/*
 * KVM paravirt_ops implementation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * Copyright (C) 2007, Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 * Copyright IBM Corporation, 2007
 *   Authors: Anthony Liguori <aliguori@us.ibm.com>
 */

#include <linux/context_tracking.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kvm_para.h>
#include <linux/cpu.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/hardirq.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/hash.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/kprobes.h>
#include <linux/debugfs.h>
#include <linux/nmi.h>
#include <linux/swait.h>
#include <asm/timer.h>
#include <asm/cpu.h>
#include <asm/traps.h>
#include <asm/desc.h>
#include <asm/tlbflush.h>
#include <asm/idle.h>
#include <asm/apic.h>
#include <asm/apicdef.h>
#include <asm/hypervisor.h>
#include <asm/kvm_guest.h>

static int kvmapf = 1;

static int parse_no_kvmapf(char *arg)
{
        kvmapf = 0;
        return 0;
}

early_param("no-kvmapf", parse_no_kvmapf);

static int steal_acc = 1;
static int parse_no_stealacc(char *arg)
{
        steal_acc = 0;
        return 0;
}

early_param("no-steal-acc", parse_no_stealacc);

static int kvmclock_vsyscall = 1;
static int parse_no_kvmclock_vsyscall(char *arg)
{
        kvmclock_vsyscall = 0;
        return 0;
}

early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);

static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
static int has_steal_clock = 0;

/*
 * No need for any "IO delay" on KVM
 */
static void kvm_io_delay(void)
{
}

#define KVM_TASK_SLEEP_HASHBITS 8
#define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)

struct kvm_task_sleep_node {
        struct hlist_node link;
        struct swait_queue_head wq;
        u32 token;
        int cpu;
        bool halted;
};

static struct kvm_task_sleep_head {
        raw_spinlock_t lock;
        struct hlist_head list;
} async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];

static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b,
                                                  u32 token)
{
        struct hlist_node *p;

        hlist_for_each(p, &b->list) {
                struct kvm_task_sleep_node *n =
                        hlist_entry(p, typeof(*n), link);
                if (n->token == token)
                        return n;
        }

        return NULL;
}

void kvm_async_pf_task_wait(u32 token)
{
        u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
        struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
        struct kvm_task_sleep_node n, *e;
        DECLARE_SWAITQUEUE(wait);

        rcu_irq_enter();

        raw_spin_lock(&b->lock);
        e = _find_apf_task(b, token);
        if (e) {
                /* dummy entry exist -> wake up was delivered ahead of PF */
                hlist_del(&e->link);
                kfree(e);
                raw_spin_unlock(&b->lock);

                rcu_irq_exit();
                return;
        }

        n.token = token;
        n.cpu = smp_processor_id();
        n.halted = is_idle_task(current) || preempt_count() > 1;
        init_swait_queue_head(&n.wq);
        hlist_add_head(&n.link, &b->list);
        raw_spin_unlock(&b->lock);

        for (;;) {
                if (!n.halted)
                        prepare_to_swait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
                if (hlist_unhashed(&n.link))
                        break;

                if (!n.halted) {
                        local_irq_enable();
                        schedule();
                        local_irq_disable();
                } else {
                        /*
                         * We cannot reschedule. So halt.
                         */
                        rcu_irq_exit();
                        native_safe_halt();
                        rcu_irq_enter();
                        local_irq_disable();
                }
        }
        if (!n.halted)
                finish_swait(&n.wq, &wait);

        rcu_irq_exit();
        return;
}
EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);

static void apf_task_wake_one(struct kvm_task_sleep_node *n)
{
        hlist_del_init(&n->link);
        if (n->halted)
                smp_send_reschedule(n->cpu);
        else if (swait_active(&n->wq))
                swake_up(&n->wq);
}

static void apf_task_wake_all(void)
{
        int i;

        for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
                struct hlist_node *p, *next;
                struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
                raw_spin_lock(&b->lock);
                hlist_for_each_safe(p, next, &b->list) {
                        struct kvm_task_sleep_node *n =
                                hlist_entry(p, typeof(*n), link);
                        if (n->cpu == smp_processor_id())
                                apf_task_wake_one(n);
                }
                raw_spin_unlock(&b->lock);
        }
}

