1 /* 2 * Copyright 2013, Michael (Ellerman|Neuling), IBM Corporation. 3 * 4 * This program is free software; you can redistribute it and/or 5 * modify it under the terms of the GNU General Public License 6 * as published by the Free Software Foundation; either version 7 * 2 of the License, or (at your option) any later version. 8 */ 9 10 #define pr_fmt(fmt) "powernv: " fmt 11 12 #include <linux/kernel.h> 13 #include <linux/cpu.h> 14 #include <linux/cpumask.h> 15 #include <linux/device.h> 16 #include <linux/gfp.h> 17 #include <linux/smp.h> 18 #include <linux/stop_machine.h> 19 20 #include <asm/cputhreads.h> 21 #include <asm/kvm_ppc.h> 22 #include <asm/machdep.h> 23 #include <asm/opal.h> 24 #include <asm/smp.h> 25 26 #include "subcore.h" 27 #include "powernv.h" 28 29 30 /* 31 * Split/unsplit procedure: 32 * 33 * A core can be in one of three states, unsplit, 2-way split, and 4-way split. 34 * 35 * The mapping to subcores_per_core is simple: 36 * 37 * State | subcores_per_core 38 * ------------|------------------ 39 * Unsplit | 1 40 * 2-way split | 2 41 * 4-way split | 4 42 * 43 * The core is split along thread boundaries, the mapping between subcores and 44 * threads is as follows: 45 * 46 * Unsplit: 47 * ---------------------------- 48 * Subcore | 0 | 49 * ---------------------------- 50 * Thread | 0 1 2 3 4 5 6 7 | 51 * ---------------------------- 52 * 53 * 2-way split: 54 * ------------------------------------- 55 * Subcore | 0 | 1 | 56 * ------------------------------------- 57 * Thread | 0 1 2 3 | 4 5 6 7 | 58 * ------------------------------------- 59 * 60 * 4-way split: 61 * ----------------------------------------- 62 * Subcore | 0 | 1 | 2 | 3 | 63 * ----------------------------------------- 64 * Thread | 0 1 | 2 3 | 4 5 | 6 7 | 65 * ----------------------------------------- 66 * 67 * 68 * Transitions 69 * ----------- 70 * 71 * It is not possible to transition between either of the split states, the 72 * core must first be unsplit. The legal transitions are: 73 * 74 * ----------- --------------- 75 * | | <----> | 2-way split | 76 * | | --------------- 77 * | Unsplit | 78 * | | --------------- 79 * | | <----> | 4-way split | 80 * ----------- --------------- 81 * 82 * Unsplitting 83 * ----------- 84 * 85 * Unsplitting is the simpler procedure. It requires thread 0 to request the 86 * unsplit while all other threads NAP. 87 * 88 * Thread 0 clears HID0_POWER8_DYNLPARDIS (Dynamic LPAR Disable). This tells 89 * the hardware that if all threads except 0 are napping, the hardware should 90 * unsplit the core. 91 * 92 * Non-zero threads are sent to a NAP loop, they don't exit the loop until they 93 * see the core unsplit. 94 * 95 * Core 0 spins waiting for the hardware to see all the other threads napping 96 * and perform the unsplit. 97 * 98 * Once thread 0 sees the unsplit, it IPIs the secondary threads to wake them 99 * out of NAP. They will then see the core unsplit and exit the NAP loop. 100 * 101 * Splitting 102 * --------- 103 * 104 * The basic splitting procedure is fairly straight forward. However it is 105 * complicated by the fact that after the split occurs, the newly created 106 * subcores are not in a fully initialised state. 107 * 108 * Most notably the subcores do not have the correct value for SDR1, which 109 * means they must not be running in virtual mode when the split occurs. The 110 * subcores have separate timebases SPRs but these are pre-synchronised by 111 * opal. 112 * 113 * To begin with secondary threads are sent to an assembly routine. There they 114 * switch to real mode, so they are immune to the uninitialised SDR1 value. 