timekeeping: Repair ktime_get_coarse*() granularity

[mirror_ubuntu-jammy-kernel.git] / drivers / hv / channel_mgmt.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>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/hyperv.h>
#include <asm/mshyperv.h>

#include "hyperv_vmbus.h"

static void init_vp_index(struct vmbus_channel *channel, u16 dev_type);

static const struct vmbus_device vmbus_devs[] = {
        /* IDE */
        { .dev_type = HV_IDE,
          HV_IDE_GUID,
          .perf_device = true,
        },

        /* SCSI */
        { .dev_type = HV_SCSI,
          HV_SCSI_GUID,
          .perf_device = true,
        },

        /* Fibre Channel */
        { .dev_type = HV_FC,
          HV_SYNTHFC_GUID,
          .perf_device = true,
        },

        /* Synthetic NIC */
        { .dev_type = HV_NIC,
          HV_NIC_GUID,
          .perf_device = true,
        },

        /* Network Direct */
        { .dev_type = HV_ND,
          HV_ND_GUID,
          .perf_device = true,
        },

        /* PCIE */
        { .dev_type = HV_PCIE,
          HV_PCIE_GUID,
          .perf_device = false,
        },

        /* Synthetic Frame Buffer */
        { .dev_type = HV_FB,
          HV_SYNTHVID_GUID,
          .perf_device = false,
        },

        /* Synthetic Keyboard */
        { .dev_type = HV_KBD,
          HV_KBD_GUID,
          .perf_device = false,
        },

        /* Synthetic MOUSE */
        { .dev_type = HV_MOUSE,
          HV_MOUSE_GUID,
          .perf_device = false,
        },

        /* KVP */
        { .dev_type = HV_KVP,
          HV_KVP_GUID,
          .perf_device = false,
        },

        /* Time Synch */
        { .dev_type = HV_TS,
          HV_TS_GUID,
          .perf_device = false,
        },

        /* Heartbeat */
        { .dev_type = HV_HB,
          HV_HEART_BEAT_GUID,
          .perf_device = false,
        },

        /* Shutdown */
        { .dev_type = HV_SHUTDOWN,
          HV_SHUTDOWN_GUID,
          .perf_device = false,
        },

        /* File copy */
        { .dev_type = HV_FCOPY,
          HV_FCOPY_GUID,
          .perf_device = false,
        },

        /* Backup */
        { .dev_type = HV_BACKUP,
          HV_VSS_GUID,
          .perf_device = false,
        },

        /* Dynamic Memory */
        { .dev_type = HV_DM,
          HV_DM_GUID,
          .perf_device = false,
        },

        /* Unknown GUID */
        { .dev_type = HV_UNKNOWN,
          .perf_device = false,
        },
};

static const struct {
        guid_t guid;
} vmbus_unsupported_devs[] = {
        { HV_AVMA1_GUID },
        { HV_AVMA2_GUID },
        { HV_RDV_GUID   },
};

/*
 * The rescinded channel may be blocked waiting for a response from the host;
 * take care of that.
 */
static void vmbus_rescind_cleanup(struct vmbus_channel *channel)
{
        struct vmbus_channel_msginfo *msginfo;
        unsigned long flags;


        spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
        channel->rescind = true;
        list_for_each_entry(msginfo, &vmbus_connection.chn_msg_list,
                                msglistentry) {

                if (msginfo->waiting_channel == channel) {
                        complete(&msginfo->waitevent);
                        break;
                }
        }
        spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
}

static bool is_unsupported_vmbus_devs(const guid_t *guid)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(vmbus_unsupported_devs); i++)
                if (guid_equal(guid, &vmbus_unsupported_devs[i].guid))
                        return true;
        return false;
}

static u16 hv_get_dev_type(const struct vmbus_channel *channel)
{
        const guid_t *guid = &channel->offermsg.offer.if_type;
        u16 i;

        if (is_hvsock_channel(channel) || is_unsupported_vmbus_devs(guid))
                return HV_UNKNOWN;

        for (i = HV_IDE; i < HV_UNKNOWN; i++) {
                if (guid_equal(guid, &vmbus_devs[i].guid))
                        return i;
        }
        pr_info("Unknown GUID: %pUl\n", guid);
        return i;
}

/**
 * vmbus_prep_negotiate_resp() - Create default response for Negotiate message
 * @icmsghdrp: Pointer to msg header structure
 * @buf: Raw buffer channel data
 * @fw_version: The framework versions we can support.
 * @fw_vercnt: The size of @fw_version.
 * @srv_version: The service versions we can support.
 * @srv_vercnt: The size of @srv_version.
 * @nego_fw_version: The selected framework version.
 * @nego_srv_version: The selected service version.
 *
 * Note: Versions are given in decreasing order.
 *
 * Set up and fill in default negotiate response message.
 * Mainly used by Hyper-V drivers.
 */
bool vmbus_prep_negotiate_resp(struct icmsg_hdr *icmsghdrp,
                                u8 *buf, const int *fw_version, int fw_vercnt,
                                const int *srv_version, int srv_vercnt,
                                int *nego_fw_version, int *nego_srv_version)
{
        int icframe_major, icframe_minor;
        int icmsg_major, icmsg_minor;
        int fw_major, fw_minor;
        int srv_major, srv_minor;
        int i, j;
        bool found_match = false;
        struct icmsg_negotiate *negop;

        icmsghdrp->icmsgsize = 0x10;
        negop = (struct icmsg_negotiate *)&buf[
                sizeof(struct vmbuspipe_hdr) +
                sizeof(struct icmsg_hdr)];

        icframe_major = negop->icframe_vercnt;
        icframe_minor = 0;

        icmsg_major = negop->icmsg_vercnt;
        icmsg_minor = 0;

