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 
enable_hotplug_cpu(int cpu)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 
disable_hotplug_cpu(int cpu)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 
vcpu_online(unsigned int cpu)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 }
vcpu_hotplug(unsigned int cpu)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 
handle_vcpu_hotplug_event(struct xenbus_watch * watch,const char * path,const char * token)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 
setup_cpu_watcher(struct notifier_block * notifier,unsigned long event,void * data)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 			disable_hotplug_cpu(cpu);
98 	}
99 
100 	return NOTIFY_DONE;
101 }
102 
setup_vcpu_hotplug_event(void)103 static int __init setup_vcpu_hotplug_event(void)
104 {
105 	static struct notifier_block xsn_cpu = {
106 		.notifier_call = setup_cpu_watcher };
107 
108 #ifdef CONFIG_X86
109 	if (!xen_pv_domain() && !xen_pvh_domain())
110 #else
111 	if (!xen_domain())
112 #endif
113 		return -ENODEV;
114 
115 	register_xenstore_notifier(&xsn_cpu);
116 
117 	return 0;
118 }
119 
120 late_initcall(setup_vcpu_hotplug_event);
121 
122