text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   *
   * Copyright (c) 2009, Microsoft Corporation.
   *
   * Authors:
   *   Haiyang Zhang <haiyangz@microsoft.com>
   *   Hank Janssen  <hjanssen@microsoft.com>
   *   K. Y. Srinivasan <kys@microsoft.com>
   */
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/hyperv.h>
  #include <linux/uio.h>
  #include <linux/vmalloc.h>
  #include <linux/slab.h>
  #include <linux/prefetch.h>
  
  #include "hyperv_vmbus.h"
  
  #define VMBUS_PKT_TRAILER	8
  
  /*
   * When we write to the ring buffer, check if the host needs to
   * be signaled. Here is the details of this protocol:
   *
   *	1. The host guarantees that while it is draining the
   *	   ring buffer, it will set the interrupt_mask to
   *	   indicate it does not need to be interrupted when
   *	   new data is placed.
   *
   *	2. The host guarantees that it will completely drain
   *	   the ring buffer before exiting the read loop. Further,
   *	   once the ring buffer is empty, it will clear the
   *	   interrupt_mask and re-check to see if new data has
   *	   arrived.
   *
   * KYS: Oct. 30, 2016:
   * It looks like Windows hosts have logic to deal with DOS attacks that
   * can be triggered if it receives interrupts when it is not expecting
   * the interrupt. The host expects interrupts only when the ring
   * transitions from empty to non-empty (or full to non full on the guest
   * to host ring).
   * So, base the signaling decision solely on the ring state until the
   * host logic is fixed.
   */
  
  static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
  {
  	struct hv_ring_buffer_info *rbi = &channel->outbound;
  
  	virt_mb();
  	if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
  		return;
  
  	/* check interrupt_mask before read_index */
  	virt_rmb();
  	/*
  	 * This is the only case we need to signal when the
  	 * ring transitions from being empty to non-empty.
  	 */
  	if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
  		++channel->intr_out_empty;
  		vmbus_setevent(channel);
  	}
  }
  
  /* Get the next write location for the specified ring buffer. */
  static inline u32
  hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
  {
  	u32 next = ring_info->ring_buffer->write_index;
  
  	return next;
  }
  
  /* Set the next write location for the specified ring buffer. */
  static inline void
  hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
  		     u32 next_write_location)
  {
  	ring_info->ring_buffer->write_index = next_write_location;
  }
  
  /* Set the next read location for the specified ring buffer. */
  static inline void
  hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
  		    u32 next_read_location)
  {
  	ring_info->ring_buffer->read_index = next_read_location;
  	ring_info->priv_read_index = next_read_location;
  }
  
  /* Get the size of the ring buffer. */
  static inline u32
  hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
  {
  	return ring_info->ring_datasize;
  }
  
  /* Get the read and write indices as u64 of the specified ring buffer. */
  static inline u64
  hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
  {
  	return (u64)ring_info->ring_buffer->write_index << 32;
  }
  
  /*
   * Helper routine to copy from source to ring buffer.
   * Assume there is enough room. Handles wrap-around in dest case only!!
   */
  static u32 hv_copyto_ringbuffer(
  	struct hv_ring_buffer_info	*ring_info,
  	u32				start_write_offset,
  	const void			*src,
  	u32				srclen)
  {
  	void *ring_buffer = hv_get_ring_buffer(ring_info);
  	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
  
  	memcpy(ring_buffer + start_write_offset, src, srclen);
  
  	start_write_offset += srclen;
  	if (start_write_offset >= ring_buffer_size)
  		start_write_offset -= ring_buffer_size;
  
  	return start_write_offset;
  }
  
  /*
   *
   * hv_get_ringbuffer_availbytes()
   *
   * Get number of bytes available to read and to write to
   * for the specified ring buffer
   */
  static void
  hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
  			     u32 *read, u32 *write)
  {
  	u32 read_loc, write_loc, dsize;
  
  	/* Capture the read/write indices before they changed */
  	read_loc = READ_ONCE(rbi->ring_buffer->read_index);
  	write_loc = READ_ONCE(rbi->ring_buffer->write_index);
  	dsize = rbi->ring_datasize;
  
  	*write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
  		read_loc - write_loc;
  	*read = dsize - *write;
  }
  
