Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1352 insertions, 0 deletions

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
new file mode 100644
index 0000000000..56f7e06c67
--- /dev/null
+++ b/drivers/hv/channel.c
@@ -0,0 +1,1352 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2009, Microsoft Corporation.
+ *
+ * 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/mm.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/hyperv.h>
+#include <linux/uio.h>
+#include <linux/interrupt.h>
+#include <linux/set_memory.h>
+#include <asm/page.h>
+#include <asm/mshyperv.h>
+
+#include "hyperv_vmbus.h"
+
+/*
+ * hv_gpadl_size - Return the real size of a gpadl, the size that Hyper-V uses
+ *
+ * For BUFFER gpadl, Hyper-V uses the exact same size as the guest does.
+ *
+ * For RING gpadl, in each ring, the guest uses one PAGE_SIZE as the header
+ * (because of the alignment requirement), however, the hypervisor only
+ * uses the first HV_HYP_PAGE_SIZE as the header, therefore leaving a
+ * (PAGE_SIZE - HV_HYP_PAGE_SIZE) gap. And since there are two rings in a
+ * ringbuffer, the total size for a RING gpadl that Hyper-V uses is the
+ * total size that the guest uses minus twice of the gap size.
+ */
+static inline u32 hv_gpadl_size(enum hv_gpadl_type type, u32 size)
+{
+	switch (type) {
+	case HV_GPADL_BUFFER:
+		return size;
+	case HV_GPADL_RING:
+		/* The size of a ringbuffer must be page-aligned */
+		BUG_ON(size % PAGE_SIZE);
+		/*
+		 * Two things to notice here:
+		 * 1) We're processing two ring buffers as a unit
+		 * 2) We're skipping any space larger than HV_HYP_PAGE_SIZE in
+		 * the first guest-size page of each of the two ring buffers.
+		 * So we effectively subtract out two guest-size pages, and add
+		 * back two Hyper-V size pages.
+		 */
+		return size - 2 * (PAGE_SIZE - HV_HYP_PAGE_SIZE);
+	}
+	BUG();
+	return 0;
+}
+
+/*
+ * hv_ring_gpadl_send_hvpgoffset - Calculate the send offset (in unit of
+ *                                 HV_HYP_PAGE) in a ring gpadl based on the
+ *                                 offset in the guest
+ *
+ * @offset: the offset (in bytes) where the send ringbuffer starts in the
+ *               virtual address space of the guest
+ */
+static inline u32 hv_ring_gpadl_send_hvpgoffset(u32 offset)
+{
+
+	/*
+	 * For RING gpadl, in each ring, the guest uses one PAGE_SIZE as the
+	 * header (because of the alignment requirement), however, the
+	 * hypervisor only uses the first HV_HYP_PAGE_SIZE as the header,
+	 * therefore leaving a (PAGE_SIZE - HV_HYP_PAGE_SIZE) gap.
+	 *
+	 * And to calculate the effective send offset in gpadl, we need to
+	 * substract this gap.
+	 */
+	return (offset - (PAGE_SIZE - HV_HYP_PAGE_SIZE)) >> HV_HYP_PAGE_SHIFT;
+}
+
+/*
+ * hv_gpadl_hvpfn - Return the Hyper-V page PFN of the @i th Hyper-V page in
+ *                  the gpadl
+ *
+ * @type: the type of the gpadl
+ * @kbuffer: the pointer to the gpadl in the guest
+ * @size: the total size (in bytes) of the gpadl
+ * @send_offset: the offset (in bytes) where the send ringbuffer starts in the
+ *               virtual address space of the guest
+ * @i: the index
+ */
+static inline u64 hv_gpadl_hvpfn(enum hv_gpadl_type type, void *kbuffer,
+				 u32 size, u32 send_offset, int i)
+{
+	int send_idx = hv_ring_gpadl_send_hvpgoffset(send_offset);
+	unsigned long delta = 0UL;
+
+	switch (type) {
+	case HV_GPADL_BUFFER:
+		break;
+	case HV_GPADL_RING:
+		if (i == 0)
+			delta = 0;
+		else if (i <= send_idx)
+			delta = PAGE_SIZE - HV_HYP_PAGE_SIZE;
+		else
+			delta = 2 * (PAGE_SIZE - HV_HYP_PAGE_SIZE);
+		break;
+	default:
+		BUG();
+		break;
+	}
+
+	return virt_to_hvpfn(kbuffer + delta + (HV_HYP_PAGE_SIZE * i));
+}
+
+/*
+ * vmbus_setevent- Trigger an event notification on the specified
+ * channel.
+ */
+void vmbus_setevent(struct vmbus_channel *channel)
+{
+	struct hv_monitor_page *monitorpage;
+
+	trace_vmbus_setevent(channel);
+
+	/*
+	 * For channels marked as in "low latency" mode
+	 * bypass the monitor page mechanism.