115 * Once in real mode they indicate that they are in real mode, and spin waiting 116 * to see the core split. 117 * 118 * Thread 0 waits to see that all secondaries are in real mode, and then begins 119 * the splitting procedure. It firstly sets HID0_POWER8_DYNLPARDIS, which 120 * prevents the hardware from unsplitting. Then it sets the appropriate HID bit 121 * to request the split, and spins waiting to see that the split has happened. 122 * 123 * Concurrently the secondaries will notice the split. When they do they set up 124 * their SPRs, notably SDR1, and then they can return to virtual mode and exit 125 * the procedure. 126 */ 127 128 /* Initialised at boot by subcore_init() */ 129 static int subcores_per_core; 130 131 /* 132 * Used to communicate to offline cpus that we want them to pop out of the 133 * offline loop and do a split or unsplit. 134 * 135 * 0 - no split happening 136 * 1 - unsplit in progress 137 * 2 - split to 2 in progress 138 * 4 - split to 4 in progress 139 */ 140 static int new_split_mode; 141 142 static cpumask_var_t cpu_offline_mask; 143 144 struct split_state { 145 u8 step; 146 u8 master; 147 }; 148 149 static DEFINE_PER_CPU(struct split_state, split_state); 150 151 static void wait_for_sync_step(int step) 152 { 153 int i, cpu = smp_processor_id(); 154 155 for (i = cpu + 1; i < cpu + threads_per_core; i++) 156 while(per_cpu(split_state, i).step < step) 157 barrier(); 158 159 /* Order the wait loop vs any subsequent loads/stores. */ 160 mb(); 161 } 162 163 static void unsplit_core(void) 164 { 165 u64 hid0, mask; 166 int i, cpu; 167 168 mask = HID0_POWER8_2LPARMODE | HID0_POWER8_4LPARMODE; 169 170 cpu = smp_processor_id(); 171 if (cpu_thread_in_core(cpu) != 0) { 172 while (mfspr(SPRN_HID0) & mask) 173 power7_nap(0); 174 175 per_cpu(split_state, cpu).step = SYNC_STEP_UNSPLIT; 176 return; 177 } 178 179 hid0 = mfspr(SPRN_HID0); 180 hid0 &= ~HID0_POWER8_DYNLPARDIS; 181 mtspr(SPRN_HID0, hid0); 182 183 while (mfspr(SPRN_HID0) & mask) 184 cpu_relax(); 185 186 /* Wake secondaries out of NAP */ 187 for (i = cpu + 1; i < cpu + threads_per_core; i++) 188 smp_send_reschedule(i); 189 190 wait_for_sync_step(SYNC_STEP_UNSPLIT); 191 } 192 193 static void split_core(int new_mode) 194 { 195 struct { u64 value; u64 mask; } split_parms[2] = { 196 { HID0_POWER8_1TO2LPAR, HID0_POWER8_2LPARMODE }, 197 { HID0_POWER8_1TO4LPAR, HID0_POWER8_4LPARMODE } 198 }; 199 int i, cpu; 200 u64 hid0; 201 202 /* Convert new_mode (2 or 4) into an index into our parms array */ 203 i = (new_mode >> 1) - 1; 204 BUG_ON(i < 0 || i > 1); 205 206 cpu = smp_processor_id(); 207 if (cpu_thread_in_core(cpu) != 0) { 208 split_core_secondary_loop(&per_cpu(split_state, cpu).step); 209 return; 210 } 211 212 wait_for_sync_step(SYNC_STEP_REAL_MODE); 213 214 /* Write new mode */ 215 hid0 = mfspr(SPRN_HID0); 216 hid0 |= HID0_POWER8_DYNLPARDIS | split_parms[i].value; 217 mtspr(SPRN_HID0, hid0); 218 219 /* Wait for it to happen */ 220 while (!(mfspr(SPRN_HID0) & split_parms[i].mask)) 221 cpu_relax(); 222 } 223 224 static void cpu_do_split(int new_mode) 225 { 226 /* 227 * At boot subcores_per_core will be 0, so we will always unsplit at 228 * boot. In the usual case where the core is already unsplit it's a 229 * nop, and this just ensures the kernel's notion of the mode is 230 * consistent with the hardware. 