xref: /netbsd-src/sys/kern/subr_pcu.c (revision a536ee5124e62c9a0051a252f7833dc8f50f44c9)
1 /*	$NetBSD: subr_pcu.c,v 1.14 2012/12/31 01:20:05 matt Exp $	*/
2 
3 /*-
4  * Copyright (c) 2011 The NetBSD Foundation, Inc.
5  * All rights reserved.
6  *
7  * This code is derived from software contributed to The NetBSD Foundation
8  * by 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  * Per CPU Unit (PCU) - is an interface to manage synchronization of any
34  * per CPU context (unit) tied with LWP context.  Typical use: FPU state.
35  *
36  * Concurrency notes:
37  *
38  *	PCU state may be loaded only by the current LWP, that is, curlwp.
39  *	Therefore, only LWP itself can set a CPU for lwp_t::l_pcu_cpu[id].
40  *
41  *	Request for a PCU release can be from owner LWP (whether PCU state
42  *	is on current CPU or remote CPU) or any other LWP running on that
43  *	CPU (in such case, owner LWP is on a remote CPU or sleeping).
44  *
45  *	In any case, PCU state can only be changed from the running CPU.
46  *	If said PCU state is on the remote CPU, a cross-call will be sent
47  *	by the owner LWP.  Therefore struct cpu_info::ci_pcu_curlwp[id]
48  *	may only be changed by current CPU, and lwp_t::l_pcu_cpu[id] may
49  *	only be unset by the CPU which has PCU state loaded.
50  *
51  *	There is a race condition: LWP may have a PCU state on a remote CPU,
52  *	which it requests to be released via cross-call.  At the same time,
53  *	other LWP on remote CPU might release existing PCU state and load
54  *	its own one.  Cross-call may arrive after this and release different
55  *	PCU state than intended.  In such case, such LWP would re-load its
56  *	PCU state again.
57  */
58 
59 #include <sys/cdefs.h>
60 __KERNEL_RCSID(0, "$NetBSD: subr_pcu.c,v 1.14 2012/12/31 01:20:05 matt Exp $");
61 
62 #include <sys/param.h>
63 #include <sys/cpu.h>
64 #include <sys/lwp.h>
65 #include <sys/pcu.h>
66 #include <sys/xcall.h>
67 
68 #if PCU_UNIT_COUNT > 0
69 
70 static inline void pcu_do_op(const pcu_ops_t *, lwp_t * const, const int);
71 static void pcu_cpu_op(const pcu_ops_t *, const int);
72 static void pcu_lwp_op(const pcu_ops_t *, lwp_t *, const int);
73 
74 __CTASSERT(PCU_KERNEL == 1);
75 
76 #define	PCU_SAVE	(PCU_LOADED << 1) /* Save PCU state to the LWP. */
77 #define	PCU_RELEASE	(PCU_SAVE << 1)	/* Release PCU state on the CPU. */
78 #define	PCU_CLAIM	(PCU_RELEASE << 1)	/* CLAIM a PCU for a LWP. */
79 
80 /* XXX */
81 extern const pcu_ops_t * const	pcu_ops_md_defs[];
82 
83 /*
84  * pcu_switchpoint: release PCU state if the LWP is being run on another CPU.
85  *
86  * On each context switches, called by mi_switch() with IPL_SCHED.
87  * 'l' is an LWP which is just we switched to.  (the new curlwp)
88  */
89 
90 void
91 pcu_switchpoint(lwp_t *l)
92 {
93 	const uint32_t pcu_kernel_inuse = l->l_pcu_used[PCU_KERNEL];
94 	uint32_t pcu_user_inuse = l->l_pcu_used[PCU_USER];
95 	/* int s; */
96 
97 	KASSERTMSG(l == curlwp, "l %p != curlwp %p", l, curlwp);
98 
99 	if (__predict_false(pcu_kernel_inuse != 0)) {
100 		for (u_int id = 0; id < PCU_UNIT_COUNT; id++) {
101 			if ((pcu_kernel_inuse & (1 << id)) == 0) {
102 				continue;
103 			}
104 			struct cpu_info * const pcu_ci = l->l_pcu_cpu[id];
105 			if (pcu_ci == NULL || pcu_ci == l->l_cpu) {
106 				continue;
107 			}
108 			const pcu_ops_t * const pcu = pcu_ops_md_defs[id];
109 			/*
110 			 * Steal the PCU away from the current owner and
111 			 * take ownership of it.
112 			 */
113 			pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE);
114 			pcu_do_op(pcu, l, PCU_KERNEL | PCU_CLAIM | PCU_RELOAD);
115 			pcu_user_inuse &= ~(1 << id);
116 		}
117 	}
118 
119 	if (__predict_true(pcu_user_inuse == 0)) {
120 		/* PCUs are not in use. */
121 		return;
122 	}
123 	/* commented out as we know we are already at IPL_SCHED */
124 	/* s = splsoftclock(); */
125 	for (u_int id = 0; id < PCU_UNIT_COUNT; id++) {
126 		if ((pcu_user_inuse & (1 << id)) == 0) {
127 			continue;
128 		}
129 		struct cpu_info * const pcu_ci = l->l_pcu_cpu[id];
130 		if (pcu_ci == NULL || pcu_ci == l->l_cpu) {
131 			continue;
132 		}
133 		const pcu_ops_t * const pcu = pcu_ops_md_defs[id];
134 		pcu->pcu_state_release(l, 0);
135 	}
136 	/* splx(s); */
137 }
138 
139 /*
140  * pcu_discard_all: discard PCU state of the given LWP.
141  *
142  * Used by exec and LWP exit.