+	 */
+	if (channel->offermsg.monitor_allocated && !channel->low_latency) {
+		vmbus_send_interrupt(channel->offermsg.child_relid);
+
+		/* Get the child to parent monitor page */
+		monitorpage = vmbus_connection.monitor_pages[1];
+
+		sync_set_bit(channel->monitor_bit,
+			(unsigned long *)&monitorpage->trigger_group
+					[channel->monitor_grp].pending);
+
+	} else {
+		vmbus_set_event(channel);
+	}
+}
+EXPORT_SYMBOL_GPL(vmbus_setevent);
+
+/* vmbus_free_ring - drop mapping of ring buffer */
+void vmbus_free_ring(struct vmbus_channel *channel)
+{
+	hv_ringbuffer_cleanup(&channel->outbound);
+	hv_ringbuffer_cleanup(&channel->inbound);
+
+	if (channel->ringbuffer_page) {
+		__free_pages(channel->ringbuffer_page,
+			     get_order(channel->ringbuffer_pagecount
+				       << PAGE_SHIFT));
+		channel->ringbuffer_page = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(vmbus_free_ring);
+
+/* vmbus_alloc_ring - allocate and map pages for ring buffer */
+int vmbus_alloc_ring(struct vmbus_channel *newchannel,
+		     u32 send_size, u32 recv_size)
+{
+	struct page *page;
+	int order;
+
+	if (send_size % PAGE_SIZE || recv_size % PAGE_SIZE)
+		return -EINVAL;
+
+	/* Allocate the ring buffer */
+	order = get_order(send_size + recv_size);
+	page = alloc_pages_node(cpu_to_node(newchannel->target_cpu),
+				GFP_KERNEL|__GFP_ZERO, order);
+
+	if (!page)
+		page = alloc_pages(GFP_KERNEL|__GFP_ZERO, order);
+
+	if (!page)
+		return -ENOMEM;
+
+	newchannel->ringbuffer_page = page;
+	newchannel->ringbuffer_pagecount = (send_size + recv_size) >> PAGE_SHIFT;
+	newchannel->ringbuffer_send_offset = send_size >> PAGE_SHIFT;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(vmbus_alloc_ring);
+
+/* Used for Hyper-V Socket: a guest client's connect() to the host */
+int vmbus_send_tl_connect_request(const guid_t *shv_guest_servie_id,
+				  const guid_t *shv_host_servie_id)
+{
+	struct vmbus_channel_tl_connect_request conn_msg;
+	int ret;
+
+	memset(&conn_msg, 0, sizeof(conn_msg));
+	conn_msg.header.msgtype = CHANNELMSG_TL_CONNECT_REQUEST;
+	conn_msg.guest_endpoint_id = *shv_guest_servie_id;
+	conn_msg.host_service_id = *shv_host_servie_id;
+
+	ret = vmbus_post_msg(&conn_msg, sizeof(conn_msg), true);
+
+	trace_vmbus_send_tl_connect_request(&conn_msg, ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vmbus_send_tl_connect_request);
+
+static int send_modifychannel_without_ack(struct vmbus_channel *channel, u32 target_vp)
+{
+	struct vmbus_channel_modifychannel msg;
+	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.header.msgtype = CHANNELMSG_MODIFYCHANNEL;
+	msg.child_relid = channel->offermsg.child_relid;
+	msg.target_vp = target_vp;
+
+	ret = vmbus_post_msg(&msg, sizeof(msg), true);
+	trace_vmbus_send_modifychannel(&msg, ret);
+
+	return ret;
+}
+
+static int send_modifychannel_with_ack(struct vmbus_channel *channel, u32 target_vp)
+{
+	struct vmbus_channel_modifychannel *msg;
+	struct vmbus_channel_msginfo *info;
+	unsigned long flags;
+	int ret;
+
+	info = kzalloc(sizeof(struct vmbus_channel_msginfo) +
+				sizeof(struct vmbus_channel_modifychannel),
+		       GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	init_completion(&info->waitevent);
+	info->waiting_channel = channel;
+
+	msg = (struct vmbus_channel_modifychannel *)info->msg;
+	msg->header.msgtype = CHANNELMSG_MODIFYCHANNEL;
+	msg->child_relid = channel->offermsg.child_relid;
+	msg->target_vp = target_vp;
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_add_tail(&info->msglistentry, &vmbus_connection.chn_msg_list);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	ret = vmbus_post_msg(msg, sizeof(*msg), true);
+	trace_vmbus_send_modifychannel(msg, ret);
+	if (ret != 0) {
+		spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+		list_del(&info->msglistentry);
+		spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+		goto free_info;
+	}
+
+	/*
+	 * Release channel_mutex; otherwise, vmbus_onoffer_rescind() could block on
+	 * the mutex and be unable to signal the completion.
+	 *
+	 * See the caller target_cpu_store() for information about the usage of the
+	 * mutex.
+	 */
+	mutex_unlock(&vmbus_connection.channel_mutex);
+	wait_for_completion(&info->waitevent);
+	mutex_lock(&vmbus_connection.channel_mutex);
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_del(&info->msglistentry);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	if (info->response.modify_response.status)
+		ret = -EAGAIN;
+
+free_info:
+	kfree(info);
+	return ret;
+}
+
+/*
+ * Set/change the vCPU (@target_vp) the channel (@child_relid) will interrupt.
+ *
+ * CHANNELMSG_MODIFYCHANNEL messages are aynchronous.  When VMbus version 5.3
+ * or later is negotiated, Hyper-V always sends an ACK in response to such a
+ * message.  For VMbus version 5.2 and earlier, it never sends an ACK.  With-
+ * out an ACK, we can not know when the host will stop interrupting the "old"
+ * vCPU and start interrupting the "new" vCPU for the given channel.
+ *
+ * The CHANNELMSG_MODIFYCHANNEL message type is supported since VMBus version
+ * VERSION_WIN10_V4_1.
+ */
+int vmbus_send_modifychannel(struct vmbus_channel *channel, u32 target_vp)
+{
+	if (vmbus_proto_version >= VERSION_WIN10_V5_3)
+		return send_modifychannel_with_ack(channel, target_vp);
+	return send_modifychannel_without_ack(channel, target_vp);
+}
+EXPORT_SYMBOL_GPL(vmbus_send_modifychannel);
+
+/*
+ * create_gpadl_header - Creates a gpadl for the specified buffer
+ */
+static int create_gpadl_header(enum hv_gpadl_type type, void *kbuffer,
+			       u32 size, u32 send_offset,
+			       struct vmbus_channel_msginfo **msginfo)
+{
+	int i;
+	int pagecount;
+	struct vmbus_channel_gpadl_header *gpadl_header;
+	struct vmbus_channel_gpadl_body *gpadl_body;
+	struct vmbus_channel_msginfo *msgheader;
+	struct vmbus_channel_msginfo *msgbody = NULL;
+	u32 msgsize;
+
+	int pfnsum, pfncount, pfnleft, pfncurr, pfnsize;
+
+	pagecount = hv_gpadl_size(type, size) >> HV_HYP_PAGE_SHIFT;
+
+	/* do we need a gpadl body msg */
+	pfnsize = MAX_SIZE_CHANNEL_MESSAGE -
+		  sizeof(struct vmbus_channel_gpadl_header) -
+		  sizeof(struct gpa_range);
+	pfncount = pfnsize / sizeof(u64);
+
+	if (pagecount > pfncount) {
+		/* we need a gpadl body */
+		/* fill in the header */
+		msgsize = sizeof(struct vmbus_channel_msginfo) +
+			  sizeof(struct vmbus_channel_gpadl_header) +
+			  sizeof(struct gpa_range) + pfncount * sizeof(u64);
+		msgheader =  kzalloc(msgsize, GFP_KERNEL);
+		if (!msgheader)
+			goto nomem;
+
+		INIT_LIST_HEAD(&msgheader->submsglist);
+		msgheader->msgsize = msgsize;
+
+		gpadl_header = (struct vmbus_channel_gpadl_header *)
+			msgheader->msg;
+		gpadl_header->rangecount = 1;
+		gpadl_header->range_buflen = sizeof(struct gpa_range) +
+					 pagecount * sizeof(u64);
+		gpadl_header->range[0].byte_offset = 0;
+		gpadl_header->range[0].byte_count = hv_gpadl_size(type, size);
+		for (i = 0; i < pfncount; i++)
+			gpadl_header->range[0].pfn_array[i] = hv_gpadl_hvpfn(
+				type, kbuffer, size, send_offset, i);
+		*msginfo = msgheader;
+
+		pfnsum = pfncount;
+		pfnleft = pagecount - pfncount;
+
+		/* how many pfns can we fit */
+		pfnsize = MAX_SIZE_CHANNEL_MESSAGE -
+			  sizeof(struct vmbus_channel_gpadl_body);
+		pfncount = pfnsize / sizeof(u64);
+
+		/* fill in the body */
+		while (pfnleft) {
+			if (pfnleft > pfncount)
+				pfncurr = pfncount;
+			else
+				pfncurr = pfnleft;
+
+			msgsize = sizeof(struct vmbus_channel_msginfo) +
+				  sizeof(struct vmbus_channel_gpadl_body) +
+				  pfncurr * sizeof(u64);
+			msgbody = kzalloc(msgsize, GFP_KERNEL);
+
+			if (!msgbody) {
+				struct vmbus_channel_msginfo *pos = NULL;
+				struct vmbus_channel_msginfo *tmp = NULL;
+				/*
+				 * Free up all the allocated messages.