void kvm_async_pf_task_wake(u32 token)
{
        u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
        struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
        struct kvm_task_sleep_node *n;

        if (token == ~0) {
                apf_task_wake_all();
                return;
        }

again:
        raw_spin_lock(&b->lock);
        n = _find_apf_task(b, token);
        if (!n) {
                /*
                 * async PF was not yet handled.
                 * Add dummy entry for the token.
                 */
                n = kzalloc(sizeof(*n), GFP_ATOMIC);
                if (!n) {
                        /*
                         * Allocation failed! Busy wait while other cpu
                         * handles async PF.
                         */
                        raw_spin_unlock(&b->lock);
                        cpu_relax();
                        goto again;
                }
                n->token = token;
                n->cpu = smp_processor_id();
                init_swait_queue_head(&n->wq);
                hlist_add_head(&n->link, &b->list);
        } else
                apf_task_wake_one(n);
        raw_spin_unlock(&b->lock);
        return;
}
EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);

u32 kvm_read_and_reset_pf_reason(void)
{
        u32 reason = 0;

        if (__this_cpu_read(apf_reason.enabled)) {
                reason = __this_cpu_read(apf_reason.reason);
                __this_cpu_write(apf_reason.reason, 0);
        }

        return reason;
}
EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);

dotraplinkage void
do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
{
        enum ctx_state prev_state;

        switch (kvm_read_and_reset_pf_reason()) {
        default:
                trace_do_page_fault(regs, error_code);
                break;
        case KVM_PV_REASON_PAGE_NOT_PRESENT:
                /* page is swapped out by the host. */
                prev_state = exception_enter();
                exit_idle();
                kvm_async_pf_task_wait((u32)read_cr2());
                exception_exit(prev_state);
                break;
        case KVM_PV_REASON_PAGE_READY:
                rcu_irq_enter();
                exit_idle();
                kvm_async_pf_task_wake((u32)read_cr2());
                rcu_irq_exit();
                break;
        }
}
NOKPROBE_SYMBOL(do_async_page_fault);

static void __init paravirt_ops_setup(void)
{
        pv_info.name = "KVM";

        /*
         * KVM isn't paravirt in the sense of paravirt_enabled.  A KVM
         * guest kernel works like a bare metal kernel with additional
         * features, and paravirt_enabled is about features that are
         * missing.
         */
        pv_info.paravirt_enabled = 0;

        if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
                pv_cpu_ops.io_delay = kvm_io_delay;

#ifdef CONFIG_X86_IO_APIC
        no_timer_check = 1;
#endif
}

static void kvm_register_steal_time(void)
{
        int cpu = smp_processor_id();
        struct kvm_steal_time *st = &per_cpu(steal_time, cpu);

        if (!has_steal_clock)
                return;

        memset(st, 0, sizeof(*st));

        wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
        pr_info("kvm-stealtime: cpu %d, msr %llx\n",
                cpu, (unsigned long long) slow_virt_to_phys(st));
}

static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;

static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
{
        /**
         * This relies on __test_and_clear_bit to modify the memory
         * in a way that is atomic with respect to the local CPU.
         * The hypervisor only accesses this memory from the local CPU so
         * there's no need for lock or memory barriers.
         * An optimization barrier is implied in apic write.
         */
        if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
                return;
        apic_write(APIC_EOI, APIC_EOI_ACK);
}

static void kvm_guest_cpu_init(void)
{
        if (!kvm_para_available())
                return;

        if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
                u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));

#ifdef CONFIG_PREEMPT
                pa |= KVM_ASYNC_PF_SEND_ALWAYS;
#endif
                wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED);
                __this_cpu_write(apf_reason.enabled, 1);
                printk(KERN_INFO"KVM setup async PF for cpu %d\n",
                       smp_processor_id());
        }

