drivers/xen/cpu_hotplug.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
0003
0004 #include <linux/notifier.h>
0005
0006 #include <xen/xen.h>
0007 #include <xen/xenbus.h>
0008
0009 #include <asm/xen/hypervisor.h>
0010 #include <asm/cpu.h>
0011
0012 static void enable_hotplug_cpu(int cpu)
0013 {
0014     if (!cpu_present(cpu))
0015         xen_arch_register_cpu(cpu);
0016
0017     set_cpu_present(cpu, true);
0018 }
0019
0020 static void disable_hotplug_cpu(int cpu)
0021 {
0022     if (!cpu_is_hotpluggable(cpu))
0023         return;
0024     lock_device_hotplug();
0025     if (cpu_online(cpu))
0026         device_offline(get_cpu_device(cpu));
0027     if (!cpu_online(cpu) && cpu_present(cpu)) {
0028         xen_arch_unregister_cpu(cpu);
0029         set_cpu_present(cpu, false);
0030     }
0031     unlock_device_hotplug();
0032 }
0033
0034 static int vcpu_online(unsigned int cpu)
0035 {
0036     int err;
0037     char dir[16], state[16];
0038
0039     sprintf(dir, "cpu/%u", cpu);
0040     err = xenbus_scanf(XBT_NIL, dir, "availability", "%15s", state);
0041     if (err != 1) {
0042         if (!xen_initial_domain())
0043             pr_err("Unable to read cpu state\n");
0044         return err;
0045     }
0046
0047     if (strcmp(state, "online") == 0)
0048         return 1;
0049     else if (strcmp(state, "offline") == 0)
0050         return 0;
0051
0052     pr_err("unknown state(%s) on CPU%d\n", state, cpu);
0053     return -EINVAL;
0054 }
0055 static void vcpu_hotplug(unsigned int cpu)
0056 {
0057     if (cpu >= nr_cpu_ids || !cpu_possible(cpu))
0058         return;
0059
0060     switch (vcpu_online(cpu)) {
0061     case 1:
0062         enable_hotplug_cpu(cpu);
0063         break;
0064     case 0:
0065         disable_hotplug_cpu(cpu);
0066         break;
0067     default:
0068         break;
0069     }
0070 }
0071
0072 static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
0073                       const char *path, const char *token)
0074 {
0075     unsigned int cpu;
0076     char *cpustr;
0077
0078     cpustr = strstr(path, "cpu/");
0079     if (cpustr != NULL) {
0080         sscanf(cpustr, "cpu/%u", &cpu);
0081         vcpu_hotplug(cpu);
0082     }
0083 }
0084
0085 static int setup_cpu_watcher(struct notifier_block *notifier,
0086                   unsigned long event, void *data)
0087 {
0088     int cpu;
0089     static struct xenbus_watch cpu_watch = {
0090         .node = "cpu",
0091         .callback = handle_vcpu_hotplug_event};
0092
0093     (void)register_xenbus_watch(&cpu_watch);
0094
0095     for_each_possible_cpu(cpu) {
0096         if (vcpu_online(cpu) == 0)
0097             disable_hotplug_cpu(cpu);
0098     }
0099
0100     return NOTIFY_DONE;
0101 }
0102
0103 static int __init setup_vcpu_hotplug_event(void)
0104 {
0105     static struct notifier_block xsn_cpu = {
0106         .notifier_call = setup_cpu_watcher };
0107
0108 #ifdef CONFIG_X86
0109     if (!xen_pv_domain() && !xen_pvh_domain())
0110 #else
0111     if (!xen_domain())
0112 #endif
0113         return -ENODEV;
0114
0115     register_xenstore_notifier(&xsn_cpu);
0116
0117     return 0;
0118 }
0119
0120 late_initcall(setup_vcpu_hotplug_event);
0121