+				 */
+				list_for_each_entry_safe(pos, tmp,
+					&msgheader->submsglist,
+					msglistentry) {
+
+					list_del(&pos->msglistentry);
+					kfree(pos);
+				}
+
+				goto nomem;
+			}
+
+			msgbody->msgsize = msgsize;
+			gpadl_body =
+				(struct vmbus_channel_gpadl_body *)msgbody->msg;
+
+			/*
+			 * Gpadl is u32 and we are using a pointer which could
+			 * be 64-bit
+			 * This is governed by the guest/host protocol and
+			 * so the hypervisor guarantees that this is ok.
+			 */
+			for (i = 0; i < pfncurr; i++)
+				gpadl_body->pfn[i] = hv_gpadl_hvpfn(type,
+					kbuffer, size, send_offset, pfnsum + i);
+
+			/* add to msg header */
+			list_add_tail(&msgbody->msglistentry,
+				      &msgheader->submsglist);
+			pfnsum += pfncurr;
+			pfnleft -= pfncurr;
+		}
+	} else {
+		/* everything fits in a header */
+		msgsize = sizeof(struct vmbus_channel_msginfo) +
+			  sizeof(struct vmbus_channel_gpadl_header) +
+			  sizeof(struct gpa_range) + pagecount * sizeof(u64);
+		msgheader = kzalloc(msgsize, GFP_KERNEL);
+		if (msgheader == NULL)
+			goto nomem;
+
+		INIT_LIST_HEAD(&msgheader->submsglist);
+		msgheader->msgsize = msgsize;
+
+		gpadl_header = (struct vmbus_channel_gpadl_header *)
+			msgheader->msg;
+		gpadl_header->rangecount = 1;
+		gpadl_header->range_buflen = sizeof(struct gpa_range) +
+					 pagecount * sizeof(u64);
+		gpadl_header->range[0].byte_offset = 0;
+		gpadl_header->range[0].byte_count = hv_gpadl_size(type, size);
+		for (i = 0; i < pagecount; i++)
+			gpadl_header->range[0].pfn_array[i] = hv_gpadl_hvpfn(
+				type, kbuffer, size, send_offset, i);
+
+		*msginfo = msgheader;
+	}
+
+	return 0;
+nomem:
+	kfree(msgheader);
+	kfree(msgbody);
+	return -ENOMEM;
+}
+
+/*
+ * __vmbus_establish_gpadl - Establish a GPADL for a buffer or ringbuffer
+ *
+ * @channel: a channel
+ * @type: the type of the corresponding GPADL, only meaningful for the guest.
+ * @kbuffer: from kmalloc or vmalloc
+ * @size: page-size multiple
+ * @send_offset: the offset (in bytes) where the send ring buffer starts,
+ *              should be 0 for BUFFER type gpadl
+ * @gpadl_handle: some funky thing
+ */
+static int __vmbus_establish_gpadl(struct vmbus_channel *channel,
+				   enum hv_gpadl_type type, void *kbuffer,
+				   u32 size, u32 send_offset,
+				   struct vmbus_gpadl *gpadl)
+{
+	struct vmbus_channel_gpadl_header *gpadlmsg;
+	struct vmbus_channel_gpadl_body *gpadl_body;
+	struct vmbus_channel_msginfo *msginfo = NULL;
+	struct vmbus_channel_msginfo *submsginfo, *tmp;
+	struct list_head *curr;
+	u32 next_gpadl_handle;
+	unsigned long flags;
+	int ret = 0;
+
+	next_gpadl_handle =
+		(atomic_inc_return(&vmbus_connection.next_gpadl_handle) - 1);
+
+	ret = create_gpadl_header(type, kbuffer, size, send_offset, &msginfo);
+	if (ret)
+		return ret;
+
+	ret = set_memory_decrypted((unsigned long)kbuffer,
+				   PFN_UP(size));
+	if (ret) {
+		dev_warn(&channel->device_obj->device,
+			 "Failed to set host visibility for new GPADL %d.\n",
+			 ret);
+		return ret;
+	}
+
+	init_completion(&msginfo->waitevent);
+	msginfo->waiting_channel = channel;
+
+	gpadlmsg = (struct vmbus_channel_gpadl_header *)msginfo->msg;
+	gpadlmsg->header.msgtype = CHANNELMSG_GPADL_HEADER;
+	gpadlmsg->child_relid = channel->offermsg.child_relid;
+	gpadlmsg->gpadl = next_gpadl_handle;
+
+
+	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);
+
+	if (channel->rescind) {
+		ret = -ENODEV;
+		goto cleanup;
+	}
+
+	ret = vmbus_post_msg(gpadlmsg, msginfo->msgsize -
+			     sizeof(*msginfo), true);
+
+	trace_vmbus_establish_gpadl_header(gpadlmsg, ret);
+
+	if (ret != 0)
+		goto cleanup;
+
+	list_for_each(curr, &msginfo->submsglist) {
+		submsginfo = (struct vmbus_channel_msginfo *)curr;
+		gpadl_body =
+			(struct vmbus_channel_gpadl_body *)submsginfo->msg;
+
+		gpadl_body->header.msgtype =
+			CHANNELMSG_GPADL_BODY;
+		gpadl_body->gpadl = next_gpadl_handle;
+
+		ret = vmbus_post_msg(gpadl_body,
+				     submsginfo->msgsize - sizeof(*submsginfo),
+				     true);
+
+		trace_vmbus_establish_gpadl_body(gpadl_body, ret);
+
+		if (ret != 0)
+			goto cleanup;
+
+	}
+	wait_for_completion(&msginfo->waitevent);
+
+	if (msginfo->response.gpadl_created.creation_status != 0) {
+		pr_err("Failed to establish GPADL: err = 0x%x\n",
+		       msginfo->response.gpadl_created.creation_status);
+
+		ret = -EDQUOT;
+		goto cleanup;
+	}
+
+	if (channel->rescind) {
+		ret = -ENODEV;
+		goto cleanup;
+	}
+
+	/* At this point, we received the gpadl created msg */
+	gpadl->gpadl_handle = gpadlmsg->gpadl;
+	gpadl->buffer = kbuffer;
+	gpadl->size = size;
+
+
+cleanup:
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_del(&msginfo->msglistentry);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+	list_for_each_entry_safe(submsginfo, tmp, &msginfo->submsglist,
