xref: /freebsd-11-stable/sys/dev/hyperv/vmbus/vmbus_chan.c

/*-
 * Copyright (c) 2009-2012,2016 Microsoft Corp.
 * Copyright (c) 2012 NetApp Inc.
 * Copyright (c) 2012 Citrix Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/sys/dev/hyperv/vmbus/hv_channel.c 302633 2016-07-12 08:28:51Z sephe $");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sysctl.h>

#include <machine/atomic.h>
#include <machine/bus.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>

#include <dev/hyperv/vmbus/hv_vmbus_priv.h>
#include <dev/hyperv/vmbus/hyperv_var.h>
#include <dev/hyperv/vmbus/vmbus_reg.h>
#include <dev/hyperv/vmbus/vmbus_var.h>

static void 	vmbus_channel_set_event(hv_vmbus_channel* channel);
static void	VmbusProcessChannelEvent(void* channel, int pending);

/**
 *  @brief Trigger an event notification on the specified channel
 */
static void
vmbus_channel_set_event(hv_vmbus_channel *channel)
{
	struct vmbus_softc *sc = channel->vmbus_sc;
	uint32_t chanid = channel->offer_msg.child_rel_id;

	atomic_set_long(&sc->vmbus_tx_evtflags[chanid >> VMBUS_EVTFLAG_SHIFT],
	    1UL << (chanid & VMBUS_EVTFLAG_MASK));

	if (channel->offer_msg.monitor_allocated) {
		hv_vmbus_monitor_page *monitor_page;

		monitor_page = sc->vmbus_mnf2;
		synch_set_bit(channel->monitor_bit,
			(uint32_t *)&monitor_page->
				trigger_group[channel->monitor_group].u.pending);
	} else {
		hypercall_signal_event(channel->ch_sigevt_dma.hv_paddr);
	}

}

static int
vmbus_channel_sysctl_monalloc(SYSCTL_HANDLER_ARGS)
{
	struct hv_vmbus_channel *chan = arg1;
	int alloc = 0;

	if (chan->offer_msg.monitor_allocated)
		alloc = 1;
	return sysctl_handle_int(oidp, &alloc, 0, req);
}

static void
vmbus_channel_sysctl_create(hv_vmbus_channel* channel)
{
	device_t dev;
	struct sysctl_oid *devch_sysctl;
	struct sysctl_oid *devch_id_sysctl, *devch_sub_sysctl;
	struct sysctl_oid *devch_id_in_sysctl, *devch_id_out_sysctl;
	struct sysctl_ctx_list *ctx;
	uint32_t ch_id;
	uint16_t sub_ch_id;
	char name[16];

	hv_vmbus_channel* primary_ch = channel->primary_channel;

	if (primary_ch == NULL) {
		dev = channel->device->device;
		ch_id = channel->offer_msg.child_rel_id;
	} else {
		dev = primary_ch->device->device;
		ch_id = primary_ch->offer_msg.child_rel_id;
		sub_ch_id = channel->offer_msg.offer.sub_channel_index;
	}
	ctx = &channel->ch_sysctl_ctx;
	sysctl_ctx_init(ctx);
	/* This creates dev.DEVNAME.DEVUNIT.channel tree */
	devch_sysctl = SYSCTL_ADD_NODE(ctx,
		    SYSCTL_CHILDREN(device_get_sysctl_tree(dev)),
		    OID_AUTO, "channel", CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");
	/* This creates dev.DEVNAME.DEVUNIT.channel.CHANID tree */
	snprintf(name, sizeof(name), "%d", ch_id);
	devch_id_sysctl = SYSCTL_ADD_NODE(ctx,
	    	    SYSCTL_CHILDREN(devch_sysctl),
	    	    OID_AUTO, name, CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");

	if (primary_ch != NULL) {
		devch_sub_sysctl = SYSCTL_ADD_NODE(ctx,
			SYSCTL_CHILDREN(devch_id_sysctl),
			OID_AUTO, "sub", CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");
		snprintf(name, sizeof(name), "%d", sub_ch_id);
		devch_id_sysctl = SYSCTL_ADD_NODE(ctx,
			SYSCTL_CHILDREN(devch_sub_sysctl),
			OID_AUTO, name, CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");

