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![Michael Kelley](/assets/img/avatar_default.png)
Fix bugs in signaling the Hyper-V host when freeing space in the
host->guest ring buffer:
1. The interrupt_mask must not be used to determine whether to signal
on the host->guest ring buffer
2. The ring buffer write_index must be read (via hv_get_bytes_to_write)
*after* pending_send_sz is read in order to avoid a race condition
3. Comparisons with pending_send_sz must treat the "equals" case as
not-enough-space
4. Don't signal if the pending_send_sz feature is not present. Older
versions of Hyper-V that don't implement this feature will poll.
Fixes: 03bad714a1
("vmbus: more host signalling avoidance")
Cc: Stable <stable@vger.kernel.org> # 4.14 and above
Signed-off-by: Michael Kelley <mhkelley@outlook.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
490 lines
14 KiB
C
490 lines
14 KiB
C
/*
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*
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* Copyright (c) 2009, Microsoft Corporation.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc., 59 Temple
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* Place - Suite 330, Boston, MA 02111-1307 USA.
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*
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* Authors:
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* Haiyang Zhang <haiyangz@microsoft.com>
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* Hank Janssen <hjanssen@microsoft.com>
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* K. Y. Srinivasan <kys@microsoft.com>
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*
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/hyperv.h>
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#include <linux/uio.h>
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#include <linux/vmalloc.h>
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#include <linux/slab.h>
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#include <linux/prefetch.h>
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#include "hyperv_vmbus.h"
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#define VMBUS_PKT_TRAILER 8
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/*
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* When we write to the ring buffer, check if the host needs to
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* be signaled. Here is the details of this protocol:
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*
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* 1. The host guarantees that while it is draining the
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* ring buffer, it will set the interrupt_mask to
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* indicate it does not need to be interrupted when
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* new data is placed.
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*
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* 2. The host guarantees that it will completely drain
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* the ring buffer before exiting the read loop. Further,
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* once the ring buffer is empty, it will clear the
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* interrupt_mask and re-check to see if new data has
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* arrived.
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*
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* KYS: Oct. 30, 2016:
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* It looks like Windows hosts have logic to deal with DOS attacks that
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* can be triggered if it receives interrupts when it is not expecting
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* the interrupt. The host expects interrupts only when the ring
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* transitions from empty to non-empty (or full to non full on the guest
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* to host ring).
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* So, base the signaling decision solely on the ring state until the
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* host logic is fixed.
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*/
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static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
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{
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struct hv_ring_buffer_info *rbi = &channel->outbound;
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virt_mb();
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if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
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return;
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/* check interrupt_mask before read_index */
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virt_rmb();
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/*
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* This is the only case we need to signal when the
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* ring transitions from being empty to non-empty.
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*/
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if (old_write == READ_ONCE(rbi->ring_buffer->read_index))
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vmbus_setevent(channel);
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}
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/* Get the next write location for the specified ring buffer. */
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static inline u32
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hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
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{
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u32 next = ring_info->ring_buffer->write_index;
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return next;
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}
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/* Set the next write location for the specified ring buffer. */
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static inline void
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hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
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u32 next_write_location)
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{
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ring_info->ring_buffer->write_index = next_write_location;
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}
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/* Set the next read location for the specified ring buffer. */
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static inline void
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hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
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u32 next_read_location)
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{
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ring_info->ring_buffer->read_index = next_read_location;
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ring_info->priv_read_index = next_read_location;
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}
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/* Get the size of the ring buffer. */
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static inline u32
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hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
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{
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return ring_info->ring_datasize;
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}
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/* Get the read and write indices as u64 of the specified ring buffer. */
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static inline u64
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hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
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{
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return (u64)ring_info->ring_buffer->write_index << 32;
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}
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/*
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* Helper routine to copy from source to ring buffer.
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* Assume there is enough room. Handles wrap-around in dest case only!!
