/*
 * Copyright (C) 2012 ARM Ltd.
 * Author: Marc Zyngier <marc.zyngier@arm.com>
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include <linux/cpu.h>
#include <linux/of_irq.h>
#include <linux/kvm.h>
#include <linux/kvm_host.h>
#include <linux/interrupt.h>

#include <clocksource/arm_arch_timer.h>
#include <asm/arch_timer.h>

#include <kvm/arm_vgic.h>
#include <kvm/arm_arch_timer.h>

#include "trace.h"

static struct timecounter *timecounter;
static struct workqueue_struct *wqueue;
static unsigned int host_vtimer_irq;

void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
{
        vcpu->arch.timer_cpu.active_cleared_last = false;
}

static cycle_t kvm_phys_timer_read(void)
{
        return timecounter->cc->read(timecounter->cc);
}

static bool timer_is_armed(struct arch_timer_cpu *timer)
{
        return timer->armed;
}

/* timer_arm: as in "arm the timer", not as in ARM the company */
static void timer_arm(struct arch_timer_cpu *timer, u64 ns)
{
        timer->armed = true;
        hrtimer_start(&timer->timer, ktime_add_ns(ktime_get(), ns),
                      HRTIMER_MODE_ABS);
}

static void timer_disarm(struct arch_timer_cpu *timer)
{
        if (timer_is_armed(timer)) {
                hrtimer_cancel(&timer->timer);
                cancel_work_sync(&timer->expired);
                timer->armed = false;
        }
}

static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
{
        struct kvm_vcpu *vcpu = *(struct kvm_vcpu **)dev_id;

        /*
         * We disable the timer in the world switch and let it be
         * handled by kvm_timer_sync_hwstate(). Getting a timer
         * interrupt at this point is a sure sign of some major
         * breakage.
         */
        pr_warn("Unexpected interrupt %d on vcpu %p\n", irq, vcpu);
        return IRQ_HANDLED;
}

/*
 * Work function for handling the backup timer that we schedule when a vcpu is
 * no longer running, but had a timer programmed to fire in the future.
 */
static void kvm_timer_inject_irq_work(struct work_struct *work)
{
        struct kvm_vcpu *vcpu;

        vcpu = container_of(work, struct kvm_vcpu, arch.timer_cpu.expired);
        vcpu->arch.timer_cpu.armed = false;

        WARN_ON(!kvm_timer_should_fire(vcpu));

        /*
         * If the vcpu is blocked we want to wake it up so that it will see
         * the timer has expired when entering the guest.
         */
        kvm_vcpu_kick(vcpu);
}

static u64 kvm_timer_compute_delta(struct kvm_vcpu *vcpu)
{
        cycle_t cval, now;

        cval = vcpu->arch.timer_cpu.cntv_cval;
        now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;

        if (now < cval) {
                u64 ns;

                ns = cyclecounter_cyc2ns(timecounter->cc,
                                         cval - now,
                                         timecounter->mask,
                                         &timecounter->frac);
                return ns;
        }

        return 0;
}

static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
{
        struct arch_timer_cpu *timer;
        struct kvm_vcpu *vcpu;
        u64 ns;

        timer = container_of(hrt, struct arch_timer_cpu, timer);
        vcpu = container_of(timer, struct kvm_vcpu, arch.timer_cpu);

        /*
         * Check that the timer has really expired from the guest's
         * PoV (NTP on the host may have forced it to expire
         * early). If we should have slept longer, restart it.
         */
        ns = kvm_timer_compute_delta(vcpu);
        if (unlikely(ns)) {
                hrtimer_forward_now(hrt, ns_to_ktime(ns));
                return HRTIMER_RESTART;
        }

        queue_work(wqueue, &timer->expired);
        return HRTIMER_NORESTART;
}

static bool kvm_timer_irq_can_fire(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        return !(timer->cntv_ctl & ARCH_TIMER_CTRL_IT_MASK) &&
                (timer->cntv_ctl & ARCH_TIMER_CTRL_ENABLE);
}

bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
        cycle_t cval, now;

        if (!kvm_timer_irq_can_fire(vcpu))
                return false;

        cval = timer->cntv_cval;
        now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;

        return cval <= now;
}

static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level)
{
        int ret;
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        BUG_ON(!vgic_initialized(vcpu->kvm));

        timer->active_cleared_last = false;
        timer->irq.level = new_level;
        trace_kvm_timer_update_irq(vcpu->vcpu_id, timer->map->virt_irq,
                                   timer->irq.level);
        ret = kvm_vgic_inject_mapped_irq(vcpu->kvm, vcpu->vcpu_id,
                                         timer->map,
                                         timer->irq.level);
        WARN_ON(ret);
}

