9 files changed, 593 insertions, 195 deletions

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 773a2f25a8f0..0b122f8c7005 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -55,7 +55,7 @@ static void vmbus_setevent(struct vmbus_channel *channel)
 					[channel->monitor_grp].pending);
 
 	} else {
-		vmbus_set_event(channel->offermsg.child_relid);
+		vmbus_set_event(channel);
 	}
 }
 
@@ -181,7 +181,7 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 	open_msg->ringbuffer_gpadlhandle = newchannel->ringbuffer_gpadlhandle;
 	open_msg->downstream_ringbuffer_pageoffset = send_ringbuffer_size >>
 						  PAGE_SHIFT;
-	open_msg->server_contextarea_gpadlhandle = 0;
+	open_msg->target_vp = newchannel->target_vp;
 
 	if (userdatalen > MAX_USER_DEFINED_BYTES) {
 		err = -EINVAL;
@@ -564,6 +564,7 @@ int vmbus_sendpacket(struct vmbus_channel *channel, const void *buffer,
 	struct scatterlist bufferlist[3];
 	u64 aligned_data = 0;
 	int ret;
+	bool signal = false;
 
 
 	/* Setup the descriptor */
@@ -580,9 +581,9 @@ int vmbus_sendpacket(struct vmbus_channel *channel, const void *buffer,
 	sg_set_buf(&bufferlist[2], &aligned_data,
 		   packetlen_aligned - packetlen);
 
-	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3);
+	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3, &signal);
 
-	if (ret == 0 && !hv_get_ringbuffer_interrupt_mask(&channel->outbound))
+	if (ret == 0 && signal)
 		vmbus_setevent(channel);
 
 	return ret;
@@ -606,6 +607,7 @@ int vmbus_sendpacket_pagebuffer(struct vmbus_channel *channel,
 	u32 packetlen_aligned;
 	struct scatterlist bufferlist[3];
 	u64 aligned_data = 0;
+	bool signal = false;
 
 	if (pagecount > MAX_PAGE_BUFFER_COUNT)
 		return -EINVAL;
@@ -641,9 +643,9 @@ int vmbus_sendpacket_pagebuffer(struct vmbus_channel *channel,
 	sg_set_buf(&bufferlist[2], &aligned_data,
 		packetlen_aligned - packetlen);
 
-	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3);
+	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3, &signal);
 
-	if (ret == 0 && !hv_get_ringbuffer_interrupt_mask(&channel->outbound))
+	if (ret == 0 && signal)
 		vmbus_setevent(channel);
 
 	return ret;
@@ -665,6 +667,7 @@ int vmbus_sendpacket_multipagebuffer(struct vmbus_channel *channel,
 	u32 packetlen_aligned;
 	struct scatterlist bufferlist[3];
 	u64 aligned_data = 0;
+	bool signal = false;
 	u32 pfncount = NUM_PAGES_SPANNED(multi_pagebuffer->offset,
 					 multi_pagebuffer->len);
 
@@ -703,9 +706,9 @@ int vmbus_sendpacket_multipagebuffer(struct vmbus_channel *channel,
 	sg_set_buf(&bufferlist[2], &aligned_data,
 		packetlen_aligned - packetlen);
 
-	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3);
+	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3, &signal);
 
-	if (ret == 0 && !hv_get_ringbuffer_interrupt_mask(&channel->outbound))
+	if (ret == 0 && signal)
 		vmbus_setevent(channel);
 
 	return ret;
@@ -732,6 +735,7 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
 	u32 packetlen;
 	u32 userlen;
 	int ret;
+	bool signal = false;
 
 	*buffer_actual_len = 0;
 	*requestid = 0;
@@ -758,8 +762,10 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
 
 	/* Copy over the packet to the user buffer */
 	ret = hv_ringbuffer_read(&channel->inbound, buffer, userlen,
-			     (desc.offset8 << 3));
+			     (desc.offset8 << 3), &signal);
 
+	if (signal)
+		vmbus_setevent(channel);
 
 	return 0;
 }
@@ -774,8 +780,8 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 {
 	struct vmpacket_descriptor desc;
 	u32 packetlen;
-	u32 userlen;
 	int ret;
+	bool signal = false;
 
 	*buffer_actual_len = 0;
 	*requestid = 0;
@@ -788,7 +794,6 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 
 
 	packetlen = desc.len8 << 3;
-	userlen = packetlen - (desc.offset8 << 3);
 
 	*buffer_actual_len = packetlen;
 
@@ -802,7 +807,11 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
 	*requestid = desc.trans_id;
 
 	/* Copy over the entire packet to the user buffer */
-	ret = hv_ringbuffer_read(&channel->inbound, buffer, packetlen, 0);
+	ret = hv_ringbuffer_read(&channel->inbound, buffer, packetlen, 0,
+				 &signal);
+
+	if (signal)
+		vmbus_setevent(channel);
 
 	return 0;
 }
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 2f84c5cff8d4..53a8600162a5 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -257,6 +257,70 @@ static void vmbus_process_offer(struct work_struct *work)
 	}
 }
 
