drivers/hv/connection.c - linux - Git at Google

 /*
  *
  * 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>
  *
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/delay.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/hyperv.h>
 #include <linux/export.h>
 #include <asm/hyperv.h>
 #include "hyperv_vmbus.h"


 struct vmbus_connection vmbus_connection = {
 	.conn_state		= DISCONNECTED,
 	.next_gpadl_handle	= ATOMIC_INIT(0xE1E10),
 };

 /*
  * Negotiated protocol version with the host.
  */
 __u32 vmbus_proto_version;
 EXPORT_SYMBOL_GPL(vmbus_proto_version);

 static __u32 vmbus_get_next_version(__u32 current_version)
 {
 	switch (current_version) {
 	case (VERSION_WIN7):
 		return VERSION_WS2008;

 	case (VERSION_WIN8):
 		return VERSION_WIN7;

 	case (VERSION_WIN8_1):
 		return VERSION_WIN8;

 	case (VERSION_WS2008):
 	default:
 		return VERSION_INVAL;
 	}
 }

 static int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo,
 					__u32 version)
 {
 	int ret = 0;
 	struct vmbus_channel_initiate_contact *msg;
 	unsigned long flags;

 	init_completion(&msginfo->waitevent);

 	msg = (struct vmbus_channel_initiate_contact *)msginfo->msg;

 	msg->header.msgtype = CHANNELMSG_INITIATE_CONTACT;
 	msg->vmbus_version_requested = version;
 	msg->interrupt_page = virt_to_phys(vmbus_connection.int_page);
 	msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages[0]);
 	msg->monitor_page2 = virt_to_phys(vmbus_connection.monitor_pages[1]);
 	if (version == VERSION_WIN8_1)
 		msg->target_vcpu = hv_context.vp_index[smp_processor_id()];

 	/*
 	 * Add to list before we send the request since we may
 	 * receive the response before returning from this routine
 	 */
 	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
 	list_add_tail(&msginfo->msglistentry,
 		      &vmbus_connection.chn_msg_list);

 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

 	ret = vmbus_post_msg(msg,
 			       sizeof(struct vmbus_channel_initiate_contact));
 	if (ret != 0) {
 		spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
 		list_del(&msginfo->msglistentry);
 		spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock,
 					flags);
 		return ret;
 	}

 	/* Wait for the connection response */
 	wait_for_completion(&msginfo->waitevent);

 	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
 	list_del(&msginfo->msglistentry);
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

 	/* Check if successful */
 	if (msginfo->response.version_response.version_supported) {
 		vmbus_connection.conn_state = CONNECTED;
 	} else {
 		return -ECONNREFUSED;
 	}

 	return ret;
 }

 /*
  * vmbus_connect - Sends a connect request on the partition service connection
  */
 int vmbus_connect(void)
 {
 	int ret = 0;
 	struct vmbus_channel_msginfo *msginfo = NULL;
 	__u32 version;

 	/* Initialize the vmbus connection */
 	vmbus_connection.conn_state = CONNECTING;
 	vmbus_connection.work_queue = create_workqueue("hv_vmbus_con");
 	if (!vmbus_connection.work_queue) {
 		ret = -ENOMEM;
 		goto cleanup;
 	}

 	INIT_LIST_HEAD(&vmbus_connection.chn_msg_list);
 	spin_lock_init(&vmbus_connection.channelmsg_lock);

 	INIT_LIST_HEAD(&vmbus_connection.chn_list);
 	spin_lock_init(&vmbus_connection.channel_lock);

 	/*
 	 * Setup the vmbus event connection for channel interrupt
 	 * abstraction stuff
 	 */
 	vmbus_connection.int_page =
 	(void *)__get_free_pages(GFP_KERNEL|__GFP_ZERO, 0);
 	if (vmbus_connection.int_page == NULL) {
 		ret = -ENOMEM;
 		goto cleanup;
 	}

 	vmbus_connection.recv_int_page = vmbus_connection.int_page;
 	vmbus_connection.send_int_page =
 		(void *)((unsigned long)vmbus_connection.int_page +
 			(PAGE_SIZE >> 1));

