| 1 | /* $NetBSD: subr_xcall.c,v 1.19 2016/11/21 00:54:21 ozaki-r Exp $ */ |
| 2 | |
| 3 | /*- |
| 4 | * Copyright (c) 2007-2010 The NetBSD Foundation, Inc. |
| 5 | * All rights reserved. |
| 6 | * |
| 7 | * This code is derived from software contributed to The NetBSD Foundation |
| 8 | * by Andrew Doran and Mindaugas Rasiukevicius. |
| 9 | * |
| 10 | * Redistribution and use in source and binary forms, with or without |
| 11 | * modification, are permitted provided that the following conditions |
| 12 | * are met: |
| 13 | * 1. Redistributions of source code must retain the above copyright |
| 14 | * notice, this list of conditions and the following disclaimer. |
| 15 | * 2. Redistributions in binary form must reproduce the above copyright |
| 16 | * notice, this list of conditions and the following disclaimer in the |
| 17 | * documentation and/or other materials provided with the distribution. |
| 18 | * |
| 19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
| 20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
| 21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| 22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
| 23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 29 | * POSSIBILITY OF SUCH DAMAGE. |
| 30 | */ |
| 31 | |
| 32 | /* |
| 33 | * Cross call support |
| 34 | * |
| 35 | * Background |
| 36 | * |
| 37 | * Sometimes it is necessary to modify hardware state that is tied |
| 38 | * directly to individual CPUs (such as a CPU's local timer), and |
| 39 | * these updates can not be done remotely by another CPU. The LWP |
| 40 | * requesting the update may be unable to guarantee that it will be |
| 41 | * running on the CPU where the update must occur, when the update |
| 42 | * occurs. |
| 43 | * |
| 44 | * Additionally, it's sometimes necessary to modify per-CPU software |
| 45 | * state from a remote CPU. Where these update operations are so |
| 46 | * rare or the access to the per-CPU data so frequent that the cost |
| 47 | * of using locking or atomic operations to provide coherency is |
| 48 | * prohibitive, another way must be found. |
| 49 | * |
| 50 | * Cross calls help to solve these types of problem by allowing |
| 51 | * any CPU in the system to request that an arbitrary function be |
| 52 | * executed on any other CPU. |
| 53 | * |
| 54 | * Implementation |
| 55 | * |
| 56 | * A slow mechanism for making 'low priority' cross calls is |
| 57 | * provided. The function to be executed runs on the remote CPU |
| 58 | * within a bound kthread. No queueing is provided, and the |
| 59 | * implementation uses global state. The function being called may |
| 60 | * block briefly on locks, but in doing so must be careful to not |
| 61 | * interfere with other cross calls in the system. The function is |
| 62 | * called with thread context and not from a soft interrupt, so it |
| 63 | * can ensure that it is not interrupting other code running on the |
| 64 | * CPU, and so has exclusive access to the CPU. Since this facility |
| 65 | * is heavyweight, it's expected that it will not be used often. |
| 66 | * |
| 67 | * Cross calls must not allocate memory, as the pagedaemon uses |
| 68 | * them (and memory allocation may need to wait on the pagedaemon). |
| 69 | * |
| 70 | * A low-overhead mechanism for high priority calls (XC_HIGHPRI) is |
| 71 | * also provided. The function to be executed runs on a software |
| 72 | * interrupt context, at IPL_SOFTSERIAL level, and is expected to |
| 73 | * be very lightweight, e.g. avoid blocking. |
