main.c - hafnium/driver/linux - Git at Google

 /*
  * Copyright 2018 Google LLC
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * version 2 as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */

 #include <linux/hrtimer.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/kthread.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/sched/task.h>
 #include <linux/slab.h>

 #include <hf/call.h>

 #define CONFIG_HAFNIUM_MAX_VMS   16
 #define CONFIG_HAFNIUM_MAX_VCPUS 32

 struct hf_vcpu {
 	spinlock_t lock;
 	struct hf_vm *vm;
 	uint32_t vcpu_index;
 	struct task_struct *task;
 	atomic_t abort_sleep;
 	struct hrtimer timer;
 };

 struct hf_vm {
 	uint32_t id;
 	uint32_t vcpu_count;
 	struct hf_vcpu *vcpu;
 };

 static struct hf_vm *hf_vms;
 static uint32_t hf_vm_count;
 static struct page *hf_send_page = NULL;
 static struct page *hf_recv_page = NULL;

 /**
  * Wakes up the kernel thread responsible for running the given vcpu.
  *
  * Returns 0 if the thread was already running, 1 otherwise.
  */
 static int hf_vcpu_wake_up(struct hf_vcpu *vcpu)
 {
 	/* Set a flag indicating that the thread should not go to sleep. */
 	atomic_set(&vcpu->abort_sleep, 1);

 	/* Set the thread to running state. */
 	return wake_up_process(vcpu->task);
 }

 /**
  * Puts the current thread to sleep. The current thread must be responsible for
  * running the given vcpu.
  *
  * Going to sleep will fail if hf_vcpu_wake_up() or kthread_stop() was called on
  * this vcpu/thread since the last time it [re]started running.
  */
 static void hf_vcpu_sleep(struct hf_vcpu *vcpu)
 {
 	int abort;

 	set_current_state(TASK_INTERRUPTIBLE);

 	/* Check the sleep-abort flag after making thread interruptible. */
 	abort = atomic_read(&vcpu->abort_sleep);
 	if (!abort && !kthread_should_stop())
 		schedule();

 	/* Set state back to running on the way out. */
 	set_current_state(TASK_RUNNING);
 }

 /**
  * Wakes up the thread associated with the vcpu that owns the given timer. This
  * is called when the timer the thread is waiting on expires.
  */
 static enum hrtimer_restart hf_vcpu_timer_expired(struct hrtimer *timer)
 {
 	struct hf_vcpu *vcpu = container_of(timer, struct hf_vcpu, timer);
 	/* TODO: Inject interrupt. */
 	hf_vcpu_wake_up(vcpu);
 	return HRTIMER_NORESTART;
 }

 /**
  * This is the main loop of each vcpu.
  */
 static int hf_vcpu_thread(void *data)
 {
 	struct hf_vcpu *vcpu = data;
 	struct hf_vcpu_run_return ret;

 	hrtimer_init(&vcpu->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	vcpu->timer.function = &hf_vcpu_timer_expired;

 	while (!kthread_should_stop()) {
 		/*
 		 * We're about to run the vcpu, so we can reset the abort-sleep
 		 * flag.
 		 */
 		atomic_set(&vcpu->abort_sleep, 0);

 		/* Call into Hafnium to run vcpu. */
 		ret = hf_vcpu_run(vcpu->vm->id, vcpu->vcpu_index);

 		switch (ret.code) {
 		/* Yield (forcibly or voluntarily). */
 		case HF_VCPU_RUN_YIELD:
 			break;

 		 /* WFI. */
 		case HF_VCPU_RUN_WAIT_FOR_INTERRUPT:
 			hf_vcpu_sleep(vcpu);
 			break;