+enum {
+	IDE = 0,
+	SCSI,
+	NIC,
+	MAX_PERF_CHN,
+};
+
+/*
+ * This is an array of device_ids (device types) that are performance critical.
+ * We attempt to distribute the interrupt load for these devices across
+ * all available CPUs.
+ */
+static const struct hv_vmbus_device_id hp_devs[] = {
+	/* IDE */
+	{ HV_IDE_GUID, },
+	/* Storage - SCSI */
+	{ HV_SCSI_GUID, },
+	/* Network */
+	{ HV_NIC_GUID, },
+};
+
+
+/*
+ * We use this state to statically distribute the channel interrupt load.
+ */
+static u32  next_vp;
+
+/*
+ * Starting with Win8, we can statically distribute the incoming
+ * channel interrupt load by binding a channel to VCPU. We
+ * implement here a simple round robin scheme for distributing
+ * the interrupt load.
+ * We will bind channels that are not performance critical to cpu 0 and
+ * performance critical channels (IDE, SCSI and Network) will be uniformly
+ * distributed across all available CPUs.
+ */
+static u32 get_vp_index(uuid_le *type_guid)
+{
+	u32 cur_cpu;
+	int i;
+	bool perf_chn = false;
+	u32 max_cpus = num_online_cpus();
+
+	for (i = IDE; i < MAX_PERF_CHN; i++) {
+		if (!memcmp(type_guid->b, hp_devs[i].guid,
+				 sizeof(uuid_le))) {
+			perf_chn = true;
+			break;
+		}
+	}
+	if ((vmbus_proto_version == VERSION_WS2008) ||
+	    (vmbus_proto_version == VERSION_WIN7) || (!perf_chn)) {
+		/*
+		 * 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.
+		 */
+		return 0;
+	}
+	cur_cpu = (++next_vp % max_cpus);
+	return 0;
+}
+
 /*
  * vmbus_onoffer - Handler for channel offers from vmbus in parent partition.
  *
@@ -275,6 +339,35 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 		return;
 	}
 
+	/*
+	 * By default we setup state to enable batched
+	 * reading. A specific service can choose to
+	 * disable this prior to opening the channel.
+	 */
+	newchannel->batched_reading = true;
+
+	/*
+	 * Setup state for signalling the host.
+	 */
+	newchannel->sig_event = (struct hv_input_signal_event *)
+				(ALIGN((unsigned long)
+				&newchannel->sig_buf,
+				HV_HYPERCALL_PARAM_ALIGN));
+
+	newchannel->sig_event->connectionid.asu32 = 0;
+	newchannel->sig_event->connectionid.u.id = VMBUS_EVENT_CONNECTION_ID;
+	newchannel->sig_event->flag_number = 0;
+	newchannel->sig_event->rsvdz = 0;
+
+	if (vmbus_proto_version != VERSION_WS2008) {
+		newchannel->is_dedicated_interrupt =
+				(offer->is_dedicated_interrupt != 0);
+		newchannel->sig_event->connectionid.u.id =
+				offer->connection_id;
+	}
+
+	newchannel->target_vp = get_vp_index(&offer->offer.if_type);
+
 	memcpy(&newchannel->offermsg, offer,
 	       sizeof(struct vmbus_channel_offer_channel));
 	newchannel->monitor_grp = (u8)offer->monitorid / 32;
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 650c9f0b6642..253a74ba245c 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -30,6 +30,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/hyperv.h>
+#include <linux/export.h>
 #include <asm/hyperv.h>
 #include "hyperv_vmbus.h"
 
@@ -40,15 +41,99 @@ struct vmbus_connection vmbus_connection = {
 };
 
 /*
+ * 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_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;
+	int t;
+
+	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);
+	msg->monitor_page2 = virt_to_phys(
+			(void *)((unsigned long)vmbus_connection.monitor_pages +
+				 PAGE_SIZE));
+
+	/*
+	 * 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 */
+	t =  wait_for_completion_timeout(&msginfo->waitevent, 5*HZ);
+	if (t == 0) {
+		spin_lock_irqsave(&vmbus_connection.channelmsg_lock,
+				flags);
+		list_del(&msginfo->msglistentry);
+		spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock,
+					flags);
+		return -ETIMEDOUT;
+	}
+
+	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;
-	int t;
 	struct vmbus_channel_msginfo *msginfo = NULL;
-	struct vmbus_channel_initiate_contact *msg;
-	unsigned long flags;
+	__u32 version;
 
 	/* Initialize the vmbus connection */
 	vmbus_connection.conn_state = CONNECTING;
@@ -99,69 +184,38 @@ int vmbus_connect(void)
 		goto cleanup;
 	}
 
-	init_completion(&msginfo->waitevent);
-
-	msg = (struct vmbus_channel_initiate_contact *)msginfo->msg;
-
-	msg->header.msgtype = CHANNELMSG_INITIATE_CONTACT;
-	msg->vmbus_version_requested = VMBUS_REVISION_NUMBER;
-	msg->interrupt_page = virt_to_phys(vmbus_connection.int_page);
-	msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages);
-	msg->monitor_page2 = virt_to_phys(
-			(void *)((unsigned long)vmbus_connection.monitor_pages +
-				 PAGE_SIZE));
-
 	/*
-	 * Add to list before we send the request since we may
-	 * receive the response before returning from this routine
+	 * 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.
 	 */
-	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);
+	version = VERSION_CURRENT;
 
