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

 // 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/io.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/hyperv.h>
 #include <linux/random.h>
 #include <linux/clockchips.h>
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <clocksource/hyperv_timer.h>
 #include <asm/mshyperv.h>
 #include "hyperv_vmbus.h"

 /* The one and only */
 struct hv_context hv_context;

 /*
  * hv_init - Main initialization routine.
  *
  * This routine must be called before any other routines in here are called
  */
 int hv_init(void)
 {
 	hv_context.cpu_context = alloc_percpu(struct hv_per_cpu_context);
 	if (!hv_context.cpu_context)
 		return -ENOMEM;
 	return 0;
 }

 /*
  * hv_post_message - Post a message using the hypervisor message IPC.
  *
  * This involves a hypercall.
  */
 int hv_post_message(union hv_connection_id connection_id,
 		  enum hv_message_type message_type,
 		  void *payload, size_t payload_size)
 {
 	struct hv_input_post_message *aligned_msg;
 	unsigned long flags;
 	u64 status;

 	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
 		return -EMSGSIZE;

 	local_irq_save(flags);

 	aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
 	aligned_msg->connectionid = connection_id;
 	aligned_msg->reserved = 0;
 	aligned_msg->message_type = message_type;
 	aligned_msg->payload_size = payload_size;
 	memcpy((void *)aligned_msg->payload, payload, payload_size);

 	if (hv_isolation_type_snp())
 		status = hv_ghcb_hypercall(HVCALL_POST_MESSAGE,
 				(void *)aligned_msg, NULL,
 				sizeof(*aligned_msg));
 	else
 		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
 				aligned_msg, NULL);

 	local_irq_restore(flags);

 	return hv_result(status);
 }

 int hv_synic_alloc(void)
 {
 	int cpu;
 	struct hv_per_cpu_context *hv_cpu;

 	/*
 	 * First, zero all per-cpu memory areas so hv_synic_free() can
 	 * detect what memory has been allocated and cleanup properly
 	 * after any failures.
 	 */
 	for_each_present_cpu(cpu) {
 		hv_cpu = per_cpu_ptr(hv_context.cpu_context, cpu);
 		memset(hv_cpu, 0, sizeof(*hv_cpu));
 	}

 	hv_context.hv_numa_map = kcalloc(nr_node_ids, sizeof(struct cpumask),
 					 GFP_KERNEL);
 	if (hv_context.hv_numa_map == NULL) {
 		pr_err("Unable to allocate NUMA map\n");
 		goto err;
 	}

 	for_each_present_cpu(cpu) {
 		hv_cpu = per_cpu_ptr(hv_context.cpu_context, cpu);

 		tasklet_init(&hv_cpu->msg_dpc,
 			     vmbus_on_msg_dpc, (unsigned long) hv_cpu);

 		/*
 		 * Synic message and event pages are allocated by paravisor.
 		 * Skip these pages allocation here.
 		 */
 		if (!hv_isolation_type_snp() && !hv_root_partition) {
 			hv_cpu->synic_message_page =
 				(void *)get_zeroed_page(GFP_ATOMIC);
 			if (hv_cpu->synic_message_page == NULL) {
 				pr_err("Unable to allocate SYNIC message page\n");
 				goto err;
 			}

 			hv_cpu->synic_event_page =
 				(void *)get_zeroed_page(GFP_ATOMIC);
 			if (hv_cpu->synic_event_page == NULL) {
 				pr_err("Unable to allocate SYNIC event page\n");
 				goto err;
 			}
 		}
 	}

 	return 0;
 err:
 	/*
 	 * Any memory allocations that succeeded will be freed when
 	 * the caller cleans up by calling hv_synic_free()
 	 */
 	return -ENOMEM;
 }


 void hv_synic_free(void)
 {
 	int cpu;

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

 		free_page((unsigned long)hv_cpu->synic_event_page);
 		free_page((unsigned long)hv_cpu->synic_message_page);
 	}

 	kfree(hv_context.hv_numa_map);
 }

 /*
  * hv_synic_init - Initialize the Synthetic Interrupt Controller.
  *
  * If it is already initialized by another entity (ie x2v shim), we need to
  * retrieve the initialized message and event pages.  Otherwise, we create and
  * initialize the message and event pages.
  */
 void hv_synic_enable_regs(unsigned int cpu)
 {
 	struct hv_per_cpu_context *hv_cpu
 		= per_cpu_ptr(hv_context.cpu_context, cpu);
 	union hv_synic_simp simp;
 	union hv_synic_siefp siefp;
 	union hv_synic_sint shared_sint;
 	union hv_synic_scontrol sctrl;