 		/* Wake up another vcpu. */
 		case HF_VCPU_RUN_WAKE_UP:
 			{
 				struct hf_vm *vm;
 				if (ret.wake_up.vm_id > hf_vm_count)
 					break;
 				vm = &hf_vms[ret.wake_up.vm_id - 1];
 				if (ret.wake_up.vcpu < vm->vcpu_count) {
 					hf_vcpu_wake_up(&vm->vcpu[ret.wake_up.vcpu]);
 				} else if (ret.wake_up.vcpu == HF_INVALID_VCPU) {
 					/* TODO: pick one to interrupt. */
 					pr_warning("No vcpu to wake.");
 				}
 			}
 			break;

 		/* Response available. */
 		case HF_VCPU_RUN_MESSAGE:
 			{
 				uint32_t i;
 				const char *buf = page_address(hf_recv_page);
 				pr_info("Received response from vm %u (%u bytes): ",
 					vcpu->vm->id, ret.message.size);
 				for (i = 0; i < ret.message.size; i++)
 					printk(KERN_CONT "%c", buf[i]);
 				printk(KERN_CONT "\n");
 				hf_mailbox_clear();
 			}
 			break;

 		case HF_VCPU_RUN_SLEEP:
 			hrtimer_start(&vcpu->timer, ret.sleep.ns, HRTIMER_MODE_REL);
 			hf_vcpu_sleep(vcpu);
 			hrtimer_cancel(&vcpu->timer);
 			break;
 		}
 	}

 	return 0;
 }

 /**
  * Frees all resources, including threads, associated with the Hafnium driver.
  */
 static void hf_free_resources(void)
 {
 	uint32_t i, j;

 	/*
 	 * First stop all worker threads. We need to do this before freeing
 	 * resources because workers may reference each other, so it is only
 	 * safe to free resources after they have all stopped.
 	 */
 	for (i = 0; i < hf_vm_count; i++) {
 		struct hf_vm *vm = &hf_vms[i];
 		for (j = 0; j < vm->vcpu_count; j++)
 			kthread_stop(vm->vcpu[j].task);
 	}

 	/* Free resources. */
 	for (i = 0; i < hf_vm_count; i++) {
 		struct hf_vm *vm = &hf_vms[i];
 		for (j = 0; j < vm->vcpu_count; j++)
 			put_task_struct(vm->vcpu[j].task);
 		kfree(vm->vcpu);
 	}

 	kfree(hf_vms);
 }

 static ssize_t hf_send_store(struct kobject *kobj, struct kobj_attribute *attr,
 			     const char *buf, size_t count)
 {
 	int64_t ret;
 	struct hf_vm *vm;

 	count = min_t(size_t, count, HF_MAILBOX_SIZE);

 	/* Copy data to send buffer. */
 	memcpy(page_address(hf_send_page), buf, count);

 	vm = &hf_vms[0];
 	ret = hf_mailbox_send(vm->id, count);
 	if (ret < 0)
 		return -EAGAIN;

 	if (ret == HF_INVALID_VCPU) {
 		/*
 		 * TODO: We need to interrupt some vcpu because none are waiting
 		 * for data.
 		 */
 		pr_warning("No vcpu to receive message.");
 		return -ENOSYS;
 	}

 	if (ret >= vm->vcpu_count)
 		return -EINVAL;

 	/* Wake up the vcpu that is going to process the data. */
 	hf_vcpu_wake_up(&vm->vcpu[ret]);

 	return count;
 }

 static struct kobject *hf_sysfs_obj = NULL;
 static struct kobj_attribute send_attr =
 	__ATTR(send, 0200, NULL, hf_send_store);

 /**
  * Initializes the Hafnium driver's sysfs interface.
  */
 static void __init hf_init_sysfs(void)
 {
 	int ret;

 	/* Create the sysfs interface to interrupt vcpus. */
 	hf_sysfs_obj = kobject_create_and_add("hafnium", kernel_kobj);
 	if (!hf_sysfs_obj) {
 		pr_err("Unable to create sysfs object");
 	} else {
 		ret = sysfs_create_file(hf_sysfs_obj, &send_attr.attr);
 		if (ret)
 			pr_err("Unable to create 'send' sysfs file");
 	}
 }