-	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);
-		goto cleanup;
-	}
+	do {
+		ret = vmbus_negotiate_version(msginfo, version);
+		if (ret == 0)
+			break;
 
-	/* Wait for the connection response */
-	t =  wait_for_completion_timeout(&msginfo->waitevent, 5*HZ);
-	if (t == 0) {
-		spin_lock_irqsave(&vmbus_connection.channelmsg_lock,
-				flags);
-		list_del(&msginfo->msglistentry);
-		spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock,
-					flags);
-		ret = -ETIMEDOUT;
-		goto cleanup;
-	}
+		version = vmbus_get_next_version(version);
+	} while (version != VERSION_INVAL);
 
-	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 {
-		pr_err("Unable to connect, "
-			"Version %d not supported by Hyper-V\n",
-			VMBUS_REVISION_NUMBER);
-		ret = -ECONNREFUSED;
+	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)
@@ -212,6 +266,9 @@ static void process_chn_event(u32 relid)
 {
 	struct vmbus_channel *channel;
 	unsigned long flags;
+	void *arg;
+	bool read_state;
+	u32 bytes_to_read;
 
 	/*
 	 * Find the channel based on this relid and invokes the
@@ -234,10 +291,29 @@ static void process_chn_event(u32 relid)
 	 */
 
 	spin_lock_irqsave(&channel->inbound_lock, flags);
-	if (channel->onchannel_callback != NULL)
-		channel->onchannel_callback(channel->channel_callback_context);
-	else
+	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);
+	}
 
 	spin_unlock_irqrestore(&channel->inbound_lock, flags);
 }
@@ -248,10 +324,32 @@ static void process_chn_event(u32 relid)
 void vmbus_on_event(unsigned long data)
 {
 	u32 dword;
-	u32 maxdword = MAX_NUM_CHANNELS_SUPPORTED >> 5;
+	u32 maxdword;
 	int bit;
 	u32 relid;
-	u32 *recv_int_page = vmbus_connection.recv_int_page;
+	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)
@@ -307,12 +405,16 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 /*
  * vmbus_set_event - Send an event notification to the parent
  */
-int vmbus_set_event(u32 child_relid)
+int vmbus_set_event(struct vmbus_channel *channel)
 {
-	/* Each u32 represents 32 channels */
-	sync_set_bit(child_relid & 31,
-		(unsigned long *)vmbus_connection.send_int_page +
-		(child_relid >> 5));
+	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();
+	return hv_signal_event(channel->sig_event);
 }
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 3648f8f0f368..1c5481da6e4a 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -27,6 +27,7 @@
 #include <linux/vmalloc.h>
 #include <linux/hyperv.h>
 #include <linux/version.h>
+#include <linux/interrupt.h>
 #include <asm/hyperv.h>
 #include "hyperv_vmbus.h"
 
@@ -34,13 +35,16 @@
 struct hv_context hv_context = {
 	.synic_initialized	= false,
 	.hypercall_page		= NULL,
-	.signal_event_param	= NULL,
-	.signal_event_buffer	= NULL,
 };
 
 /*
  * query_hypervisor_info - Get version info of the windows hypervisor
  */
+unsigned int host_info_eax;
+unsigned int host_info_ebx;
+unsigned int host_info_ecx;
+unsigned int host_info_edx;
+
 static int query_hypervisor_info(void)
 {
 	unsigned int eax;
@@ -70,13 +74,10 @@ static int query_hypervisor_info(void)
 		edx = 0;
 		op = HVCPUID_VERSION;
 		cpuid(op, &eax, &ebx, &ecx, &edx);
-		pr_info("Hyper-V Host OS Build:%d-%d.%d-%d-%d.%d\n",
-			    eax,
-			    ebx >> 16,
-			    ebx & 0xFFFF,
-			    ecx,
-			    edx >> 24,
-			    edx & 0xFFFFFF);
+		host_info_eax = eax;
+		host_info_ebx = ebx;
+		host_info_ecx = ecx;
+		host_info_edx = edx;
 	}
 	return max_leaf;
 }
@@ -137,6 +138,10 @@ int hv_init(void)
 	memset(hv_context.synic_event_page, 0, sizeof(void *) * NR_CPUS);
 	memset(hv_context.synic_message_page, 0,
 	       sizeof(void *) * NR_CPUS);
+	memset(hv_context.vp_index, 0,
+	       sizeof(int) * NR_CPUS);
+	memset(hv_context.event_dpc, 0,
+	       sizeof(void *) * NR_CPUS);
 
 	max_leaf = query_hypervisor_info();
 
@@ -168,24 +173,6 @@ int hv_init(void)
 
 	hv_context.hypercall_page = virtaddr;
 