 	/* Setup the Synic's message page */
 	simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
 	simp.simp_enabled = 1;

 	if (hv_isolation_type_snp() || hv_root_partition) {
 		/* Mask out vTOM bit. ioremap_cache() maps decrypted */
 		u64 base = (simp.base_simp_gpa << HV_HYP_PAGE_SHIFT) &
 				~ms_hyperv.shared_gpa_boundary;
 		hv_cpu->synic_message_page
 			= (void *)ioremap_cache(base, HV_HYP_PAGE_SIZE);
 		if (!hv_cpu->synic_message_page)
 			pr_err("Fail to map synic message page.\n");
 	} else {
 		simp.base_simp_gpa = virt_to_phys(hv_cpu->synic_message_page)
 			>> HV_HYP_PAGE_SHIFT;
 	}

 	hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);

 	/* Setup the Synic's event page */
 	siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
 	siefp.siefp_enabled = 1;

 	if (hv_isolation_type_snp() || hv_root_partition) {
 		/* Mask out vTOM bit. ioremap_cache() maps decrypted */
 		u64 base = (siefp.base_siefp_gpa << HV_HYP_PAGE_SHIFT) &
 				~ms_hyperv.shared_gpa_boundary;
 		hv_cpu->synic_event_page
 			= (void *)ioremap_cache(base, HV_HYP_PAGE_SIZE);
 		if (!hv_cpu->synic_event_page)
 			pr_err("Fail to map synic event page.\n");
 	} else {
 		siefp.base_siefp_gpa = virt_to_phys(hv_cpu->synic_event_page)
 			>> HV_HYP_PAGE_SHIFT;
 	}

 	hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);

 	/* Setup the shared SINT. */
 	if (vmbus_irq != -1)
 		enable_percpu_irq(vmbus_irq, 0);
 	shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
 					VMBUS_MESSAGE_SINT);

 	shared_sint.vector = vmbus_interrupt;
 	shared_sint.masked = false;

 	/*
 	 * On architectures where Hyper-V doesn't support AEOI (e.g., ARM64),
 	 * it doesn't provide a recommendation flag and AEOI must be disabled.
 	 */
 #ifdef HV_DEPRECATING_AEOI_RECOMMENDED
 	shared_sint.auto_eoi =
 			!(ms_hyperv.hints & HV_DEPRECATING_AEOI_RECOMMENDED);
 #else
 	shared_sint.auto_eoi = 0;
 #endif
 	hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
 				shared_sint.as_uint64);

 	/* Enable the global synic bit */
 	sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
 	sctrl.enable = 1;

 	hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
 }

 int hv_synic_init(unsigned int cpu)
 {
 	hv_synic_enable_regs(cpu);

 	hv_stimer_legacy_init(cpu, VMBUS_MESSAGE_SINT);

 	return 0;
 }

 /*
  * hv_synic_cleanup - Cleanup routine for hv_synic_init().
  */
 void hv_synic_disable_regs(unsigned int cpu)
 {
 	struct hv_per_cpu_context *hv_cpu
 		= per_cpu_ptr(hv_context.cpu_context, cpu);
 	union hv_synic_sint shared_sint;
 	union hv_synic_simp simp;
 	union hv_synic_siefp siefp;
 	union hv_synic_scontrol sctrl;

 	shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
 					VMBUS_MESSAGE_SINT);

 	shared_sint.masked = 1;

 	/* Need to correctly cleanup in the case of SMP!!! */
 	/* Disable the interrupt */
 	hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
 				shared_sint.as_uint64);

 	simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
 	/*
 	 * In Isolation VM, sim and sief pages are allocated by
 	 * paravisor. These pages also will be used by kdump
 	 * kernel. So just reset enable bit here and keep page
 	 * addresses.
 	 */
 	simp.simp_enabled = 0;
 	if (hv_isolation_type_snp() || hv_root_partition) {
 		iounmap(hv_cpu->synic_message_page);
 		hv_cpu->synic_message_page = NULL;
 	} else {
 		simp.base_simp_gpa = 0;
 	}

 	hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);

 	siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
 	siefp.siefp_enabled = 0;

 	if (hv_isolation_type_snp() || hv_root_partition) {
 		iounmap(hv_cpu->synic_event_page);
 		hv_cpu->synic_event_page = NULL;
 	} else {
 		siefp.base_siefp_gpa = 0;
 	}

 	hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);