+				 msglistentry) {
+		kfree(submsginfo);
+	}
+
+	kfree(msginfo);
+
+	if (ret)
+		set_memory_encrypted((unsigned long)kbuffer,
+				     PFN_UP(size));
+
+	return ret;
+}
+
+/*
+ * vmbus_establish_gpadl - Establish a GPADL for the specified buffer
+ *
+ * @channel: a channel
+ * @kbuffer: from kmalloc or vmalloc
+ * @size: page-size multiple
+ * @gpadl_handle: some funky thing
+ */
+int vmbus_establish_gpadl(struct vmbus_channel *channel, void *kbuffer,
+			  u32 size, struct vmbus_gpadl *gpadl)
+{
+	return __vmbus_establish_gpadl(channel, HV_GPADL_BUFFER, kbuffer, size,
+				       0U, gpadl);
+}
+EXPORT_SYMBOL_GPL(vmbus_establish_gpadl);
+
+/**
+ * request_arr_init - Allocates memory for the requestor array. Each slot
+ * keeps track of the next available slot in the array. Initially, each
+ * slot points to the next one (as in a Linked List). The last slot
+ * does not point to anything, so its value is U64_MAX by default.
+ * @size The size of the array
+ */
+static u64 *request_arr_init(u32 size)
+{
+	int i;
+	u64 *req_arr;
+
+	req_arr = kcalloc(size, sizeof(u64), GFP_KERNEL);
+	if (!req_arr)
+		return NULL;
+
+	for (i = 0; i < size - 1; i++)
+		req_arr[i] = i + 1;
+
+	/* Last slot (no more available slots) */
+	req_arr[i] = U64_MAX;
+
+	return req_arr;
+}
+
+/*
+ * vmbus_alloc_requestor - Initializes @rqstor's fields.
+ * Index 0 is the first free slot
+ * @size: Size of the requestor array
+ */
+static int vmbus_alloc_requestor(struct vmbus_requestor *rqstor, u32 size)
+{
+	u64 *rqst_arr;
+	unsigned long *bitmap;
+
+	rqst_arr = request_arr_init(size);
+	if (!rqst_arr)
+		return -ENOMEM;
+
+	bitmap = bitmap_zalloc(size, GFP_KERNEL);
+	if (!bitmap) {
+		kfree(rqst_arr);
+		return -ENOMEM;
+	}
+
+	rqstor->req_arr = rqst_arr;
+	rqstor->req_bitmap = bitmap;
+	rqstor->size = size;
+	rqstor->next_request_id = 0;
+	spin_lock_init(&rqstor->req_lock);
+
+	return 0;
+}
+
+/*
+ * vmbus_free_requestor - Frees memory allocated for @rqstor
+ * @rqstor: Pointer to the requestor struct
+ */
+static void vmbus_free_requestor(struct vmbus_requestor *rqstor)
+{
+	kfree(rqstor->req_arr);
+	bitmap_free(rqstor->req_bitmap);
+}
+
+static int __vmbus_open(struct vmbus_channel *newchannel,
+		       void *userdata, u32 userdatalen,
+		       void (*onchannelcallback)(void *context), void *context)
+{
+	struct vmbus_channel_open_channel *open_msg;
+	struct vmbus_channel_msginfo *open_info = NULL;
+	struct page *page = newchannel->ringbuffer_page;
+	u32 send_pages, recv_pages;
+	unsigned long flags;
+	int err;
+
+	if (userdatalen > MAX_USER_DEFINED_BYTES)
+		return -EINVAL;
+
+	send_pages = newchannel->ringbuffer_send_offset;
+	recv_pages = newchannel->ringbuffer_pagecount - send_pages;
+
+	if (newchannel->state != CHANNEL_OPEN_STATE)
+		return -EINVAL;
+
+	/* Create and init requestor */
+	if (newchannel->rqstor_size) {
+		if (vmbus_alloc_requestor(&newchannel->requestor, newchannel->rqstor_size))
+			return -ENOMEM;
+	}
+
+	newchannel->state = CHANNEL_OPENING_STATE;
+	newchannel->onchannel_callback = onchannelcallback;
+	newchannel->channel_callback_context = context;
+
+	if (!newchannel->max_pkt_size)
+		newchannel->max_pkt_size = VMBUS_DEFAULT_MAX_PKT_SIZE;
+
+	/* Establish the gpadl for the ring buffer */
+	newchannel->ringbuffer_gpadlhandle.gpadl_handle = 0;
+
+	err = __vmbus_establish_gpadl(newchannel, HV_GPADL_RING,
+				      page_address(newchannel->ringbuffer_page),
+				      (send_pages + recv_pages) << PAGE_SHIFT,
+				      newchannel->ringbuffer_send_offset << PAGE_SHIFT,
+				      &newchannel->ringbuffer_gpadlhandle);
+	if (err)
+		goto error_clean_ring;
+
+	err = hv_ringbuffer_init(&newchannel->outbound,
+				 page, send_pages, 0);
+	if (err)
+		goto error_free_gpadl;
+
+	err = hv_ringbuffer_init(&newchannel->inbound, &page[send_pages],
+				 recv_pages, newchannel->max_pkt_size);
+	if (err)
+		goto error_free_gpadl;
+
+	/* Create and init the channel open message */
+	open_info = kzalloc(sizeof(*open_info) +
+			   sizeof(struct vmbus_channel_open_channel),
+			   GFP_KERNEL);
+	if (!open_info) {
+		err = -ENOMEM;
+		goto error_free_gpadl;
+	}
+
+	init_completion(&open_info->waitevent);
+	open_info->waiting_channel = newchannel;
+
+	open_msg = (struct vmbus_channel_open_channel *)open_info->msg;
+	open_msg->header.msgtype = CHANNELMSG_OPENCHANNEL;
+	open_msg->openid = newchannel->offermsg.child_relid;
+	open_msg->child_relid = newchannel->offermsg.child_relid;
+	open_msg->ringbuffer_gpadlhandle
+		= newchannel->ringbuffer_gpadlhandle.gpadl_handle;
+	/*
+	 * The unit of ->downstream_ringbuffer_pageoffset is HV_HYP_PAGE and
+	 * the unit of ->ringbuffer_send_offset (i.e. send_pages) is PAGE, so
+	 * here we calculate it into HV_HYP_PAGE.