| 74 | */ |
| 75 | |
| 76 | #include <sys/cdefs.h> |
| 77 | __KERNEL_RCSID(0, "$NetBSD: subr_xcall.c,v 1.19 2016/11/21 00:54:21 ozaki-r Exp $" ); |
| 78 | |
| 79 | #include <sys/types.h> |
| 80 | #include <sys/param.h> |
| 81 | #include <sys/xcall.h> |
| 82 | #include <sys/mutex.h> |
| 83 | #include <sys/condvar.h> |
| 84 | #include <sys/evcnt.h> |
| 85 | #include <sys/kthread.h> |
| 86 | #include <sys/cpu.h> |
| 87 | |
| 88 | #ifdef _RUMPKERNEL |
| 89 | #include "rump_private.h" |
| 90 | #endif |
| 91 | |
| 92 | /* Cross-call state box. */ |
| 93 | typedef struct { |
| 94 | kmutex_t xc_lock; |
| 95 | kcondvar_t xc_busy; |
| 96 | xcfunc_t xc_func; |
| 97 | void * xc_arg1; |
| 98 | void * xc_arg2; |
| 99 | uint64_t xc_headp; |
| 100 | uint64_t xc_donep; |
| 101 | } xc_state_t; |
| 102 | |
| 103 | /* Bit indicating high (1) or low (0) priority. */ |
| 104 | #define XC_PRI_BIT (1ULL << 63) |
| 105 | |
| 106 | /* Low priority xcall structures. */ |
| 107 | static xc_state_t xc_low_pri __cacheline_aligned; |
| 108 | |
| 109 | /* High priority xcall structures. */ |
| 110 | static xc_state_t xc_high_pri __cacheline_aligned; |
| 111 | static void * xc_sih __cacheline_aligned; |
| 112 | |
| 113 | /* Event counters. */ |
| 114 | static struct evcnt xc_unicast_ev __cacheline_aligned; |
| 115 | static struct evcnt xc_broadcast_ev __cacheline_aligned; |
| 116 | |
| 117 | static void xc_init(void); |
| 118 | static void xc_thread(void *); |
| 119 | |
| 120 | static inline uint64_t xc_highpri(xcfunc_t, void *, void *, struct cpu_info *); |
| 121 | static inline uint64_t xc_lowpri(xcfunc_t, void *, void *, struct cpu_info *); |
| 122 | |
| 123 | /* |
| 124 | * xc_init: |
| 125 | * |
| 126 | * Initialize low and high priority cross-call structures. |
| 127 | */ |
| 128 | static void |
| 129 | xc_init(void) |
| 130 | { |
| 131 | xc_state_t *xclo = &xc_low_pri, *xchi = &xc_high_pri; |
| 132 | |
| 133 | memset(xclo, 0, sizeof(xc_state_t)); |
| 134 | mutex_init(&xclo->xc_lock, MUTEX_DEFAULT, IPL_NONE); |
| 135 | cv_init(&xclo->xc_busy, "xclocv" ); |
| 136 | |
| 137 | memset(xchi, 0, sizeof(xc_state_t)); |
| 138 | mutex_init(&xchi->xc_lock, MUTEX_DEFAULT, IPL_SOFTSERIAL); |
| 139 | cv_init(&xchi->xc_busy, "xchicv" ); |
| 140 | xc_sih = softint_establish(SOFTINT_SERIAL | SOFTINT_MPSAFE, |
| 141 | xc__highpri_intr, NULL); |
| 142 | KASSERT(xc_sih != NULL); |
| 143 | |
| 144 | evcnt_attach_dynamic(&xc_unicast_ev, EVCNT_TYPE_MISC, NULL, |
| 145 | "crosscall" , "unicast" ); |
| 146 | evcnt_attach_dynamic(&xc_broadcast_ev, EVCNT_TYPE_MISC, NULL, |
| 147 | "crosscall" , "broadcast" ); |
| 148 | } |
| 149 | |
| 150 | /* |
| 151 | * xc_init_cpu: |
| 152 | * |
| 153 | * Initialize the cross-call subsystem. Called once for each CPU |
| 154 | * in the system as they are attached. |
| 155 | */ |
| 156 | void |
| 157 | xc_init_cpu(struct cpu_info *ci) |
| 158 | { |
| 159 | static bool again = false; |
| 160 | int error __diagused; |
| 161 | |
| 162 | if (!again) { |
| 163 | /* Autoconfiguration will prevent re-entry. */ |
| 164 | xc_init(); |
| 165 | again = true; |
| 166 | } |
| 167 | cv_init(&ci->ci_data.cpu_xcall, "xcall" ); |
| 168 | error = kthread_create(PRI_XCALL, KTHREAD_MPSAFE, ci, xc_thread, |
| 169 | NULL, NULL, "xcall/%u" , ci->ci_index); |
| 170 | KASSERT(error == 0); |
| 171 | } |
| 172 | |
| 173 | /* |
| 174 | * xc_broadcast: |
| 175 | * |
| 176 | * Trigger a call on all CPUs in the system. |
| 177 | */ |
| 178 | uint64_t |
| 179 | xc_broadcast(u_int flags, xcfunc_t func, void *arg1, void *arg2) |