		SYSCTL_ADD_UINT(ctx, SYSCTL_CHILDREN(devch_id_sysctl),
		    OID_AUTO, "chanid", CTLFLAG_RD,
		    &channel->offer_msg.child_rel_id, 0, "channel id");
	}
	SYSCTL_ADD_UINT(ctx, SYSCTL_CHILDREN(devch_id_sysctl), OID_AUTO,
	    "cpu", CTLFLAG_RD, &channel->target_cpu, 0, "owner CPU id");
	SYSCTL_ADD_PROC(ctx, SYSCTL_CHILDREN(devch_id_sysctl), OID_AUTO,
	    "monitor_allocated", CTLTYPE_INT | CTLFLAG_RD | CTLFLAG_MPSAFE,
	    channel, 0, vmbus_channel_sysctl_monalloc, "I",
	    "is monitor allocated to this channel");

	devch_id_in_sysctl = SYSCTL_ADD_NODE(ctx,
                    SYSCTL_CHILDREN(devch_id_sysctl),
                    OID_AUTO,
		    "in",
		    CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");
	devch_id_out_sysctl = SYSCTL_ADD_NODE(ctx,
                    SYSCTL_CHILDREN(devch_id_sysctl),
                    OID_AUTO,
		    "out",
		    CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "");
	hv_ring_buffer_stat(ctx,
		SYSCTL_CHILDREN(devch_id_in_sysctl),
		&(channel->inbound),
		"inbound ring buffer stats");
	hv_ring_buffer_stat(ctx,
		SYSCTL_CHILDREN(devch_id_out_sysctl),
		&(channel->outbound),
		"outbound ring buffer stats");
}

/**
 * @brief Open the specified channel
 */
int
hv_vmbus_channel_open(
	hv_vmbus_channel*		new_channel,
	uint32_t			send_ring_buffer_size,
	uint32_t			recv_ring_buffer_size,
	void*				user_data,
	uint32_t			user_data_len,
	hv_vmbus_pfn_channel_callback	pfn_on_channel_callback,
	void* 				context)
{
	struct vmbus_softc *sc = new_channel->vmbus_sc;
	const struct vmbus_chanmsg_chopen_resp *resp;
	const struct vmbus_message *msg;
	struct vmbus_chanmsg_chopen *req;
	struct vmbus_msghc *mh;
	uint32_t status;
	int ret = 0;
	void *in, *out;

	if (user_data_len > VMBUS_CHANMSG_CHOPEN_UDATA_SIZE) {
		device_printf(sc->vmbus_dev,
		    "invalid udata len %u for chan%u\n",
		    user_data_len, new_channel->offer_msg.child_rel_id);
		return EINVAL;
	}

	mtx_lock(&new_channel->sc_lock);
	if (new_channel->state == HV_CHANNEL_OPEN_STATE) {
	    new_channel->state = HV_CHANNEL_OPENING_STATE;
	} else {
	    mtx_unlock(&new_channel->sc_lock);
	    if(bootverbose)
		printf("VMBUS: Trying to open channel <%p> which in "
		    "%d state.\n", new_channel, new_channel->state);
	    return (EINVAL);
	}
	mtx_unlock(&new_channel->sc_lock);

	new_channel->on_channel_callback = pfn_on_channel_callback;
	new_channel->channel_callback_context = context;

	vmbus_on_channel_open(new_channel);

	new_channel->rxq = VMBUS_PCPU_GET(new_channel->vmbus_sc, event_tq,
	    new_channel->target_cpu);
	TASK_INIT(&new_channel->channel_task, 0, VmbusProcessChannelEvent, new_channel);