+	 */
+	open_msg->downstream_ringbuffer_pageoffset =
+		hv_ring_gpadl_send_hvpgoffset(send_pages << PAGE_SHIFT);
+	open_msg->target_vp = hv_cpu_number_to_vp_number(newchannel->target_cpu);
+
+	if (userdatalen)
+		memcpy(open_msg->userdata, userdata, userdatalen);
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_add_tail(&open_info->msglistentry,
+		      &vmbus_connection.chn_msg_list);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	if (newchannel->rescind) {
+		err = -ENODEV;
+		goto error_clean_msglist;
+	}
+
+	err = vmbus_post_msg(open_msg,
+			     sizeof(struct vmbus_channel_open_channel), true);
+
+	trace_vmbus_open(open_msg, err);
+
+	if (err != 0)
+		goto error_clean_msglist;
+
+	wait_for_completion(&open_info->waitevent);
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_del(&open_info->msglistentry);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	if (newchannel->rescind) {
+		err = -ENODEV;
+		goto error_free_info;
+	}
+
+	if (open_info->response.open_result.status) {
+		err = -EAGAIN;
+		goto error_free_info;
+	}
+
+	newchannel->state = CHANNEL_OPENED_STATE;
+	kfree(open_info);
+	return 0;
+
+error_clean_msglist:
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_del(&open_info->msglistentry);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+error_free_info:
+	kfree(open_info);
+error_free_gpadl:
+	vmbus_teardown_gpadl(newchannel, &newchannel->ringbuffer_gpadlhandle);
+error_clean_ring:
+	hv_ringbuffer_cleanup(&newchannel->outbound);
+	hv_ringbuffer_cleanup(&newchannel->inbound);
+	vmbus_free_requestor(&newchannel->requestor);
+	newchannel->state = CHANNEL_OPEN_STATE;
+	return err;
+}
+
+/*
+ * vmbus_connect_ring - Open the channel but reuse ring buffer
+ */
+int vmbus_connect_ring(struct vmbus_channel *newchannel,
+		       void (*onchannelcallback)(void *context), void *context)
+{
+	return  __vmbus_open(newchannel, NULL, 0, onchannelcallback, context);
+}
+EXPORT_SYMBOL_GPL(vmbus_connect_ring);
+
+/*
+ * vmbus_open - Open the specified channel.
+ */
+int vmbus_open(struct vmbus_channel *newchannel,
+	       u32 send_ringbuffer_size, u32 recv_ringbuffer_size,
+	       void *userdata, u32 userdatalen,
+	       void (*onchannelcallback)(void *context), void *context)
+{
+	int err;
+
+	err = vmbus_alloc_ring(newchannel, send_ringbuffer_size,
+			       recv_ringbuffer_size);
+	if (err)
+		return err;
+
+	err = __vmbus_open(newchannel, userdata, userdatalen,
+			   onchannelcallback, context);
+	if (err)
+		vmbus_free_ring(newchannel);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(vmbus_open);
+
+/*
+ * vmbus_teardown_gpadl -Teardown the specified GPADL handle
+ */
+int vmbus_teardown_gpadl(struct vmbus_channel *channel, struct vmbus_gpadl *gpadl)
+{
+	struct vmbus_channel_gpadl_teardown *msg;
+	struct vmbus_channel_msginfo *info;
+	unsigned long flags;
+	int ret;
+
+	info = kzalloc(sizeof(*info) +
+		       sizeof(struct vmbus_channel_gpadl_teardown), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	init_completion(&info->waitevent);
+	info->waiting_channel = channel;
+
+	msg = (struct vmbus_channel_gpadl_teardown *)info->msg;
+
+	msg->header.msgtype = CHANNELMSG_GPADL_TEARDOWN;
+	msg->child_relid = channel->offermsg.child_relid;
+	msg->gpadl = gpadl->gpadl_handle;
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_add_tail(&info->msglistentry,
+		      &vmbus_connection.chn_msg_list);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	if (channel->rescind)
+		goto post_msg_err;
+
+	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_gpadl_teardown),
+			     true);
+
+	trace_vmbus_teardown_gpadl(msg, ret);
+
+	if (ret)
+		goto post_msg_err;
+
+	wait_for_completion(&info->waitevent);
+
+	gpadl->gpadl_handle = 0;
+
+post_msg_err:
+	/*
+	 * If the channel has been rescinded;
+	 * we will be awakened by the rescind
+	 * handler; set the error code to zero so we don't leak memory.