-	/* Setup the global signal event param for the signal event hypercall */
-	hv_context.signal_event_buffer =
-			kmalloc(sizeof(struct hv_input_signal_event_buffer),
-				GFP_KERNEL);
-	if (!hv_context.signal_event_buffer)
-		goto cleanup;
-
-	hv_context.signal_event_param =
-		(struct hv_input_signal_event *)
-			(ALIGN((unsigned long)
-				  hv_context.signal_event_buffer,
-				  HV_HYPERCALL_PARAM_ALIGN));
-	hv_context.signal_event_param->connectionid.asu32 = 0;
-	hv_context.signal_event_param->connectionid.u.id =
-						VMBUS_EVENT_CONNECTION_ID;
-	hv_context.signal_event_param->flag_number = 0;
-	hv_context.signal_event_param->rsvdz = 0;
-
 	return 0;
 
 cleanup:
@@ -213,10 +200,6 @@ void hv_cleanup(void)
 	/* Reset our OS id */
 	wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 
-	kfree(hv_context.signal_event_buffer);
-	hv_context.signal_event_buffer = NULL;
-	hv_context.signal_event_param = NULL;
-
 	if (hv_context.hypercall_page) {
 		hypercall_msr.as_uint64 = 0;
 		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
@@ -273,13 +256,12 @@ int hv_post_message(union hv_connection_id connection_id,
  *
  * This involves a hypercall.
  */
-u16 hv_signal_event(void)
+u16 hv_signal_event(void *con_id)
 {
 	u16 status;
 
-	status = do_hypercall(HVCALL_SIGNAL_EVENT,
-			       hv_context.signal_event_param,
-			       NULL) & 0xFFFF;
+	status = (do_hypercall(HVCALL_SIGNAL_EVENT, con_id, NULL) & 0xFFFF);
+
 	return status;
 }
 
@@ -297,6 +279,7 @@ void hv_synic_init(void *irqarg)
 	union hv_synic_siefp siefp;
 	union hv_synic_sint shared_sint;
 	union hv_synic_scontrol sctrl;
+	u64 vp_index;
 
 	u32 irq_vector = *((u32 *)(irqarg));
 	int cpu = smp_processor_id();
@@ -307,6 +290,15 @@ void hv_synic_init(void *irqarg)
 	/* Check the version */
 	rdmsrl(HV_X64_MSR_SVERSION, version);
 
+	hv_context.event_dpc[cpu] = (struct tasklet_struct *)
+					kmalloc(sizeof(struct tasklet_struct),
+						GFP_ATOMIC);
+	if (hv_context.event_dpc[cpu] == NULL) {
+		pr_err("Unable to allocate event dpc\n");
+		goto cleanup;
+	}
+	tasklet_init(hv_context.event_dpc[cpu], vmbus_on_event, cpu);
+
 	hv_context.synic_message_page[cpu] =
 		(void *)get_zeroed_page(GFP_ATOMIC);
 
@@ -345,7 +337,7 @@ void hv_synic_init(void *irqarg)
 	shared_sint.as_uint64 = 0;
 	shared_sint.vector = irq_vector; /* HV_SHARED_SINT_IDT_VECTOR + 0x20; */
 	shared_sint.masked = false;
-	shared_sint.auto_eoi = false;
+	shared_sint.auto_eoi = true;
 
 	wrmsrl(HV_X64_MSR_SINT0 + VMBUS_MESSAGE_SINT, shared_sint.as_uint64);
 
@@ -356,6 +348,14 @@ void hv_synic_init(void *irqarg)
 	wrmsrl(HV_X64_MSR_SCONTROL, sctrl.as_uint64);
 
 	hv_context.synic_initialized = true;
+
+	/*
+	 * Setup the mapping between Hyper-V's notion
+	 * of cpuid and Linux' notion of cpuid.
+	 * This array will be indexed using Linux cpuid.
+	 */
+	rdmsrl(HV_X64_MSR_VP_INDEX, vp_index);
+	hv_context.vp_index[cpu] = (u32)vp_index;
 	return;
 
 cleanup:
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index dd289fd179ca..37873213e24f 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -29,7 +29,6 @@
 #include <linux/memory_hotplug.h>
 #include <linux/memory.h>
 #include <linux/notifier.h>
-#include <linux/mman.h>
 #include <linux/percpu_counter.h>
 
 #include <linux/hyperv.h>
@@ -415,10 +414,17 @@ struct dm_info_msg {
 
 static bool hot_add;
 static bool do_hot_add;
+/*
+ * Delay reporting memory pressure by
+ * the specified number of seconds.
+ */
+static uint pressure_report_delay = 30;
 
 module_param(hot_add, bool, (S_IRUGO | S_IWUSR));
 MODULE_PARM_DESC(hot_add, "If set attempt memory hot_add");
 
+module_param(pressure_report_delay, uint, (S_IRUGO | S_IWUSR));
+MODULE_PARM_DESC(pressure_report_delay, "Delay in secs in reporting pressure");
 static atomic_t trans_id = ATOMIC_INIT(0);
 
 static int dm_ring_size = (5 * PAGE_SIZE);
@@ -517,6 +523,34 @@ static void process_info(struct hv_dynmem_device *dm, struct dm_info_msg *msg)
 	}
 }
 