	/* Allocate the ring buffer */
	out = contigmalloc((send_ring_buffer_size + recv_ring_buffer_size),
	    M_DEVBUF, M_ZERO, 0UL, BUS_SPACE_MAXADDR, PAGE_SIZE, 0);
	KASSERT(out != NULL,
	    ("Error VMBUS: contigmalloc failed to allocate Ring Buffer!"));
	if (out == NULL)
		return (ENOMEM);

	in = ((uint8_t *) out + send_ring_buffer_size);

	new_channel->ring_buffer_pages = out;
	new_channel->ring_buffer_page_count = (send_ring_buffer_size +
	    recv_ring_buffer_size) >> PAGE_SHIFT;
	new_channel->ring_buffer_size = send_ring_buffer_size +
	    recv_ring_buffer_size;

	hv_vmbus_ring_buffer_init(
		&new_channel->outbound,
		out,
		send_ring_buffer_size);

	hv_vmbus_ring_buffer_init(
		&new_channel->inbound,
		in,
		recv_ring_buffer_size);

	/* Create sysctl tree for this channel */
	vmbus_channel_sysctl_create(new_channel);

	/**
	 * Establish the gpadl for the ring buffer
	 */
	new_channel->ring_buffer_gpadl_handle = 0;

	ret = hv_vmbus_channel_establish_gpadl(new_channel,
		new_channel->outbound.ring_buffer,
		send_ring_buffer_size + recv_ring_buffer_size,
		&new_channel->ring_buffer_gpadl_handle);

	/*
	 * Open channel w/ the bufring GPADL on the target CPU.
	 */
	mh = vmbus_msghc_get(sc, sizeof(*req));
	if (mh == NULL) {
		device_printf(sc->vmbus_dev,
		    "can not get msg hypercall for chopen(chan%u)\n",
		    new_channel->offer_msg.child_rel_id);
		return ENXIO;
	}

	req = vmbus_msghc_dataptr(mh);
	req->chm_hdr.chm_type = VMBUS_CHANMSG_TYPE_CHOPEN;
	req->chm_chanid = new_channel->offer_msg.child_rel_id;
	req->chm_openid = new_channel->offer_msg.child_rel_id;
	req->chm_gpadl = new_channel->ring_buffer_gpadl_handle;
	req->chm_vcpuid = new_channel->target_vcpu;
	req->chm_rxbr_pgofs = send_ring_buffer_size >> PAGE_SHIFT;
	if (user_data_len)
		memcpy(req->chm_udata, user_data, user_data_len);

	ret = vmbus_msghc_exec(sc, mh);
	if (ret != 0) {
		device_printf(sc->vmbus_dev,
		    "chopen(chan%u) msg hypercall exec failed: %d\n",
		    new_channel->offer_msg.child_rel_id, ret);
		vmbus_msghc_put(sc, mh);
		return ret;
	}

	msg = vmbus_msghc_wait_result(sc, mh);
	resp = (const struct vmbus_chanmsg_chopen_resp *)msg->msg_data;
	status = resp->chm_status;

	vmbus_msghc_put(sc, mh);

	if (status == 0) {
		new_channel->state = HV_CHANNEL_OPENED_STATE;
		if (bootverbose) {
			device_printf(sc->vmbus_dev, "chan%u opened\n",
			    new_channel->offer_msg.child_rel_id);
		}
	} else {
		device_printf(sc->vmbus_dev, "failed to open chan%u\n",
		    new_channel->offer_msg.child_rel_id);
		ret = ENXIO;
	}
	return (ret);
}