+	 */
+	if (channel->rescind)
+		ret = 0;
+
+	spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
+	list_del(&info->msglistentry);
+	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
+
+	kfree(info);
+
+	ret = set_memory_encrypted((unsigned long)gpadl->buffer,
+				   PFN_UP(gpadl->size));
+	if (ret)
+		pr_warn("Fail to set mem host visibility in GPADL teardown %d.\n", ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vmbus_teardown_gpadl);
+
+void vmbus_reset_channel_cb(struct vmbus_channel *channel)
+{
+	unsigned long flags;
+
+	/*
+	 * vmbus_on_event(), running in the per-channel tasklet, can race
+	 * with vmbus_close_internal() in the case of SMP guest, e.g., when
+	 * the former is accessing channel->inbound.ring_buffer, the latter
+	 * could be freeing the ring_buffer pages, so here we must stop it
+	 * first.
+	 *
+	 * vmbus_chan_sched() might call the netvsc driver callback function
+	 * that ends up scheduling NAPI work that accesses the ring buffer.
+	 * At this point, we have to ensure that any such work is completed
+	 * and that the channel ring buffer is no longer being accessed, cf.
+	 * the calls to napi_disable() in netvsc_device_remove().
+	 */
+	tasklet_disable(&channel->callback_event);
+
+	/* See the inline comments in vmbus_chan_sched(). */
+	spin_lock_irqsave(&channel->sched_lock, flags);
+	channel->onchannel_callback = NULL;
+	spin_unlock_irqrestore(&channel->sched_lock, flags);
+
+	channel->sc_creation_callback = NULL;
+
+	/* Re-enable tasklet for use on re-open */
+	tasklet_enable(&channel->callback_event);
+}
+
+static int vmbus_close_internal(struct vmbus_channel *channel)
+{
+	struct vmbus_channel_close_channel *msg;
+	int ret;
+
+	vmbus_reset_channel_cb(channel);
+
+	/*
+	 * In case a device driver's probe() fails (e.g.,
+	 * util_probe() -> vmbus_open() returns -ENOMEM) and the device is
+	 * rescinded later (e.g., we dynamically disable an Integrated Service
+	 * in Hyper-V Manager), the driver's remove() invokes vmbus_close():
+	 * here we should skip most of the below cleanup work.
+	 */
+	if (channel->state != CHANNEL_OPENED_STATE)
+		return -EINVAL;
+
+	channel->state = CHANNEL_OPEN_STATE;
+
+	/* Send a closing message */
+
+	msg = &channel->close_msg.msg;
+
+	msg->header.msgtype = CHANNELMSG_CLOSECHANNEL;
+	msg->child_relid = channel->offermsg.child_relid;
+
+	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_close_channel),
+			     true);
+
+	trace_vmbus_close_internal(msg, ret);
+
+	if (ret) {
+		pr_err("Close failed: close post msg return is %d\n", ret);
+		/*
+		 * If we failed to post the close msg,
+		 * it is perhaps better to leak memory.
+		 */
+	}
+
+	/* Tear down the gpadl for the channel's ring buffer */
+	else if (channel->ringbuffer_gpadlhandle.gpadl_handle) {
+		ret = vmbus_teardown_gpadl(channel, &channel->ringbuffer_gpadlhandle);
+		if (ret) {
+			pr_err("Close failed: teardown gpadl return %d\n", ret);
+			/*
+			 * If we failed to teardown gpadl,
+			 * it is perhaps better to leak memory.
+			 */
+		}
+	}
+
+	if (!ret)
+		vmbus_free_requestor(&channel->requestor);
+
+	return ret;
+}
+
+/* disconnect ring - close all channels */
+int vmbus_disconnect_ring(struct vmbus_channel *channel)
+{
+	struct vmbus_channel *cur_channel, *tmp;
+	int ret;
+
+	if (channel->primary_channel != NULL)
+		return -EINVAL;
+
+	list_for_each_entry_safe(cur_channel, tmp, &channel->sc_list, sc_list) {
+		if (cur_channel->rescind)
+			wait_for_completion(&cur_channel->rescind_event);
+
+		mutex_lock(&vmbus_connection.channel_mutex);
+		if (vmbus_close_internal(cur_channel) == 0) {
+			vmbus_free_ring(cur_channel);
+
+			if (cur_channel->rescind)
+				hv_process_channel_removal(cur_channel);
+		}
+		mutex_unlock(&vmbus_connection.channel_mutex);
+	}
+
+	/*
+	 * Now close the primary.
+	 */
+	mutex_lock(&vmbus_connection.channel_mutex);
+	ret = vmbus_close_internal(channel);
+	mutex_unlock(&vmbus_connection.channel_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vmbus_disconnect_ring);
+
+/*
+ * vmbus_close - Close the specified channel
+ */
+void vmbus_close(struct vmbus_channel *channel)
+{
+	if (vmbus_disconnect_ring(channel) == 0)
+		vmbus_free_ring(channel);
+}
+EXPORT_SYMBOL_GPL(vmbus_close);
+
+/**
+ * vmbus_sendpacket_getid() - Send the specified buffer on the given channel
+ * @channel: Pointer to vmbus_channel structure
+ * @buffer: Pointer to the buffer you want to send the data from.
+ * @bufferlen: Maximum size of what the buffer holds.
+ * @requestid: Identifier of the request
+ * @trans_id: Identifier of the transaction associated to this request, if
+ *            the send is successful; undefined, otherwise.
+ * @type: Type of packet that is being sent e.g. negotiate, time
+ *	  packet etc.
+ * @flags: 0 or VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED
+ *
+ * Sends data in @buffer directly to Hyper-V via the vmbus.
+ * This will send the data unparsed to Hyper-V.
+ *
+ * Mainly used by Hyper-V drivers.