 	/*
 	 * Setup the monitor notification facility. The 1st page for
 	 * parent->child and the 2nd page for child->parent
 	 */
 	vmbus_connection.monitor_pages[0] = (void *)__get_free_pages((GFP_KERNEL|__GFP_ZERO), 0);
 	vmbus_connection.monitor_pages[1] = (void *)__get_free_pages((GFP_KERNEL|__GFP_ZERO), 0);
 	if ((vmbus_connection.monitor_pages[0] == NULL) ||
 	    (vmbus_connection.monitor_pages[1] == NULL)) {
 		ret = -ENOMEM;
 		goto cleanup;
 	}

 	msginfo = kzalloc(sizeof(*msginfo) +
 			  sizeof(struct vmbus_channel_initiate_contact),
 			  GFP_KERNEL);
 	if (msginfo == NULL) {
 		ret = -ENOMEM;
 		goto cleanup;
 	}

 	/*
 	 * Negotiate a compatible VMBUS version number with the
 	 * host. We start with the highest number we can support
 	 * and work our way down until we negotiate a compatible
 	 * version.
 	 */

 	version = VERSION_CURRENT;

 	do {
 		ret = vmbus_negotiate_version(msginfo, version);
 		if (ret == -ETIMEDOUT)
 			goto cleanup;

 		if (vmbus_connection.conn_state == CONNECTED)
 			break;

 		version = vmbus_get_next_version(version);
 	} while (version != VERSION_INVAL);

 	if (version == VERSION_INVAL)
 		goto cleanup;

 	vmbus_proto_version = version;
 	pr_info("Hyper-V Host Build:%d-%d.%d-%d-%d.%d; Vmbus version:%d.%d\n",
 		    host_info_eax, host_info_ebx >> 16,
 		    host_info_ebx & 0xFFFF, host_info_ecx,
 		    host_info_edx >> 24, host_info_edx & 0xFFFFFF,
 		    version >> 16, version & 0xFFFF);

 	kfree(msginfo);
 	return 0;

 cleanup:
 	pr_err("Unable to connect to host\n");
 	vmbus_connection.conn_state = DISCONNECTED;

 	if (vmbus_connection.work_queue)
 		destroy_workqueue(vmbus_connection.work_queue);

 	if (vmbus_connection.int_page) {
 		free_pages((unsigned long)vmbus_connection.int_page, 0);
 		vmbus_connection.int_page = NULL;
 	}

 	free_pages((unsigned long)vmbus_connection.monitor_pages[0], 1);
 	free_pages((unsigned long)vmbus_connection.monitor_pages[1], 1);
 	vmbus_connection.monitor_pages[0] = NULL;
 	vmbus_connection.monitor_pages[1] = NULL;

 	kfree(msginfo);

 	return ret;
 }

 /*
  * Map the given relid to the corresponding channel based on the
  * per-cpu list of channels that have been affinitized to this CPU.
  * This will be used in the channel callback path as we can do this
  * mapping in a lock-free fashion.
  */
 static struct vmbus_channel *pcpu_relid2channel(u32 relid)
 {
 	struct vmbus_channel *channel;
 	struct vmbus_channel *found_channel  = NULL;
 	int cpu = smp_processor_id();
 	struct list_head *pcpu_head = &hv_context.percpu_list[cpu];

 	list_for_each_entry(channel, pcpu_head, percpu_list) {
 		if (channel->offermsg.child_relid == relid) {
 			found_channel = channel;
 			break;
 		}
 	}

 	return found_channel;
 }

 /*
  * relid2channel - Get the channel object given its
  * child relative id (ie channel id)
  */
 struct vmbus_channel *relid2channel(u32 relid)
 {
 	struct vmbus_channel *channel;
 	struct vmbus_channel *found_channel  = NULL;
 	unsigned long flags;
 	struct list_head *cur, *tmp;
 	struct vmbus_channel *cur_sc;

 	spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		if (channel->offermsg.child_relid == relid) {
 			found_channel = channel;
 			break;
 		} else if (!list_empty(&channel->sc_list)) {
 			/*
 			 * Deal with sub-channels.
 			 */
 			list_for_each_safe(cur, tmp, &channel->sc_list) {
 				cur_sc = list_entry(cur, struct vmbus_channel,
 							sc_list);
 				if (cur_sc->offermsg.child_relid == relid) {
 					found_channel = cur_sc;
 					break;
 				}
 			}
 		}
 	}
 	spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);

 	return found_channel;
 }

 /*
  * process_chn_event - Process a channel event notification
  */
 static void process_chn_event(u32 relid)
 {
 	struct vmbus_channel *channel;
 	void *arg;
 	bool read_state;
 	u32 bytes_to_read;

