info->ring_lock, flags); 332 333 hv_signal_on_write(old_write, channel); 334 335 if (channel->rescind) 336 return -ENODEV; 337 338 return 0; 339} 340 341int hv_ringbuffer_read(struct vmbus_channel *channel, 342 void *buffer, u32 buflen, u32 *buffer_actual_len, 343 u64 *requestid, bool raw) 344{ 345 struct vmpacket_descriptor *desc; 346 u32 packetlen, offset; 347 348 if (unlikely(buflen == 0)) 349 return -EINVAL; 350 351 *buffer_actual_len = 0; 352 *requestid = 0; 353 354 /* Make sure there is something to read */ 355 desc = hv_pkt_iter_first(channel); 356 if (desc == NULL) { 357 /* 358 * No error is set when there is even no header, drivers are 359 * supposed to analyze buffer_actual_len. 360 */ 361 return 0; 362 } 363 364 offset = raw ? 0 : (desc->offset8 << 3); 365 packetlen = (desc->len8 << 3) - offset; 366 *buffer_actual_len = packetlen; 367 *requestid = desc->trans_id; 368 369 if (unlikely(packetlen > buflen)) 370 return -ENOBUFS; 371 372 /* since ring is double mapped, only one copy is necessary */ 373 memcpy(buffer, (const char *)desc + offset, packetlen); 374 375 /* Advance ring index to next packet descriptor */ 376 __hv_pkt_iter_next(channel, desc); 377 378 /* Notify host of update */ 379 hv_pkt_iter_close(channel); 380 381 return 0; 382} 383 384/* 385 * Determine number of bytes available in ring buffer after 386 * the current iterator (priv_read_index) location. 387 * 388 * This is similar to hv_get_bytes_to_read but with private 389 * read index instead. 390 */ 391static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi) 392{ 393 u32 priv_read_loc = rbi->priv_read_index; 394 u32 write_loc; 395 396 /* 397 * The Hyper-V host writes the packet data, then uses 398 * store_release() to update the write_index. Use load_acquire() 399 * here to prevent loads of the packet data from being re-ordered 400 * before the read of the write_index and potentially getting 401 * stale data. 402 */ 403 write_loc = virt_load_acquire(&rbi->ring_buffer->write_index); 404 405 if (write_loc >= priv_read_loc) 406 return write_loc - priv_read_loc; 407 else 408 return (rbi->ring_datasize - priv_read_loc) + write_loc; 409} 410 411/* 412 * Get first vmbus packet from ring buffer after read_index 413 * 414 * If ring buffer is empty, returns NULL and no other action needed. 415 */ 416struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel) 417{ 418 struct hv_ring_buffer_info *rbi = &channel->inbound; 419 struct vmpacket_descriptor *desc; 420 421 hv_debug_delay_test(channel, MESSAGE_DELAY); 422 if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor)) 423 return NULL; 424 425 desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index; 426 if (desc) 427 prefetch((char *)desc + (desc->len8 << 3)); 428 429 return desc; 430} 431EXPORT_SYMBOL_GPL(hv_pkt_iter_first); 432 433/* 434 * Get next vmbus packet from ring buffer. 435 * 436 * Advances the current location (priv_read_index) and checks for more 437 * data. If the end of the ring buffer is reached, then return NULL. 438 */ 439struct vmpacket_descriptor * 440__hv_pkt_iter_next(struct vmbus_channel *channel, 441 const struct vmpacket_descriptor *desc) 442{ 443 struct hv_ring_buffer_info *rbi = &channel->inbound; 444 u32 packetlen = desc->len8 << 3; 445 u32 dsize = rbi->ring_datasize; 446 447 hv_debug_delay_test(channel, MESSAGE_DELAY); 448 /* bump offset to next potential packet */ 449 rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER; 450 if (rbi->priv_read_index >= dsize) 451 rbi->priv_read_index -= dsize; 452 453 /* more data? */ 454 return hv_pkt_iter_first(channel); 455} 456EXPORT_SYMBOL_GPL(__hv_pkt_iter_next); 457 458/* How many bytes were read in this iterator cycle */ 459static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi, 460 u32 start_read_index) 461{ 462 if (rbi->priv_read_index >= start_read_index) 463 return rbi->priv_read_index - start_read_index; 464 else 465 return rbi->ring_datasize - start_read_index + 466 rbi->priv_read_index; 467} 468 469/* 470 * Update host ring buffer after iterating over packets. If the host has 471 * stopped queuing new entries because it found the ring buffer full, and 472 * sufficient space is being freed up, signal the host. But be careful to 473 * only signal the host when necessary, both for performance reasons and 474 * because Hyper-V protects itself by throttling guests that signal 475 * inappropriately. 