 	/* Disable the global synic bit */
 	sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
 	sctrl.enable = 0;
 	hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);

 	if (vmbus_irq != -1)
 		disable_percpu_irq(vmbus_irq);
 }

 #define HV_MAX_TRIES 3
 /*
  * Scan the event flags page of 'this' CPU looking for any bit that is set.  If we find one
  * bit set, then wait for a few milliseconds.  Repeat these steps for a maximum of 3 times.
  * Return 'true', if there is still any set bit after this operation; 'false', otherwise.
  *
  * If a bit is set, that means there is a pending channel interrupt.  The expectation is
  * that the normal interrupt handling mechanism will find and process the channel interrupt
  * "very soon", and in the process clear the bit.
  */
 static bool hv_synic_event_pending(void)
 {
 	struct hv_per_cpu_context *hv_cpu = this_cpu_ptr(hv_context.cpu_context);
 	union hv_synic_event_flags *event =
 		(union hv_synic_event_flags *)hv_cpu->synic_event_page + VMBUS_MESSAGE_SINT;
 	unsigned long *recv_int_page = event->flags; /* assumes VMBus version >= VERSION_WIN8 */
 	bool pending;
 	u32 relid;
 	int tries = 0;

 retry:
 	pending = false;
 	for_each_set_bit(relid, recv_int_page, HV_EVENT_FLAGS_COUNT) {
 		/* Special case - VMBus channel protocol messages */
 		if (relid == 0)
 			continue;
 		pending = true;
 		break;
 	}
 	if (pending && tries++ < HV_MAX_TRIES) {
 		usleep_range(10000, 20000);
 		goto retry;
 	}
 	return pending;
 }

 int hv_synic_cleanup(unsigned int cpu)
 {
 	struct vmbus_channel *channel, *sc;
 	bool channel_found = false;

 	if (vmbus_connection.conn_state != CONNECTED)
 		goto always_cleanup;

 	/*
 	 * Hyper-V does not provide a way to change the connect CPU once
 	 * it is set; we must prevent the connect CPU from going offline
 	 * while the VM is running normally. But in the panic or kexec()
 	 * path where the vmbus is already disconnected, the CPU must be
 	 * allowed to shut down.
 	 */
 	if (cpu == VMBUS_CONNECT_CPU)
 		return -EBUSY;

 	/*
 	 * Search for channels which are bound to the CPU we're about to
 	 * cleanup.  In case we find one and vmbus is still connected, we
 	 * fail; this will effectively prevent CPU offlining.
 	 *
 	 * TODO: Re-bind the channels to different CPUs.
 	 */
 	mutex_lock(&vmbus_connection.channel_mutex);
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		if (channel->target_cpu == cpu) {
 			channel_found = true;
 			break;
 		}
 		list_for_each_entry(sc, &channel->sc_list, sc_list) {
 			if (sc->target_cpu == cpu) {
 				channel_found = true;
 				break;
 			}
 		}
 		if (channel_found)
 			break;
 	}
 	mutex_unlock(&vmbus_connection.channel_mutex);

 	if (channel_found)
 		return -EBUSY;

 	/*
 	 * channel_found == false means that any channels that were previously
 	 * assigned to the CPU have been reassigned elsewhere with a call of
 	 * vmbus_send_modifychannel().  Scan the event flags page looking for
 	 * bits that are set and waiting with a timeout for vmbus_chan_sched()
 	 * to process such bits.  If bits are still set after this operation
 	 * and VMBus is connected, fail the CPU offlining operation.
 	 */
 	if (vmbus_proto_version >= VERSION_WIN10_V4_1 && hv_synic_event_pending())
 		return -EBUSY;

 always_cleanup:
 	hv_stimer_legacy_cleanup(cpu);

 	hv_synic_disable_regs(cpu);

 	return 0;
 }
	// 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/io.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/hyperv.h>
	#include <linux/random.h>
	#include <linux/clockchips.h>
	#include <linux/delay.h>
	#include <linux/interrupt.h>
	#include <clocksource/hyperv_timer.h>
	#include <asm/mshyperv.h>
	#include "hyperv_vmbus.h"