 /**
  * Initializes the Hafnium driver by creating a thread for each vCPU of each
  * virtual machine.
  */
 static int __init hf_init(void)
 {
 	int64_t ret;
 	uint32_t i, j;
 	uint32_t total_vm_count;
 	uint32_t total_vcpu_count;

 	/* Allocate a page for send and receive buffers. */
 	hf_send_page = alloc_page(GFP_KERNEL);
 	if (!hf_send_page) {
 		pr_err("Unable to allocate send buffer\n");
 		return -ENOMEM;
 	}

 	hf_recv_page = alloc_page(GFP_KERNEL);
 	if (!hf_recv_page) {
 		__free_page(hf_send_page);
 		pr_err("Unable to allocate receive buffer\n");
 		return -ENOMEM;
 	}

 	/*
 	 * Configure both addresses. Once configured, we cannot free these pages
 	 * because the hypervisor will use them, even if the module is
 	 * unloaded.
 	 */
 	ret = hf_vm_configure(page_to_phys(hf_send_page),
 			      page_to_phys(hf_recv_page));
 	if (ret) {
 		__free_page(hf_send_page);
 		__free_page(hf_recv_page);
 		/* TODO: We may want to grab this information from hypervisor
 		 * and go from there. */
 		pr_err("Unable to configure VM\n");
 		return -EIO;
 	}

 	/* Get the number of VMs. */
 	ret = hf_vm_get_count();
 	if (ret < 0) {
 		pr_err("Unable to retrieve number of VMs: %lld\n", ret);
 		return -EIO;
 	}

 	/* Confirm the maximum number of VMs looks sane. */
 	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VMS < 1);
 	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VMS > U16_MAX);

 	/* Validate the number of VMs. There must at least be the primary. */
 	if (ret < 1 || ret > CONFIG_HAFNIUM_MAX_VMS) {
 		pr_err("Number of VMs is out of range: %lld\n", ret);
 		return -EDQUOT;
 	}

 	/* Only track the secondary VMs. */
 	total_vm_count = ret - 1;
 	hf_vms = kmalloc(sizeof(struct hf_vm) * total_vm_count, GFP_KERNEL);
 	if (!hf_vms)
 		return -ENOMEM;

 	/* Initialize each VM. */
 	total_vcpu_count = 0;
 	for (i = 0; i < total_vm_count; i++) {
 		struct hf_vm *vm = &hf_vms[i];

 		/* Adjust the ID as only the secondaries are tracked. */
 		vm->id = i + 1;

 		ret = hf_vcpu_get_count(vm->id);
 		if (ret < 0) {
 			pr_err("HF_VCPU_GET_COUNT failed for vm=%u: %lld", vm->id,
 			       ret);
 			ret = -EIO;
 			goto fail_with_cleanup;
 		}

 		/* Avoid overflowing the vcpu count. */
 		if (ret > (U32_MAX - total_vcpu_count)) {
 			pr_err("Too many vcpus: %u\n", total_vcpu_count);
 			ret = -EDQUOT;
 			goto fail_with_cleanup;
 		}

 		/* Confirm the maximum number of VCPUs looks sane. */
 		BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VCPUS < 1);
 		BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VCPUS > U16_MAX);

 		/* Enforce the limit on vcpus. */
 		total_vcpu_count += ret;
 		if (total_vcpu_count > CONFIG_HAFNIUM_MAX_VCPUS) {
 			pr_err("Too many vcpus: %u\n", total_vcpu_count);
 			ret = -EDQUOT;
 			goto fail_with_cleanup;
 		}

 		vm->vcpu_count = ret;
 		vm->vcpu = kmalloc(sizeof(struct hf_vcpu) * vm->vcpu_count,
 				   GFP_KERNEL);
 		if (!vm->vcpu) {
 			pr_err("No memory for %u vcpus for vm %u",
 			       vm->vcpu_count, vm->id);
 			ret = -ENOMEM;
 			goto fail_with_cleanup;
 		}

