/*
 * 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;
	struct hrtimer timer;
	bool pending_irq;
};

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 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);
	wake_up_process(vcpu->task);
	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()) {
		unsigned long flags;
		size_t irqs;

		set_current_state(TASK_RUNNING);

		/* Determine if we must interrupt the vcpu. */
		spin_lock_irqsave(&vcpu->lock, flags);
		irqs = vcpu->pending_irq ? 1 : 0;
		vcpu->pending_irq = false;
		spin_unlock_irqrestore(&vcpu->lock, flags);

		/* 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:
			set_current_state(TASK_INTERRUPTIBLE);
			if (kthread_should_stop())
				break;
			schedule();
			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) {
					wake_up_process(vm->vcpu[ret.wake_up.vcpu].task);
				} 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:
			set_current_state(TASK_INTERRUPTIBLE);
			if (kthread_should_stop())
				break;
			hrtimer_start(&vcpu->timer, ret.sleep.ns, HRTIMER_MODE_REL);
			schedule();
			hrtimer_cancel(&vcpu->timer);
			break;
		}
	}

	set_current_state(TASK_RUNNING);

	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_interrupt_store(struct kobject *kobj,
				  struct kobj_attribute *attr, const char *buf,
				  size_t count)
{
	struct hf_vcpu *vcpu;
	unsigned long flags;
	struct task_struct *task;

	/* TODO: Parse input to determine which vcpu to interrupt. */
	/* TODO: Check bounds. */

	vcpu = &hf_vms[0].vcpu[0];

	spin_lock_irqsave(&vcpu->lock, flags);
	vcpu->pending_irq = true;
	/* TODO: Do we need to increment the task's ref count here? */
	task = vcpu->task;
	spin_unlock_irqrestore(&vcpu->lock, flags);

	/* Wake up the task. If it's already running, kick it out. */
	/* TODO: There's a race here: the kick may happen right before we go
	 * to the hypervisor. */
	if (wake_up_process(task) == 0)
		kick_process(task);

	return count;
}

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. */
	/* TODO: There's a race where thread may get wake up before it
	 * goes to sleep. Fix this. */
	wake_up_process(vm->vcpu[ret].task);

	return count;
}

static struct kobject *hf_sysfs_obj = NULL;
static struct kobj_attribute interrupt_attr =
	__ATTR(interrupt, 0200, NULL, hf_interrupt_store);
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, &interrupt_attr.attr);
		if (ret)
			pr_err("Unable to create 'interrupt' sysfs file");

		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;
			vcpu->pending_irq = false;
		}
	}

	/* 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);