Linux 4.19-rc5

[linux/fpc-iii.git] / drivers / hv / ring_buffer.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;
}

/*
 *
 * 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. */
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 = 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);

        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);

/* 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;

        vmbus_setevent(channel);
}
EXPORT_SYMBOL_GPL(hv_pkt_iter_close);