 	/*
 	 * Find the channel based on this relid and invokes the
 	 * channel callback to process the event
 	 */
 	channel = pcpu_relid2channel(relid);

 	if (!channel) {
 		pr_err("channel not found for relid - %u\n", relid);
 		return;
 	}

 	/*
 	 * A channel once created is persistent even when there
 	 * is no driver handling the device. An unloading driver
 	 * sets the onchannel_callback to NULL on the same CPU
 	 * as where this interrupt is handled (in an interrupt context).
 	 * Thus, checking and invoking the driver specific callback takes
 	 * care of orderly unloading of the driver.
 	 */

 	if (channel->onchannel_callback != NULL) {
 		arg = channel->channel_callback_context;
 		read_state = channel->batched_reading;
 		/*
 		 * This callback reads the messages sent by the host.
 		 * We can 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 {
 			hv_begin_read(&channel->inbound);
 			channel->onchannel_callback(arg);
 			bytes_to_read = hv_end_read(&channel->inbound);
 		} while (read_state && (bytes_to_read != 0));
 	} else {
 		pr_err("no channel callback for relid - %u\n", relid);
 	}

 }

 /*
  * vmbus_on_event - Handler for events
  */
 void vmbus_on_event(unsigned long data)
 {
 	u32 dword;
 	u32 maxdword;
 	int bit;
 	u32 relid;
 	u32 *recv_int_page = NULL;
 	void *page_addr;
 	int cpu = smp_processor_id();
 	union hv_synic_event_flags *event;

 	if ((vmbus_proto_version == VERSION_WS2008) ||
 		(vmbus_proto_version == VERSION_WIN7)) {
 		maxdword = MAX_NUM_CHANNELS_SUPPORTED >> 5;
 		recv_int_page = vmbus_connection.recv_int_page;
 	} else {
 		/*
 		 * When the host is win8 and beyond, the event page
 		 * can be directly checked to get the id of the channel
 		 * that has the interrupt pending.
 		 */
 		maxdword = HV_EVENT_FLAGS_DWORD_COUNT;
 		page_addr = hv_context.synic_event_page[cpu];
 		event = (union hv_synic_event_flags *)page_addr +
 						 VMBUS_MESSAGE_SINT;
 		recv_int_page = event->flags32;
 	}


 	/* Check events */
 	if (!recv_int_page)
 		return;
 	for (dword = 0; dword < maxdword; dword++) {
 		if (!recv_int_page[dword])
 			continue;
 		for (bit = 0; bit < 32; bit++) {
 			if (sync_test_and_clear_bit(bit,
 				(unsigned long *)&recv_int_page[dword])) {
 				relid = (dword << 5) + bit;

 				if (relid == 0)
 					/*
 					 * Special case - vmbus
 					 * channel protocol msg
 					 */
 					continue;

 				process_chn_event(relid);
 			}
 		}
 	}
 }

 /*
  * vmbus_post_msg - Send a msg on the vmbus's message connection
  */
 int vmbus_post_msg(void *buffer, size_t buflen)
 {
 	union hv_connection_id conn_id;
 	int ret = 0;
 	int retries = 0;

 	conn_id.asu32 = 0;
 	conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;

 	/*
 	 * hv_post_message() can have transient failures because of
 	 * insufficient resources. Retry the operation a couple of
 	 * times before giving up.
 	 */
 	while (retries < 3) {
 		ret =  hv_post_message(conn_id, 1, buffer, buflen);
 		if (ret != HV_STATUS_INSUFFICIENT_BUFFERS)
 			return ret;
 		retries++;
 		msleep(100);
 	}
 	return ret;
 }