        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
                unsigned long pa;
                /* Size alignment is implied but just to make it explicit. */
                BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
                __this_cpu_write(kvm_apic_eoi, 0);
                pa = slow_virt_to_phys(this_cpu_ptr(&kvm_apic_eoi))
                        | KVM_MSR_ENABLED;
                wrmsrl(MSR_KVM_PV_EOI_EN, pa);
        }

        if (has_steal_clock)
                kvm_register_steal_time();
}

static void kvm_pv_disable_apf(void)
{
        if (!__this_cpu_read(apf_reason.enabled))
                return;

        wrmsrl(MSR_KVM_ASYNC_PF_EN, 0);
        __this_cpu_write(apf_reason.enabled, 0);

        printk(KERN_INFO"Unregister pv shared memory for cpu %d\n",
               smp_processor_id());
}

static void kvm_pv_guest_cpu_reboot(void *unused)
{
        /*
         * We disable PV EOI before we load a new kernel by kexec,
         * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
         * New kernel can re-enable when it boots.
         */
        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
                wrmsrl(MSR_KVM_PV_EOI_EN, 0);
        kvm_pv_disable_apf();
        kvm_disable_steal_time();
}

static int kvm_pv_reboot_notify(struct notifier_block *nb,
                                unsigned long code, void *unused)
{
        if (code == SYS_RESTART)
                on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
        return NOTIFY_DONE;
}

static struct notifier_block kvm_pv_reboot_nb = {
        .notifier_call = kvm_pv_reboot_notify,
};

static u64 kvm_steal_clock(int cpu)
{
        u64 steal;
        struct kvm_steal_time *src;
        int version;

        src = &per_cpu(steal_time, cpu);
        do {
                version = src->version;
                rmb();
                steal = src->steal;
                rmb();
        } while ((version & 1) || (version != src->version));

        return steal;
}

void kvm_disable_steal_time(void)
{
        if (!has_steal_clock)
                return;

        wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
}

#ifdef CONFIG_SMP
static void __init kvm_smp_prepare_boot_cpu(void)
{
        kvm_guest_cpu_init();
        native_smp_prepare_boot_cpu();
        kvm_spinlock_init();
}

static void kvm_guest_cpu_online(void *dummy)
{
        kvm_guest_cpu_init();
}

static void kvm_guest_cpu_offline(void *dummy)
{
        kvm_disable_steal_time();
        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
                wrmsrl(MSR_KVM_PV_EOI_EN, 0);
        kvm_pv_disable_apf();
        apf_task_wake_all();
}

static int kvm_cpu_notify(struct notifier_block *self, unsigned long action,
                          void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        switch (action) {
        case CPU_ONLINE:
        case CPU_DOWN_FAILED:
        case CPU_ONLINE_FROZEN:
                smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0);
                break;
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
                smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1);
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block kvm_cpu_notifier = {
        .notifier_call  = kvm_cpu_notify,
};
#endif

static void __init kvm_apf_trap_init(void)
{
        set_intr_gate(14, async_page_fault);
}

void __init kvm_guest_init(void)
{
        int i;

        if (!kvm_para_available())
                return;

        paravirt_ops_setup();
        register_reboot_notifier(&kvm_pv_reboot_nb);
        for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
                raw_spin_lock_init(&async_pf_sleepers[i].lock);
        if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
                x86_init.irqs.trap_init = kvm_apf_trap_init;

        if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
                has_steal_clock = 1;
                pv_time_ops.steal_clock = kvm_steal_clock;
        }

        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
                apic_set_eoi_write(kvm_guest_apic_eoi_write);

        if (kvmclock_vsyscall)
                kvm_setup_vsyscall_timeinfo();

#ifdef CONFIG_SMP
        smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
        register_cpu_notifier(&kvm_cpu_notifier);
#else
        kvm_guest_cpu_init();
#endif

        /*
         * Hard lockup detection is enabled by default. Disable it, as guests
         * can get false positives too easily, for example if the host is
         * overcommitted.
         */
        hardlockup_detector_disable();
}

static noinline uint32_t __kvm_cpuid_base(void)
{
        if (boot_cpu_data.cpuid_level < 0)
                return 0;       /* So we don't blow up on old processors */

        if (cpu_has_hypervisor)
                return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);

        return 0;
}

static inline uint32_t kvm_cpuid_base(void)
{
        static int kvm_cpuid_base = -1;

        if (kvm_cpuid_base == -1)
                kvm_cpuid_base = __kvm_cpuid_base();

        return kvm_cpuid_base;
}

bool kvm_para_available(void)
{
        return kvm_cpuid_base() != 0;
}
EXPORT_SYMBOL_GPL(kvm_para_available);

unsigned int kvm_arch_para_features(void)
{
        return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES);
}

static uint32_t __init kvm_detect(void)
{
        return kvm_cpuid_base();
}

const struct hypervisor_x86 x86_hyper_kvm __refconst = {
        .name                   = "KVM",
        .detect                 = kvm_detect,
        .x2apic_available       = kvm_para_available,
};
EXPORT_SYMBOL_GPL(x86_hyper_kvm);

static __init int activate_jump_labels(void)
{
        if (has_steal_clock) {
                static_key_slow_inc(&paravirt_steal_enabled);
                if (steal_acc)
                        static_key_slow_inc(&paravirt_steal_rq_enabled);
        }

        return 0;
}
arch_initcall(activate_jump_labels);