| 180 | { |
| 181 | |
| 182 | KASSERT(!cpu_intr_p() && !cpu_softintr_p()); |
| 183 | |
| 184 | if ((flags & XC_HIGHPRI) != 0) { |
| 185 | return xc_highpri(func, arg1, arg2, NULL); |
| 186 | } else { |
| 187 | return xc_lowpri(func, arg1, arg2, NULL); |
| 188 | } |
| 189 | } |
| 190 | |
| 191 | /* |
| 192 | * xc_unicast: |
| 193 | * |
| 194 | * Trigger a call on one CPU. |
| 195 | */ |
| 196 | uint64_t |
| 197 | xc_unicast(u_int flags, xcfunc_t func, void *arg1, void *arg2, |
| 198 | struct cpu_info *ci) |
| 199 | { |
| 200 | |
| 201 | KASSERT(ci != NULL); |
| 202 | KASSERT(!cpu_intr_p() && !cpu_softintr_p()); |
| 203 | |
| 204 | if ((flags & XC_HIGHPRI) != 0) { |
| 205 | return xc_highpri(func, arg1, arg2, ci); |
| 206 | } else { |
| 207 | return xc_lowpri(func, arg1, arg2, ci); |
| 208 | } |
| 209 | } |
| 210 | |
| 211 | /* |
| 212 | * xc_wait: |
| 213 | * |
| 214 | * Wait for a cross call to complete. |
| 215 | */ |
| 216 | void |
| 217 | xc_wait(uint64_t where) |
| 218 | { |
| 219 | xc_state_t *xc; |
| 220 | |
| 221 | KASSERT(!cpu_intr_p() && !cpu_softintr_p()); |
| 222 | |
| 223 | /* Determine whether it is high or low priority cross-call. */ |
| 224 | if ((where & XC_PRI_BIT) != 0) { |
| 225 | xc = &xc_high_pri; |
| 226 | where &= ~XC_PRI_BIT; |
| 227 | } else { |
| 228 | xc = &xc_low_pri; |
| 229 | } |
| 230 | |
| 231 | /* Fast path, if already done. */ |
| 232 | if (xc->xc_donep >= where) { |
| 233 | return; |
| 234 | } |
| 235 | |
| 236 | /* Slow path: block until awoken. */ |
| 237 | mutex_enter(&xc->xc_lock); |
| 238 | while (xc->xc_donep < where) { |
| 239 | cv_wait(&xc->xc_busy, &xc->xc_lock); |
| 240 | } |
| 241 | mutex_exit(&xc->xc_lock); |
| 242 | } |
| 243 | |
| 244 | /* |
| 245 | * xc_lowpri: |
| 246 | * |
| 247 | * Trigger a low priority call on one or more CPUs. |
| 248 | */ |
| 249 | static inline uint64_t |
| 250 | xc_lowpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci) |
| 251 | { |
| 252 | xc_state_t *xc = &xc_low_pri; |
| 253 | CPU_INFO_ITERATOR cii; |
| 254 | uint64_t where; |
| 255 | |
| 256 | mutex_enter(&xc->xc_lock); |
| 257 | while (xc->xc_headp != xc->xc_donep) { |
| 258 | cv_wait(&xc->xc_busy, &xc->xc_lock); |
| 259 | } |
| 260 | xc->xc_arg1 = arg1; |
| 261 | xc->xc_arg2 = arg2; |
| 262 | xc->xc_func = func; |
| 263 | if (ci == NULL) { |
| 264 | xc_broadcast_ev.ev_count++; |
| 265 | for (CPU_INFO_FOREACH(cii, ci)) { |
| 266 | if ((ci->ci_schedstate.spc_flags & SPCF_RUNNING) == 0) |
| 267 | continue; |
| 268 | xc->xc_headp += 1; |
| 269 | ci->ci_data.cpu_xcall_pending = true; |
| 270 | cv_signal(&ci->ci_data.cpu_xcall); |
| 271 | } |
| 272 | } else { |
| 273 | xc_unicast_ev.ev_count++; |
| 274 | xc->xc_headp += 1; |
| 275 | ci->ci_data.cpu_xcall_pending = true; |
| 276 | cv_signal(&ci->ci_data.cpu_xcall); |
| 277 | } |
| 278 | KASSERT(xc->xc_donep < xc->xc_headp); |
| 279 | where = xc->xc_headp; |
| 280 | mutex_exit(&xc->xc_lock); |
| 281 | |
| 282 | /* Return a low priority ticket. */ |
| 283 | KASSERT((where & XC_PRI_BIT) == 0); |
| 284 | return where; |
| 285 | } |
| 286 | |
| 287 | /* |
| 288 | * xc_thread: |
| 289 | * |
| 290 | * One thread per-CPU to dispatch low priority calls. |
| 291 | */ |
| 292 | static void |
| 293 | xc_thread(void *cookie) |
| 294 | { |
| 295 | struct cpu_info *ci = curcpu(); |
| 296 | xc_state_t *xc = &xc_low_pri; |
| 297 | void *arg1, *arg2; |
| 298 | xcfunc_t func; |
| 299 | |
| 300 | mutex_enter(&xc->xc_lock); |
| 301 | for (;;) { |