 /*
  * vmbus_set_event - Send an event notification to the parent
  */
 int vmbus_set_event(struct vmbus_channel *channel)
 {
 	u32 child_relid = channel->offermsg.child_relid;

 	if (!channel->is_dedicated_interrupt) {
 		/* Each u32 represents 32 channels */
 		sync_set_bit(child_relid & 31,
 			(unsigned long *)vmbus_connection.send_int_page +
 			(child_relid >> 5));
 	}

 	return hv_signal_event(channel->sig_event);
 }
	/*
	*
	* 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>
	*
	*/
	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/kernel.h>
	#include <linux/sched.h>
	#include <linux/wait.h>
	#include <linux/delay.h>
	#include <linux/mm.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/hyperv.h>
	#include <linux/export.h>
	#include <asm/hyperv.h>
	#include "hyperv_vmbus.h"


	struct vmbus_connection vmbus_connection = {
	.conn_state = DISCONNECTED,
	.next_gpadl_handle = ATOMIC_INIT(0xE1E10),
	};

	/*
	* Negotiated protocol version with the host.
	*/
	__u32 vmbus_proto_version;
	EXPORT_SYMBOL_GPL(vmbus_proto_version);

	static __u32 vmbus_get_next_version(__u32 current_version)
	{
	switch (current_version) {
	case (VERSION_WIN7):
	return VERSION_WS2008;

	case (VERSION_WIN8):
	return VERSION_WIN7;

	case (VERSION_WIN8_1):
	return VERSION_WIN8;

	case (VERSION_WS2008):
	default:
	return VERSION_INVAL;
	}
	}

	static int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo,
	__u32 version)
	{
	int ret = 0;
	struct vmbus_channel_initiate_contact *msg;
	unsigned long flags;

	init_completion(&msginfo->waitevent);

	msg = (struct vmbus_channel_initiate_contact *)msginfo->msg;

	msg->header.msgtype = CHANNELMSG_INITIATE_CONTACT;
	msg->vmbus_version_requested = version;
	msg->interrupt_page = virt_to_phys(vmbus_connection.int_page);
	msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages[0]);
	msg->monitor_page2 = virt_to_phys(vmbus_connection.monitor_pages[1]);
	if (version == VERSION_WIN8_1)
	msg->target_vcpu = hv_context.vp_index[smp_processor_id()];

	/*
	* Add to list before we send the request since we may
	* receive the response before returning from this routine
	*/
	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
	list_add_tail(&msginfo->msglistentry,
	&vmbus_connection.chn_msg_list);

	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

	ret = vmbus_post_msg(msg,
	sizeof(struct vmbus_channel_initiate_contact));
	if (ret != 0) {
	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
	list_del(&msginfo->msglistentry);
	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock,
	flags);
	return ret;
	}

	/* Wait for the connection response */
	wait_for_completion(&msginfo->waitevent);

	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
	list_del(&msginfo->msglistentry);
	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);

	/* Check if successful */
	if (msginfo->response.version_response.version_supported) {
	vmbus_connection.conn_state = CONNECTED;
	} else {
	return -ECONNREFUSED;
	}

	return ret;
	}

	/*
	* vmbus_connect - Sends a connect request on the partition service connection
	*/
	int vmbus_connect(void)
	{
	int ret = 0;
	struct vmbus_channel_msginfo *msginfo = NULL;
	__u32 version;

	/* Initialize the vmbus connection */
	vmbus_connection.conn_state = CONNECTING;
	vmbus_connection.work_queue = create_workqueue("hv_vmbus_con");
	if (!vmbus_connection.work_queue) {
	ret = -ENOMEM;
	goto cleanup;
	}

	INIT_LIST_HEAD(&vmbus_connection.chn_msg_list);
	spin_lock_init(&vmbus_connection.channelmsg_lock);

	INIT_LIST_HEAD(&vmbus_connection.chn_list);
	spin_lock_init(&vmbus_connection.channel_lock);

	/*
	* Setup the vmbus event connection for channel interrupt
	* abstraction stuff
	*/
	vmbus_connection.int_page =
	(void *)__get_free_pages(GFP_KERNEL\|__GFP_ZERO, 0);
	if (vmbus_connection.int_page == NULL) {
	ret = -ENOMEM;
	goto cleanup;
	}

	vmbus_connection.recv_int_page = vmbus_connection.int_page;
	vmbus_connection.send_int_page =
	(void *)((unsigned long)vmbus_connection.int_page +
	(PAGE_SIZE >> 1));