+ */
+int vmbus_sendpacket_getid(struct vmbus_channel *channel, void *buffer,
+			   u32 bufferlen, u64 requestid, u64 *trans_id,
+			   enum vmbus_packet_type type, u32 flags)
+{
+	struct vmpacket_descriptor desc;
+	u32 packetlen = sizeof(struct vmpacket_descriptor) + bufferlen;
+	u32 packetlen_aligned = ALIGN(packetlen, sizeof(u64));
+	struct kvec bufferlist[3];
+	u64 aligned_data = 0;
+	int num_vecs = ((bufferlen != 0) ? 3 : 1);
+
+
+	/* Setup the descriptor */
+	desc.type = type; /* VmbusPacketTypeDataInBand; */
+	desc.flags = flags; /* VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED; */
+	/* in 8-bytes granularity */
+	desc.offset8 = sizeof(struct vmpacket_descriptor) >> 3;
+	desc.len8 = (u16)(packetlen_aligned >> 3);
+	desc.trans_id = VMBUS_RQST_ERROR; /* will be updated in hv_ringbuffer_write() */
+
+	bufferlist[0].iov_base = &desc;
+	bufferlist[0].iov_len = sizeof(struct vmpacket_descriptor);
+	bufferlist[1].iov_base = buffer;
+	bufferlist[1].iov_len = bufferlen;
+	bufferlist[2].iov_base = &aligned_data;
+	bufferlist[2].iov_len = (packetlen_aligned - packetlen);
+
+	return hv_ringbuffer_write(channel, bufferlist, num_vecs, requestid, trans_id);
+}
+EXPORT_SYMBOL(vmbus_sendpacket_getid);
+
+/**
+ * vmbus_sendpacket() - Send the specified buffer on the given channel
+ * @channel: Pointer to vmbus_channel structure
+ * @buffer: Pointer to the buffer you want to send the data from.
+ * @bufferlen: Maximum size of what the buffer holds.
+ * @requestid: Identifier of the request
+ * @type: Type of packet that is being sent e.g. negotiate, time
+ *	  packet etc.
+ * @flags: 0 or VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED
+ *
+ * Sends data in @buffer directly to Hyper-V via the vmbus.
+ * This will send the data unparsed to Hyper-V.
+ *
+ * Mainly used by Hyper-V drivers.
+ */
+int vmbus_sendpacket(struct vmbus_channel *channel, void *buffer,
+		     u32 bufferlen, u64 requestid,
+		     enum vmbus_packet_type type, u32 flags)
+{
+	return vmbus_sendpacket_getid(channel, buffer, bufferlen,
+				      requestid, NULL, type, flags);
+}
+EXPORT_SYMBOL(vmbus_sendpacket);
+
+/*
+ * vmbus_sendpacket_pagebuffer - Send a range of single-page buffer
+ * packets using a GPADL Direct packet type. This interface allows you
+ * to control notifying the host. This will be useful for sending
+ * batched data. Also the sender can control the send flags
+ * explicitly.
+ */
+int vmbus_sendpacket_pagebuffer(struct vmbus_channel *channel,
+				struct hv_page_buffer pagebuffers[],
+				u32 pagecount, void *buffer, u32 bufferlen,
+				u64 requestid)
+{
+	int i;
+	struct vmbus_channel_packet_page_buffer desc;
+	u32 descsize;
+	u32 packetlen;
+	u32 packetlen_aligned;
+	struct kvec bufferlist[3];
+	u64 aligned_data = 0;
+
+	if (pagecount > MAX_PAGE_BUFFER_COUNT)
+		return -EINVAL;
+
+	/*
+	 * Adjust the size down since vmbus_channel_packet_page_buffer is the
+	 * largest size we support
+	 */
+	descsize = sizeof(struct vmbus_channel_packet_page_buffer) -
+			  ((MAX_PAGE_BUFFER_COUNT - pagecount) *
+			  sizeof(struct hv_page_buffer));
+	packetlen = descsize + bufferlen;
+	packetlen_aligned = ALIGN(packetlen, sizeof(u64));
+
+	/* Setup the descriptor */
+	desc.type = VM_PKT_DATA_USING_GPA_DIRECT;
+	desc.flags = VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
+	desc.dataoffset8 = descsize >> 3; /* in 8-bytes granularity */
+	desc.length8 = (u16)(packetlen_aligned >> 3);
+	desc.transactionid = VMBUS_RQST_ERROR; /* will be updated in hv_ringbuffer_write() */
+	desc.reserved = 0;
+	desc.rangecount = pagecount;
+
+	for (i = 0; i < pagecount; i++) {
+		desc.range[i].len = pagebuffers[i].len;
+		desc.range[i].offset = pagebuffers[i].offset;
+		desc.range[i].pfn	 = pagebuffers[i].pfn;
+	}
+
+	bufferlist[0].iov_base = &desc;
+	bufferlist[0].iov_len = descsize;
+	bufferlist[1].iov_base = buffer;
+	bufferlist[1].iov_len = bufferlen;
+	bufferlist[2].iov_base = &aligned_data;
+	bufferlist[2].iov_len = (packetlen_aligned - packetlen);
+
+	return hv_ringbuffer_write(channel, bufferlist, 3, requestid, NULL);
+}
+EXPORT_SYMBOL_GPL(vmbus_sendpacket_pagebuffer);
+
+/*
+ * vmbus_sendpacket_multipagebuffer - Send a multi-page buffer packet
+ * using a GPADL Direct packet type.
+ * The buffer includes the vmbus descriptor.
+ */
+int vmbus_sendpacket_mpb_desc(struct vmbus_channel *channel,
+			      struct vmbus_packet_mpb_array *desc,
+			      u32 desc_size,
+			      void *buffer, u32 bufferlen, u64 requestid)
+{
+	u32 packetlen;
+	u32 packetlen_aligned;
+	struct kvec bufferlist[3];
+	u64 aligned_data = 0;
+
+	packetlen = desc_size + bufferlen;
+	packetlen_aligned = ALIGN(packetlen, sizeof(u64));
+
+	/* Setup the descriptor */
+	desc->type = VM_PKT_DATA_USING_GPA_DIRECT;
+	desc->flags = VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
+	desc->dataoffset8 = desc_size >> 3; /* in 8-bytes granularity */
+	desc->length8 = (u16)(packetlen_aligned >> 3);
+	desc->transactionid = VMBUS_RQST_ERROR; /* will be updated in hv_ringbuffer_write() */
+	desc->reserved = 0;
+	desc->rangecount = 1;
+
+	bufferlist[0].iov_base = desc;
+	bufferlist[0].iov_len = desc_size;
+	bufferlist[1].iov_base = buffer;
+	bufferlist[1].iov_len = bufferlen;
+	bufferlist[2].iov_base = &aligned_data;
+	bufferlist[2].iov_len = (packetlen_aligned - packetlen);
+
+	return hv_ringbuffer_write(channel, bufferlist, 3, requestid, NULL);
+}
+EXPORT_SYMBOL_GPL(vmbus_sendpacket_mpb_desc);
+
+/**
+ * __vmbus_recvpacket() - Retrieve the user packet on the specified channel
+ * @channel: Pointer to vmbus_channel structure
+ * @buffer: Pointer to the buffer you want to receive the data into.