  /* Get various debug metrics for the specified ring buffer. */
  int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
  				struct hv_ring_buffer_debug_info *debug_info)
  {
  	u32 bytes_avail_towrite;
  	u32 bytes_avail_toread;
  
  	mutex_lock(&ring_info->ring_buffer_mutex);
  
  	if (!ring_info->ring_buffer) {
  		mutex_unlock(&ring_info->ring_buffer_mutex);
  		return -EINVAL;
  	}
  
  	hv_get_ringbuffer_availbytes(ring_info,
  				     &bytes_avail_toread,
  				     &bytes_avail_towrite);
  	debug_info->bytes_avail_toread = bytes_avail_toread;
  	debug_info->bytes_avail_towrite = bytes_avail_towrite;
  	debug_info->current_read_index = ring_info->ring_buffer->read_index;
  	debug_info->current_write_index = ring_info->ring_buffer->write_index;
  	debug_info->current_interrupt_mask
  		= ring_info->ring_buffer->interrupt_mask;
  	mutex_unlock(&ring_info->ring_buffer_mutex);
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
  
  /* Initialize a channel's ring buffer info mutex locks */
  void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
  {
  	mutex_init(&channel->inbound.ring_buffer_mutex);
  	mutex_init(&channel->outbound.ring_buffer_mutex);
  }
  
  /* Initialize the ring buffer. */
  int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
  		       struct page *pages, u32 page_cnt)
  {
  	int i;
  	struct page **pages_wraparound;
  
  	BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
  
  	/*
  	 * First page holds struct hv_ring_buffer, do wraparound mapping for
  	 * the rest.
  	 */
  	pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *),
  				   GFP_KERNEL);
  	if (!pages_wraparound)
  		return -ENOMEM;
  
  	pages_wraparound[0] = pages;
  	for (i = 0; i < 2 * (page_cnt - 1); i++)
  		pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
  
  	ring_info->ring_buffer = (struct hv_ring_buffer *)
  		vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
  
  	kfree(pages_wraparound);
  
  
  	if (!ring_info->ring_buffer)
  		return -ENOMEM;
  
  	ring_info->ring_buffer->read_index =
  		ring_info->ring_buffer->write_index = 0;
  
  	/* Set the feature bit for enabling flow control. */
  	ring_info->ring_buffer->feature_bits.value = 1;
  
  	ring_info->ring_size = page_cnt << PAGE_SHIFT;
  	ring_info->ring_size_div10_reciprocal =
  		reciprocal_value(ring_info->ring_size / 10);
  	ring_info->ring_datasize = ring_info->ring_size -
  		sizeof(struct hv_ring_buffer);
  	ring_info->priv_read_index = 0;
  
  	spin_lock_init(&ring_info->ring_lock);
  
  	return 0;
  }
  
  /* Cleanup the ring buffer. */
  void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
  {
  	mutex_lock(&ring_info->ring_buffer_mutex);
  	vunmap(ring_info->ring_buffer);
  	ring_info->ring_buffer = NULL;
  	mutex_unlock(&ring_info->ring_buffer_mutex);
  }
  
  /* Write to the ring buffer. */
  int hv_ringbuffer_write(struct vmbus_channel *channel,
  			const struct kvec *kv_list, u32 kv_count)
  {
  	int i;
  	u32 bytes_avail_towrite;
  	u32 totalbytes_towrite = sizeof(u64);
  	u32 next_write_location;
  	u32 old_write;
  	u64 prev_indices;
  	unsigned long flags;
  	struct hv_ring_buffer_info *outring_info = &channel->outbound;
  
  	if (channel->rescind)
  		return -ENODEV;
  
  	for (i = 0; i < kv_count; i++)
  		totalbytes_towrite += kv_list[i].iov_len;
  
  	spin_lock_irqsave(&outring_info->ring_lock, flags);
  
  	bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
  
  	/*
  	 * If there is only room for the packet, assume it is full.
  	 * Otherwise, the next time around, we think the ring buffer
  	 * is empty since the read index == write index.
  	 */
  	if (bytes_avail_towrite <= totalbytes_towrite) {
  		++channel->out_full_total;
  
  		if (!channel->out_full_flag) {
  			++channel->out_full_first;
  			channel->out_full_flag = true;
  		}
  
  		spin_unlock_irqrestore(&outring_info->ring_lock, flags);
  		return -EAGAIN;
  	}
  
  	channel->out_full_flag = false;
  