        /*
         * Select the framework version number we will
         * support.
         */

        for (i = 0; i < fw_vercnt; i++) {
                fw_major = (fw_version[i] >> 16);
                fw_minor = (fw_version[i] & 0xFFFF);

                for (j = 0; j < negop->icframe_vercnt; j++) {
                        if ((negop->icversion_data[j].major == fw_major) &&
                            (negop->icversion_data[j].minor == fw_minor)) {
                                icframe_major = negop->icversion_data[j].major;
                                icframe_minor = negop->icversion_data[j].minor;
                                found_match = true;
                                break;
                        }
                }

                if (found_match)
                        break;
        }

        if (!found_match)
                goto fw_error;

        found_match = false;

        for (i = 0; i < srv_vercnt; i++) {
                srv_major = (srv_version[i] >> 16);
                srv_minor = (srv_version[i] & 0xFFFF);

                for (j = negop->icframe_vercnt;
                        (j < negop->icframe_vercnt + negop->icmsg_vercnt);
                        j++) {

                        if ((negop->icversion_data[j].major == srv_major) &&
                                (negop->icversion_data[j].minor == srv_minor)) {

                                icmsg_major = negop->icversion_data[j].major;
                                icmsg_minor = negop->icversion_data[j].minor;
                                found_match = true;
                                break;
                        }
                }

                if (found_match)
                        break;
        }

        /*
         * Respond with the framework and service
         * version numbers we can support.
         */

fw_error:
        if (!found_match) {
                negop->icframe_vercnt = 0;
                negop->icmsg_vercnt = 0;
        } else {
                negop->icframe_vercnt = 1;
                negop->icmsg_vercnt = 1;
        }

        if (nego_fw_version)
                *nego_fw_version = (icframe_major << 16) | icframe_minor;

        if (nego_srv_version)
                *nego_srv_version = (icmsg_major << 16) | icmsg_minor;

        negop->icversion_data[0].major = icframe_major;
        negop->icversion_data[0].minor = icframe_minor;
        negop->icversion_data[1].major = icmsg_major;
        negop->icversion_data[1].minor = icmsg_minor;
        return found_match;
}

EXPORT_SYMBOL_GPL(vmbus_prep_negotiate_resp);

/*
 * alloc_channel - Allocate and initialize a vmbus channel object
 */
static struct vmbus_channel *alloc_channel(void)
{
        struct vmbus_channel *channel;

        channel = kzalloc(sizeof(*channel), GFP_ATOMIC);
        if (!channel)
                return NULL;

        spin_lock_init(&channel->lock);
        init_completion(&channel->rescind_event);

        INIT_LIST_HEAD(&channel->sc_list);
        INIT_LIST_HEAD(&channel->percpu_list);

        tasklet_init(&channel->callback_event,
                     vmbus_on_event, (unsigned long)channel);

        hv_ringbuffer_pre_init(channel);

        return channel;
}

/*
 * free_channel - Release the resources used by the vmbus channel object
 */
static void free_channel(struct vmbus_channel *channel)
{
        tasklet_kill(&channel->callback_event);
        vmbus_remove_channel_attr_group(channel);

        kobject_put(&channel->kobj);
}

static void percpu_channel_enq(void *arg)
{
        struct vmbus_channel *channel = arg;
        struct hv_per_cpu_context *hv_cpu
                = this_cpu_ptr(hv_context.cpu_context);

        list_add_tail_rcu(&channel->percpu_list, &hv_cpu->chan_list);
}

static void percpu_channel_deq(void *arg)
{
        struct vmbus_channel *channel = arg;

        list_del_rcu(&channel->percpu_list);
}


static void vmbus_release_relid(u32 relid)
{
        struct vmbus_channel_relid_released msg;
        int ret;

        memset(&msg, 0, sizeof(struct vmbus_channel_relid_released));
        msg.child_relid = relid;
        msg.header.msgtype = CHANNELMSG_RELID_RELEASED;
        ret = vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released),
                             true);

        trace_vmbus_release_relid(&msg, ret);
}

void hv_process_channel_removal(struct vmbus_channel *channel)
{
        struct vmbus_channel *primary_channel;
        unsigned long flags;

        BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
        BUG_ON(!channel->rescind);

        if (channel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(channel->target_cpu,
                                         percpu_channel_deq, channel, true);
        } else {
                percpu_channel_deq(channel);
                put_cpu();
        }

        if (channel->primary_channel == NULL) {
                list_del(&channel->listentry);

                primary_channel = channel;
        } else {
                primary_channel = channel->primary_channel;
                spin_lock_irqsave(&primary_channel->lock, flags);
                list_del(&channel->sc_list);
                spin_unlock_irqrestore(&primary_channel->lock, flags);
        }

        /*
         * We need to free the bit for init_vp_index() to work in the case
         * of sub-channel, when we reload drivers like hv_netvsc.
         */
        if (channel->affinity_policy == HV_LOCALIZED)
                cpumask_clear_cpu(channel->target_cpu,
                                  &primary_channel->alloced_cpus_in_node);

        vmbus_release_relid(channel->offermsg.child_relid);

        free_channel(channel);
}

void vmbus_free_channels(void)
{
        struct vmbus_channel *channel, *tmp;

        list_for_each_entry_safe(channel, tmp, &vmbus_connection.chn_list,
                listentry) {
                /* hv_process_channel_removal() needs this */
                channel->rescind = true;

                vmbus_device_unregister(channel->device_obj);
        }
}

/* Note: the function can run concurrently for primary/sub channels. */
static void vmbus_add_channel_work(struct work_struct *work)
{
        struct vmbus_channel *newchannel =
                container_of(work, struct vmbus_channel, add_channel_work);
        struct vmbus_channel *primary_channel = newchannel->primary_channel;
        unsigned long flags;
        u16 dev_type;
        int ret;

        dev_type = hv_get_dev_type(newchannel);

        init_vp_index(newchannel, dev_type);

        if (newchannel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(newchannel->target_cpu,
                                         percpu_channel_enq,
                                         newchannel, true);
        } else {
                percpu_channel_enq(newchannel);
                put_cpu();
        }

        /*
         * This state is used to indicate a successful open
         * so that when we do close the channel normally, we
         * can cleanup properly.
         */
        newchannel->state = CHANNEL_OPEN_STATE;

        if (primary_channel != NULL) {
                /* newchannel is a sub-channel. */
                struct hv_device *dev = primary_channel->device_obj;

                if (vmbus_add_channel_kobj(dev, newchannel))
                        goto err_deq_chan;

                if (primary_channel->sc_creation_callback != NULL)
                        primary_channel->sc_creation_callback(newchannel);

                newchannel->probe_done = true;
                return;
        }

        /*
         * Start the process of binding the primary channel to the driver
         */
        newchannel->device_obj = vmbus_device_create(
                &newchannel->offermsg.offer.if_type,
                &newchannel->offermsg.offer.if_instance,
                newchannel);
        if (!newchannel->device_obj)
                goto err_deq_chan;

        newchannel->device_obj->device_id = dev_type;
        /*
         * Add the new device to the bus. This will kick off device-driver
         * binding which eventually invokes the device driver's AddDevice()
         * method.
         */
        ret = vmbus_device_register(newchannel->device_obj);

        if (ret != 0) {
                pr_err("unable to add child device object (relid %d)\n",
                        newchannel->offermsg.child_relid);
                kfree(newchannel->device_obj);
                goto err_deq_chan;
        }

        newchannel->probe_done = true;
        return;

err_deq_chan:
        mutex_lock(&vmbus_connection.channel_mutex);

        /*
         * We need to set the flag, otherwise
         * vmbus_onoffer_rescind() can be blocked.
         */
        newchannel->probe_done = true;

        if (primary_channel == NULL) {
                list_del(&newchannel->listentry);
        } else {
                spin_lock_irqsave(&primary_channel->lock, flags);
                list_del(&newchannel->sc_list);
                spin_unlock_irqrestore(&primary_channel->lock, flags);
        }

        mutex_unlock(&vmbus_connection.channel_mutex);

        if (newchannel->target_cpu != get_cpu()) {
                put_cpu();
                smp_call_function_single(newchannel->target_cpu,
                                         percpu_channel_deq,
                                         newchannel, true);
        } else {
                percpu_channel_deq(newchannel);
                put_cpu();
        }

        vmbus_release_relid(newchannel->offermsg.child_relid);

        free_channel(newchannel);
}

/*
 * vmbus_process_offer - Process the offer by creating a channel/device
 * associated with this offer
 */
static void vmbus_process_offer(struct vmbus_channel *newchannel)
{
        struct vmbus_channel *channel;
        struct workqueue_struct *wq;
        unsigned long flags;
        bool fnew = true;

        mutex_lock(&vmbus_connection.channel_mutex);

