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 */ 19 static 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 */ 25 static 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 */ 31 static DEFINE_MUTEX(umwait_lock); 32 33 static void umwait_update_control_msr(void * unused) 34 { 35 lockdep_assert_irqs_disabled(); 36 wrmsr(MSR_IA32_UMWAIT_CONTROL, READ_ONCE(umwait_control_cached), 0); 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 */ 54 static 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 */ 66 static 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 wrmsr(MSR_IA32_UMWAIT_CONTROL, orig_umwait_control_cached, 0); 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 */ 89 static void umwait_syscore_resume(void) 90 { 91 umwait_update_control_msr(NULL); 92 } 93 94 static 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 */ 104 static inline bool umwait_ctrl_c02_enabled(u32 ctrl) 105 { 106 return !(ctrl & MSR_IA32_UMWAIT_CONTROL_C02_DISABLE); 107 } 108 109 static inline u32 umwait_ctrl_max_time(u32 ctrl) 110 { 111 return ctrl & MSR_IA32_UMWAIT_CONTROL_TIME_MASK; 112 } 113 114 static 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(umwait_update_control_msr, NULL, 1); 124 } 125 126 static ssize_t 127 enable_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, "%d\n", umwait_ctrl_c02_enabled(ctrl)); 132 } 133 134 static 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(buf, &c02_enable); 143 if (ret) 144 return ret; 145 146 mutex_lock(&umwait_lock); 147 148 ctrl = READ_ONCE(umwait_control_cached); 149 if (c02_enable != umwait_ctrl_c02_enabled(ctrl)) 150 umwait_update_control(ctrl, c02_enable); 151 152 mutex_unlock(&umwait_lock); 153 154 return count; 155 } 156 static DEVICE_ATTR_RW(enable_c02); 157 158 static ssize_t 159 max_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, "%u\n", umwait_ctrl_max_time(ctrl)); 164 } 165 166 static 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(buf, 0, &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(&umwait_lock); 182 183 ctrl = READ_ONCE(umwait_control_cached); 184 if (max_time != umwait_ctrl_max_time(ctrl)) 185 umwait_update_control(max_time, umwait_ctrl_c02_enabled(ctrl)); 186 187 mutex_unlock(&umwait_lock); 188 189 return count; 190 } 191 static DEVICE_ATTR_RW(max_time); 192 193 static struct attribute *umwait_attrs[] = { 194 &dev_attr_enable_c02.attr, 195 &dev_attr_max_time.attr, 196 NULL 197 }; 198 199 static struct attribute_group umwait_attr_group = { 200 .attrs = umwait_attrs, 201 .name = "umwait_control", 202 }; 203 204 static 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 rdmsrl(MSR_IA32_UMWAIT_CONTROL, orig_umwait_control_cached); 218 219 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "umwait:online", 220 umwait_cpu_online, 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(&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(&cpu_subsys); 236 if (dev) { 237 ret = sysfs_create_group(&dev->kobj, &umwait_attr_group); 238 put_device(dev); 239 } 240 return ret; 241 } 242 device_initcall(umwait_init); 243