+unsigned long compute_balloon_floor(void)
+{
+	unsigned long min_pages;
+#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
+	/* Simple continuous piecewiese linear function:
+	 *  max MiB -> min MiB  gradient
+	 *       0         0
+	 *      16        16
+	 *      32        24
+	 *     128        72    (1/2)
+	 *     512       168    (1/4)
+	 *    2048       360    (1/8)
+	 *    8192       552    (1/32)
+	 *   32768      1320
+	 *  131072      4392
+	 */
+	if (totalram_pages < MB2PAGES(128))
+		min_pages = MB2PAGES(8) + (totalram_pages >> 1);
+	else if (totalram_pages < MB2PAGES(512))
+		min_pages = MB2PAGES(40) + (totalram_pages >> 2);
+	else if (totalram_pages < MB2PAGES(2048))
+		min_pages = MB2PAGES(104) + (totalram_pages >> 3);
+	else
+		min_pages = MB2PAGES(296) + (totalram_pages >> 5);
+#undef MB2PAGES
+	return min_pages;
+}
+
 /*
  * Post our status as it relates memory pressure to the
  * host. Host expects the guests to post this status
@@ -530,15 +564,30 @@ static void process_info(struct hv_dynmem_device *dm, struct dm_info_msg *msg)
 static void post_status(struct hv_dynmem_device *dm)
 {
 	struct dm_status status;
+	struct sysinfo val;
 
-
+	if (pressure_report_delay > 0) {
+		--pressure_report_delay;
+		return;
+	}
+	si_meminfo(&val);
 	memset(&status, 0, sizeof(struct dm_status));
 	status.hdr.type = DM_STATUS_REPORT;
 	status.hdr.size = sizeof(struct dm_status);
 	status.hdr.trans_id = atomic_inc_return(&trans_id);
 
-
-	status.num_committed = vm_memory_committed();
+	/*
+	 * The host expects the guest to report free memory.
+	 * Further, the host expects the pressure information to
+	 * include the ballooned out pages.
+	 * For a given amount of memory that we are managing, we
+	 * need to compute a floor below which we should not balloon.
+	 * Compute this and add it to the pressure report.
+	 */
+	status.num_avail = val.freeram;
+	status.num_committed = vm_memory_committed() +
+				dm->num_pages_ballooned +
+				compute_balloon_floor();
 
 	vmbus_sendpacket(dm->dev->channel, &status,
 				sizeof(struct dm_status),
@@ -547,8 +596,6 @@ static void post_status(struct hv_dynmem_device *dm)
 
 }
 
-
-
 static void free_balloon_pages(struct hv_dynmem_device *dm,
 			 union dm_mem_page_range *range_array)
 {
@@ -1013,9 +1060,7 @@ static int balloon_remove(struct hv_device *dev)
 static const struct hv_vmbus_device_id id_table[] = {
 	/* Dynamic Memory Class ID */
 	/* 525074DC-8985-46e2-8057-A307DC18A502 */
-	{ VMBUS_DEVICE(0xdc, 0x74, 0x50, 0X52, 0x85, 0x89, 0xe2, 0x46,
-		       0x80, 0x57, 0xa3, 0x07, 0xdc, 0x18, 0xa5, 0x02)
-	},
+	{ HV_DM_GUID, },
 	{ },
 };
 
diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index a0667de7a04c..1d4cbd8e8261 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -49,6 +49,16 @@ static struct hv_util_service util_kvp = {
 	.util_deinit = hv_kvp_deinit,
 };
 
+static void perform_shutdown(struct work_struct *dummy)
+{
+	orderly_poweroff(true);
+}
+
+/*
+ * Perform the shutdown operation in a thread context.
+ */
+static DECLARE_WORK(shutdown_work, perform_shutdown);
+
 static void shutdown_onchannelcallback(void *context)
 {
 	struct vmbus_channel *channel = context;
@@ -106,7 +116,7 @@ static void shutdown_onchannelcallback(void *context)
 	}
 
 	if (execute_shutdown == true)
-		orderly_poweroff(true);
+		schedule_work(&shutdown_work);
 }
 
 /*
@@ -274,6 +284,16 @@ static int util_probe(struct hv_device *dev,
 		}
 	}
 
+	/*
+	 * The set of services managed by the util driver are not performance
+	 * critical and do not need batched reading. Furthermore, some services
+	 * such as KVP can only handle one message from the host at a time.
+	 * Turn off batched reading for all util drivers before we open the
+	 * channel.
+	 */
+
+	set_channel_read_state(dev->channel, false);
+
 	ret = vmbus_open(dev->channel, 4 * PAGE_SIZE, 4 * PAGE_SIZE, NULL, 0,
 			srv->util_cb, dev->channel);
 	if (ret)
@@ -304,21 +324,21 @@ static int util_remove(struct hv_device *dev)
 