        /*
         * Now that we have acquired the channel_mutex,
         * we can release the potentially racing rescind thread.
         */
        atomic_dec(&vmbus_connection.offer_in_progress);

        list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
                if (guid_equal(&channel->offermsg.offer.if_type,
                               &newchannel->offermsg.offer.if_type) &&
                    guid_equal(&channel->offermsg.offer.if_instance,
                               &newchannel->offermsg.offer.if_instance)) {
                        fnew = false;
                        break;
                }
        }

        if (fnew)
                list_add_tail(&newchannel->listentry,
                              &vmbus_connection.chn_list);
        else {
                /*
                 * Check to see if this is a valid sub-channel.
                 */
                if (newchannel->offermsg.offer.sub_channel_index == 0) {
                        mutex_unlock(&vmbus_connection.channel_mutex);
                        /*
                         * Don't call free_channel(), because newchannel->kobj
                         * is not initialized yet.
                         */
                        kfree(newchannel);
                        WARN_ON_ONCE(1);
                        return;
                }
                /*
                 * Process the sub-channel.
                 */
                newchannel->primary_channel = channel;
                spin_lock_irqsave(&channel->lock, flags);
                list_add_tail(&newchannel->sc_list, &channel->sc_list);
                spin_unlock_irqrestore(&channel->lock, flags);
        }

        mutex_unlock(&vmbus_connection.channel_mutex);

        /*
         * vmbus_process_offer() mustn't call channel->sc_creation_callback()
         * directly for sub-channels, because sc_creation_callback() ->
         * vmbus_open() may never get the host's response to the
         * OPEN_CHANNEL message (the host may rescind a channel at any time,
         * e.g. in the case of hot removing a NIC), and vmbus_onoffer_rescind()
         * may not wake up the vmbus_open() as it's blocked due to a non-zero
         * vmbus_connection.offer_in_progress, and finally we have a deadlock.
         *
         * The above is also true for primary channels, if the related device
         * drivers use sync probing mode by default.
         *
         * And, usually the handling of primary channels and sub-channels can
         * depend on each other, so we should offload them to different
         * workqueues to avoid possible deadlock, e.g. in sync-probing mode,
         * NIC1's netvsc_subchan_work() can race with NIC2's netvsc_probe() ->
         * rtnl_lock(), and causes deadlock: the former gets the rtnl_lock
         * and waits for all the sub-channels to appear, but the latter
         * can't get the rtnl_lock and this blocks the handling of
         * sub-channels.
         */
        INIT_WORK(&newchannel->add_channel_work, vmbus_add_channel_work);
        wq = fnew ? vmbus_connection.handle_primary_chan_wq :
                    vmbus_connection.handle_sub_chan_wq;
        queue_work(wq, &newchannel->add_channel_work);
}

/*
 * We use this state to statically distribute the channel interrupt load.
 */
static int next_numa_node_id;
/*
 * init_vp_index() accesses global variables like next_numa_node_id, and
 * it can run concurrently for primary channels and sub-channels: see
 * vmbus_process_offer(), so we need the lock to protect the global
 * variables.
 */
static DEFINE_SPINLOCK(bind_channel_to_cpu_lock);

/*
 * Starting with Win8, we can statically distribute the incoming
 * channel interrupt load by binding a channel to VCPU.
 * We distribute the interrupt loads to one or more NUMA nodes based on
 * the channel's affinity_policy.
 *
 * For pre-win8 hosts or non-performance critical channels we assign the
 * first CPU in the first NUMA node.
 */
static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
{
        u32 cur_cpu;
        bool perf_chn = vmbus_devs[dev_type].perf_device;
        struct vmbus_channel *primary = channel->primary_channel;
        int next_node;
        cpumask_var_t available_mask;
        struct cpumask *alloced_mask;

        if ((vmbus_proto_version == VERSION_WS2008) ||
            (vmbus_proto_version == VERSION_WIN7) || (!perf_chn) ||
            !alloc_cpumask_var(&available_mask, GFP_KERNEL)) {
                /*
                 * Prior to win8, all channel interrupts are
                 * delivered on cpu 0.
                 * Also if the channel is not a performance critical
                 * channel, bind it to cpu 0.
                 * In case alloc_cpumask_var() fails, bind it to cpu 0.
                 */
                channel->numa_node = 0;
                channel->target_cpu = 0;
                channel->target_vp = hv_cpu_number_to_vp_number(0);
                return;
        }

        spin_lock(&bind_channel_to_cpu_lock);

        /*
         * Based on the channel affinity policy, we will assign the NUMA
         * nodes.
         */

        if ((channel->affinity_policy == HV_BALANCED) || (!primary)) {
                while (true) {
                        next_node = next_numa_node_id++;
                        if (next_node == nr_node_ids) {
                                next_node = next_numa_node_id = 0;
                                continue;
                        }
                        if (cpumask_empty(cpumask_of_node(next_node)))
                                continue;
                        break;
                }
                channel->numa_node = next_node;
                primary = channel;
        }
        alloced_mask = &hv_context.hv_numa_map[primary->numa_node];

        if (cpumask_weight(alloced_mask) ==
            cpumask_weight(cpumask_of_node(primary->numa_node))) {
                /*
                 * We have cycled through all the CPUs in the node;
                 * reset the alloced map.
                 */
                cpumask_clear(alloced_mask);
        }

        cpumask_xor(available_mask, alloced_mask,
                    cpumask_of_node(primary->numa_node));

        cur_cpu = -1;