/*
 * Check if there was a change in the timer state (should we raise or lower
 * the line level to the GIC).
 */
static int kvm_timer_update_state(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        /*
         * If userspace modified the timer registers via SET_ONE_REG before
         * the vgic was initialized, we mustn't set the timer->irq.level value
         * because the guest would never see the interrupt.  Instead wait
         * until we call this function from kvm_timer_flush_hwstate.
         */
        if (!vgic_initialized(vcpu->kvm))
                return -ENODEV;

        if (kvm_timer_should_fire(vcpu) != timer->irq.level)
                kvm_timer_update_irq(vcpu, !timer->irq.level);

        return 0;
}

/*
 * Schedule the background timer before calling kvm_vcpu_block, so that this
 * thread is removed from its waitqueue and made runnable when there's a timer
 * interrupt to handle.
 */
void kvm_timer_schedule(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        BUG_ON(timer_is_armed(timer));

        /*
         * No need to schedule a background timer if the guest timer has
         * already expired, because kvm_vcpu_block will return before putting
         * the thread to sleep.
         */
        if (kvm_timer_should_fire(vcpu))
                return;

        /*
         * If the timer is not capable of raising interrupts (disabled or
         * masked), then there's no more work for us to do.
         */
        if (!kvm_timer_irq_can_fire(vcpu))
                return;

        /*  The timer has not yet expired, schedule a background timer */
        timer_arm(timer, kvm_timer_compute_delta(vcpu));
}

void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
        timer_disarm(timer);
}

/**
 * kvm_timer_flush_hwstate - prepare to move the virt timer to the cpu
 * @vcpu: The vcpu pointer
 *
 * Check if the virtual timer has expired while we were running in the host,
 * and inject an interrupt if that was the case.
 */
void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
        bool phys_active;
        int ret;

        if (kvm_timer_update_state(vcpu))
                return;

        /*
        * If we enter the guest with the virtual input level to the VGIC
        * asserted, then we have already told the VGIC what we need to, and
        * we don't need to exit from the guest until the guest deactivates
        * the already injected interrupt, so therefore we should set the
        * hardware active state to prevent unnecessary exits from the guest.
        *
        * Also, if we enter the guest with the virtual timer interrupt active,
        * then it must be active on the physical distributor, because we set
        * the HW bit and the guest must be able to deactivate the virtual and
        * physical interrupt at the same time.
        *
        * Conversely, if the virtual input level is deasserted and the virtual
        * interrupt is not active, then always clear the hardware active state
        * to ensure that hardware interrupts from the timer triggers a guest
        * exit.
        */
        if (timer->irq.level || kvm_vgic_map_is_active(vcpu, timer->map))
                phys_active = true;
        else
                phys_active = false;

        /*
         * We want to avoid hitting the (re)distributor as much as
         * possible, as this is a potentially expensive MMIO access
         * (not to mention locks in the irq layer), and a solution for
         * this is to cache the "active" state in memory.
         *
         * Things to consider: we cannot cache an "active set" state,
         * because the HW can change this behind our back (it becomes
         * "clear" in the HW). We must then restrict the caching to
         * the "clear" state.
         *
         * The cache is invalidated on:
         * - vcpu put, indicating that the HW cannot be trusted to be
         *   in a sane state on the next vcpu load,
         * - any change in the interrupt state
         *
         * Usage conditions:
         * - cached value is "active clear"
         * - value to be programmed is "active clear"
         */
        if (timer->active_cleared_last && !phys_active)
                return;

        ret = irq_set_irqchip_state(timer->map->irq,
                                    IRQCHIP_STATE_ACTIVE,
                                    phys_active);
        WARN_ON(ret);

        timer->active_cleared_last = !phys_active;
}

/**
 * kvm_timer_sync_hwstate - sync timer state from cpu
 * @vcpu: The vcpu pointer
 *
 * Check if the virtual timer has expired while we were running in the guest,
 * and inject an interrupt if that was the case.
 */
void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        BUG_ON(timer_is_armed(timer));

        /*
         * The guest could have modified the timer registers or the timer
         * could have expired, update the timer state.
         */
        kvm_timer_update_state(vcpu);
}

int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
                         const struct kvm_irq_level *irq)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
        struct irq_phys_map *map;

        /*
         * The vcpu timer irq number cannot be determined in
         * kvm_timer_vcpu_init() because it is called much before
         * kvm_vcpu_set_target(). To handle this, we determine
         * vcpu timer irq number when the vcpu is reset.
         */
        timer->irq.irq = irq->irq;

        /*
         * The bits in CNTV_CTL are architecturally reset to UNKNOWN for ARMv8
         * and to 0 for ARMv7.  We provide an implementation that always
         * resets the timer to be disabled and unmasked and is compliant with
         * the ARMv7 architecture.
         */
        timer->cntv_ctl = 0;
        kvm_timer_update_state(vcpu);