 static const struct hv_vmbus_device_id id_table[] = {
 	/* Shutdown guid */
-	{ VMBUS_DEVICE(0x31, 0x60, 0x0B, 0X0E, 0x13, 0x52, 0x34, 0x49,
-		       0x81, 0x8B, 0x38, 0XD9, 0x0C, 0xED, 0x39, 0xDB)
-	  .driver_data = (unsigned long)&util_shutdown },
+	{ HV_SHUTDOWN_GUID,
+	  .driver_data = (unsigned long)&util_shutdown
+	},
 	/* Time synch guid */
-	{ VMBUS_DEVICE(0x30, 0xe6, 0x27, 0x95, 0xae, 0xd0, 0x7b, 0x49,
-		       0xad, 0xce, 0xe8, 0x0a, 0xb0, 0x17, 0x5c, 0xaf)
-	  .driver_data = (unsigned long)&util_timesynch },
+	{ HV_TS_GUID,
+	  .driver_data = (unsigned long)&util_timesynch
+	},
 	/* Heartbeat guid */
-	{ VMBUS_DEVICE(0x39, 0x4f, 0x16, 0x57, 0x15, 0x91, 0x78, 0x4e,
-		       0xab, 0x55, 0x38, 0x2f, 0x3b, 0xd5, 0x42, 0x2d)
-	  .driver_data = (unsigned long)&util_heartbeat },
+	{ HV_HEART_BEAT_GUID,
+	  .driver_data = (unsigned long)&util_heartbeat
+	},
 	/* KVP guid */
-	{ VMBUS_DEVICE(0xe7, 0xf4, 0xa0, 0xa9, 0x45, 0x5a, 0x96, 0x4d,
-		       0xb8, 0x27, 0x8a, 0x84, 0x1e, 0x8c, 0x3,  0xe6)
-	  .driver_data = (unsigned long)&util_kvp },
+	{ HV_KVP_GUID,
+	  .driver_data = (unsigned long)&util_kvp
+	},
 	{ },
 };
 
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index d8d1fadb398a..12f2f9e989f7 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -101,15 +101,6 @@ enum hv_message_type {
 /* Define invalid partition identifier. */
 #define HV_PARTITION_ID_INVALID		((u64)0x0)
 
-/* Define connection identifier type. */
-union hv_connection_id {
-	u32 asu32;
-	struct {
-		u32 id:24;
-		u32 reserved:8;
-	} u;
-};
-
 /* Define port identifier type. */
 union hv_port_id {
 	u32 asu32;
@@ -338,13 +329,6 @@ struct hv_input_post_message {
 	u64 payload[HV_MESSAGE_PAYLOAD_QWORD_COUNT];
 };
 
-/* Definition of the hv_signal_event hypercall input structure. */
-struct hv_input_signal_event {
-	union hv_connection_id connectionid;
-	u16 flag_number;
-	u16 rsvdz;
-};
-
 /*
  * Versioning definitions used for guests reporting themselves to the
  * hypervisor, and visa versa.
@@ -498,11 +482,6 @@ static const uuid_le VMBUS_SERVICE_ID = {
 
 
 
-struct hv_input_signal_event_buffer {
-	u64 align8;
-	struct hv_input_signal_event event;
-};
-
 struct hv_context {
 	/* We only support running on top of Hyper-V
 	* So at this point this really can only contain the Hyper-V ID
@@ -513,16 +492,24 @@ struct hv_context {
 
 	bool synic_initialized;
 
-	/*
-	 * This is used as an input param to HvCallSignalEvent hypercall. The
-	 * input param is immutable in our usage and must be dynamic mem (vs
-	 * stack or global). */
-	struct hv_input_signal_event_buffer *signal_event_buffer;
-	/* 8-bytes aligned of the buffer above */
-	struct hv_input_signal_event *signal_event_param;
-
 	void *synic_message_page[NR_CPUS];
 	void *synic_event_page[NR_CPUS];
+	/*
+	 * Hypervisor's notion of virtual processor ID is different from
+	 * Linux' notion of CPU ID. This information can only be retrieved
+	 * in the context of the calling CPU. Setup a map for easy access
+	 * to this information:
+	 *
+	 * vp_index[a] is the Hyper-V's processor ID corresponding to
+	 * Linux cpuid 'a'.
+	 */
+	u32 vp_index[NR_CPUS];
+	/*
+	 * Starting with win8, we can take channel interrupts on any CPU;
+	 * we will manage the tasklet that handles events on a per CPU
+	 * basis.
+	 */
+	struct tasklet_struct *event_dpc[NR_CPUS];
 };
 
 extern struct hv_context hv_context;
@@ -538,12 +525,19 @@ extern int hv_post_message(union hv_connection_id connection_id,
 			 enum hv_message_type message_type,
 			 void *payload, size_t payload_size);
 
-extern u16 hv_signal_event(void);
+extern u16 hv_signal_event(void *con_id);
 
 extern void hv_synic_init(void *irqarg);
 
 extern void hv_synic_cleanup(void *arg);
 
+/*
+ * Host version information.
+ */
+extern unsigned int host_info_eax;
+extern unsigned int host_info_ebx;
+extern unsigned int host_info_ecx;
+extern unsigned int host_info_edx;
 
 /* Interface */
 
@@ -555,7 +549,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info);
 
 int hv_ringbuffer_write(struct hv_ring_buffer_info *ring_info,
 		    struct scatterlist *sglist,
-		    u32 sgcount);
+		    u32 sgcount, bool *signal);
 
 int hv_ringbuffer_peek(struct hv_ring_buffer_info *ring_info, void *buffer,
 		   u32 buflen);
@@ -563,13 +557,16 @@ int hv_ringbuffer_peek(struct hv_ring_buffer_info *ring_info, void *buffer,
 int hv_ringbuffer_read(struct hv_ring_buffer_info *ring_info,
 		   void *buffer,
 		   u32 buflen,
-		   u32 offset);
+		   u32 offset, bool *signal);
 
-u32 hv_get_ringbuffer_interrupt_mask(struct hv_ring_buffer_info *ring_info);
 
 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 			    struct hv_ring_buffer_debug_info *debug_info);
 