+ * @bufferlen: Maximum size of what the buffer can hold.
+ * @buffer_actual_len: The actual size of the data after it was received.
+ * @requestid: Identifier of the request
+ * @raw: true means keep the vmpacket_descriptor header in the received data.
+ *
+ * Receives directly from the hyper-v vmbus and puts the data it received
+ * into Buffer. This will receive the data unparsed from hyper-v.
+ *
+ * Mainly used by Hyper-V drivers.
+ */
+static inline int
+__vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
+		   u32 bufferlen, u32 *buffer_actual_len, u64 *requestid,
+		   bool raw)
+{
+	return hv_ringbuffer_read(channel, buffer, bufferlen,
+				  buffer_actual_len, requestid, raw);
+
+}
+
+int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
+		     u32 bufferlen, u32 *buffer_actual_len,
+		     u64 *requestid)
+{
+	return __vmbus_recvpacket(channel, buffer, bufferlen,
+				  buffer_actual_len, requestid, false);
+}
+EXPORT_SYMBOL(vmbus_recvpacket);
+
+/*
+ * vmbus_recvpacket_raw - Retrieve the raw packet on the specified channel
+ */
+int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
+			      u32 bufferlen, u32 *buffer_actual_len,
+			      u64 *requestid)
+{
+	return __vmbus_recvpacket(channel, buffer, bufferlen,
+				  buffer_actual_len, requestid, true);
+}
+EXPORT_SYMBOL_GPL(vmbus_recvpacket_raw);
+
+/*
+ * vmbus_next_request_id - Returns a new request id. It is also
+ * the index at which the guest memory address is stored.
+ * Uses a spin lock to avoid race conditions.
+ * @channel: Pointer to the VMbus channel struct
+ * @rqst_add: Guest memory address to be stored in the array
+ */
+u64 vmbus_next_request_id(struct vmbus_channel *channel, u64 rqst_addr)
+{
+	struct vmbus_requestor *rqstor = &channel->requestor;
+	unsigned long flags;
+	u64 current_id;
+
+	/* Check rqstor has been initialized */
+	if (!channel->rqstor_size)
+		return VMBUS_NO_RQSTOR;
+
+	lock_requestor(channel, flags);
+	current_id = rqstor->next_request_id;
+
+	/* Requestor array is full */
+	if (current_id >= rqstor->size) {
+		unlock_requestor(channel, flags);
+		return VMBUS_RQST_ERROR;
+	}
+
+	rqstor->next_request_id = rqstor->req_arr[current_id];
+	rqstor->req_arr[current_id] = rqst_addr;
+
+	/* The already held spin lock provides atomicity */
+	bitmap_set(rqstor->req_bitmap, current_id, 1);
+
+	unlock_requestor(channel, flags);
+
+	/*
+	 * Cannot return an ID of 0, which is reserved for an unsolicited
+	 * message from Hyper-V; Hyper-V does not acknowledge (respond to)
+	 * VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED requests with ID of
+	 * 0 sent by the guest.
+	 */
+	return current_id + 1;
+}
+EXPORT_SYMBOL_GPL(vmbus_next_request_id);
+
+/* As in vmbus_request_addr_match() but without the requestor lock */
+u64 __vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
+			       u64 rqst_addr)
+{
+	struct vmbus_requestor *rqstor = &channel->requestor;
+	u64 req_addr;
+
+	/* Check rqstor has been initialized */
+	if (!channel->rqstor_size)
+		return VMBUS_NO_RQSTOR;
+
+	/* Hyper-V can send an unsolicited message with ID of 0 */
+	if (!trans_id)
+		return VMBUS_RQST_ERROR;
+
+	/* Data corresponding to trans_id is stored at trans_id - 1 */
+	trans_id--;
+
+	/* Invalid trans_id */
+	if (trans_id >= rqstor->size || !test_bit(trans_id, rqstor->req_bitmap))
+		return VMBUS_RQST_ERROR;
+
+	req_addr = rqstor->req_arr[trans_id];
+	if (rqst_addr == VMBUS_RQST_ADDR_ANY || req_addr == rqst_addr) {
+		rqstor->req_arr[trans_id] = rqstor->next_request_id;
+		rqstor->next_request_id = trans_id;
+
+		/* The already held spin lock provides atomicity */
+		bitmap_clear(rqstor->req_bitmap, trans_id, 1);
+	}
+
+	return req_addr;
+}
+EXPORT_SYMBOL_GPL(__vmbus_request_addr_match);
+
+/*
+ * vmbus_request_addr_match - Clears/removes @trans_id from the @channel's
+ * requestor, provided the memory address stored at @trans_id equals @rqst_addr
+ * (or provided @rqst_addr matches the sentinel value VMBUS_RQST_ADDR_ANY).
+ *
+ * Returns the memory address stored at @trans_id, or VMBUS_RQST_ERROR if
+ * @trans_id is not contained in the requestor.
+ *
+ * Acquires and releases the requestor spin lock.
+ */
+u64 vmbus_request_addr_match(struct vmbus_channel *channel, u64 trans_id,
+			     u64 rqst_addr)
+{
+	unsigned long flags;
+	u64 req_addr;
+
+	lock_requestor(channel, flags);
+	req_addr = __vmbus_request_addr_match(channel, trans_id, rqst_addr);
+	unlock_requestor(channel, flags);
+
+	return req_addr;
+}
+EXPORT_SYMBOL_GPL(vmbus_request_addr_match);
+
+/*
+ * vmbus_request_addr - Returns the memory address stored at @trans_id
+ * in @rqstor. Uses a spin lock to avoid race conditions.
+ * @channel: Pointer to the VMbus channel struct
+ * @trans_id: Request id sent back from Hyper-V. Becomes the requestor's
+ * next request id.
+ */
+u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id)
+{
+	return vmbus_request_addr_match(channel, trans_id, VMBUS_RQST_ADDR_ANY);
+}
+EXPORT_SYMBOL_GPL(vmbus_request_addr);