        if (primary->affinity_policy == HV_LOCALIZED) {
                /*
                 * Normally Hyper-V host doesn't create more subchannels
                 * than there are VCPUs on the node but it is possible when not
                 * all present VCPUs on the node are initialized by guest.
                 * Clear the alloced_cpus_in_node to start over.
                 */
                if (cpumask_equal(&primary->alloced_cpus_in_node,
                                  cpumask_of_node(primary->numa_node)))
                        cpumask_clear(&primary->alloced_cpus_in_node);
        }

        while (true) {
                cur_cpu = cpumask_next(cur_cpu, available_mask);
                if (cur_cpu >= nr_cpu_ids) {
                        cur_cpu = -1;
                        cpumask_copy(available_mask,
                                     cpumask_of_node(primary->numa_node));
                        continue;
                }

                if (primary->affinity_policy == HV_LOCALIZED) {
                        /*
                         * NOTE: in the case of sub-channel, we clear the
                         * sub-channel related bit(s) in
                         * primary->alloced_cpus_in_node in
                         * hv_process_channel_removal(), so when we
                         * reload drivers like hv_netvsc in SMP guest, here
                         * we're able to re-allocate
                         * bit from primary->alloced_cpus_in_node.
                         */
                        if (!cpumask_test_cpu(cur_cpu,
                                              &primary->alloced_cpus_in_node)) {
                                cpumask_set_cpu(cur_cpu,
                                                &primary->alloced_cpus_in_node);
                                cpumask_set_cpu(cur_cpu, alloced_mask);
                                break;
                        }
                } else {
                        cpumask_set_cpu(cur_cpu, alloced_mask);
                        break;
                }
        }

        channel->target_cpu = cur_cpu;
        channel->target_vp = hv_cpu_number_to_vp_number(cur_cpu);

        spin_unlock(&bind_channel_to_cpu_lock);

        free_cpumask_var(available_mask);
}

static void vmbus_wait_for_unload(void)
{
        int cpu;
        void *page_addr;
        struct hv_message *msg;
        struct vmbus_channel_message_header *hdr;
        u32 message_type;

        /*
         * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
         * used for initial contact or to CPU0 depending on host version. When
         * we're crashing on a different CPU let's hope that IRQ handler on
         * the cpu which receives CHANNELMSG_UNLOAD_RESPONSE is still
         * functional and vmbus_unload_response() will complete
         * vmbus_connection.unload_event. If not, the last thing we can do is
         * read message pages for all CPUs directly.
         */
        while (1) {
                if (completion_done(&vmbus_connection.unload_event))
                        break;

                for_each_online_cpu(cpu) {
                        struct hv_per_cpu_context *hv_cpu
                                = per_cpu_ptr(hv_context.cpu_context, cpu);

                        page_addr = hv_cpu->synic_message_page;
                        msg = (struct hv_message *)page_addr
                                + VMBUS_MESSAGE_SINT;

                        message_type = READ_ONCE(msg->header.message_type);
                        if (message_type == HVMSG_NONE)
                                continue;

                        hdr = (struct vmbus_channel_message_header *)
                                msg->u.payload;

                        if (hdr->msgtype == CHANNELMSG_UNLOAD_RESPONSE)
                                complete(&vmbus_connection.unload_event);

                        vmbus_signal_eom(msg, message_type);
                }

                mdelay(10);
        }

        /*
         * We're crashing and already got the UNLOAD_RESPONSE, cleanup all
         * maybe-pending messages on all CPUs to be able to receive new
         * messages after we reconnect.
         */
        for_each_online_cpu(cpu) {
                struct hv_per_cpu_context *hv_cpu
                        = per_cpu_ptr(hv_context.cpu_context, cpu);

                page_addr = hv_cpu->synic_message_page;
                msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
                msg->header.message_type = HVMSG_NONE;
        }
}

/*
 * vmbus_unload_response - Handler for the unload response.
 */
static void vmbus_unload_response(struct vmbus_channel_message_header *hdr)
{
        /*
         * This is a global event; just wakeup the waiting thread.
         * Once we successfully unload, we can cleanup the monitor state.
         */
        complete(&vmbus_connection.unload_event);
}

void vmbus_initiate_unload(bool crash)
{
        struct vmbus_channel_message_header hdr;

        /* Pre-Win2012R2 hosts don't support reconnect */
        if (vmbus_proto_version < VERSION_WIN8_1)
                return;

        init_completion(&vmbus_connection.unload_event);
        memset(&hdr, 0, sizeof(struct vmbus_channel_message_header));
        hdr.msgtype = CHANNELMSG_UNLOAD;
        vmbus_post_msg(&hdr, sizeof(struct vmbus_channel_message_header),
                       !crash);

        /*
         * vmbus_initiate_unload() is also called on crash and the crash can be
         * happening in an interrupt context, where scheduling is impossible.
         */
        if (!crash)
                wait_for_completion(&vmbus_connection.unload_event);
        else
                vmbus_wait_for_unload();
}

/*
 * vmbus_onoffer - Handler for channel offers from vmbus in parent partition.
 *
 */
static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_offer_channel *offer;
        struct vmbus_channel *newchannel;

        offer = (struct vmbus_channel_offer_channel *)hdr;

        trace_vmbus_onoffer(offer);

