linux-stable/drivers/hv/ring_buffer.c
Stephen Hemminger 15e1674de7 vmbus: add prefetch to ring buffer iterator
When iterating over incoming ring elements from the host, prefetch
the next descriptor so that it is cache hot.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-07-17 17:16:05 +02:00

449 lines
12 KiB
C

/*
*
* Copyright (c) 2009, Microsoft Corporation.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc., 59 Temple
* Place - Suite 330, Boston, MA 02111-1307 USA.
*
* 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))
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;
}
/* Get various debug metrics for the specified ring buffer. */
void hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
struct hv_ring_buffer_debug_info *debug_info)
{
u32 bytes_avail_towrite;
u32 bytes_avail_toread;
if (ring_info->ring_buffer) {
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;
}
}
EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
/* 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));
memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
/*
* First page holds struct hv_ring_buffer, do wraparound mapping for
* the rest.
*/
pages_wraparound = kzalloc(sizeof(struct page *) * (page_cnt * 2 - 1),
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_datasize = ring_info->ring_size -
sizeof(struct hv_ring_buffer);
spin_lock_init(&ring_info->ring_lock);
return 0;
}
/* Cleanup the ring buffer. */
void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
{
vunmap(ring_info->ring_buffer);
}
/* 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) {
spin_unlock_irqrestore(&outring_info->ring_lock, flags);
return -EAGAIN;
}
/* 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;
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;
/* 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);
/*
* Update host ring buffer after iterating over packets.
*/
void hv_pkt_iter_close(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
u32 orig_write_sz = hv_get_bytes_to_write(rbi);
/*
* 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();
rbi->ring_buffer->read_index = rbi->priv_read_index;
/*
* Issue a full memory barrier before making the signaling decision.
* Here is the reason for having this barrier:
* If the reading of the pend_sz (in this function)
* were to be reordered and read before we commit the new read
* index (in the calling function) we could
* have a problem. If the host were to set the pending_sz after we
* have sampled pending_sz and go to sleep before we commit the
* read index, we could miss sending the interrupt. Issue a full
* memory barrier to address this.
*/
virt_mb();
/* If host has disabled notifications then skip */
if (rbi->ring_buffer->interrupt_mask)
return;
if (rbi->ring_buffer->feature_bits.feat_pending_send_sz) {
u32 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
/*
* If there was space before we began iteration,
* then host was not blocked. Also handles case where
* pending_sz is zero then host has nothing pending
* and does not need to be signaled.
*/
if (orig_write_sz > pending_sz)
return;
/* If pending write will not fit, don't give false hope. */
if (hv_get_bytes_to_write(rbi) < pending_sz)
return;
}
vmbus_setevent(channel);
}
EXPORT_SYMBOL_GPL(hv_pkt_iter_close);