	/*
	* Setup the monitor notification facility. The 1st page for
	* parent->child and the 2nd page for child->parent
	*/
	vmbus_connection.monitor_pages[0] = (void *)__get_free_pages((GFP_KERNEL\|__GFP_ZERO), 0);
	vmbus_connection.monitor_pages[1] = (void *)__get_free_pages((GFP_KERNEL\|__GFP_ZERO), 0);
	if ((vmbus_connection.monitor_pages[0] == NULL) \|\|
	(vmbus_connection.monitor_pages[1] == NULL)) {
	ret = -ENOMEM;
	goto cleanup;
	}

	msginfo = kzalloc(sizeof(*msginfo) +
	sizeof(struct vmbus_channel_initiate_contact),
	GFP_KERNEL);
	if (msginfo == NULL) {
	ret = -ENOMEM;
	goto cleanup;
	}

	/*
	* Negotiate a compatible VMBUS version number with the
	* host. We start with the highest number we can support
	* and work our way down until we negotiate a compatible
	* version.
	*/

	version = VERSION_CURRENT;

	do {
	ret = vmbus_negotiate_version(msginfo, version);
	if (ret == -ETIMEDOUT)
	goto cleanup;

	if (vmbus_connection.conn_state == CONNECTED)
	break;

	version = vmbus_get_next_version(version);
	} while (version != VERSION_INVAL);

	if (version == VERSION_INVAL)
	goto cleanup;

	vmbus_proto_version = version;
	pr_info("Hyper-V Host Build:%d-%d.%d-%d-%d.%d; Vmbus version:%d.%d\n",
	host_info_eax, host_info_ebx >> 16,
	host_info_ebx & 0xFFFF, host_info_ecx,
	host_info_edx >> 24, host_info_edx & 0xFFFFFF,
	version >> 16, version & 0xFFFF);

	kfree(msginfo);
	return 0;

	cleanup:
	pr_err("Unable to connect to host\n");
	vmbus_connection.conn_state = DISCONNECTED;

	if (vmbus_connection.work_queue)
	destroy_workqueue(vmbus_connection.work_queue);

	if (vmbus_connection.int_page) {
	free_pages((unsigned long)vmbus_connection.int_page, 0);
	vmbus_connection.int_page = NULL;
	}

	free_pages((unsigned long)vmbus_connection.monitor_pages[0], 1);
	free_pages((unsigned long)vmbus_connection.monitor_pages[1], 1);
	vmbus_connection.monitor_pages[0] = NULL;
	vmbus_connection.monitor_pages[1] = NULL;

	kfree(msginfo);

	return ret;
	}

	/*
	* Map the given relid to the corresponding channel based on the
	* per-cpu list of channels that have been affinitized to this CPU.
	* This will be used in the channel callback path as we can do this
	* mapping in a lock-free fashion.
	*/
	static struct vmbus_channel *pcpu_relid2channel(u32 relid)
	{
	struct vmbus_channel *channel;
	struct vmbus_channel *found_channel = NULL;
	int cpu = smp_processor_id();
	struct list_head *pcpu_head = &hv_context.percpu_list[cpu];

	list_for_each_entry(channel, pcpu_head, percpu_list) {
	if (channel->offermsg.child_relid == relid) {
	found_channel = channel;
	break;
	}
	}

	return found_channel;
	}

	/*
	* relid2channel - Get the channel object given its
	* child relative id (ie channel id)
	*/
	struct vmbus_channel *relid2channel(u32 relid)
	{
	struct vmbus_channel *channel;
	struct vmbus_channel *found_channel = NULL;
	unsigned long flags;
	struct list_head cur, tmp;
	struct vmbus_channel *cur_sc;

	spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
	if (channel->offermsg.child_relid == relid) {
	found_channel = channel;
	break;
	} else if (!list_empty(&channel->sc_list)) {
	/*
	* Deal with sub-channels.
	*/
	list_for_each_safe(cur, tmp, &channel->sc_list) {
	cur_sc = list_entry(cur, struct vmbus_channel,
	sc_list);
	if (cur_sc->offermsg.child_relid == relid) {
	found_channel = cur_sc;
	break;
	}
	}
	}
	}
	spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);

	return found_channel;
	}

	/*
	* process_chn_event - Process a channel event notification
	*/
	static void process_chn_event(u32 relid)
	{
	struct vmbus_channel *channel;
	void *arg;
	bool read_state;
	u32 bytes_to_read;