        /* Allocate the channel object and save this offer. */
        newchannel = alloc_channel();
        if (!newchannel) {
                vmbus_release_relid(offer->child_relid);
                atomic_dec(&vmbus_connection.offer_in_progress);
                pr_err("Unable to allocate channel object\n");
                return;
        }

        /*
         * Setup state for signalling the host.
         */
        newchannel->sig_event = VMBUS_EVENT_CONNECTION_ID;

        if (vmbus_proto_version != VERSION_WS2008) {
                newchannel->is_dedicated_interrupt =
                                (offer->is_dedicated_interrupt != 0);
                newchannel->sig_event = offer->connection_id;
        }

        memcpy(&newchannel->offermsg, offer,
               sizeof(struct vmbus_channel_offer_channel));
        newchannel->monitor_grp = (u8)offer->monitorid / 32;
        newchannel->monitor_bit = (u8)offer->monitorid % 32;

        vmbus_process_offer(newchannel);
}

/*
 * vmbus_onoffer_rescind - Rescind offer handler.
 *
 * We queue a work item to process this offer synchronously
 */
static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_rescind_offer *rescind;
        struct vmbus_channel *channel;
        struct device *dev;

        rescind = (struct vmbus_channel_rescind_offer *)hdr;

        trace_vmbus_onoffer_rescind(rescind);

        /*
         * The offer msg and the corresponding rescind msg
         * from the host are guranteed to be ordered -
         * offer comes in first and then the rescind.
         * Since we process these events in work elements,
         * and with preemption, we may end up processing
         * the events out of order. Given that we handle these
         * work elements on the same CPU, this is possible only
         * in the case of preemption. In any case wait here
         * until the offer processing has moved beyond the
         * point where the channel is discoverable.
         */

        while (atomic_read(&vmbus_connection.offer_in_progress) != 0) {
                /*
                 * We wait here until any channel offer is currently
                 * being processed.
                 */
                msleep(1);
        }

        mutex_lock(&vmbus_connection.channel_mutex);
        channel = relid2channel(rescind->child_relid);
        mutex_unlock(&vmbus_connection.channel_mutex);

        if (channel == NULL) {
                /*
                 * We failed in processing the offer message;
                 * we would have cleaned up the relid in that
                 * failure path.
                 */
                return;
        }

        /*
         * Before setting channel->rescind in vmbus_rescind_cleanup(), we
         * should make sure the channel callback is not running any more.
         */
        vmbus_reset_channel_cb(channel);

        /*
         * Now wait for offer handling to complete.
         */
        vmbus_rescind_cleanup(channel);
        while (READ_ONCE(channel->probe_done) == false) {
                /*
                 * We wait here until any channel offer is currently
                 * being processed.
                 */
                msleep(1);
        }

        /*
         * At this point, the rescind handling can proceed safely.
         */

        if (channel->device_obj) {
                if (channel->chn_rescind_callback) {
                        channel->chn_rescind_callback(channel);
                        return;
                }
                /*
                 * We will have to unregister this device from the
                 * driver core.
                 */
                dev = get_device(&channel->device_obj->device);
                if (dev) {
                        vmbus_device_unregister(channel->device_obj);
                        put_device(dev);
                }
        }
        if (channel->primary_channel != NULL) {
                /*
                 * Sub-channel is being rescinded. Following is the channel
                 * close sequence when initiated from the driveri (refer to
                 * vmbus_close() for details):
                 * 1. Close all sub-channels first
                 * 2. Then close the primary channel.
                 */
                mutex_lock(&vmbus_connection.channel_mutex);
                if (channel->state == CHANNEL_OPEN_STATE) {
                        /*
                         * The channel is currently not open;
                         * it is safe for us to cleanup the channel.
                         */
                        hv_process_channel_removal(channel);
                } else {
                        complete(&channel->rescind_event);
                }
                mutex_unlock(&vmbus_connection.channel_mutex);
        }
}

void vmbus_hvsock_device_unregister(struct vmbus_channel *channel)
{
        BUG_ON(!is_hvsock_channel(channel));

        /* We always get a rescind msg when a connection is closed. */
        while (!READ_ONCE(channel->probe_done) || !READ_ONCE(channel->rescind))
                msleep(1);

        vmbus_device_unregister(channel->device_obj);
}
EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);


/*
 * vmbus_onoffers_delivered -
 * This is invoked when all offers have been delivered.
 *
 * Nothing to do here.
 */
static void vmbus_onoffers_delivered(
                        struct vmbus_channel_message_header *hdr)
{
}

/*
 * vmbus_onopen_result - Open result handler.
 *
 * This is invoked when we received a response to our channel open request.
 * Find the matching request, copy the response and signal the requesting
 * thread.
 */
static void vmbus_onopen_result(struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_open_result *result;
        struct vmbus_channel_msginfo *msginfo;
        struct vmbus_channel_message_header *requestheader;
        struct vmbus_channel_open_channel *openmsg;
        unsigned long flags;

        result = (struct vmbus_channel_open_result *)hdr;

        trace_vmbus_onopen_result(result);