 		/* Update the number of initialized VMs. */
 		hf_vm_count = i + 1;

 		/* Create a kernel thread for each vcpu. */
 		for (j = 0; j < vm->vcpu_count; j++) {
 			struct hf_vcpu *vcpu = &vm->vcpu[j];
 			vcpu->task = kthread_create(hf_vcpu_thread, vcpu,
 						    "vcpu_thread_%u_%u",
 						    vm->id, j);
 			if (IS_ERR(vcpu->task)) {
 				pr_err("Error creating task (vm=%u,vcpu=%u)"
 				       ": %ld\n", vm->id, j, PTR_ERR(vcpu->task));
 				vm->vcpu_count = j;
 				ret = PTR_ERR(vcpu->task);
 				goto fail_with_cleanup;
 			}

 			get_task_struct(vcpu->task);
 			spin_lock_init(&vcpu->lock);
 			vcpu->vm = vm;
 			vcpu->vcpu_index = j;
 			atomic_set(&vcpu->abort_sleep, 0);
 		}
 	}

 	/* Start running threads now that all is initialized. */
 	for (i = 0; i < hf_vm_count; i++) {
 		struct hf_vm *vm = &hf_vms[i];
 		for (j = 0; j < vm->vcpu_count; j++)
 			wake_up_process(vm->vcpu[j].task);
 	}

 	/* Dump vm/vcpu count info. */
 	pr_info("Hafnium successfully loaded with %u VMs:\n", hf_vm_count);
 	for (i = 0; i < hf_vm_count; i++) {
 		struct hf_vm *vm = &hf_vms[i];
 		pr_info("\tVM %u: %u vCPUS\n", vm->id, vm->vcpu_count);
 	}

 	hf_init_sysfs();

 	return 0;

 fail_with_cleanup:
 	hf_free_resources();
 	return ret;
 }

 /**
  * Frees up all resources used by the Hafnium driver in preparation for
  * unloading it.
  */
 static void __exit hf_exit(void)
 {
 	if (hf_sysfs_obj)
 		kobject_put(hf_sysfs_obj);

 	pr_info("Preparing to unload Hafnium\n");
 	hf_free_resources();
 	pr_info("Hafnium ready to unload\n");
 }

 MODULE_LICENSE("GPL");

 module_init(hf_init);
 module_exit(hf_exit);
	/*
	* Copyright 2018 Google LLC
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* version 2 as published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	*/

	#include <linux/hrtimer.h>
	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/kthread.h>
	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/sched/task.h>
	#include <linux/slab.h>

	#include <hf/call.h>

	#define CONFIG_HAFNIUM_MAX_VMS 16
	#define CONFIG_HAFNIUM_MAX_VCPUS 32

	struct hf_vcpu {
	spinlock_t lock;
	struct hf_vm *vm;
	uint32_t vcpu_index;
	struct task_struct *task;
	atomic_t abort_sleep;
	struct hrtimer timer;
	};

	struct hf_vm {
	uint32_t id;
	uint32_t vcpu_count;
	struct hf_vcpu *vcpu;
	};

	static struct hf_vm *hf_vms;
	static uint32_t hf_vm_count;
	static struct page *hf_send_page = NULL;
	static struct page *hf_recv_page = NULL;

	/**
	* Wakes up the kernel thread responsible for running the given vcpu.
	*
	* Returns 0 if the thread was already running, 1 otherwise.
	*/
	static int hf_vcpu_wake_up(struct hf_vcpu *vcpu)
	{
	/* Set a flag indicating that the thread should not go to sleep. */
	atomic_set(&vcpu->abort_sleep, 1);

	/* Set the thread to running state. */
	return wake_up_process(vcpu->task);
	}

	/**
	* Puts the current thread to sleep. The current thread must be responsible for
	* running the given vcpu.
	*
	* Going to sleep will fail if hf_vcpu_wake_up() or kthread_stop() was called on
	* this vcpu/thread since the last time it [re]started running.
	*/
	static void hf_vcpu_sleep(struct hf_vcpu *vcpu)
	{
	int abort;

	set_current_state(TASK_INTERRUPTIBLE);