	/* The one and only */
	struct hv_context hv_context;

	/*
	* hv_init - Main initialization routine.
	*
	* This routine must be called before any other routines in here are called
	*/
	int hv_init(void)
	{
	hv_context.cpu_context = alloc_percpu(struct hv_per_cpu_context);
	if (!hv_context.cpu_context)
	return -ENOMEM;
	return 0;
	}

	/*
	* hv_post_message - Post a message using the hypervisor message IPC.
	*
	* This involves a hypercall.
	*/
	int hv_post_message(union hv_connection_id connection_id,
	enum hv_message_type message_type,
	void *payload, size_t payload_size)
	{
	struct hv_input_post_message *aligned_msg;
	unsigned long flags;
	u64 status;

	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
	return -EMSGSIZE;

	local_irq_save(flags);

	aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
	aligned_msg->connectionid = connection_id;
	aligned_msg->reserved = 0;
	aligned_msg->message_type = message_type;
	aligned_msg->payload_size = payload_size;
	memcpy((void *)aligned_msg->payload, payload, payload_size);

	if (hv_isolation_type_snp())
	status = hv_ghcb_hypercall(HVCALL_POST_MESSAGE,
	(void *)aligned_msg, NULL,
	sizeof(*aligned_msg));
	else
	status = hv_do_hypercall(HVCALL_POST_MESSAGE,
	aligned_msg, NULL);

	local_irq_restore(flags);

	return hv_result(status);
	}

	int hv_synic_alloc(void)
	{
	int cpu;
	struct hv_per_cpu_context *hv_cpu;

	/*
	* First, zero all per-cpu memory areas so hv_synic_free() can
	* detect what memory has been allocated and cleanup properly
	* after any failures.
	*/
	for_each_present_cpu(cpu) {
	hv_cpu = per_cpu_ptr(hv_context.cpu_context, cpu);
	memset(hv_cpu, 0, sizeof(*hv_cpu));
	}

	hv_context.hv_numa_map = kcalloc(nr_node_ids, sizeof(struct cpumask),
	GFP_KERNEL);
	if (hv_context.hv_numa_map == NULL) {
	pr_err("Unable to allocate NUMA map\n");
	goto err;
	}

	for_each_present_cpu(cpu) {
	hv_cpu = per_cpu_ptr(hv_context.cpu_context, cpu);

	tasklet_init(&hv_cpu->msg_dpc,
	vmbus_on_msg_dpc, (unsigned long) hv_cpu);

	/*
	* Synic message and event pages are allocated by paravisor.
	* Skip these pages allocation here.
	*/
	if (!hv_isolation_type_snp() && !hv_root_partition) {
	hv_cpu->synic_message_page =
	(void *)get_zeroed_page(GFP_ATOMIC);
	if (hv_cpu->synic_message_page == NULL) {
	pr_err("Unable to allocate SYNIC message page\n");
	goto err;
	}

	hv_cpu->synic_event_page =
	(void *)get_zeroed_page(GFP_ATOMIC);
	if (hv_cpu->synic_event_page == NULL) {
	pr_err("Unable to allocate SYNIC event page\n");
	goto err;
	}
	}
	}

	return 0;
	err:
	/*
	* Any memory allocations that succeeded will be freed when
	* the caller cleans up by calling hv_synic_free()
	*/
	return -ENOMEM;
	}


	void hv_synic_free(void)
	{
	int cpu;

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

	free_page((unsigned long)hv_cpu->synic_event_page);
	free_page((unsigned long)hv_cpu->synic_message_page);
	}

	kfree(hv_context.hv_numa_map);
	}

	/*
	* hv_synic_init - Initialize the Synthetic Interrupt Controller.
	*
	* If it is already initialized by another entity (ie x2v shim), we need to
	* retrieve the initialized message and event pages. Otherwise, we create and
	* initialize the message and event pages.
	*/
	void hv_synic_enable_regs(unsigned int cpu)
	{
	struct hv_per_cpu_context *hv_cpu
	= per_cpu_ptr(hv_context.cpu_context, cpu);
	union hv_synic_simp simp;
	union hv_synic_siefp siefp;
	union hv_synic_sint shared_sint;
	union hv_synic_scontrol sctrl;