        /*
         * Find the open msg, copy the result and signal/unblock the wait event
         */
        spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);

        list_for_each_entry(msginfo, &vmbus_connection.chn_msg_list,
                                msglistentry) {
                requestheader =
                        (struct vmbus_channel_message_header *)msginfo->msg;

                if (requestheader->msgtype == CHANNELMSG_OPENCHANNEL) {
                        openmsg =
                        (struct vmbus_channel_open_channel *)msginfo->msg;
                        if (openmsg->child_relid == result->child_relid &&
                            openmsg->openid == result->openid) {
                                memcpy(&msginfo->response.open_result,
                                       result,
                                       sizeof(
                                        struct vmbus_channel_open_result));
                                complete(&msginfo->waitevent);
                                break;
                        }
                }
        }
        spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
}

/*
 * vmbus_ongpadl_created - GPADL created handler.
 *
 * This is invoked when we received a response to our gpadl create request.
 * Find the matching request, copy the response and signal the requesting
 * thread.
 */
static void vmbus_ongpadl_created(struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_gpadl_created *gpadlcreated;
        struct vmbus_channel_msginfo *msginfo;
        struct vmbus_channel_message_header *requestheader;
        struct vmbus_channel_gpadl_header *gpadlheader;
        unsigned long flags;

        gpadlcreated = (struct vmbus_channel_gpadl_created *)hdr;

        trace_vmbus_ongpadl_created(gpadlcreated);

        /*
         * Find the establish msg, copy the result and signal/unblock the wait
         * event
         */
        spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);

        list_for_each_entry(msginfo, &vmbus_connection.chn_msg_list,
                                msglistentry) {
                requestheader =
                        (struct vmbus_channel_message_header *)msginfo->msg;

                if (requestheader->msgtype == CHANNELMSG_GPADL_HEADER) {
                        gpadlheader =
                        (struct vmbus_channel_gpadl_header *)requestheader;

                        if ((gpadlcreated->child_relid ==
                             gpadlheader->child_relid) &&
                            (gpadlcreated->gpadl == gpadlheader->gpadl)) {
                                memcpy(&msginfo->response.gpadl_created,
                                       gpadlcreated,
                                       sizeof(
                                        struct vmbus_channel_gpadl_created));
                                complete(&msginfo->waitevent);
                                break;
                        }
                }
        }
        spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
}

/*
 * vmbus_ongpadl_torndown - GPADL torndown handler.
 *
 * This is invoked when we received a response to our gpadl teardown request.
 * Find the matching request, copy the response and signal the requesting
 * thread.
 */
static void vmbus_ongpadl_torndown(
                        struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_gpadl_torndown *gpadl_torndown;
        struct vmbus_channel_msginfo *msginfo;
        struct vmbus_channel_message_header *requestheader;
        struct vmbus_channel_gpadl_teardown *gpadl_teardown;
        unsigned long flags;

        gpadl_torndown = (struct vmbus_channel_gpadl_torndown *)hdr;

        trace_vmbus_ongpadl_torndown(gpadl_torndown);

        /*
         * Find the open msg, copy the result and signal/unblock the wait event
         */
        spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);

        list_for_each_entry(msginfo, &vmbus_connection.chn_msg_list,
                                msglistentry) {
                requestheader =
                        (struct vmbus_channel_message_header *)msginfo->msg;

                if (requestheader->msgtype == CHANNELMSG_GPADL_TEARDOWN) {
                        gpadl_teardown =
                        (struct vmbus_channel_gpadl_teardown *)requestheader;

                        if (gpadl_torndown->gpadl == gpadl_teardown->gpadl) {
                                memcpy(&msginfo->response.gpadl_torndown,
                                       gpadl_torndown,
                                       sizeof(
                                        struct vmbus_channel_gpadl_torndown));
                                complete(&msginfo->waitevent);
                                break;
                        }
                }
        }
        spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
}

/*
 * vmbus_onversion_response - Version response handler
 *
 * This is invoked when we received a response to our initiate contact request.
 * Find the matching request, copy the response and signal the requesting
 * thread.
 */
static void vmbus_onversion_response(
                struct vmbus_channel_message_header *hdr)
{
        struct vmbus_channel_msginfo *msginfo;
        struct vmbus_channel_message_header *requestheader;
        struct vmbus_channel_version_response *version_response;
        unsigned long flags;

        version_response = (struct vmbus_channel_version_response *)hdr;

        trace_vmbus_onversion_response(version_response);

        spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);

        list_for_each_entry(msginfo, &vmbus_connection.chn_msg_list,
                                msglistentry) {
                requestheader =
                        (struct vmbus_channel_message_header *)msginfo->msg;

                if (requestheader->msgtype ==
                    CHANNELMSG_INITIATE_CONTACT) {
                        memcpy(&msginfo->response.version_response,
                              version_response,
                              sizeof(struct vmbus_channel_version_response));
                        complete(&msginfo->waitevent);
                }
        }
        spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
}