+void hv_begin_read(struct hv_ring_buffer_info *rbi);
+
+u32 hv_end_read(struct hv_ring_buffer_info *rbi);
+
 /*
  * Maximum channels is determined by the size of the interrupt page
  * which is PAGE_SIZE. 1/2 of PAGE_SIZE is for send endpoint interrupt
@@ -657,7 +654,7 @@ int vmbus_connect(void);
 
 int vmbus_post_msg(void *buffer, size_t buflen);
 
-int vmbus_set_event(u32 child_relid);
+int vmbus_set_event(struct vmbus_channel *channel);
 
 void vmbus_on_event(unsigned long data);
 
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 7233c88f01b8..cafa72ffdc30 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -29,6 +29,105 @@
 
 #include "hyperv_vmbus.h"
 
+void hv_begin_read(struct hv_ring_buffer_info *rbi)
+{
+	rbi->ring_buffer->interrupt_mask = 1;
+	smp_mb();
+}
+
+u32 hv_end_read(struct hv_ring_buffer_info *rbi)
+{
+	u32 read;
+	u32 write;
+
+	rbi->ring_buffer->interrupt_mask = 0;
+	smp_mb();
+
+	/*
+	 * Now check to see if the ring buffer is still empty.
+	 * If it is not, we raced and we need to process new
+	 * incoming messages.
+	 */
+	hv_get_ringbuffer_availbytes(rbi, &read, &write);
+
+	return read;
+}
+
+/*
+ * When we write to the ring buffer, check if the host needs to
+ * be signaled. Here is the details of this protocol:
+ *
+ *	1. The host guarantees that while it is draining the
+ *	   ring buffer, it will set the interrupt_mask to
+ *	   indicate it does not need to be interrupted when
+ *	   new data is placed.
+ *
+ *	2. The host guarantees that it will completely drain
+ *	   the ring buffer before exiting the read loop. Further,
+ *	   once the ring buffer is empty, it will clear the
+ *	   interrupt_mask and re-check to see if new data has
+ *	   arrived.
+ */
+
+static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
+{
+	if (rbi->ring_buffer->interrupt_mask)
+		return false;
+
+	/*
+	 * This is the only case we need to signal when the
+	 * ring transitions from being empty to non-empty.
+	 */
+	if (old_write == rbi->ring_buffer->read_index)
+		return true;
+
+	return false;
+}
+
+/*
+ * To optimize the flow management on the send-side,
+ * when the sender is blocked because of lack of
+ * sufficient space in the ring buffer, potential the
+ * consumer of the ring buffer can signal the producer.
+ * This is controlled by the following parameters:
+ *
+ * 1. pending_send_sz: This is the size in bytes that the
+ *    producer is trying to send.
+ * 2. The feature bit feat_pending_send_sz set to indicate if
+ *    the consumer of the ring will signal when the ring
+ *    state transitions from being full to a state where
+ *    there is room for the producer to send the pending packet.
+ */
+
+static bool hv_need_to_signal_on_read(u32 old_rd,
+					 struct hv_ring_buffer_info *rbi)
+{
+	u32 prev_write_sz;
+	u32 cur_write_sz;
+	u32 r_size;
+	u32 write_loc = rbi->ring_buffer->write_index;
+	u32 read_loc = rbi->ring_buffer->read_index;
+	u32 pending_sz = rbi->ring_buffer->pending_send_sz;
+
+	/*
+	 * If the other end is not blocked on write don't bother.
+	 */
+	if (pending_sz == 0)
+		return false;
+
+	r_size = rbi->ring_datasize;
+	cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
+			read_loc - write_loc;
+
+	prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
+			old_rd - write_loc;
+
+
+	if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
+		return true;
+
+	return false;
+}
 
 /*
  * hv_get_next_write_location()
@@ -239,19 +338,6 @@ void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 	}
 }
 
-
-/*
- *
- * hv_get_ringbuffer_interrupt_mask()
- *
- * Get the interrupt mask for the specified ring buffer
- *
- */
-u32 hv_get_ringbuffer_interrupt_mask(struct hv_ring_buffer_info *rbi)
-{
-	return rbi->ring_buffer->interrupt_mask;
-}
-
 /*
  *
  * hv_ringbuffer_init()
@@ -298,7 +384,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
  *
  */
 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
-		    struct scatterlist *sglist, u32 sgcount)
+		    struct scatterlist *sglist, u32 sgcount, bool *signal)
 {
 	int i = 0;
 	u32 bytes_avail_towrite;
@@ -307,6 +393,7 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 
 	struct scatterlist *sg;
 	u32 next_write_location;
+	u32 old_write;
 	u64 prev_indices = 0;
 	unsigned long flags;
 
@@ -335,6 +422,8 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 	/* Write to the ring buffer */
 	next_write_location = hv_get_next_write_location(outring_info);
 
+	old_write = next_write_location;
+
 	for_each_sg(sglist, sg, sgcount, i)
 	{
 		next_write_location = hv_copyto_ringbuffer(outring_info,
@@ -351,14 +440,16 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 					     &prev_indices,
 					     sizeof(u64));
 
-	/* Make sure we flush all writes before updating the writeIndex */
-	smp_wmb();
+	/* Issue a full memory barrier before updating the write index */
+	smp_mb();
 