        /*
         * Tell the VGIC that the virtual interrupt is tied to a
         * physical interrupt. We do that once per VCPU.
         */
        map = kvm_vgic_map_phys_irq(vcpu, irq->irq, host_vtimer_irq);
        if (WARN_ON(IS_ERR(map)))
                return PTR_ERR(map);

        timer->map = map;
        return 0;
}

void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        INIT_WORK(&timer->expired, kvm_timer_inject_irq_work);
        hrtimer_init(&timer->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
        timer->timer.function = kvm_timer_expire;
}

static void kvm_timer_init_interrupt(void *info)
{
        enable_percpu_irq(host_vtimer_irq, 0);
}

int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        switch (regid) {
        case KVM_REG_ARM_TIMER_CTL:
                timer->cntv_ctl = value;
                break;
        case KVM_REG_ARM_TIMER_CNT:
                vcpu->kvm->arch.timer.cntvoff = kvm_phys_timer_read() - value;
                break;
        case KVM_REG_ARM_TIMER_CVAL:
                timer->cntv_cval = value;
                break;
        default:
                return -1;
        }

        kvm_timer_update_state(vcpu);
        return 0;
}

u64 kvm_arm_timer_get_reg(struct kvm_vcpu *vcpu, u64 regid)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        switch (regid) {
        case KVM_REG_ARM_TIMER_CTL:
                return timer->cntv_ctl;
        case KVM_REG_ARM_TIMER_CNT:
                return kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
        case KVM_REG_ARM_TIMER_CVAL:
                return timer->cntv_cval;
        }
        return (u64)-1;
}

static int kvm_timer_cpu_notify(struct notifier_block *self,
                                unsigned long action, void *cpu)
{
        switch (action) {
        case CPU_STARTING:
        case CPU_STARTING_FROZEN:
                kvm_timer_init_interrupt(NULL);
                break;
        case CPU_DYING:
        case CPU_DYING_FROZEN:
                disable_percpu_irq(host_vtimer_irq);
                break;
        }

        return NOTIFY_OK;
}

static struct notifier_block kvm_timer_cpu_nb = {
        .notifier_call = kvm_timer_cpu_notify,
};

static const struct of_device_id arch_timer_of_match[] = {
        { .compatible   = "arm,armv7-timer",    },
        { .compatible   = "arm,armv8-timer",    },
        {},
};

int kvm_timer_hyp_init(void)
{
        struct device_node *np;
        unsigned int ppi;
        int err;

        timecounter = arch_timer_get_timecounter();
        if (!timecounter)
                return -ENODEV;

        np = of_find_matching_node(NULL, arch_timer_of_match);
        if (!np) {
                kvm_err("kvm_arch_timer: can't find DT node\n");
                return -ENODEV;
        }

        ppi = irq_of_parse_and_map(np, 2);
        if (!ppi) {
                kvm_err("kvm_arch_timer: no virtual timer interrupt\n");
                err = -EINVAL;
                goto out;
        }

        err = request_percpu_irq(ppi, kvm_arch_timer_handler,
                                 "kvm guest timer", kvm_get_running_vcpus());
        if (err) {
                kvm_err("kvm_arch_timer: can't request interrupt %d (%d)\n",
                        ppi, err);
                goto out;
        }

        host_vtimer_irq = ppi;

        err = __register_cpu_notifier(&kvm_timer_cpu_nb);
        if (err) {
                kvm_err("Cannot register timer CPU notifier\n");
                goto out_free;
        }

        wqueue = create_singlethread_workqueue("kvm_arch_timer");
        if (!wqueue) {
                err = -ENOMEM;
                goto out_free;
        }

        kvm_info("%s IRQ%d\n", np->name, ppi);
        on_each_cpu(kvm_timer_init_interrupt, NULL, 1);

        goto out;
out_free:
        free_percpu_irq(ppi, kvm_get_running_vcpus());
out:
        of_node_put(np);
        return err;
}

void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu)
{
        struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

        timer_disarm(timer);
        if (timer->map)
                kvm_vgic_unmap_phys_irq(vcpu, timer->map);
}

void kvm_timer_enable(struct kvm *kvm)
{
        if (kvm->arch.timer.enabled)
                return;

        /*
         * There is a potential race here between VCPUs starting for the first
         * time, which may be enabling the timer multiple times.  That doesn't
         * hurt though, because we're just setting a variable to the same
         * variable that it already was.  The important thing is that all
         * VCPUs have the enabled variable set, before entering the guest, if
         * the arch timers are enabled.
         */
        if (timecounter && wqueue)
                kvm->arch.timer.enabled = 1;
}

void kvm_timer_init(struct kvm *kvm)
{
        kvm->arch.timer.cntvoff = kvm_phys_timer_read();
}