/* Channel message dispatch table */
const struct vmbus_channel_message_table_entry
channel_message_table[CHANNELMSG_COUNT] = {
        { CHANNELMSG_INVALID,                   0, NULL },
        { CHANNELMSG_OFFERCHANNEL,              0, vmbus_onoffer },
        { CHANNELMSG_RESCIND_CHANNELOFFER,      0, vmbus_onoffer_rescind },
        { CHANNELMSG_REQUESTOFFERS,             0, NULL },
        { CHANNELMSG_ALLOFFERS_DELIVERED,       1, vmbus_onoffers_delivered },
        { CHANNELMSG_OPENCHANNEL,               0, NULL },
        { CHANNELMSG_OPENCHANNEL_RESULT,        1, vmbus_onopen_result },
        { CHANNELMSG_CLOSECHANNEL,              0, NULL },
        { CHANNELMSG_GPADL_HEADER,              0, NULL },
        { CHANNELMSG_GPADL_BODY,                0, NULL },
        { CHANNELMSG_GPADL_CREATED,             1, vmbus_ongpadl_created },
        { CHANNELMSG_GPADL_TEARDOWN,            0, NULL },
        { CHANNELMSG_GPADL_TORNDOWN,            1, vmbus_ongpadl_torndown },
        { CHANNELMSG_RELID_RELEASED,            0, NULL },
        { CHANNELMSG_INITIATE_CONTACT,          0, NULL },
        { CHANNELMSG_VERSION_RESPONSE,          1, vmbus_onversion_response },
        { CHANNELMSG_UNLOAD,                    0, NULL },
        { CHANNELMSG_UNLOAD_RESPONSE,           1, vmbus_unload_response },
        { CHANNELMSG_18,                        0, NULL },
        { CHANNELMSG_19,                        0, NULL },
        { CHANNELMSG_20,                        0, NULL },
        { CHANNELMSG_TL_CONNECT_REQUEST,        0, NULL },
};

/*
 * vmbus_onmessage - Handler for channel protocol messages.
 *
 * This is invoked in the vmbus worker thread context.
 */
void vmbus_onmessage(void *context)
{
        struct hv_message *msg = context;
        struct vmbus_channel_message_header *hdr;
        int size;

        hdr = (struct vmbus_channel_message_header *)msg->u.payload;
        size = msg->header.payload_size;

        trace_vmbus_on_message(hdr);

        if (hdr->msgtype >= CHANNELMSG_COUNT) {
                pr_err("Received invalid channel message type %d size %d\n",
                           hdr->msgtype, size);
                print_hex_dump_bytes("", DUMP_PREFIX_NONE,
                                     (unsigned char *)msg->u.payload, size);
                return;
        }

        if (channel_message_table[hdr->msgtype].message_handler)
                channel_message_table[hdr->msgtype].message_handler(hdr);
        else
                pr_err("Unhandled channel message type %d\n", hdr->msgtype);
}

/*
 * vmbus_request_offers - Send a request to get all our pending offers.
 */
int vmbus_request_offers(void)
{
        struct vmbus_channel_message_header *msg;
        struct vmbus_channel_msginfo *msginfo;
        int ret;

        msginfo = kmalloc(sizeof(*msginfo) +
                          sizeof(struct vmbus_channel_message_header),
                          GFP_KERNEL);
        if (!msginfo)
                return -ENOMEM;

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

        msg->msgtype = CHANNELMSG_REQUESTOFFERS;

        ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_message_header),
                             true);

        trace_vmbus_request_offers(ret);

        if (ret != 0) {
                pr_err("Unable to request offers - %d\n", ret);

                goto cleanup;
        }

cleanup:
        kfree(msginfo);

        return ret;
}

static void invoke_sc_cb(struct vmbus_channel *primary_channel)
{
        struct list_head *cur, *tmp;
        struct vmbus_channel *cur_channel;

        if (primary_channel->sc_creation_callback == NULL)
                return;

        list_for_each_safe(cur, tmp, &primary_channel->sc_list) {
                cur_channel = list_entry(cur, struct vmbus_channel, sc_list);

                primary_channel->sc_creation_callback(cur_channel);
        }
}

void vmbus_set_sc_create_callback(struct vmbus_channel *primary_channel,
                                void (*sc_cr_cb)(struct vmbus_channel *new_sc))
{
        primary_channel->sc_creation_callback = sc_cr_cb;
}
EXPORT_SYMBOL_GPL(vmbus_set_sc_create_callback);

bool vmbus_are_subchannels_present(struct vmbus_channel *primary)
{
        bool ret;

        ret = !list_empty(&primary->sc_list);

        if (ret) {
                /*
                 * Invoke the callback on sub-channel creation.
                 * This will present a uniform interface to the
                 * clients.
                 */
                invoke_sc_cb(primary);
        }

        return ret;
}
EXPORT_SYMBOL_GPL(vmbus_are_subchannels_present);

void vmbus_set_chn_rescind_callback(struct vmbus_channel *channel,
                void (*chn_rescind_cb)(struct vmbus_channel *))
{
        channel->chn_rescind_callback = chn_rescind_cb;
}
EXPORT_SYMBOL_GPL(vmbus_set_chn_rescind_callback);