476 * 477 * Determining when to signal is tricky. There are three key data inputs 478 * that must be handled in this order to avoid race conditions: 479 * 480 * 1. Update the read_index 481 * 2. Read the pending_send_sz 482 * 3. Read the current write_index 483 * 484 * The interrupt_mask is not used to determine when to signal. The 485 * interrupt_mask is used only on the guest->host ring buffer when 486 * sending requests to the host. The host does not use it on the host-> 487 * guest ring buffer to indicate whether it should be signaled. 488 */ 489void hv_pkt_iter_close(struct vmbus_channel *channel) 490{ 491 struct hv_ring_buffer_info *rbi = &channel->inbound; 492 u32 curr_write_sz, pending_sz, bytes_read, start_read_index; 493 494 /* 495 * Make sure all reads are done before we update the read index since 496 * the writer may start writing to the read area once the read index 497 * is updated. 498 */ 499 virt_rmb(); 500 start_read_index = rbi->ring_buffer->read_index; 501 rbi->ring_buffer->read_index = rbi->priv_read_index; 502 503 /* 504 * Older versions of Hyper-V (before WS2102 and Win8) do not 505 * implement pending_send_sz and simply poll if the host->guest 506 * ring buffer is full. No signaling is needed or expected. 507 */ 508 if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz) 509 return; 510 511 /* 512 * Issue a full memory barrier before making the signaling decision. 513 * If reading pending_send_sz were to be reordered and happen 514 * before we commit the new read_index, a race could occur. If the 515 * host were to set the pending_send_sz after we have sampled 516 * pending_send_sz, and the ring buffer blocks before we commit the 517 * read index, we could miss sending the interrupt. Issue a full 518 * memory barrier to address this. 519 */ 520 virt_mb(); 521 522 /* 523 * If the pending_send_sz is zero, then the ring buffer is not 524 * blocked and there is no need to signal. This is far by the 525 * most common case, so exit quickly for best performance. 526 */ 527 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz); 528 if (!pending_sz) 529 return; 530 531 /* 532 * Ensure the read of write_index in hv_get_bytes_to_write() 533 * happens after the read of pending_send_sz. 534 */ 535 virt_rmb(); 536 curr_write_sz = hv_get_bytes_to_write(rbi); 537 bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index); 538 539 /* 540 * We want to signal the host only if we're transitioning 541 * from a "not enough free space" state to a "enough free 542 * space" state. For example, it's possible that this function 543 * could run and free up enough space to signal the host, and then 544 * run again and free up additional space before the host has a 545 * chance to clear the pending_send_sz. The 2nd invocation would 546 * be a null transition from "enough free space" to "enough free 547 * space", which doesn't warrant a signal. 548 * 549 * Exactly filling the ring buffer is treated as "not enough 550 * space". The ring buffer always must have at least one byte 551 * empty so the empty and full conditions are distinguishable. 552 * hv_get_bytes_to_write() doesn't fully tell the truth in 553 * this regard. 554 * 555 * So first check if we were in the "enough free space" state 556 * before we began the iteration. If so, the host was not 557 * blocked, and there's no need to signal. 558 */ 559 if (curr_write_sz - bytes_read > pending_sz) 560 return; 561 562 /* 563 * Similarly, if the new state is "not enough space", then 564 * there's no need to signal. 565 */ 566 if (curr_write_sz <= pending_sz) 567 return; 568 569 ++channel->intr_in_full; 570 vmbus_setevent(channel); 571} 572EXPORT_SYMBOL_GPL(hv_pkt_iter_close); 573