	/* Setup the Synic's message page */
	simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
	simp.simp_enabled = 1;

	if (hv_isolation_type_snp() \|\| hv_root_partition) {
	/* Mask out vTOM bit. ioremap_cache() maps decrypted */
	u64 base = (simp.base_simp_gpa << HV_HYP_PAGE_SHIFT) &
	~ms_hyperv.shared_gpa_boundary;
	hv_cpu->synic_message_page
	= (void *)ioremap_cache(base, HV_HYP_PAGE_SIZE);
	if (!hv_cpu->synic_message_page)
	pr_err("Fail to map synic message page.\n");
	} else {
	simp.base_simp_gpa = virt_to_phys(hv_cpu->synic_message_page)
	>> HV_HYP_PAGE_SHIFT;
	}

	hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);

	/* Setup the Synic's event page */
	siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
	siefp.siefp_enabled = 1;

	if (hv_isolation_type_snp() \|\| hv_root_partition) {
	/* Mask out vTOM bit. ioremap_cache() maps decrypted */
	u64 base = (siefp.base_siefp_gpa << HV_HYP_PAGE_SHIFT) &
	~ms_hyperv.shared_gpa_boundary;
	hv_cpu->synic_event_page
	= (void *)ioremap_cache(base, HV_HYP_PAGE_SIZE);
	if (!hv_cpu->synic_event_page)
	pr_err("Fail to map synic event page.\n");
	} else {
	siefp.base_siefp_gpa = virt_to_phys(hv_cpu->synic_event_page)
	>> HV_HYP_PAGE_SHIFT;
	}

	hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);

	/* Setup the shared SINT. */
	if (vmbus_irq != -1)
	enable_percpu_irq(vmbus_irq, 0);
	shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
	VMBUS_MESSAGE_SINT);

	shared_sint.vector = vmbus_interrupt;
	shared_sint.masked = false;

	/*
	* On architectures where Hyper-V doesn't support AEOI (e.g., ARM64),
	* it doesn't provide a recommendation flag and AEOI must be disabled.
	*/
	#ifdef HV_DEPRECATING_AEOI_RECOMMENDED
	shared_sint.auto_eoi =
	!(ms_hyperv.hints & HV_DEPRECATING_AEOI_RECOMMENDED);
	#else
	shared_sint.auto_eoi = 0;
	#endif
	hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
	shared_sint.as_uint64);

	/* Enable the global synic bit */
	sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
	sctrl.enable = 1;

	hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);
	}

	int hv_synic_init(unsigned int cpu)
	{
	hv_synic_enable_regs(cpu);

	hv_stimer_legacy_init(cpu, VMBUS_MESSAGE_SINT);

	return 0;
	}

	/*
	* hv_synic_cleanup - Cleanup routine for hv_synic_init().
	*/
	void hv_synic_disable_regs(unsigned int cpu)
	{
	struct hv_per_cpu_context *hv_cpu
	= per_cpu_ptr(hv_context.cpu_context, cpu);
	union hv_synic_sint shared_sint;
	union hv_synic_simp simp;
	union hv_synic_siefp siefp;
	union hv_synic_scontrol sctrl;

	shared_sint.as_uint64 = hv_get_register(HV_REGISTER_SINT0 +
	VMBUS_MESSAGE_SINT);

	shared_sint.masked = 1;

	/* Need to correctly cleanup in the case of SMP!!! */
	/* Disable the interrupt */
	hv_set_register(HV_REGISTER_SINT0 + VMBUS_MESSAGE_SINT,
	shared_sint.as_uint64);

	simp.as_uint64 = hv_get_register(HV_REGISTER_SIMP);
	/*
	* In Isolation VM, sim and sief pages are allocated by
	* paravisor. These pages also will be used by kdump
	* kernel. So just reset enable bit here and keep page
	* addresses.
	*/
	simp.simp_enabled = 0;
	if (hv_isolation_type_snp() \|\| hv_root_partition) {
	iounmap(hv_cpu->synic_message_page);
	hv_cpu->synic_message_page = NULL;
	} else {
	simp.base_simp_gpa = 0;
	}

	hv_set_register(HV_REGISTER_SIMP, simp.as_uint64);

	siefp.as_uint64 = hv_get_register(HV_REGISTER_SIEFP);
	siefp.siefp_enabled = 0;

	if (hv_isolation_type_snp() \|\| hv_root_partition) {
	iounmap(hv_cpu->synic_event_page);
	hv_cpu->synic_event_page = NULL;
	} else {
	siefp.base_siefp_gpa = 0;
	}

	hv_set_register(HV_REGISTER_SIEFP, siefp.as_uint64);