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*/
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static u32 hv_copyto_ringbuffer(
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struct hv_ring_buffer_info *ring_info,
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u32 start_write_offset,
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const void *src,
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u32 srclen)
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{
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void *ring_buffer = hv_get_ring_buffer(ring_info);
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u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
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memcpy(ring_buffer + start_write_offset, src, srclen);
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start_write_offset += srclen;
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if (start_write_offset >= ring_buffer_size)
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start_write_offset -= ring_buffer_size;
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return start_write_offset;
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}
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/*
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*
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* hv_get_ringbuffer_availbytes()
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*
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* Get number of bytes available to read and to write to
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* for the specified ring buffer
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*/
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static void
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hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
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u32 *read, u32 *write)
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{
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u32 read_loc, write_loc, dsize;
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/* Capture the read/write indices before they changed */
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read_loc = READ_ONCE(rbi->ring_buffer->read_index);
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write_loc = READ_ONCE(rbi->ring_buffer->write_index);
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dsize = rbi->ring_datasize;
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*write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
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read_loc - write_loc;
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*read = dsize - *write;
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}
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/* Get various debug metrics for the specified ring buffer. */
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void hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
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struct hv_ring_buffer_debug_info *debug_info)
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{
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u32 bytes_avail_towrite;
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u32 bytes_avail_toread;
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if (ring_info->ring_buffer) {
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hv_get_ringbuffer_availbytes(ring_info,
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&bytes_avail_toread,
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&bytes_avail_towrite);
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debug_info->bytes_avail_toread = bytes_avail_toread;
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debug_info->bytes_avail_towrite = bytes_avail_towrite;
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debug_info->current_read_index =
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ring_info->ring_buffer->read_index;
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debug_info->current_write_index =
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ring_info->ring_buffer->write_index;
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debug_info->current_interrupt_mask =
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ring_info->ring_buffer->interrupt_mask;
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}
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}
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EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
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/* Initialize the ring buffer. */
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int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
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struct page *pages, u32 page_cnt)
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{
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int i;
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struct page **pages_wraparound;
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BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
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memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
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/*
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* First page holds struct hv_ring_buffer, do wraparound mapping for
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* the rest.
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*/
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pages_wraparound = kzalloc(sizeof(struct page *) * (page_cnt * 2 - 1),
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GFP_KERNEL);
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if (!pages_wraparound)
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return -ENOMEM;
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pages_wraparound[0] = pages;
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for (i = 0; i < 2 * (page_cnt - 1); i++)
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pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
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ring_info->ring_buffer = (struct hv_ring_buffer *)
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vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
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kfree(pages_wraparound);
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if (!ring_info->ring_buffer)
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return -ENOMEM;
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ring_info->ring_buffer->read_index =
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ring_info->ring_buffer->write_index = 0;
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/* Set the feature bit for enabling flow control. */
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ring_info->ring_buffer->feature_bits.value = 1;
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ring_info->ring_size = page_cnt << PAGE_SHIFT;
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ring_info->ring_datasize = ring_info->ring_size -
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sizeof(struct hv_ring_buffer);
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spin_lock_init(&ring_info->ring_lock);
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return 0;
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}
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/* Cleanup the ring buffer. */
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void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
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{
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vunmap(ring_info->ring_buffer);
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}
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/* Write to the ring buffer. */
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int hv_ringbuffer_write(struct vmbus_channel *channel,
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const struct kvec *kv_list, u32 kv_count)
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{
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int i;
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u32 bytes_avail_towrite;
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u32 totalbytes_towrite = sizeof(u64);
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u32 next_write_location;
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u32 old_write;
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u64 prev_indices;
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unsigned long flags;
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struct hv_ring_buffer_info *outring_info = &channel->outbound;
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if (channel->rescind)
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return -ENODEV;
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for (i = 0; i < kv_count; i++)
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totalbytes_towrite += kv_list[i].iov_len;
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spin_lock_irqsave(&outring_info->ring_lock, flags);
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bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
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/*
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* If there is only room for the packet, assume it is full.
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* Otherwise, the next time around, we think the ring buffer
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* is empty since the read index == write index.
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*/
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if (bytes_avail_towrite <= totalbytes_towrite) {
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spin_unlock_irqrestore(&outring_info->ring_lock, flags);
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return -EAGAIN;
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}
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/* Write to the ring buffer */
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next_write_location = hv_get_next_write_location(outring_info);
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old_write = next_write_location;
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for (i = 0; i < kv_count; i++) {
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next_write_location = hv_copyto_ringbuffer(outring_info,
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next_write_location,
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kv_list[i].iov_base,
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kv_list[i].iov_len);
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}
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/* Set previous packet start */
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prev_indices = hv_get_ring_bufferindices(outring_info);
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next_write_location = hv_copyto_ringbuffer(outring_info,
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next_write_location,
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&prev_indices,
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sizeof(u64));
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/* Issue a full memory barrier before updating the write index */
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virt_mb();
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/* Now, update the write location */
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hv_set_next_write_location(outring_info, next_write_location);
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spin_unlock_irqrestore(&outring_info->ring_lock, flags);
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hv_signal_on_write(old_write, channel);
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if (channel->rescind)
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return -ENODEV;
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return 0;
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}
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int hv_ringbuffer_read(struct vmbus_channel *channel,
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void *buffer, u32 buflen, u32 *buffer_actual_len,
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u64 *requestid, bool raw)
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{
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struct vmpacket_descriptor *desc;
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u32 packetlen, offset;
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if (unlikely(buflen == 0))
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return -EINVAL;
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*buffer_actual_len = 0;
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*requestid = 0;
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/* Make sure there is something to read */
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desc = hv_pkt_iter_first(channel);
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if (desc == NULL) {
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/*
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* No error is set when there is even no header, drivers are
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* supposed to analyze buffer_actual_len.
