drivers/xen/cpu_hotplug.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
   3
   4 #include <linux/notifier.h>
   5
   6 #include <xen/xen.h>
   7 #include <xen/xenbus.h>
   8
   9 #include <asm/xen/hypervisor.h>
  10 #include <asm/cpu.h>
  11
  12 static void enable_hotplug_cpu(int cpu)
  13 {
  14         if (!cpu_present(cpu))
  15                 xen_arch_register_cpu(cpu);
  16
  17         set_cpu_present(cpu, true);
  18 }
  19
  20 static void disable_hotplug_cpu(int cpu)
  21 {
  22         if (!cpu_is_hotpluggable(cpu))
  23                 return;
  24         lock_device_hotplug();
  25         if (cpu_online(cpu))
  26                 device_offline(get_cpu_device(cpu));
  27         if (!cpu_online(cpu) && cpu_present(cpu)) {
  28                 xen_arch_unregister_cpu(cpu);
  29                 set_cpu_present(cpu, false);
  30         }
  31         unlock_device_hotplug();
  32 }
  33
  34 static int vcpu_online(unsigned int cpu)
  35 {
  36         int err;
  37         char dir[16], state[16];
  38
  39         sprintf(dir, "cpu/%u", cpu);
  40         err = xenbus_scanf(XBT_NIL, dir, "availability", "%15s", state);
  41         if (err != 1) {
  42                 if (!xen_initial_domain())
  43                         pr_err("Unable to read cpu state\n");
  44                 return err;
  45         }
  46
  47         if (strcmp(state, "online") == 0)
  48                 return 1;
  49         else if (strcmp(state, "offline") == 0)
  50                 return 0;
  51
  52         pr_err("unknown state(%s) on CPU%d\n", state, cpu);
  53         return -EINVAL;
  54 }
  55 static void vcpu_hotplug(unsigned int cpu)
  56 {
  57         if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
  58                 return;
  59
  60         switch (vcpu_online(cpu)) {
  61         case 1:
  62                 enable_hotplug_cpu(cpu);
  63                 break;
  64         case 0:
  65                 disable_hotplug_cpu(cpu);
  66                 break;
  67         default:
  68                 break;
  69         }
  70 }
  71
  72 static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
  73                                       const char *path, const char *token)
  74 {
  75         unsigned int cpu;
  76         char *cpustr;
  77
  78         cpustr = strstr(path, "cpu/");
  79         if (cpustr != NULL) {
  80                 sscanf(cpustr, "cpu/%u", &cpu);
  81                 vcpu_hotplug(cpu);
  82         }
  83 }
  84
  85 static int setup_cpu_watcher(struct notifier_block *notifier,
  86                               unsigned long event, void *data)
  87 {
  88         int cpu;
  89         static struct xenbus_watch cpu_watch = {
  90                 .node = "cpu",
  91                 .callback = handle_vcpu_hotplug_event};
  92
  93         (void)register_xenbus_watch(&cpu_watch);
  94
  95         for_each_possible_cpu(cpu) {
  96                 if (vcpu_online(cpu) == 0) {
  97                         (void)cpu_down(cpu);
  98                         set_cpu_present(cpu, false);
  99                 }
 100         }
 101
 102         return NOTIFY_DONE;
 103 }
 104
 105 static int __init setup_vcpu_hotplug_event(void)
 106 {
 107         static struct notifier_block xsn_cpu = {
 108                 .notifier_call = setup_cpu_watcher };
 109
 110 #ifdef CONFIG_X86
 111         if (!xen_pv_domain() && !xen_pvh_domain())
 112 #else
 113         if (!xen_domain())
 114 #endif
 115                 return -ENODEV;
 116
 117         register_xenstore_notifier(&xsn_cpu);
 118
 119         return 0;
 120 }
 121
 122 arch_initcall(setup_vcpu_hotplug_event);
 123