1// SPDX-License-Identifier: GPL-2.0
2#include <linux/syscore_ops.h>
3#include <linux/suspend.h>
4#include <linux/cpu.h>
5
6#include <asm/msr.h>
7#include <asm/mwait.h>
8
9#define UMWAIT_C02_ENABLE 0
10
11#define UMWAIT_CTRL_VAL(max_time, c02_disable) \
12 (((max_time) & MSR_IA32_UMWAIT_CONTROL_TIME_MASK) | \
13 ((c02_disable) & MSR_IA32_UMWAIT_CONTROL_C02_DISABLE))
14
15/*
16 * Cache IA32_UMWAIT_CONTROL MSR. This is a systemwide control. By default,
17 * umwait max time is 100000 in TSC-quanta and C0.2 is enabled
18 */
19static u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLE);
20
21/*
22 * Cache the original IA32_UMWAIT_CONTROL MSR value which is configured by
23 * hardware or BIOS before kernel boot.
24 */
25static u32 orig_umwait_control_cached __ro_after_init;
26
27/*
28 * Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR in
29 * the sysfs write functions.
30 */
31static DEFINE_MUTEX(umwait_lock);
32
33static void umwait_update_control_msr(void * unused)
34{
35 lockdep_assert_irqs_disabled();
36 wrmsrq(MSR_IA32_UMWAIT_CONTROL, READ_ONCE(umwait_control_cached));
37}
38
39/*
40 * The CPU hotplug callback sets the control MSR to the global control
41 * value.
42 *
43 * Disable interrupts so the read of umwait_control_cached and the WRMSR
44 * are protected against a concurrent sysfs write. Otherwise the sysfs
45 * write could update the cached value after it had been read on this CPU
46 * and issue the IPI before the old value had been written. The IPI would
47 * interrupt, write the new value and after return from IPI the previous
48 * value would be written by this CPU.
49 *
50 * With interrupts disabled the upcoming CPU either sees the new control
51 * value or the IPI is updating this CPU to the new control value after
52 * interrupts have been reenabled.
53 */
54static int umwait_cpu_online(unsigned int cpu)
55{
56 local_irq_disable();
57 umwait_update_control_msr(NULL);
58 local_irq_enable();
59 return 0;
60}
61
62/*
63 * The CPU hotplug callback sets the control MSR to the original control
64 * value.
65 */
66static int umwait_cpu_offline(unsigned int cpu)
67{
68 /*
69 * This code is protected by the CPU hotplug already and
70 * orig_umwait_control_cached is never changed after it caches
71 * the original control MSR value in umwait_init(). So there
72 * is no race condition here.
73 */
74 wrmsrq(MSR_IA32_UMWAIT_CONTROL, val: orig_umwait_control_cached);
75
76 return 0;
77}
78
79/*
80 * On resume, restore IA32_UMWAIT_CONTROL MSR on the boot processor which
81 * is the only active CPU at this time. The MSR is set up on the APs via the
82 * CPU hotplug callback.
83 *
84 * This function is invoked on resume from suspend and hibernation. On
85 * resume from suspend the restore should be not required, but we neither
86 * trust the firmware nor does it matter if the same value is written
87 * again.
88 */
89static void umwait_syscore_resume(void)
90{
91 umwait_update_control_msr(NULL);
92}
93
94static struct syscore_ops umwait_syscore_ops = {
95 .resume = umwait_syscore_resume,
96};
97
98/* sysfs interface */
99
100/*
101 * When bit 0 in IA32_UMWAIT_CONTROL MSR is 1, C0.2 is disabled.
102 * Otherwise, C0.2 is enabled.