	/* Check the sleep-abort flag after making thread interruptible. */
	abort = atomic_read(&vcpu->abort_sleep);
	if (!abort && !kthread_should_stop())
	schedule();

	/* Set state back to running on the way out. */
	set_current_state(TASK_RUNNING);
	}

	/**
	* Wakes up the thread associated with the vcpu that owns the given timer. This
	* is called when the timer the thread is waiting on expires.
	*/
	static enum hrtimer_restart hf_vcpu_timer_expired(struct hrtimer *timer)
	{
	struct hf_vcpu *vcpu = container_of(timer, struct hf_vcpu, timer);
	/* TODO: Inject interrupt. */
	hf_vcpu_wake_up(vcpu);
	return HRTIMER_NORESTART;
	}

	/**
	* This is the main loop of each vcpu.
	*/
	static int hf_vcpu_thread(void *data)
	{
	struct hf_vcpu *vcpu = data;
	struct hf_vcpu_run_return ret;

	hrtimer_init(&vcpu->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	vcpu->timer.function = &hf_vcpu_timer_expired;

	while (!kthread_should_stop()) {
	/*
	* We're about to run the vcpu, so we can reset the abort-sleep
	* flag.
	*/
	atomic_set(&vcpu->abort_sleep, 0);

	/* Call into Hafnium to run vcpu. */
	ret = hf_vcpu_run(vcpu->vm->id, vcpu->vcpu_index);

	switch (ret.code) {
	/* Yield (forcibly or voluntarily). */
	case HF_VCPU_RUN_YIELD:
	break;

	/* WFI. */
	case HF_VCPU_RUN_WAIT_FOR_INTERRUPT:
	hf_vcpu_sleep(vcpu);
	break;

	/* Wake up another vcpu. */
	case HF_VCPU_RUN_WAKE_UP:
	{
	struct hf_vm *vm;
	if (ret.wake_up.vm_id > hf_vm_count)
	break;
	vm = &hf_vms[ret.wake_up.vm_id - 1];
	if (ret.wake_up.vcpu < vm->vcpu_count) {
	hf_vcpu_wake_up(&vm->vcpu[ret.wake_up.vcpu]);
	} else if (ret.wake_up.vcpu == HF_INVALID_VCPU) {
	/* TODO: pick one to interrupt. */
	pr_warning("No vcpu to wake.");
	}
	}
	break;

	/* Response available. */
	case HF_VCPU_RUN_MESSAGE:
	{
	uint32_t i;
	const char *buf = page_address(hf_recv_page);
	pr_info("Received response from vm %u (%u bytes): ",
	vcpu->vm->id, ret.message.size);
	for (i = 0; i < ret.message.size; i++)
	printk(KERN_CONT "%c", buf[i]);
	printk(KERN_CONT "\n");
	hf_mailbox_clear();
	}
	break;

	case HF_VCPU_RUN_SLEEP:
	hrtimer_start(&vcpu->timer, ret.sleep.ns, HRTIMER_MODE_REL);
	hf_vcpu_sleep(vcpu);
	hrtimer_cancel(&vcpu->timer);
	break;
	}
	}

	return 0;
	}

	/**
	* Frees all resources, including threads, associated with the Hafnium driver.
	*/
	static void hf_free_resources(void)
	{
	uint32_t i, j;

	/*
	* First stop all worker threads. We need to do this before freeing
	* resources because workers may reference each other, so it is only
	* safe to free resources after they have all stopped.
	*/
	for (i = 0; i < hf_vm_count; i++) {
	struct hf_vm *vm = &hf_vms[i];
	for (j = 0; j < vm->vcpu_count; j++)
	kthread_stop(vm->vcpu[j].task);
	}