/**
 * @brief Establish a GPADL for the specified buffer
 */
int
hv_vmbus_channel_establish_gpadl(struct hv_vmbus_channel *channel,
    void *contig_buffer, uint32_t size, uint32_t *gpadl0)
{
	struct vmbus_softc *sc = channel->vmbus_sc;
	struct vmbus_msghc *mh;
	struct vmbus_chanmsg_gpadl_conn *req;
	const struct vmbus_message *msg;
	size_t reqsz;
	uint32_t gpadl, status;
	int page_count, range_len, i, cnt, error;
	uint64_t page_id, paddr;

	/*
	 * Preliminary checks.
	 */

	KASSERT((size & PAGE_MASK) == 0,
	    ("invalid GPA size %u, not multiple page size", size));
	page_count = size >> PAGE_SHIFT;

	paddr = hv_get_phys_addr(contig_buffer);
	KASSERT((paddr & PAGE_MASK) == 0,
	    ("GPA is not page aligned %jx", (uintmax_t)paddr));
	page_id = paddr >> PAGE_SHIFT;

	range_len = __offsetof(struct vmbus_gpa_range, gpa_page[page_count]);
	/*
	 * We don't support multiple GPA ranges.
	 */
	if (range_len > UINT16_MAX) {
		device_printf(sc->vmbus_dev, "GPA too large, %d pages\n",
		    page_count);
		return EOPNOTSUPP;
	}

	/*
	 * Allocate GPADL id.
	 */
	gpadl = vmbus_gpadl_alloc(sc);
	*gpadl0 = gpadl;

	/*
	 * Connect this GPADL to the target channel.
	 *
	 * NOTE:
	 * Since each message can only hold small set of page
	 * addresses, several messages may be required to
	 * complete the connection.
	 */
	if (page_count > VMBUS_CHANMSG_GPADL_CONN_PGMAX)
		cnt = VMBUS_CHANMSG_GPADL_CONN_PGMAX;
	else
		cnt = page_count;
	page_count -= cnt;

	reqsz = __offsetof(struct vmbus_chanmsg_gpadl_conn,
	    chm_range.gpa_page[cnt]);
	mh = vmbus_msghc_get(sc, reqsz);
	if (mh == NULL) {
		device_printf(sc->vmbus_dev,
		    "can not get msg hypercall for gpadl->chan%u\n",
		    channel->offer_msg.child_rel_id);
		return EIO;
	}

	req = vmbus_msghc_dataptr(mh);
	req->chm_hdr.chm_type = VMBUS_CHANMSG_TYPE_GPADL_CONN;
	req->chm_chanid = channel->offer_msg.child_rel_id;
	req->chm_gpadl = gpadl;
	req->chm_range_len = range_len;
	req->chm_range_cnt = 1;
	req->chm_range.gpa_len = size;
	req->chm_range.gpa_ofs = 0;
	for (i = 0; i < cnt; ++i)
		req->chm_range.gpa_page[i] = page_id++;

	error = vmbus_msghc_exec(sc, mh);
	if (error) {
		device_printf(sc->vmbus_dev,
		    "gpadl->chan%u msg hypercall exec failed: %d\n",
		    channel->offer_msg.child_rel_id, error);
		vmbus_msghc_put(sc, mh);
		return error;
	}

	while (page_count > 0) {
		struct vmbus_chanmsg_gpadl_subconn *subreq;

		if (page_count > VMBUS_CHANMSG_GPADL_SUBCONN_PGMAX)
			cnt = VMBUS_CHANMSG_GPADL_SUBCONN_PGMAX;
		else
			cnt = page_count;
		page_count -= cnt;

		reqsz = __offsetof(struct vmbus_chanmsg_gpadl_subconn,
		    chm_gpa_page[cnt]);
		vmbus_msghc_reset(mh, reqsz);

		subreq = vmbus_msghc_dataptr(mh);
		subreq->chm_hdr.chm_type = VMBUS_CHANMSG_TYPE_GPADL_SUBCONN;
		subreq->chm_gpadl = gpadl;
		for (i = 0; i < cnt; ++i)
			subreq->chm_gpa_page[i] = page_id++;

