// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Copyright (C) 2013 Citrix Systems
 *
 * Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
 */

#define pr_fmt(fmt) "arm-pv: " fmt

#include <linux/arm-smccc.h>
#include <linux/cpuhotplug.h>
#include <linux/export.h>
#include <linux/io.h>
#include <linux/jump_label.h>
#include <linux/printk.h>
#include <linux/psci.h>
#include <linux/reboot.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/static_call.h>
#include <linux/sched/cputime.h>

#include <asm/paravirt.h>
#include <asm/pvclock-abi.h>
#include <asm/smp_plat.h>

struct pv_time_stolen_time_region {
        struct pvclock_vcpu_stolen_time __rcu *kaddr;
};

static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region);

static bool steal_acc = true;
static int __init parse_no_stealacc(char *arg)
{
        steal_acc = false;
        return 0;
}

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

/* return stolen time in ns by asking the hypervisor */
static u64 para_steal_clock(int cpu)
{
        struct pvclock_vcpu_stolen_time *kaddr = NULL;
        struct pv_time_stolen_time_region *reg;
        u64 ret = 0;

        reg = per_cpu_ptr(&stolen_time_region, cpu);

        /*
         * paravirt_steal_clock() may be called before the CPU
         * online notification callback runs. Until the callback
         * has run we just return zero.
         */
        rcu_read_lock();
        kaddr = rcu_dereference(reg->kaddr);
        if (!kaddr) {
                rcu_read_unlock();
                return 0;
        }

        ret = le64_to_cpu(READ_ONCE(kaddr->stolen_time));
        rcu_read_unlock();
        return ret;
}

static int stolen_time_cpu_down_prepare(unsigned int cpu)
{
        struct pvclock_vcpu_stolen_time *kaddr = NULL;
        struct pv_time_stolen_time_region *reg;

        reg = this_cpu_ptr(&stolen_time_region);
        if (!reg->kaddr)
                return 0;

        kaddr = rcu_replace_pointer(reg->kaddr, NULL, true);
        synchronize_rcu();
        memunmap(kaddr);

        return 0;
}

static int stolen_time_cpu_online(unsigned int cpu)
{
        struct pvclock_vcpu_stolen_time *kaddr = NULL;
        struct pv_time_stolen_time_region *reg;
        struct arm_smccc_res res;

        reg = this_cpu_ptr(&stolen_time_region);

        arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_ST, &res);

        if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
                return -EINVAL;

        kaddr = memremap(res.a0,
                              sizeof(struct pvclock_vcpu_stolen_time),
                              MEMREMAP_WB);

        rcu_assign_pointer(reg->kaddr, kaddr);

        if (!reg->kaddr) {
                pr_warn("Failed to map stolen time data structure\n");
                return -ENOMEM;
        }

        if (le32_to_cpu(kaddr->revision) != 0 ||
            le32_to_cpu(kaddr->attributes) != 0) {
                pr_warn_once("Unexpected revision or attributes in stolen time data\n");
                return -ENXIO;
        }

        return 0;
}

static int __init pv_time_init_stolen_time(void)
{
        int ret;

        ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
                                "hypervisor/arm/pvtime:online",
                                stolen_time_cpu_online,
                                stolen_time_cpu_down_prepare);
        if (ret < 0)
                return ret;
        return 0;
}

static bool __init has_pv_steal_clock(void)
{
        struct arm_smccc_res res;

        arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
                             ARM_SMCCC_HV_PV_TIME_FEATURES, &res);

        if (res.a0 != SMCCC_RET_SUCCESS)
                return false;

        arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_FEATURES,
                             ARM_SMCCC_HV_PV_TIME_ST, &res);

        return (res.a0 == SMCCC_RET_SUCCESS);
}

int __init pv_time_init(void)
{
        int ret;

        if (!has_pv_steal_clock())
                return 0;

        ret = pv_time_init_stolen_time();
        if (ret)
                return ret;

        static_call_update(pv_steal_clock, para_steal_clock);

        static_key_slow_inc(&paravirt_steal_enabled);
        if (steal_acc)
                static_key_slow_inc(&paravirt_steal_rq_enabled);

        pr_info("using stolen time PV\n");

        return 0;
}