	/* Free resources. */
	for (i = 0; i < hf_vm_count; i++) {
	struct hf_vm *vm = &hf_vms[i];
	for (j = 0; j < vm->vcpu_count; j++)
	put_task_struct(vm->vcpu[j].task);
	kfree(vm->vcpu);
	}

	kfree(hf_vms);
	}

	static ssize_t hf_send_store(struct kobject kobj, struct kobj_attribute attr,
	const char *buf, size_t count)
	{
	int64_t ret;
	struct hf_vm *vm;

	count = min_t(size_t, count, HF_MAILBOX_SIZE);

	/* Copy data to send buffer. */
	memcpy(page_address(hf_send_page), buf, count);

	vm = &hf_vms[0];
	ret = hf_mailbox_send(vm->id, count);
	if (ret < 0)
	return -EAGAIN;

	if (ret == HF_INVALID_VCPU) {
	/*
	* TODO: We need to interrupt some vcpu because none are waiting
	* for data.
	*/
	pr_warning("No vcpu to receive message.");
	return -ENOSYS;
	}

	if (ret >= vm->vcpu_count)
	return -EINVAL;

	/* Wake up the vcpu that is going to process the data. */
	hf_vcpu_wake_up(&vm->vcpu[ret]);

	return count;
	}

	static struct kobject *hf_sysfs_obj = NULL;
	static struct kobj_attribute send_attr =
	__ATTR(send, 0200, NULL, hf_send_store);

	/**
	* Initializes the Hafnium driver's sysfs interface.
	*/
	static void __init hf_init_sysfs(void)
	{
	int ret;

	/* Create the sysfs interface to interrupt vcpus. */
	hf_sysfs_obj = kobject_create_and_add("hafnium", kernel_kobj);
	if (!hf_sysfs_obj) {
	pr_err("Unable to create sysfs object");
	} else {
	ret = sysfs_create_file(hf_sysfs_obj, &send_attr.attr);
	if (ret)
	pr_err("Unable to create 'send' sysfs file");
	}
	}

	/**
	* Initializes the Hafnium driver by creating a thread for each vCPU of each
	* virtual machine.
	*/
	static int __init hf_init(void)
	{
	int64_t ret;
	uint32_t i, j;
	uint32_t total_vm_count;
	uint32_t total_vcpu_count;

	/* Allocate a page for send and receive buffers. */
	hf_send_page = alloc_page(GFP_KERNEL);
	if (!hf_send_page) {
	pr_err("Unable to allocate send buffer\n");
	return -ENOMEM;
	}

	hf_recv_page = alloc_page(GFP_KERNEL);
	if (!hf_recv_page) {
	__free_page(hf_send_page);
	pr_err("Unable to allocate receive buffer\n");
	return -ENOMEM;
	}

	/*
	* Configure both addresses. Once configured, we cannot free these pages
	* because the hypervisor will use them, even if the module is
	* unloaded.
	*/
	ret = hf_vm_configure(page_to_phys(hf_send_page),
	page_to_phys(hf_recv_page));
	if (ret) {
	__free_page(hf_send_page);
	__free_page(hf_recv_page);
	/* TODO: We may want to grab this information from hypervisor
	* and go from there. */
	pr_err("Unable to configure VM\n");
	return -EIO;
	}

	/* Get the number of VMs. */
	ret = hf_vm_get_count();
	if (ret < 0) {
	pr_err("Unable to retrieve number of VMs: %lld\n", ret);
	return -EIO;
	}

	/* Confirm the maximum number of VMs looks sane. */
	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VMS < 1);
	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VMS > U16_MAX);

	/* Validate the number of VMs. There must at least be the primary. */
	if (ret < 1 \|\| ret > CONFIG_HAFNIUM_MAX_VMS) {
	pr_err("Number of VMs is out of range: %lld\n", ret);
	return -EDQUOT;
	}

	/* Only track the secondary VMs. */
	total_vm_count = ret - 1;
	hf_vms = kmalloc(sizeof(struct hf_vm) * total_vm_count, GFP_KERNEL);
	if (!hf_vms)
	return -ENOMEM;