	/*
	* Find the channel based on this relid and invokes the
	* channel callback to process the event
	*/
	channel = pcpu_relid2channel(relid);

	if (!channel) {
	pr_err("channel not found for relid - %u\n", relid);
	return;
	}

	/*
	* A channel once created is persistent even when there
	* is no driver handling the device. An unloading driver
	* sets the onchannel_callback to NULL on the same CPU
	* as where this interrupt is handled (in an interrupt context).
	* Thus, checking and invoking the driver specific callback takes
	* care of orderly unloading of the driver.
	*/

	if (channel->onchannel_callback != NULL) {
	arg = channel->channel_callback_context;
	read_state = channel->batched_reading;
	/*
	* This callback reads the messages sent by the host.
	* We can 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 {
	hv_begin_read(&channel->inbound);
	channel->onchannel_callback(arg);
	bytes_to_read = hv_end_read(&channel->inbound);
	} while (read_state && (bytes_to_read != 0));
	} else {
	pr_err("no channel callback for relid - %u\n", relid);
	}

	}

	/*
	* vmbus_on_event - Handler for events
	*/
	void vmbus_on_event(unsigned long data)
	{
	u32 dword;
	u32 maxdword;
	int bit;
	u32 relid;
	u32 *recv_int_page = NULL;
	void *page_addr;
	int cpu = smp_processor_id();
	union hv_synic_event_flags *event;

	if ((vmbus_proto_version == VERSION_WS2008) \|\|
	(vmbus_proto_version == VERSION_WIN7)) {
	maxdword = MAX_NUM_CHANNELS_SUPPORTED >> 5;
	recv_int_page = vmbus_connection.recv_int_page;
	} else {
	/*
	* When the host is win8 and beyond, the event page
	* can be directly checked to get the id of the channel
	* that has the interrupt pending.
	*/
	maxdword = HV_EVENT_FLAGS_DWORD_COUNT;
	page_addr = hv_context.synic_event_page[cpu];
	event = (union hv_synic_event_flags *)page_addr +
	VMBUS_MESSAGE_SINT;
	recv_int_page = event->flags32;
	}



	/* Check events */
	if (!recv_int_page)
	return;
	for (dword = 0; dword < maxdword; dword++) {
	if (!recv_int_page[dword])
	continue;
	for (bit = 0; bit < 32; bit++) {
	if (sync_test_and_clear_bit(bit,
	(unsigned long *)&recv_int_page[dword])) {
	relid = (dword << 5) + bit;

	if (relid == 0)
	/*
	* Special case - vmbus
	* channel protocol msg
	*/
	continue;

	process_chn_event(relid);
	}
	}
	}
	}

	/*
	* vmbus_post_msg - Send a msg on the vmbus's message connection
	*/
	int vmbus_post_msg(void *buffer, size_t buflen)
	{
	union hv_connection_id conn_id;
	int ret = 0;
	int retries = 0;

	conn_id.asu32 = 0;
	conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;

	/*
	* hv_post_message() can have transient failures because of
	* insufficient resources. Retry the operation a couple of
	* times before giving up.
	*/
	while (retries < 3) {
	ret = hv_post_message(conn_id, 1, buffer, buflen);
	if (ret != HV_STATUS_INSUFFICIENT_BUFFERS)
	return ret;
	retries++;
	msleep(100);
	}
	return ret;
	}

	/*
	* vmbus_set_event - Send an event notification to the parent
	*/
	int vmbus_set_event(struct vmbus_channel *channel)
	{
	u32 child_relid = channel->offermsg.child_relid;

	if (!channel->is_dedicated_interrupt) {
	/* Each u32 represents 32 channels */
	sync_set_bit(child_relid & 31,
	(unsigned long *)vmbus_connection.send_int_page +
	(child_relid >> 5));
	}

	return hv_signal_event(channel->sig_event);
	}