  	/* Write to the ring buffer */
  	next_write_location = hv_get_next_write_location(outring_info);
  
  	old_write = next_write_location;
  
  	for (i = 0; i < kv_count; i++) {
  		next_write_location = hv_copyto_ringbuffer(outring_info,
  						     next_write_location,
  						     kv_list[i].iov_base,
  						     kv_list[i].iov_len);
  	}
  
  	/* Set previous packet start */
  	prev_indices = hv_get_ring_bufferindices(outring_info);
  
  	next_write_location = hv_copyto_ringbuffer(outring_info,
  					     next_write_location,
  					     &prev_indices,
  					     sizeof(u64));
  
  	/* Issue a full memory barrier before updating the write index */
  	virt_mb();
  
  	/* Now, update the write location */
  	hv_set_next_write_location(outring_info, next_write_location);
  
  
  	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
  
  	hv_signal_on_write(old_write, channel);
  
  	if (channel->rescind)
  		return -ENODEV;
  
  	return 0;
  }
  
  int hv_ringbuffer_read(struct vmbus_channel *channel,
  		       void *buffer, u32 buflen, u32 *buffer_actual_len,
  		       u64 *requestid, bool raw)
  {
  	struct vmpacket_descriptor *desc;
  	u32 packetlen, offset;
  
  	if (unlikely(buflen == 0))
  		return -EINVAL;
  
  	*buffer_actual_len = 0;
  	*requestid = 0;
  
  	/* Make sure there is something to read */
  	desc = hv_pkt_iter_first(channel);
  	if (desc == NULL) {
  		/*
  		 * No error is set when there is even no header, drivers are
  		 * supposed to analyze buffer_actual_len.
  		 */
  		return 0;
  	}
  
  	offset = raw ? 0 : (desc->offset8 << 3);
  	packetlen = (desc->len8 << 3) - offset;
  	*buffer_actual_len = packetlen;
  	*requestid = desc->trans_id;
  
  	if (unlikely(packetlen > buflen))
  		return -ENOBUFS;
  
  	/* since ring is double mapped, only one copy is necessary */
  	memcpy(buffer, (const char *)desc + offset, packetlen);
  
  	/* Advance ring index to next packet descriptor */
  	__hv_pkt_iter_next(channel, desc);
  
  	/* Notify host of update */
  	hv_pkt_iter_close(channel);
  
  	return 0;
  }
  
  /*
   * Determine number of bytes available in ring buffer after
   * the current iterator (priv_read_index) location.
   *
   * This is similar to hv_get_bytes_to_read but with private
   * read index instead.
   */
  static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
  {
  	u32 priv_read_loc = rbi->priv_read_index;
  	u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
  
  	if (write_loc >= priv_read_loc)
  		return write_loc - priv_read_loc;
  	else
  		return (rbi->ring_datasize - priv_read_loc) + write_loc;
  }
  
  /*
   * Get first vmbus packet from ring buffer after read_index
   *
   * If ring buffer is empty, returns NULL and no other action needed.
   */
  struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
  {
  	struct hv_ring_buffer_info *rbi = &channel->inbound;
  	struct vmpacket_descriptor *desc;
  
  	hv_debug_delay_test(channel, MESSAGE_DELAY);
  	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
  		return NULL;
  
  	desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
  	if (desc)
  		prefetch((char *)desc + (desc->len8 << 3));
  
  	return desc;
  }
  EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
  
  /*
   * Get next vmbus packet from ring buffer.
   *
   * Advances the current location (priv_read_index) and checks for more
   * data. If the end of the ring buffer is reached, then return NULL.
   */
  struct vmpacket_descriptor *
  __hv_pkt_iter_next(struct vmbus_channel *channel,
  		   const struct vmpacket_descriptor *desc)
  {
  	struct hv_ring_buffer_info *rbi = &channel->inbound;
  	u32 packetlen = desc->len8 << 3;
  	u32 dsize = rbi->ring_datasize;
  
  	hv_debug_delay_test(channel, MESSAGE_DELAY);
  	/* bump offset to next potential packet */
  	rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
  	if (rbi->priv_read_index >= dsize)
  		rbi->priv_read_index -= dsize;
  