 	/* Now, update the write location */
 	hv_set_next_write_location(outring_info, next_write_location);
 
 
 	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
+
+	*signal = hv_need_to_signal(old_write, outring_info);
 	return 0;
 }
 
@@ -414,13 +505,14 @@ int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
  *
  */
 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
-		   u32 buflen, u32 offset)
+		   u32 buflen, u32 offset, bool *signal)
 {
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;
 	u32 next_read_location = 0;
 	u64 prev_indices = 0;
 	unsigned long flags;
+	u32 old_read;
 
 	if (buflen <= 0)
 		return -EINVAL;
@@ -431,6 +523,8 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 				&bytes_avail_toread,
 				&bytes_avail_towrite);
 
+	old_read = bytes_avail_toread;
+
 	/* Make sure there is something to read */
 	if (bytes_avail_toread < buflen) {
 		spin_unlock_irqrestore(&inring_info->ring_lock, flags);
@@ -461,5 +555,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 
 	spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 
+	*signal = hv_need_to_signal_on_read(old_read, inring_info);
+
 	return 0;
 }
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 8e1a9ec53003..cf19dfa5ead1 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -33,6 +33,7 @@
 #include <acpi/acpi_bus.h>
 #include <linux/completion.h>
 #include <linux/hyperv.h>
+#include <linux/kernel_stat.h>
 #include <asm/hyperv.h>
 #include <asm/hypervisor.h>
 #include "hyperv_vmbus.h"
@@ -41,7 +42,6 @@
 static struct acpi_device  *hv_acpi_dev;
 
 static struct tasklet_struct msg_dpc;
-static struct tasklet_struct event_dpc;
 static struct completion probe_event;
 static int irq;
 
@@ -454,21 +454,40 @@ static irqreturn_t vmbus_isr(int irq, void *dev_id)
 	union hv_synic_event_flags *event;
 	bool handled = false;
 
+	page_addr = hv_context.synic_event_page[cpu];
+	if (page_addr == NULL)
+		return IRQ_NONE;
+
+	event = (union hv_synic_event_flags *)page_addr +
+					 VMBUS_MESSAGE_SINT;
 	/*
 	 * Check for events before checking for messages. This is the order
 	 * in which events and messages are checked in Windows guests on
 	 * Hyper-V, and the Windows team suggested we do the same.
 	 */
 
-	page_addr = hv_context.synic_event_page[cpu];
-	event = (union hv_synic_event_flags *)page_addr + VMBUS_MESSAGE_SINT;
+	if ((vmbus_proto_version == VERSION_WS2008) ||
+		(vmbus_proto_version == VERSION_WIN7)) {
 
-	/* Since we are a child, we only need to check bit 0 */
-	if (sync_test_and_clear_bit(0, (unsigned long *) &event->flags32[0])) {
+		/* Since we are a child, we only need to check bit 0 */
+		if (sync_test_and_clear_bit(0,
+			(unsigned long *) &event->flags32[0])) {
+			handled = true;
+		}
+	} else {
+		/*
+		 * Our host is win8 or above. The signaling mechanism
+		 * has changed and we can directly look at the event page.
+		 * If bit n is set then we have an interrup on the channel
+		 * whose id is n.
+		 */
 		handled = true;
-		tasklet_schedule(&event_dpc);
 	}
 
+	if (handled)
+		tasklet_schedule(hv_context.event_dpc[cpu]);
+
+
 	page_addr = hv_context.synic_message_page[cpu];
 	msg = (struct hv_message *)page_addr + VMBUS_MESSAGE_SINT;
 
@@ -485,6 +504,19 @@ static irqreturn_t vmbus_isr(int irq, void *dev_id)
 }
 
 /*
+ * vmbus interrupt flow handler:
+ * vmbus interrupts can concurrently occur on multiple CPUs and
+ * can be handled concurrently.
+ */
+
+static void vmbus_flow_handler(unsigned int irq, struct irq_desc *desc)
+{
+	kstat_incr_irqs_this_cpu(irq, desc);
+
+	desc->action->handler(irq, desc->action->dev_id);
+}
+
+/*
  * vmbus_bus_init -Main vmbus driver initialization routine.
  *
  * Here, we
@@ -506,7 +538,6 @@ static int vmbus_bus_init(int irq)
 	}
 
 	tasklet_init(&msg_dpc, vmbus_on_msg_dpc, 0);
-	tasklet_init(&event_dpc, vmbus_on_event, 0);
 
 	ret = bus_register(&hv_bus);
 	if (ret)
@@ -520,6 +551,13 @@ static int vmbus_bus_init(int irq)
 		goto err_unregister;
 	}
 
+	/*
+	 * Vmbus interrupts can be handled concurrently on
+	 * different CPUs. Establish an appropriate interrupt flow
+	 * handler that can support this model.
+	 */
+	irq_set_handler(irq, vmbus_flow_handler);
+
 	vector = IRQ0_VECTOR + irq;
 
 	/*
@@ -575,8 +613,6 @@ int __vmbus_driver_register(struct hv_driver *hv_driver, struct module *owner, c
 
 	ret = driver_register(&hv_driver->driver);
 
-	vmbus_request_offers();
-
 	return ret;
 }
 EXPORT_SYMBOL_GPL(__vmbus_driver_register);