/*  KVM paravirtual clock driver. A clocksource implementation
    Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.

    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, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <linux/clocksource.h>
#include <linux/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/msr.h>
#include <asm/apic.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/memblock.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>

#include <asm/x86_init.h>
#include <asm/reboot.h>
#include <asm/kvmclock.h>

static int kvmclock __ro_after_init = 1;
static int msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
static int msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;
static u64 kvm_sched_clock_offset;

static int parse_no_kvmclock(char *arg)
{
        kvmclock = 0;
        return 0;
}
early_param("no-kvmclock", parse_no_kvmclock);

/* The hypervisor will put information about time periodically here */
static struct pvclock_vsyscall_time_info *hv_clock;
static struct pvclock_wall_clock wall_clock;

struct pvclock_vsyscall_time_info *pvclock_pvti_cpu0_va(void)
{
        return hv_clock;
}
EXPORT_SYMBOL_GPL(pvclock_pvti_cpu0_va);

/*
 * The wallclock is the time of day when we booted. Since then, some time may
 * have elapsed since the hypervisor wrote the data. So we try to account for
 * that with system time
 */
static void kvm_get_wallclock(struct timespec *now)
{
        struct pvclock_vcpu_time_info *vcpu_time;
        int low, high;
        int cpu;

        low = (int)__pa_symbol(&wall_clock);
        high = ((u64)__pa_symbol(&wall_clock) >> 32);

        native_write_msr(msr_kvm_wall_clock, low, high);

        cpu = get_cpu();

        vcpu_time = &hv_clock[cpu].pvti;
        pvclock_read_wallclock(&wall_clock, vcpu_time, now);

        put_cpu();
}

static int kvm_set_wallclock(const struct timespec *now)
{
        return -1;
}

static u64 kvm_clock_read(void)
{
        struct pvclock_vcpu_time_info *src;
        u64 ret;
        int cpu;

        preempt_disable_notrace();
        cpu = smp_processor_id();
        src = &hv_clock[cpu].pvti;
        ret = pvclock_clocksource_read(src);
        preempt_enable_notrace();
        return ret;
}

static u64 kvm_clock_get_cycles(struct clocksource *cs)
{
        return kvm_clock_read();
}

static u64 kvm_sched_clock_read(void)
{
        return kvm_clock_read() - kvm_sched_clock_offset;
}

static inline void kvm_sched_clock_init(bool stable)
{
        if (!stable) {
                pv_time_ops.sched_clock = kvm_clock_read;
                clear_sched_clock_stable();
                return;
        }

        kvm_sched_clock_offset = kvm_clock_read();
        pv_time_ops.sched_clock = kvm_sched_clock_read;

        printk(KERN_INFO "kvm-clock: using sched offset of %llu cycles\n",
                        kvm_sched_clock_offset);

        BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
                 sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
}

/*
 * If we don't do that, there is the possibility that the guest
 * will calibrate under heavy load - thus, getting a lower lpj -
 * and execute the delays themselves without load. This is wrong,
 * because no delay loop can finish beforehand.
 * Any heuristics is subject to fail, because ultimately, a large
 * poll of guests can be running and trouble each other. So we preset
 * lpj here
 */
static unsigned long kvm_get_tsc_khz(void)
{
        struct pvclock_vcpu_time_info *src;
        int cpu;
        unsigned long tsc_khz;

        cpu = get_cpu();
        src = &hv_clock[cpu].pvti;
        tsc_khz = pvclock_tsc_khz(src);
        put_cpu();
        return tsc_khz;
}

static void kvm_get_preset_lpj(void)
{
        unsigned long khz;
        u64 lpj;

        khz = kvm_get_tsc_khz();

        lpj = ((u64)khz * 1000);
        do_div(lpj, HZ);
        preset_lpj = lpj;
}

bool kvm_check_and_clear_guest_paused(void)
{
        bool ret = false;
        struct pvclock_vcpu_time_info *src;
        int cpu = smp_processor_id();

        if (!hv_clock)
                return ret;

        src = &hv_clock[cpu].pvti;
        if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
                src->flags &= ~PVCLOCK_GUEST_STOPPED;
                pvclock_touch_watchdogs();
                ret = true;
        }

        return ret;
}

struct clocksource kvm_clock = {
        .name = "kvm-clock",
        .read = kvm_clock_get_cycles,
        .rating = 400,
        .mask = CLOCKSOURCE_MASK(64),
        .flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
EXPORT_SYMBOL_GPL(kvm_clock);