		vmbus_msghc_exec_noresult(mh);
	}
	KASSERT(page_count == 0, ("invalid page count %d", page_count));

	msg = vmbus_msghc_wait_result(sc, mh);
	status = ((const struct vmbus_chanmsg_gpadl_connresp *)
	    msg->msg_data)->chm_status;

	vmbus_msghc_put(sc, mh);

	if (status != 0) {
		device_printf(sc->vmbus_dev, "gpadl->chan%u failed: "
		    "status %u\n", channel->offer_msg.child_rel_id, status);
		return EIO;
	} else {
		if (bootverbose) {
			device_printf(sc->vmbus_dev, "gpadl->chan%u "
			    "succeeded\n", channel->offer_msg.child_rel_id);
		}
	}
	return 0;
}

/*
 * Disconnect the GPA from the target channel
 */
int
hv_vmbus_channel_teardown_gpdal(struct hv_vmbus_channel *chan, uint32_t gpadl)
{
	struct vmbus_softc *sc = chan->vmbus_sc;
	struct vmbus_msghc *mh;
	struct vmbus_chanmsg_gpadl_disconn *req;
	int error;

	mh = vmbus_msghc_get(sc, sizeof(*req));
	if (mh == NULL) {
		device_printf(sc->vmbus_dev,
		    "can not get msg hypercall for gpa x->chan%u\n",
		    chan->offer_msg.child_rel_id);
		return EBUSY;
	}

	req = vmbus_msghc_dataptr(mh);
	req->chm_hdr.chm_type = VMBUS_CHANMSG_TYPE_GPADL_DISCONN;
	req->chm_chanid = chan->offer_msg.child_rel_id;
	req->chm_gpadl = gpadl;

	error = vmbus_msghc_exec(sc, mh);
	if (error) {
		device_printf(sc->vmbus_dev,
		    "gpa x->chan%u msg hypercall exec failed: %d\n",
		    chan->offer_msg.child_rel_id, error);
		vmbus_msghc_put(sc, mh);
		return error;
	}

	vmbus_msghc_wait_result(sc, mh);
	/* Discard result; no useful information */
	vmbus_msghc_put(sc, mh);

	return 0;
}

static void
hv_vmbus_channel_close_internal(hv_vmbus_channel *channel)
{
	struct vmbus_softc *sc = channel->vmbus_sc;
	struct vmbus_msghc *mh;
	struct vmbus_chanmsg_chclose *req;
	struct taskqueue *rxq = channel->rxq;
	int error;

	channel->state = HV_CHANNEL_OPEN_STATE;
	sysctl_ctx_free(&channel->ch_sysctl_ctx);

	/*
	 * set rxq to NULL to avoid more requests be scheduled
	 */
	channel->rxq = NULL;
	taskqueue_drain(rxq, &channel->channel_task);
	channel->on_channel_callback = NULL;

	/**
	 * Send a closing message
	 */

	mh = vmbus_msghc_get(sc, sizeof(*req));
	if (mh == NULL) {
		device_printf(sc->vmbus_dev,
		    "can not get msg hypercall for chclose(chan%u)\n",
		    channel->offer_msg.child_rel_id);
		return;
	}

	req = vmbus_msghc_dataptr(mh);
	req->chm_hdr.chm_type = VMBUS_CHANMSG_TYPE_CHCLOSE;
	req->chm_chanid = channel->offer_msg.child_rel_id;

	error = vmbus_msghc_exec_noresult(mh);
	vmbus_msghc_put(sc, mh);

	if (error) {
		device_printf(sc->vmbus_dev,
		    "chclose(chan%u) msg hypercall exec failed: %d\n",
		    channel->offer_msg.child_rel_id, error);
		return;
	} else if (bootverbose) {
		device_printf(sc->vmbus_dev, "close chan%u\n",
		    channel->offer_msg.child_rel_id);
	}