	/* Initialize each VM. */
	total_vcpu_count = 0;
	for (i = 0; i < total_vm_count; i++) {
	struct hf_vm *vm = &hf_vms[i];

	/* Adjust the ID as only the secondaries are tracked. */
	vm->id = i + 1;

	ret = hf_vcpu_get_count(vm->id);
	if (ret < 0) {
	pr_err("HF_VCPU_GET_COUNT failed for vm=%u: %lld", vm->id,
	ret);
	ret = -EIO;
	goto fail_with_cleanup;
	}

	/* Avoid overflowing the vcpu count. */
	if (ret > (U32_MAX - total_vcpu_count)) {
	pr_err("Too many vcpus: %u\n", total_vcpu_count);
	ret = -EDQUOT;
	goto fail_with_cleanup;
	}

	/* Confirm the maximum number of VCPUs looks sane. */
	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VCPUS < 1);
	BUILD_BUG_ON(CONFIG_HAFNIUM_MAX_VCPUS > U16_MAX);

	/* Enforce the limit on vcpus. */
	total_vcpu_count += ret;
	if (total_vcpu_count > CONFIG_HAFNIUM_MAX_VCPUS) {
	pr_err("Too many vcpus: %u\n", total_vcpu_count);
	ret = -EDQUOT;
	goto fail_with_cleanup;
	}

	vm->vcpu_count = ret;
	vm->vcpu = kmalloc(sizeof(struct hf_vcpu) * vm->vcpu_count,
	GFP_KERNEL);
	if (!vm->vcpu) {
	pr_err("No memory for %u vcpus for vm %u",
	vm->vcpu_count, vm->id);
	ret = -ENOMEM;
	goto fail_with_cleanup;
	}

	/* Update the number of initialized VMs. */
	hf_vm_count = i + 1;

	/* Create a kernel thread for each vcpu. */
	for (j = 0; j < vm->vcpu_count; j++) {
	struct hf_vcpu *vcpu = &vm->vcpu[j];
	vcpu->task = kthread_create(hf_vcpu_thread, vcpu,
	"vcpu_thread_%u_%u",
	vm->id, j);
	if (IS_ERR(vcpu->task)) {
	pr_err("Error creating task (vm=%u,vcpu=%u)"
	": %ld\n", vm->id, j, PTR_ERR(vcpu->task));
	vm->vcpu_count = j;
	ret = PTR_ERR(vcpu->task);
	goto fail_with_cleanup;
	}

	get_task_struct(vcpu->task);
	spin_lock_init(&vcpu->lock);
	vcpu->vm = vm;
	vcpu->vcpu_index = j;
	atomic_set(&vcpu->abort_sleep, 0);
	}
	}

	/* Start running threads now that all is initialized. */
	for (i = 0; i < hf_vm_count; i++) {
	struct hf_vm *vm = &hf_vms[i];
	for (j = 0; j < vm->vcpu_count; j++)
	wake_up_process(vm->vcpu[j].task);
	}

	/* Dump vm/vcpu count info. */
	pr_info("Hafnium successfully loaded with %u VMs:\n", hf_vm_count);
	for (i = 0; i < hf_vm_count; i++) {
	struct hf_vm *vm = &hf_vms[i];
	pr_info("\tVM %u: %u vCPUS\n", vm->id, vm->vcpu_count);
	}

	hf_init_sysfs();

	return 0;

	fail_with_cleanup:
	hf_free_resources();
	return ret;
	}

	/**
	* Frees up all resources used by the Hafnium driver in preparation for
	* unloading it.
	*/
	static void __exit hf_exit(void)
	{
	if (hf_sysfs_obj)
	kobject_put(hf_sysfs_obj);

	pr_info("Preparing to unload Hafnium\n");
	hf_free_resources();
	pr_info("Hafnium ready to unload\n");
	}

	MODULE_LICENSE("GPL");

	module_init(hf_init);
	module_exit(hf_exit);