| 302 | while (!ci->ci_data.cpu_xcall_pending) { |
| 303 | if (xc->xc_headp == xc->xc_donep) { |
| 304 | cv_broadcast(&xc->xc_busy); |
| 305 | } |
| 306 | cv_wait(&ci->ci_data.cpu_xcall, &xc->xc_lock); |
| 307 | KASSERT(ci == curcpu()); |
| 308 | } |
| 309 | ci->ci_data.cpu_xcall_pending = false; |
| 310 | func = xc->xc_func; |
| 311 | arg1 = xc->xc_arg1; |
| 312 | arg2 = xc->xc_arg2; |
| 313 | mutex_exit(&xc->xc_lock); |
| 314 | |
| 315 | KASSERT(func != NULL); |
| 316 | (*func)(arg1, arg2); |
| 317 | |
| 318 | mutex_enter(&xc->xc_lock); |
| 319 | xc->xc_donep++; |
| 320 | } |
| 321 | /* NOTREACHED */ |
| 322 | } |
| 323 | |
| 324 | /* |
| 325 | * xc_ipi_handler: |
| 326 | * |
| 327 | * Handler of cross-call IPI. |
| 328 | */ |
| 329 | void |
| 330 | xc_ipi_handler(void) |
| 331 | { |
| 332 | /* Executes xc__highpri_intr() via software interrupt. */ |
| 333 | softint_schedule(xc_sih); |
| 334 | } |
| 335 | |
| 336 | /* |
| 337 | * xc__highpri_intr: |
| 338 | * |
| 339 | * A software interrupt handler for high priority calls. |
| 340 | */ |
| 341 | void |
| 342 | xc__highpri_intr(void *dummy) |
| 343 | { |
| 344 | xc_state_t *xc = &xc_high_pri; |
| 345 | void *arg1, *arg2; |
| 346 | xcfunc_t func; |
| 347 | |
| 348 | KASSERT(!cpu_intr_p()); |
| 349 | /* |
| 350 | * Lock-less fetch of function and its arguments. |
| 351 | * Safe since it cannot change at this point. |
| 352 | */ |
| 353 | KASSERT(xc->xc_donep < xc->xc_headp); |
| 354 | func = xc->xc_func; |
| 355 | arg1 = xc->xc_arg1; |
| 356 | arg2 = xc->xc_arg2; |
| 357 | |
| 358 | KASSERT(func != NULL); |
| 359 | (*func)(arg1, arg2); |
| 360 | |
| 361 | /* |
| 362 | * Note the request as done, and if we have reached the head, |
| 363 | * cross-call has been processed - notify waiters, if any. |
| 364 | */ |
| 365 | mutex_enter(&xc->xc_lock); |
| 366 | if (++xc->xc_donep == xc->xc_headp) { |
| 367 | cv_broadcast(&xc->xc_busy); |
| 368 | } |
| 369 | mutex_exit(&xc->xc_lock); |
| 370 | } |
| 371 | |
| 372 | /* |
| 373 | * xc_highpri: |
| 374 | * |
| 375 | * Trigger a high priority call on one or more CPUs. |
| 376 | */ |
| 377 | static inline uint64_t |
| 378 | xc_highpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci) |
| 379 | { |
| 380 | xc_state_t *xc = &xc_high_pri; |
| 381 | uint64_t where; |
| 382 | |
| 383 | mutex_enter(&xc->xc_lock); |
| 384 | while (xc->xc_headp != xc->xc_donep) { |
| 385 | cv_wait(&xc->xc_busy, &xc->xc_lock); |
| 386 | } |
| 387 | xc->xc_func = func; |
| 388 | xc->xc_arg1 = arg1; |
| 389 | xc->xc_arg2 = arg2; |
| 390 | xc->xc_headp += (ci ? 1 : ncpu); |
| 391 | where = xc->xc_headp; |
| 392 | mutex_exit(&xc->xc_lock); |
| 393 | |
| 394 | /* |
| 395 | * Send the IPI once lock is released. |
| 396 | * Note: it will handle the local CPU case. |
| 397 | */ |
| 398 | |
| 399 | #ifdef _RUMPKERNEL |
| 400 | rump_xc_highpri(ci); |
| 401 | #else |
| 402 | #ifdef MULTIPROCESSOR |
| 403 | kpreempt_disable(); |
| 404 | if (curcpu() == ci) { |
| 405 | /* Unicast: local CPU. */ |
| 406 | xc_ipi_handler(); |
| 407 | } else if (ci) { |
| 408 | /* Unicast: remote CPU. */ |
| 409 | xc_send_ipi(ci); |
| 410 | } else { |
| 411 | /* Broadcast: all, including local. */ |
| 412 | xc_send_ipi(NULL); |
| 413 | xc_ipi_handler(); |
| 414 | } |
| 415 | kpreempt_enable(); |
| 416 | #else |
| 417 | KASSERT(ci == NULL || curcpu() == ci); |
| 418 | xc_ipi_handler(); |
| 419 | #endif |
| 420 | #endif |
| 421 | |
| 422 | /* Indicate a high priority ticket. */ |
| 423 | return (where | XC_PRI_BIT); |
| 424 | } |
| 425 | |