	/* Tear down the gpadl for the channel's ring buffer */
	if (channel->ring_buffer_gpadl_handle) {
		hv_vmbus_channel_teardown_gpdal(channel,
			channel->ring_buffer_gpadl_handle);
	}

	/* TODO: Send a msg to release the childRelId */

	/* cleanup the ring buffers for this channel */
	hv_ring_buffer_cleanup(&channel->outbound);
	hv_ring_buffer_cleanup(&channel->inbound);

	contigfree(channel->ring_buffer_pages, channel->ring_buffer_size,
	    M_DEVBUF);
}

/**
 * @brief Close the specified channel
 */
void
hv_vmbus_channel_close(hv_vmbus_channel *channel)
{
	hv_vmbus_channel*	sub_channel;

	if (channel->primary_channel != NULL) {
		/*
		 * We only close multi-channels when the primary is
		 * closed.
		 */
		return;
	}

	/*
	 * Close all multi-channels first.
	 */
	TAILQ_FOREACH(sub_channel, &channel->sc_list_anchor,
	    sc_list_entry) {
		if (sub_channel->state != HV_CHANNEL_OPENED_STATE)
			continue;
		hv_vmbus_channel_close_internal(sub_channel);
	}
	/*
	 * Then close the primary channel.
	 */
	hv_vmbus_channel_close_internal(channel);
}

/**
 * @brief Send the specified buffer on the given channel
 */
int
hv_vmbus_channel_send_packet(
	hv_vmbus_channel*	channel,
	void*			buffer,
	uint32_t		buffer_len,
	uint64_t		request_id,
	hv_vmbus_packet_type	type,
	uint32_t		flags)
{
	int			ret = 0;
	hv_vm_packet_descriptor	desc;
	uint32_t		packet_len;
	uint64_t		aligned_data;
	uint32_t		packet_len_aligned;
	boolean_t		need_sig;
	hv_vmbus_sg_buffer_list	buffer_list[3];

	packet_len = sizeof(hv_vm_packet_descriptor) + buffer_len;
	packet_len_aligned = HV_ALIGN_UP(packet_len, sizeof(uint64_t));
	aligned_data = 0;

	/* Setup the descriptor */
	desc.type = type;   /* HV_VMBUS_PACKET_TYPE_DATA_IN_BAND;             */
	desc.flags = flags; /* HV_VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED */
			    /* in 8-bytes granularity */
	desc.data_offset8 = sizeof(hv_vm_packet_descriptor) >> 3;
	desc.length8 = (uint16_t) (packet_len_aligned >> 3);
	desc.transaction_id = request_id;

	buffer_list[0].data = &desc;
	buffer_list[0].length = sizeof(hv_vm_packet_descriptor);

	buffer_list[1].data = buffer;
	buffer_list[1].length = buffer_len;

	buffer_list[2].data = &aligned_data;
	buffer_list[2].length = packet_len_aligned - packet_len;

	ret = hv_ring_buffer_write(&channel->outbound, buffer_list, 3,
	    &need_sig);

	/* TODO: We should determine if this is optional */
	if (ret == 0 && need_sig) {
		vmbus_channel_set_event(channel);
	}

	return (ret);
}

/**
 * @brief Send a range of single-page buffer packets using
 * a GPADL Direct packet type
 */
int
hv_vmbus_channel_send_packet_pagebuffer(
	hv_vmbus_channel*	channel,
	hv_vmbus_page_buffer	page_buffers[],
	uint32_t		page_count,
	void*			buffer,
	uint32_t		buffer_len,
	uint64_t		request_id)
{

	int					ret = 0;
	boolean_t				need_sig;
	uint32_t				packet_len;
	uint32_t				page_buflen;
	uint32_t				packetLen_aligned;
	hv_vmbus_sg_buffer_list			buffer_list[4];
	hv_vmbus_channel_packet_page_buffer	desc;
	uint32_t				descSize;
	uint64_t				alignedData = 0;

	if (page_count > HV_MAX_PAGE_BUFFER_COUNT)
		return (EINVAL);