231 */ 232 if (subcores_per_core != 1) 233 unsplit_core(); 234 235 if (new_mode != 1) 236 split_core(new_mode); 237 238 mb(); 239 per_cpu(split_state, smp_processor_id()).step = SYNC_STEP_FINISHED; 240 } 241 242 bool cpu_core_split_required(void) 243 { 244 smp_rmb(); 245 246 if (!new_split_mode) 247 return false; 248 249 cpu_do_split(new_split_mode); 250 251 return true; 252 } 253 254 static int cpu_update_split_mode(void *data) 255 { 256 int cpu, new_mode = *(int *)data; 257 258 if (this_cpu_ptr(&split_state)->master) { 259 new_split_mode = new_mode; 260 smp_wmb(); 261 262 cpumask_andnot(cpu_offline_mask, cpu_present_mask, 263 cpu_online_mask); 264 265 /* This should work even though the cpu is offline */ 266 for_each_cpu(cpu, cpu_offline_mask) 267 smp_send_reschedule(cpu); 268 } 269 270 cpu_do_split(new_mode); 271 272 if (this_cpu_ptr(&split_state)->master) { 273 /* Wait for all cpus to finish before we touch subcores_per_core */ 274 for_each_present_cpu(cpu) { 275 if (cpu >= setup_max_cpus) 276 break; 277 278 while(per_cpu(split_state, cpu).step < SYNC_STEP_FINISHED) 279 barrier(); 280 } 281 282 new_split_mode = 0; 283 284 /* Make the new mode public */ 285 subcores_per_core = new_mode; 286 threads_per_subcore = threads_per_core / subcores_per_core; 287 288 /* Make sure the new mode is written before we exit */ 289 mb(); 290 } 291 292 return 0; 293 } 294 295 static int set_subcores_per_core(int new_mode) 296 { 297 struct split_state *state; 298 int cpu; 299 300 if (kvm_hv_mode_active()) { 301 pr_err("Unable to change split core mode while KVM active.\n"); 302 return -EBUSY; 303 } 304 305 /* 306 * We are only called at boot, or from the sysfs write. If that ever 307 * changes we'll need a lock here. 308 */ 309 BUG_ON(new_mode < 1 || new_mode > 4 || new_mode == 3); 310 311 for_each_present_cpu(cpu) { 312 state = &per_cpu(split_state, cpu); 313 state->step = SYNC_STEP_INITIAL; 314 state->master = 0; 315 } 316 317 get_online_cpus(); 318 319 /* This cpu will update the globals before exiting stop machine */ 320 this_cpu_ptr(&split_state)->master = 1; 321 322 /* Ensure state is consistent before we call the other cpus */ 323 mb(); 324 325 stop_machine(cpu_update_split_mode, &new_mode, cpu_online_mask); 326 327 put_online_cpus(); 328 329 return 0; 330 } 331 332 static ssize_t __used store_subcores_per_core(struct device *dev, 333 struct device_attribute *attr, const char *buf, 334 size_t count) 335 { 336 unsigned long val; 337 int rc; 338 339 /* We are serialised by the attribute lock */ 340 341 rc = sscanf(buf, "%lx", &val); 342 if (rc != 1) 343 return -EINVAL; 344 345 switch (val) { 346 case 1: 347 case 2: 348 case 4: 349 if (subcores_per_core == val) 350 /* Nothing to do */ 351 goto out; 352 break; 353 default: 354 return -EINVAL; 355 } 356 357 rc = set_subcores_per_core(val); 358 if (rc) 359 return rc; 360 361 out: 362 return count; 363 } 364 365 static ssize_t show_subcores_per_core(struct device *dev, 366 struct device_attribute *attr, char *buf) 367 { 368 return sprintf(buf, "%x\n", subcores_per_core); 369 } 370 371 static DEVICE_ATTR(subcores_per_core, 0644, 372 show_subcores_per_core, store_subcores_per_core); 373 374 static int subcore_init(void) 375 { 376 if (!cpu_has_feature(CPU_FTR_ARCH_207S)) 377 return 0; 378 379 /* 380 * We need all threads in a core to be present to split/unsplit so 381 * continue only if max_cpus are aligned to threads_per_core. 382 */ 383 if (setup_max_cpus % threads_per_core) 384 return 0; 385 386 BUG_ON(!alloc_cpumask_var(&cpu_offline_mask, GFP_KERNEL)); 387 388 set_subcores_per_core(1); 389 390 return device_create_file(cpu_subsys.dev_root, 391 &dev_attr_subcores_per_core); 392 } 393 machine_device_initcall(powernv, subcore_init); 394