// SPDX-License-Identifier: GPL-2.0
/*
 * Xen stolen ticks accounting.
 */
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/math64.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/static_call.h>
#include <linux/sched/cputime.h>

#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

#include <xen/events.h>
#include <xen/features.h>
#include <xen/interface/xen.h>
#include <xen/interface/vcpu.h>
#include <xen/xen-ops.h>

/* runstate info updated by Xen */
static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);

static DEFINE_PER_CPU(u64[4], old_runstate_time);

/* return an consistent snapshot of 64-bit time/counter value */
static u64 get64(const u64 *p)
{
        u64 ret;

        if (BITS_PER_LONG < 64) {
                u32 *p32 = (u32 *)p;
                u32 h, l, h2;

                /*
                 * Read high then low, and then make sure high is
                 * still the same; this will only loop if low wraps
                 * and carries into high.
                 * XXX some clean way to make this endian-proof?
                 */
                do {
                        h = READ_ONCE(p32[1]);
                        l = READ_ONCE(p32[0]);
                        h2 = READ_ONCE(p32[1]);
                } while(h2 != h);

                ret = (((u64)h) << 32) | l;
        } else
                ret = READ_ONCE(*p);

        return ret;
}

static void xen_get_runstate_snapshot_cpu_delta(
                              struct vcpu_runstate_info *res, unsigned int cpu)
{
        u64 state_time;
        struct vcpu_runstate_info *state;

        BUG_ON(preemptible());

        state = per_cpu_ptr(&xen_runstate, cpu);

        do {
                state_time = get64(&state->state_entry_time);
                rmb();  /* Hypervisor might update data. */
                *res = __READ_ONCE(*state);
                rmb();  /* Hypervisor might update data. */
        } while (get64(&state->state_entry_time) != state_time ||
                 (state_time & XEN_RUNSTATE_UPDATE));
}

static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res,
                                          unsigned int cpu)
{
        int i;

        xen_get_runstate_snapshot_cpu_delta(res, cpu);

        for (i = 0; i < 4; i++)
                res->time[i] += per_cpu(old_runstate_time, cpu)[i];
}

void xen_manage_runstate_time(int action)
{
        static struct vcpu_runstate_info *runstate_delta;
        struct vcpu_runstate_info state;
        int cpu, i;

        switch (action) {
        case -1: /* backup runstate time before suspend */
                if (unlikely(runstate_delta))
                        pr_warn_once("%s: memory leak as runstate_delta is not NULL\n",
                                        __func__);

                runstate_delta = kmalloc_objs(*runstate_delta,
                                              num_possible_cpus(), GFP_ATOMIC);
                if (unlikely(!runstate_delta)) {
                        pr_warn("%s: failed to allocate runstate_delta\n",
                                        __func__);
                        return;
                }

                for_each_possible_cpu(cpu) {
                        xen_get_runstate_snapshot_cpu_delta(&state, cpu);
                        memcpy(runstate_delta[cpu].time, state.time,
                                        sizeof(runstate_delta[cpu].time));
                }

                break;

        case 0: /* backup runstate time after resume */
                if (unlikely(!runstate_delta)) {
                        pr_warn("%s: cannot accumulate runstate time as runstate_delta is NULL\n",
                                        __func__);
                        return;
                }

                for_each_possible_cpu(cpu) {
                        for (i = 0; i < 4; i++)
                                per_cpu(old_runstate_time, cpu)[i] +=
                                        runstate_delta[cpu].time[i];
                }

                break;

        default: /* do not accumulate runstate time for checkpointing */
                break;
        }

        if (action != -1 && runstate_delta) {
                kfree(runstate_delta);
                runstate_delta = NULL;
        }
}

/* return true when a vcpu could run but has no real cpu to run on */
bool xen_vcpu_stolen(int vcpu)
{
        return per_cpu(xen_runstate, vcpu).state == RUNSTATE_runnable;
}

u64 xen_steal_clock(int cpu)
{
        struct vcpu_runstate_info state;

        xen_get_runstate_snapshot_cpu(&state, cpu);
        return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
}

void xen_setup_runstate_info(int cpu)
{
        struct vcpu_register_runstate_memory_area area;

        area.addr.v = &per_cpu(xen_runstate, cpu);

        if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
                               xen_vcpu_nr(cpu), &area))
                BUG();
}

void __init xen_time_setup_guest(void)
{
        bool xen_runstate_remote;

        xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable,
                                        VMASST_TYPE_runstate_update_flag);

        static_call_update(pv_steal_clock, xen_steal_clock);

        static_key_slow_inc(&paravirt_steal_enabled);
        if (xen_runstate_remote)
                static_key_slow_inc(&paravirt_steal_rq_enabled);
}