	/*
	 * Adjust the size down since hv_vmbus_channel_packet_page_buffer
	 *  is the largest size we support
	 */
	descSize = __offsetof(hv_vmbus_channel_packet_page_buffer, range);
	page_buflen = sizeof(hv_vmbus_page_buffer) * page_count;
	packet_len = descSize + page_buflen + buffer_len;
	packetLen_aligned = HV_ALIGN_UP(packet_len, sizeof(uint64_t));

	/* Setup the descriptor */
	desc.type = HV_VMBUS_PACKET_TYPE_DATA_USING_GPA_DIRECT;
	desc.flags = HV_VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
	/* in 8-bytes granularity */
	desc.data_offset8 = (descSize + page_buflen) >> 3;
	desc.length8 = (uint16_t) (packetLen_aligned >> 3);
	desc.transaction_id = request_id;
	desc.range_count = page_count;

	buffer_list[0].data = &desc;
	buffer_list[0].length = descSize;

	buffer_list[1].data = page_buffers;
	buffer_list[1].length = page_buflen;

	buffer_list[2].data = buffer;
	buffer_list[2].length = buffer_len;

	buffer_list[3].data = &alignedData;
	buffer_list[3].length = packetLen_aligned - packet_len;

	ret = hv_ring_buffer_write(&channel->outbound, buffer_list, 4,
	    &need_sig);

	/* TODO: We should determine if this is optional */
	if (ret == 0 && need_sig) {
		vmbus_channel_set_event(channel);
	}

	return (ret);
}

/**
 * @brief Send a multi-page buffer packet using a GPADL Direct packet type
 */
int
hv_vmbus_channel_send_packet_multipagebuffer(
	hv_vmbus_channel*		channel,
	hv_vmbus_multipage_buffer*	multi_page_buffer,
	void*				buffer,
	uint32_t			buffer_len,
	uint64_t			request_id)
{

	int			ret = 0;
	uint32_t		desc_size;
	boolean_t		need_sig;
	uint32_t		packet_len;
	uint32_t		packet_len_aligned;
	uint32_t		pfn_count;
	uint64_t		aligned_data = 0;
	hv_vmbus_sg_buffer_list	buffer_list[3];
	hv_vmbus_channel_packet_multipage_buffer desc;

	pfn_count =
	    HV_NUM_PAGES_SPANNED(
		    multi_page_buffer->offset,
		    multi_page_buffer->length);

	if ((pfn_count == 0) || (pfn_count > HV_MAX_MULTIPAGE_BUFFER_COUNT))
	    return (EINVAL);
	/*
	 * Adjust the size down since hv_vmbus_channel_packet_multipage_buffer
	 * is the largest size we support
	 */
	desc_size =
	    sizeof(hv_vmbus_channel_packet_multipage_buffer) -
		    ((HV_MAX_MULTIPAGE_BUFFER_COUNT - pfn_count) *
			sizeof(uint64_t));
	packet_len = desc_size + buffer_len;
	packet_len_aligned = HV_ALIGN_UP(packet_len, sizeof(uint64_t));

	/*
	 * Setup the descriptor
	 */
	desc.type = HV_VMBUS_PACKET_TYPE_DATA_USING_GPA_DIRECT;
	desc.flags = HV_VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
	desc.data_offset8 = desc_size >> 3; /* in 8-bytes granularity */
	desc.length8 = (uint16_t) (packet_len_aligned >> 3);
	desc.transaction_id = request_id;
	desc.range_count = 1;

	desc.range.length = multi_page_buffer->length;
	desc.range.offset = multi_page_buffer->offset;

	memcpy(desc.range.pfn_array, multi_page_buffer->pfn_array,
		pfn_count * sizeof(uint64_t));

	buffer_list[0].data = &desc;
	buffer_list[0].length = desc_size;

	buffer_list[1].data = buffer;
	buffer_list[1].length = buffer_len;

	buffer_list[2].data = &aligned_data;
	buffer_list[2].length = packet_len_aligned - packet_len;

	ret = hv_ring_buffer_write(&channel->outbound, buffer_list, 3,
	    &need_sig);