103 */
104static inline bool umwait_ctrl_c02_enabled(u32 ctrl)
105{
106 return !(ctrl & MSR_IA32_UMWAIT_CONTROL_C02_DISABLE);
107}
108
109static inline u32 umwait_ctrl_max_time(u32 ctrl)
110{
111 return ctrl & MSR_IA32_UMWAIT_CONTROL_TIME_MASK;
112}
113
114static inline void umwait_update_control(u32 maxtime, bool c02_enable)
115{
116 u32 ctrl = maxtime & MSR_IA32_UMWAIT_CONTROL_TIME_MASK;
117
118 if (!c02_enable)
119 ctrl |= MSR_IA32_UMWAIT_CONTROL_C02_DISABLE;
120
121 WRITE_ONCE(umwait_control_cached, ctrl);
122 /* Propagate to all CPUs */
123 on_each_cpu(func: umwait_update_control_msr, NULL, wait: 1);
124}
125
126static ssize_t
127enable_c02_show(struct device *dev, struct device_attribute *attr, char *buf)
128{
129 u32 ctrl = READ_ONCE(umwait_control_cached);
130
131 return sprintf(buf, fmt: "%d\n", umwait_ctrl_c02_enabled(ctrl));
132}
133
134static ssize_t enable_c02_store(struct device *dev,
135 struct device_attribute *attr,
136 const char *buf, size_t count)
137{
138 bool c02_enable;
139 u32 ctrl;
140 int ret;
141
142 ret = kstrtobool(s: buf, res: &c02_enable);
143 if (ret)
144 return ret;
145
146 mutex_lock(lock: &umwait_lock);
147
148 ctrl = READ_ONCE(umwait_control_cached);
149 if (c02_enable != umwait_ctrl_c02_enabled(ctrl))
150 umwait_update_control(maxtime: ctrl, c02_enable);
151
152 mutex_unlock(lock: &umwait_lock);
153
154 return count;
155}
156static DEVICE_ATTR_RW(enable_c02);
157
158static ssize_t
159max_time_show(struct device *kobj, struct device_attribute *attr, char *buf)
160{
161 u32 ctrl = READ_ONCE(umwait_control_cached);
162
163 return sprintf(buf, fmt: "%u\n", umwait_ctrl_max_time(ctrl));
164}
165
166static ssize_t max_time_store(struct device *kobj,
167 struct device_attribute *attr,
168 const char *buf, size_t count)
169{
170 u32 max_time, ctrl;
171 int ret;
172
173 ret = kstrtou32(s: buf, base: 0, res: &max_time);
174 if (ret)
175 return ret;
176
177 /* bits[1:0] must be zero */
178 if (max_time & ~MSR_IA32_UMWAIT_CONTROL_TIME_MASK)
179 return -EINVAL;
180
181 mutex_lock(lock: &umwait_lock);
182
183 ctrl = READ_ONCE(umwait_control_cached);
184 if (max_time != umwait_ctrl_max_time(ctrl))
185 umwait_update_control(maxtime: max_time, c02_enable: umwait_ctrl_c02_enabled(ctrl));
186
187 mutex_unlock(lock: &umwait_lock);
188
189 return count;
190}
191static DEVICE_ATTR_RW(max_time);
192
193static struct attribute *umwait_attrs[] = {
194 &dev_attr_enable_c02.attr,
195 &dev_attr_max_time.attr,
196 NULL
197};
198
199static struct attribute_group umwait_attr_group = {
200 .attrs = umwait_attrs,
201 .name = "umwait_control",
202};
203
204static int __init umwait_init(void)
205{
206 struct device *dev;
207 int ret;
208
209 if (!boot_cpu_has(X86_FEATURE_WAITPKG))
210 return -ENODEV;
211
212 /*
213 * Cache the original control MSR value before the control MSR is
214 * changed. This is the only place where orig_umwait_control_cached
215 * is modified.
216 */
217 rdmsrq(MSR_IA32_UMWAIT_CONTROL, orig_umwait_control_cached);
218
219 ret = cpuhp_setup_state(state: CPUHP_AP_ONLINE_DYN, name: "umwait:online",
220 startup: umwait_cpu_online, teardown: umwait_cpu_offline);
221 if (ret < 0) {
222 /*
223 * On failure, the control MSR on all CPUs has the
224 * original control value.
225 */
226 return ret;
227 }
228
229 register_syscore_ops(ops: &umwait_syscore_ops);
230
231 /*
232 * Add umwait control interface. Ignore failure, so at least the
233 * default values are set up in case the machine manages to boot.
234 */
235 dev = bus_get_dev_root(bus: &cpu_subsys);
236 if (dev) {
237 ret = sysfs_create_group(kobj: &dev->kobj, grp: &umwait_attr_group);
238 put_device(dev);
239 }
240 return ret;
241}
242device_initcall(umwait_init);
243