#ifdef CONFIG_PARAVIRT_SPINLOCKS

/* Kick a cpu by its apicid. Used to wake up a halted vcpu */
static void kvm_kick_cpu(int cpu)
{
        int apicid;
        unsigned long flags = 0;

        apicid = per_cpu(x86_cpu_to_apicid, cpu);
        kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
}


#ifdef CONFIG_QUEUED_SPINLOCKS

#include <asm/qspinlock.h>

static void kvm_wait(u8 *ptr, u8 val)
{
        unsigned long flags;

        if (in_nmi())
                return;

        local_irq_save(flags);

        if (READ_ONCE(*ptr) != val)
                goto out;

        /*
         * halt until it's our turn and kicked. Note that we do safe halt
         * for irq enabled case to avoid hang when lock info is overwritten
         * in irq spinlock slowpath and no spurious interrupt occur to save us.
         */
        if (arch_irqs_disabled_flags(flags))
                halt();
        else
                safe_halt();

out:
        local_irq_restore(flags);
}

#else /* !CONFIG_QUEUED_SPINLOCKS */

enum kvm_contention_stat {
        TAKEN_SLOW,
        TAKEN_SLOW_PICKUP,
        RELEASED_SLOW,
        RELEASED_SLOW_KICKED,
        NR_CONTENTION_STATS
};

#ifdef CONFIG_KVM_DEBUG_FS
#define HISTO_BUCKETS   30

static struct kvm_spinlock_stats
{
        u32 contention_stats[NR_CONTENTION_STATS];
        u32 histo_spin_blocked[HISTO_BUCKETS+1];
        u64 time_blocked;
} spinlock_stats;

static u8 zero_stats;

static inline void check_zero(void)
{
        u8 ret;
        u8 old;

        old = READ_ONCE(zero_stats);
        if (unlikely(old)) {
                ret = cmpxchg(&zero_stats, old, 0);
                /* This ensures only one fellow resets the stat */
                if (ret == old)
                        memset(&spinlock_stats, 0, sizeof(spinlock_stats));
        }
}

static inline void add_stats(enum kvm_contention_stat var, u32 val)
{
        check_zero();
        spinlock_stats.contention_stats[var] += val;
}


static inline u64 spin_time_start(void)
{
        return sched_clock();
}

static void __spin_time_accum(u64 delta, u32 *array)
{
        unsigned index;

        index = ilog2(delta);
        check_zero();

        if (index < HISTO_BUCKETS)
                array[index]++;
        else
                array[HISTO_BUCKETS]++;
}

static inline void spin_time_accum_blocked(u64 start)
{
        u32 delta;

        delta = sched_clock() - start;
        __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
        spinlock_stats.time_blocked += delta;
}

static struct dentry *d_spin_debug;
static struct dentry *d_kvm_debug;

static struct dentry *kvm_init_debugfs(void)
{
        d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
        if (!d_kvm_debug)
                printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");

        return d_kvm_debug;
}

static int __init kvm_spinlock_debugfs(void)
{
        struct dentry *d_kvm;

        d_kvm = kvm_init_debugfs();
        if (d_kvm == NULL)
                return -ENOMEM;

        d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);

        debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);

        debugfs_create_u32("taken_slow", 0444, d_spin_debug,
                   &spinlock_stats.contention_stats[TAKEN_SLOW]);
        debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
                   &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);

        debugfs_create_u32("released_slow", 0444, d_spin_debug,
                   &spinlock_stats.contention_stats[RELEASED_SLOW]);
        debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
                   &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);

        debugfs_create_u64("time_blocked", 0444, d_spin_debug,
                           &spinlock_stats.time_blocked);

        debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
                     spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);

        return 0;
}
fs_initcall(kvm_spinlock_debugfs);
#else  /* !CONFIG_KVM_DEBUG_FS */
static inline void add_stats(enum kvm_contention_stat var, u32 val)
{
}

static inline u64 spin_time_start(void)
{
        return 0;
}

static inline void spin_time_accum_blocked(u64 start)
{
}
#endif  /* CONFIG_KVM_DEBUG_FS */

struct kvm_lock_waiting {
        struct arch_spinlock *lock;
        __ticket_t want;
};