	/* TODO: We should determine if this is optional */
	if (ret == 0 && need_sig) {
	    vmbus_channel_set_event(channel);
	}

	return (ret);
}

/**
 * @brief Retrieve the user packet on the specified channel
 */
int
hv_vmbus_channel_recv_packet(
	hv_vmbus_channel*	channel,
	void*			Buffer,
	uint32_t		buffer_len,
	uint32_t*		buffer_actual_len,
	uint64_t*		request_id)
{
	int			ret;
	uint32_t		user_len;
	uint32_t		packet_len;
	hv_vm_packet_descriptor	desc;

	*buffer_actual_len = 0;
	*request_id = 0;

	ret = hv_ring_buffer_peek(&channel->inbound, &desc,
		sizeof(hv_vm_packet_descriptor));
	if (ret != 0)
		return (0);

	packet_len = desc.length8 << 3;
	user_len = packet_len - (desc.data_offset8 << 3);

	*buffer_actual_len = user_len;

	if (user_len > buffer_len)
		return (EINVAL);

	*request_id = desc.transaction_id;

	/* Copy over the packet to the user buffer */
	ret = hv_ring_buffer_read(&channel->inbound, Buffer, user_len,
		(desc.data_offset8 << 3));

	return (0);
}

/**
 * @brief Retrieve the raw packet on the specified channel
 */
int
hv_vmbus_channel_recv_packet_raw(
	hv_vmbus_channel*	channel,
	void*			buffer,
	uint32_t		buffer_len,
	uint32_t*		buffer_actual_len,
	uint64_t*		request_id)
{
	int		ret;
	uint32_t	packetLen;
	hv_vm_packet_descriptor	desc;

	*buffer_actual_len = 0;
	*request_id = 0;

	ret = hv_ring_buffer_peek(
		&channel->inbound, &desc,
		sizeof(hv_vm_packet_descriptor));

	if (ret != 0)
	    return (0);

	packetLen = desc.length8 << 3;
	*buffer_actual_len = packetLen;

	if (packetLen > buffer_len)
	    return (ENOBUFS);

	*request_id = desc.transaction_id;

	/* Copy over the entire packet to the user buffer */
	ret = hv_ring_buffer_read(&channel->inbound, buffer, packetLen, 0);

	return (0);
}


/**
 * Process a channel event notification
 */
static void
VmbusProcessChannelEvent(void* context, int pending)
{
	void* arg;
	uint32_t bytes_to_read;
	hv_vmbus_channel* channel = (hv_vmbus_channel*)context;
	boolean_t is_batched_reading;

	if (channel->on_channel_callback != NULL) {
		arg = channel->channel_callback_context;
		is_batched_reading = channel->batched_reading;
		/*
		 * Optimize host to guest signaling by ensuring:
		 * 1. While reading the channel, we disable interrupts from
		 *    host.
		 * 2. Ensure that we process all posted messages from the host
		 *    before returning from this callback.
		 * 3. Once we return, enable signaling from the host. Once this
		 *    state is set we check to see if additional packets are
		 *    available to read. In this case we repeat the process.
		 */
		do {
			if (is_batched_reading)
				hv_ring_buffer_read_begin(&channel->inbound);

			channel->on_channel_callback(arg);

			if (is_batched_reading)
				bytes_to_read =
				    hv_ring_buffer_read_end(&channel->inbound);
			else
				bytes_to_read = 0;
		} while (is_batched_reading && (bytes_to_read != 0));
	}
}