	/* Disable the global synic bit */
	sctrl.as_uint64 = hv_get_register(HV_REGISTER_SCONTROL);
	sctrl.enable = 0;
	hv_set_register(HV_REGISTER_SCONTROL, sctrl.as_uint64);

	if (vmbus_irq != -1)
	disable_percpu_irq(vmbus_irq);
	}

	#define HV_MAX_TRIES 3
	/*
	* Scan the event flags page of 'this' CPU looking for any bit that is set. If we find one
	* bit set, then wait for a few milliseconds. Repeat these steps for a maximum of 3 times.
	* Return 'true', if there is still any set bit after this operation; 'false', otherwise.
	*
	* If a bit is set, that means there is a pending channel interrupt. The expectation is
	* that the normal interrupt handling mechanism will find and process the channel interrupt
	* "very soon", and in the process clear the bit.
	*/
	static bool hv_synic_event_pending(void)
	{
	struct hv_per_cpu_context *hv_cpu = this_cpu_ptr(hv_context.cpu_context);
	union hv_synic_event_flags *event =
	(union hv_synic_event_flags *)hv_cpu->synic_event_page + VMBUS_MESSAGE_SINT;
	unsigned long recv_int_page = event->flags; / assumes VMBus version >= VERSION_WIN8 */
	bool pending;
	u32 relid;
	int tries = 0;

	retry:
	pending = false;
	for_each_set_bit(relid, recv_int_page, HV_EVENT_FLAGS_COUNT) {
	/* Special case - VMBus channel protocol messages */
	if (relid == 0)
	continue;
	pending = true;
	break;
	}
	if (pending && tries++ < HV_MAX_TRIES) {
	usleep_range(10000, 20000);
	goto retry;
	}
	return pending;
	}

	int hv_synic_cleanup(unsigned int cpu)
	{
	struct vmbus_channel channel, sc;
	bool channel_found = false;

	if (vmbus_connection.conn_state != CONNECTED)
	goto always_cleanup;

	/*
	* Hyper-V does not provide a way to change the connect CPU once
	* it is set; we must prevent the connect CPU from going offline
	* while the VM is running normally. But in the panic or kexec()
	* path where the vmbus is already disconnected, the CPU must be
	* allowed to shut down.
	*/
	if (cpu == VMBUS_CONNECT_CPU)
	return -EBUSY;

	/*
	* Search for channels which are bound to the CPU we're about to
	* cleanup. In case we find one and vmbus is still connected, we
	* fail; this will effectively prevent CPU offlining.
	*
	* TODO: Re-bind the channels to different CPUs.
	*/
	mutex_lock(&vmbus_connection.channel_mutex);
	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
	if (channel->target_cpu == cpu) {
	channel_found = true;
	break;
	}
	list_for_each_entry(sc, &channel->sc_list, sc_list) {
	if (sc->target_cpu == cpu) {
	channel_found = true;
	break;
	}
	}
	if (channel_found)
	break;
	}
	mutex_unlock(&vmbus_connection.channel_mutex);

	if (channel_found)
	return -EBUSY;

	/*
	* channel_found == false means that any channels that were previously
	* assigned to the CPU have been reassigned elsewhere with a call of
	* vmbus_send_modifychannel(). Scan the event flags page looking for
	* bits that are set and waiting with a timeout for vmbus_chan_sched()
	* to process such bits. If bits are still set after this operation
	* and VMBus is connected, fail the CPU offlining operation.
	*/
	if (vmbus_proto_version >= VERSION_WIN10_V4_1 && hv_synic_event_pending())
	return -EBUSY;

	always_cleanup:
	hv_stimer_legacy_cleanup(cpu);

	hv_synic_disable_regs(cpu);

	return 0;
	}