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*/
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return 0;
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}
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offset = raw ? 0 : (desc->offset8 << 3);
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packetlen = (desc->len8 << 3) - offset;
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*buffer_actual_len = packetlen;
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*requestid = desc->trans_id;
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if (unlikely(packetlen > buflen))
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return -ENOBUFS;
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/* since ring is double mapped, only one copy is necessary */
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memcpy(buffer, (const char *)desc + offset, packetlen);
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/* Advance ring index to next packet descriptor */
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__hv_pkt_iter_next(channel, desc);
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/* Notify host of update */
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hv_pkt_iter_close(channel);
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return 0;
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}
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/*
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* Determine number of bytes available in ring buffer after
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* the current iterator (priv_read_index) location.
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*
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* This is similar to hv_get_bytes_to_read but with private
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* read index instead.
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*/
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static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
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{
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u32 priv_read_loc = rbi->priv_read_index;
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u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index);
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if (write_loc >= priv_read_loc)
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return write_loc - priv_read_loc;
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else
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return (rbi->ring_datasize - priv_read_loc) + write_loc;
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}
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/*
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* Get first vmbus packet from ring buffer after read_index
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*
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* If ring buffer is empty, returns NULL and no other action needed.
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*/
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struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
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{
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struct hv_ring_buffer_info *rbi = &channel->inbound;
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struct vmpacket_descriptor *desc;
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if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
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return NULL;
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desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index;
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if (desc)
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prefetch((char *)desc + (desc->len8 << 3));
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return desc;
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}
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EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
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/*
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* Get next vmbus packet from ring buffer.
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*
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* Advances the current location (priv_read_index) and checks for more
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* data. If the end of the ring buffer is reached, then return NULL.
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*/
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struct vmpacket_descriptor *
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__hv_pkt_iter_next(struct vmbus_channel *channel,
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const struct vmpacket_descriptor *desc)
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{
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struct hv_ring_buffer_info *rbi = &channel->inbound;
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u32 packetlen = desc->len8 << 3;
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u32 dsize = rbi->ring_datasize;
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/* bump offset to next potential packet */
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rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
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if (rbi->priv_read_index >= dsize)
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rbi->priv_read_index -= dsize;
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/* more data? */
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return hv_pkt_iter_first(channel);
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}
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EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
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/* How many bytes were read in this iterator cycle */
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static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
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u32 start_read_index)
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{
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if (rbi->priv_read_index >= start_read_index)
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return rbi->priv_read_index - start_read_index;
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else
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return rbi->ring_datasize - start_read_index +
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rbi->priv_read_index;
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}
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/*
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* Update host ring buffer after iterating over packets.
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*/
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void hv_pkt_iter_close(struct vmbus_channel *channel)
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{
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struct hv_ring_buffer_info *rbi = &channel->inbound;
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u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
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/*
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* Make sure all reads are done before we update the read index since
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* the writer may start writing to the read area once the read index
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* is updated.
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*/
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virt_rmb();
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start_read_index = rbi->ring_buffer->read_index;
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rbi->ring_buffer->read_index = rbi->priv_read_index;
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if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
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return;
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/*
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* Issue a full memory barrier before making the signaling decision.
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* Here is the reason for having this barrier:
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* If the reading of the pend_sz (in this function)
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* were to be reordered and read before we commit the new read
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* index (in the calling function) we could
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* have a problem. If the host were to set the pending_sz after we
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* have sampled pending_sz and go to sleep before we commit the
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* read index, we could miss sending the interrupt. Issue a full
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* memory barrier to address this.
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*/
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virt_mb();
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pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
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if (!pending_sz)
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return;
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/*
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* Ensure the read of write_index in hv_get_bytes_to_write()
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* happens after the read of pending_send_sz.
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*/
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virt_rmb();
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curr_write_sz = hv_get_bytes_to_write(rbi);
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bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
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/*
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* If there was space before we began iteration,
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* then host was not blocked.
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*/
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if (curr_write_sz - bytes_read > pending_sz)
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return;
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/* If pending write will not fit, don't give false hope. */
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if (curr_write_sz <= pending_sz)
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return;
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vmbus_setevent(channel);
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}
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EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
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