  	/* more data? */
  	return hv_pkt_iter_first(channel);
  }
  EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
  
  /* How many bytes were read in this iterator cycle */
  static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
  					u32 start_read_index)
  {
  	if (rbi->priv_read_index >= start_read_index)
  		return rbi->priv_read_index - start_read_index;
  	else
  		return rbi->ring_datasize - start_read_index +
  			rbi->priv_read_index;
  }
  
  /*
   * Update host ring buffer after iterating over packets. If the host has
   * stopped queuing new entries because it found the ring buffer full, and
   * sufficient space is being freed up, signal the host. But be careful to
   * only signal the host when necessary, both for performance reasons and
   * because Hyper-V protects itself by throttling guests that signal
   * inappropriately.
   *
   * Determining when to signal is tricky. There are three key data inputs
   * that must be handled in this order to avoid race conditions:
   *
   * 1. Update the read_index
   * 2. Read the pending_send_sz
   * 3. Read the current write_index
   *
   * The interrupt_mask is not used to determine when to signal. The
   * interrupt_mask is used only on the guest->host ring buffer when
   * sending requests to the host. The host does not use it on the host->
   * guest ring buffer to indicate whether it should be signaled.
   */
  void hv_pkt_iter_close(struct vmbus_channel *channel)
  {
  	struct hv_ring_buffer_info *rbi = &channel->inbound;
  	u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
  
  	/*
  	 * Make sure all reads are done before we update the read index since
  	 * the writer may start writing to the read area once the read index
  	 * is updated.
  	 */
  	virt_rmb();
  	start_read_index = rbi->ring_buffer->read_index;
  	rbi->ring_buffer->read_index = rbi->priv_read_index;
  
  	/*
  	 * Older versions of Hyper-V (before WS2102 and Win8) do not
  	 * implement pending_send_sz and simply poll if the host->guest
  	 * ring buffer is full.  No signaling is needed or expected.
  	 */
  	if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
  		return;
  
  	/*
  	 * Issue a full memory barrier before making the signaling decision.
  	 * If reading pending_send_sz were to be reordered and happen
  	 * before we commit the new read_index, a race could occur.  If the
  	 * host were to set the pending_send_sz after we have sampled
  	 * pending_send_sz, and the ring buffer blocks before we commit the
  	 * read index, we could miss sending the interrupt. Issue a full
  	 * memory barrier to address this.
  	 */
  	virt_mb();
  
  	/*
  	 * If the pending_send_sz is zero, then the ring buffer is not
  	 * blocked and there is no need to signal.  This is far by the
  	 * most common case, so exit quickly for best performance.
  	 */
  	pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
  	if (!pending_sz)
  		return;
  
  	/*
  	 * Ensure the read of write_index in hv_get_bytes_to_write()
  	 * happens after the read of pending_send_sz.
  	 */
  	virt_rmb();
  	curr_write_sz = hv_get_bytes_to_write(rbi);
  	bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
  
  	/*
  	 * We want to signal the host only if we're transitioning
  	 * from a "not enough free space" state to a "enough free
  	 * space" state.  For example, it's possible that this function
  	 * could run and free up enough space to signal the host, and then
  	 * run again and free up additional space before the host has a
  	 * chance to clear the pending_send_sz.  The 2nd invocation would
  	 * be a null transition from "enough free space" to "enough free
  	 * space", which doesn't warrant a signal.
  	 *
  	 * Exactly filling the ring buffer is treated as "not enough
  	 * space". The ring buffer always must have at least one byte
  	 * empty so the empty and full conditions are distinguishable.
  	 * hv_get_bytes_to_write() doesn't fully tell the truth in
  	 * this regard.
  	 *
  	 * So first check if we were in the "enough free space" state
  	 * before we began the iteration. If so, the host was not
  	 * blocked, and there's no need to signal.
  	 */
  	if (curr_write_sz - bytes_read > pending_sz)
  		return;
  
  	/*
  	 * Similarly, if the new state is "not enough space", then
  	 * there's no need to signal.
  	 */
  	if (curr_write_sz <= pending_sz)
  		return;
  
  	++channel->intr_in_full;
  	vmbus_setevent(channel);
  }
  EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
  