/* cpus 'waiting' on a spinlock to become available */
static cpumask_t waiting_cpus;

/* Track spinlock on which a cpu is waiting */
static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);

__visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
{
        struct kvm_lock_waiting *w;
        int cpu;
        u64 start;
        unsigned long flags;
        __ticket_t head;

        if (in_nmi())
                return;

        w = this_cpu_ptr(&klock_waiting);
        cpu = smp_processor_id();
        start = spin_time_start();

        /*
         * Make sure an interrupt handler can't upset things in a
         * partially setup state.
         */
        local_irq_save(flags);

        /*
         * The ordering protocol on this is that the "lock" pointer
         * may only be set non-NULL if the "want" ticket is correct.
         * If we're updating "want", we must first clear "lock".
         */
        w->lock = NULL;
        smp_wmb();
        w->want = want;
        smp_wmb();
        w->lock = lock;

        add_stats(TAKEN_SLOW, 1);

        /*
         * This uses set_bit, which is atomic but we should not rely on its
         * reordering gurantees. So barrier is needed after this call.
         */
        cpumask_set_cpu(cpu, &waiting_cpus);

        barrier();

        /*
         * Mark entry to slowpath before doing the pickup test to make
         * sure we don't deadlock with an unlocker.
         */
        __ticket_enter_slowpath(lock);

        /* make sure enter_slowpath, which is atomic does not cross the read */
        smp_mb__after_atomic();

        /*
         * check again make sure it didn't become free while
         * we weren't looking.
         */
        head = READ_ONCE(lock->tickets.head);
        if (__tickets_equal(head, want)) {
                add_stats(TAKEN_SLOW_PICKUP, 1);
                goto out;
        }

        /*
         * halt until it's our turn and kicked. Note that we do safe halt
         * for irq enabled case to avoid hang when lock info is overwritten
         * in irq spinlock slowpath and no spurious interrupt occur to save us.
         */
        if (arch_irqs_disabled_flags(flags))
                halt();
        else
                safe_halt();

out:
        cpumask_clear_cpu(cpu, &waiting_cpus);
        w->lock = NULL;
        local_irq_restore(flags);
        spin_time_accum_blocked(start);
}
PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);

/* Kick vcpu waiting on @lock->head to reach value @ticket */
static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
{
        int cpu;

        add_stats(RELEASED_SLOW, 1);
        for_each_cpu(cpu, &waiting_cpus) {
                const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
                if (READ_ONCE(w->lock) == lock &&
                    READ_ONCE(w->want) == ticket) {
                        add_stats(RELEASED_SLOW_KICKED, 1);
                        kvm_kick_cpu(cpu);
                        break;
                }
        }
}

#endif /* !CONFIG_QUEUED_SPINLOCKS */

/*
 * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
 */
void __init kvm_spinlock_init(void)
{
        if (!kvm_para_available())
                return;
        /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
        if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
                return;

#ifdef CONFIG_QUEUED_SPINLOCKS
        __pv_init_lock_hash();
        pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
        pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
        pv_lock_ops.wait = kvm_wait;
        pv_lock_ops.kick = kvm_kick_cpu;
#else /* !CONFIG_QUEUED_SPINLOCKS */
        pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
        pv_lock_ops.unlock_kick = kvm_unlock_kick;
#endif
}

static __init int kvm_spinlock_init_jump(void)
{
        if (!kvm_para_available())
                return 0;
        if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
                return 0;

        static_key_slow_inc(&paravirt_ticketlocks_enabled);
        printk(KERN_INFO "KVM setup paravirtual spinlock\n");

        return 0;
}
early_initcall(kvm_spinlock_init_jump);

#endif  /* CONFIG_PARAVIRT_SPINLOCKS */