// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

#include <linux/notifier.h>

#include <xen/xen.h>
#include <xen/xenbus.h>

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

static void enable_hotplug_cpu(int cpu)
{
        if (!cpu_present(cpu))
                xen_arch_register_cpu(cpu);

        set_cpu_present(cpu, true);
}

static void disable_hotplug_cpu(int cpu)
{
        if (!cpu_is_hotpluggable(cpu))
                return;
        lock_device_hotplug();
        if (cpu_online(cpu))
                device_offline(get_cpu_device(cpu));
        if (!cpu_online(cpu) && cpu_present(cpu)) {
                xen_arch_unregister_cpu(cpu);
                set_cpu_present(cpu, false);
        }
        unlock_device_hotplug();
}

static int vcpu_online(unsigned int cpu)
{
        int err;
        char dir[16], state[16];

        sprintf(dir, "cpu/%u", cpu);
        err = xenbus_scanf(XBT_NIL, dir, "availability", "%15s", state);
        if (err != 1) {
                if (!xen_initial_domain())
                        pr_err("Unable to read cpu state\n");
                return err;
        }

        if (strcmp(state, "online") == 0)
                return 1;
        else if (strcmp(state, "offline") == 0)
                return 0;

        pr_err("unknown state(%s) on CPU%d\n", state, cpu);
        return -EINVAL;
}
static void vcpu_hotplug(unsigned int cpu)
{
        if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
                return;

        switch (vcpu_online(cpu)) {
        case 1:
                enable_hotplug_cpu(cpu);
                break;
        case 0:
                disable_hotplug_cpu(cpu);
                break;
        default:
                break;
        }
}

static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
                                      const char *path, const char *token)
{
        unsigned int cpu;
        char *cpustr;

        cpustr = strstr(path, "cpu/");
        if (cpustr != NULL) {
                sscanf(cpustr, "cpu/%u", &cpu);
                vcpu_hotplug(cpu);
        }
}

static int setup_cpu_watcher(struct notifier_block *notifier,
                              unsigned long event, void *data)
{
        int cpu;
        static struct xenbus_watch cpu_watch = {
                .node = "cpu",
                .callback = handle_vcpu_hotplug_event};

        (void)register_xenbus_watch(&cpu_watch);

        for_each_possible_cpu(cpu) {
                if (vcpu_online(cpu) == 0)
                        disable_hotplug_cpu(cpu);
        }

        return NOTIFY_DONE;
}

static int __init setup_vcpu_hotplug_event(void)
{
        static struct notifier_block xsn_cpu = {
                .notifier_call = setup_cpu_watcher };

#ifdef CONFIG_X86
        if (!xen_pv_domain() && !xen_pvh_domain())
#else
        if (!xen_domain())
#endif
                return -ENODEV;

        register_xenstore_notifier(&xsn_cpu);

        return 0;
}

late_initcall(setup_vcpu_hotplug_event);