int kvm_register_clock(char *txt)
{
        int cpu = smp_processor_id();
        int low, high, ret;
        struct pvclock_vcpu_time_info *src;

        if (!hv_clock)
                return 0;

        src = &hv_clock[cpu].pvti;
        low = (int)slow_virt_to_phys(src) | 1;
        high = ((u64)slow_virt_to_phys(src) >> 32);
        ret = native_write_msr_safe(msr_kvm_system_time, low, high);
        printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
               cpu, high, low, txt);

        return ret;
}

static void kvm_save_sched_clock_state(void)
{
}

static void kvm_restore_sched_clock_state(void)
{
        kvm_register_clock("primary cpu clock, resume");
}

#ifdef CONFIG_X86_LOCAL_APIC
static void kvm_setup_secondary_clock(void)
{
        /*
         * Now that the first cpu already had this clocksource initialized,
         * we shouldn't fail.
         */
        WARN_ON(kvm_register_clock("secondary cpu clock"));
}
#endif

/*
 * After the clock is registered, the host will keep writing to the
 * registered memory location. If the guest happens to shutdown, this memory
 * won't be valid. In cases like kexec, in which you install a new kernel, this
 * means a random memory location will be kept being written. So before any
 * kind of shutdown from our side, we unregister the clock by writing anything
 * that does not have the 'enable' bit set in the msr
 */
#ifdef CONFIG_KEXEC_CORE
static void kvm_crash_shutdown(struct pt_regs *regs)
{
        native_write_msr(msr_kvm_system_time, 0, 0);
        kvm_disable_steal_time();
        native_machine_crash_shutdown(regs);
}
#endif

static void kvm_shutdown(void)
{
        native_write_msr(msr_kvm_system_time, 0, 0);
        kvm_disable_steal_time();
        native_machine_shutdown();
}

void __init kvmclock_init(void)
{
        struct pvclock_vcpu_time_info *vcpu_time;
        unsigned long mem;
        int size, cpu;
        u8 flags;

        size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS);

        if (!kvm_para_available())
                return;

        if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
                msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
                msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
        } else if (!(kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)))
                return;

        printk(KERN_INFO "kvm-clock: Using msrs %x and %x",
                msr_kvm_system_time, msr_kvm_wall_clock);

        mem = memblock_alloc(size, PAGE_SIZE);
        if (!mem)
                return;
        hv_clock = __va(mem);
        memset(hv_clock, 0, size);

        if (kvm_register_clock("primary cpu clock")) {
                hv_clock = NULL;
                memblock_free(mem, size);
                return;
        }

        if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
                pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

        cpu = get_cpu();
        vcpu_time = &hv_clock[cpu].pvti;
        flags = pvclock_read_flags(vcpu_time);

        kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
        put_cpu();

        x86_platform.calibrate_tsc = kvm_get_tsc_khz;
        x86_platform.calibrate_cpu = kvm_get_tsc_khz;
        x86_platform.get_wallclock = kvm_get_wallclock;
        x86_platform.set_wallclock = kvm_set_wallclock;
#ifdef CONFIG_X86_LOCAL_APIC
        x86_cpuinit.early_percpu_clock_init =
                kvm_setup_secondary_clock;
#endif
        x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
        x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
        machine_ops.shutdown  = kvm_shutdown;
#ifdef CONFIG_KEXEC_CORE
        machine_ops.crash_shutdown  = kvm_crash_shutdown;
#endif
        kvm_get_preset_lpj();
        clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
        pv_info.name = "KVM";
}

int __init kvm_setup_vsyscall_timeinfo(void)
{
#ifdef CONFIG_X86_64
        int cpu;
        u8 flags;
        struct pvclock_vcpu_time_info *vcpu_time;
        unsigned int size;

        if (!hv_clock)
                return 0;

        size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS);

        cpu = get_cpu();

        vcpu_time = &hv_clock[cpu].pvti;
        flags = pvclock_read_flags(vcpu_time);

        if (!(flags & PVCLOCK_TSC_STABLE_BIT)) {
                put_cpu();
                return 1;
        }

        put_cpu();

        kvm_clock.archdata.vclock_mode = VCLOCK_PVCLOCK;
#endif
        return 0;
}