143  */
144 
145 void
146 pcu_discard_all(lwp_t *l)
147 {
148 	const uint32_t pcu_inuse = l->l_pcu_used[PCU_USER];
149 
150 	KASSERT(l == curlwp || ((l->l_flag & LW_SYSTEM) && pcu_inuse == 0));
151 	KASSERT(l->l_pcu_used[PCU_KERNEL] == 0);
152 
153 	if (__predict_true(pcu_inuse == 0)) {
154 		/* PCUs are not in use. */
155 		return;
156 	}
157 	const int s = splsoftclock();
158 	for (u_int id = 0; id < PCU_UNIT_COUNT; id++) {
159 		if ((pcu_inuse & (1 << id)) == 0) {
160 			continue;
161 		}
162 		if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
163 			continue;
164 		}
165 		const pcu_ops_t * const pcu = pcu_ops_md_defs[id];
166 		/*
167 		 * We aren't releasing since this LWP isn't giving up PCU,
168 		 * just saving it.
169 		 */
170 		pcu_lwp_op(pcu, l, PCU_RELEASE);
171 	}
172 	l->l_pcu_used[PCU_USER] = 0;
173 	splx(s);
174 }
175 
176 /*
177  * pcu_save_all: save PCU state of the given LWP so that eg. coredump can
178  * examine it.
179  */
180 
181 void
182 pcu_save_all(lwp_t *l)
183 {
184 	const uint32_t pcu_inuse = l->l_pcu_used[PCU_USER];
185 	/*
186 	 * Unless LW_WCORE, we aren't releasing since this LWP isn't giving
187 	 * up PCU, just saving it.
188 	 */
189 	const int flags = PCU_SAVE | (l->l_flag & LW_WCORE ? PCU_RELEASE : 0);
190 
191 	/*
192 	 * Normally we save for the current LWP, but sometimes we get called
193 	 * with a different LWP (forking a system LWP or doing a coredump of
194 	 * a process with multiple threads) and we need to deal with that.
195 	 */
196 	KASSERT(l == curlwp
197 	    || (((l->l_flag & LW_SYSTEM)
198 		 || (curlwp->l_proc == l->l_proc && l->l_stat == LSSUSPENDED))
199 	        && pcu_inuse == 0));
200 	KASSERT(l->l_pcu_used[PCU_KERNEL] == 0);
201 
202 	if (__predict_true(pcu_inuse == 0)) {
203 		/* PCUs are not in use. */
204 		return;
205 	}
206 	const int s = splsoftclock();
207 	for (u_int id = 0; id < PCU_UNIT_COUNT; id++) {
208 		if ((pcu_inuse & (1 << id)) == 0) {
209 			continue;
210 		}
211 		if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
212 			continue;
213 		}
214 		const pcu_ops_t * const pcu = pcu_ops_md_defs[id];
215 		pcu_lwp_op(pcu, l, flags);
216 	}
217 	splx(s);
218 }
219 
220 /*
221  * pcu_do_op: save/release PCU state on the current CPU.
222  *
223  * => Must be called at IPL_SOFTCLOCK or from the soft-interrupt.
224  */
225 static inline void
226 pcu_do_op(const pcu_ops_t *pcu, lwp_t * const l, const int flags)
227 {
228 	struct cpu_info * const ci = curcpu();
229 	const u_int id = pcu->pcu_id;
230 	u_int state_flags = flags & (PCU_KERNEL|PCU_RELOAD|PCU_ENABLE);
231 	uint32_t id_mask = 1 << id;
232 	const bool kernel_p = (l->l_pcu_used[PCU_KERNEL] & id_mask) != 0;
233 
234 	KASSERT(l->l_pcu_cpu[id] == (flags & PCU_CLAIM ? NULL : ci));
235 
236 	if (flags & PCU_SAVE) {
237 		pcu->pcu_state_save(l, (kernel_p ? PCU_KERNEL : 0));
238 	}
239 	if (flags & PCU_RELEASE) {
240 		pcu->pcu_state_release(l, state_flags);
241 		if (flags & PCU_KERNEL) {
242 			l->l_pcu_used[PCU_KERNEL] &= ~id_mask;
243 		}
244 		ci->ci_pcu_curlwp[id] = NULL;
245 		l->l_pcu_cpu[id] = NULL;
246 	}
247 	if (flags & PCU_CLAIM) {
248 		if (l->l_pcu_used[(flags & PCU_KERNEL)] & id_mask)
249 			state_flags |= PCU_LOADED;
250 		pcu->pcu_state_load(l, state_flags);
251 		l->l_pcu_cpu[id] = ci;
252 		ci->ci_pcu_curlwp[id] = l;
253 		l->l_pcu_used[flags & PCU_KERNEL] |= id_mask;
254 	}
255 	if (flags == PCU_KERNEL) {
256 		KASSERT(ci->ci_pcu_curlwp[id] == l);
257 		pcu->pcu_state_save(l, 0);
258 		l->l_pcu_used[PCU_KERNEL] |= id_mask;
259 	}
260 }
261 
262 /*
263  * pcu_cpu_op: helper routine to call pcu_do_op() via xcall(9) or
264  * by pcu_load.
265  */
266 static void
267 pcu_cpu_op(const pcu_ops_t *pcu, const int flags)
268 {
269 	const u_int id = pcu->pcu_id;
270 	lwp_t * const l = curcpu()->ci_pcu_curlwp[id];
271 
272 	//KASSERT(cpu_softintr_p());
273 
274 	/* If no state - nothing to do. */
275 	if (l == NULL) {
276 		return;
277 	}
278 	pcu_do_op(pcu, l, flags);
279 }
280 
281 /*
282  * pcu_lwp_op: perform PCU state save, release or both operations on LWP.
283  */
284 static void
285 pcu_lwp_op(const pcu_ops_t *pcu, lwp_t *l, const int flags)
286 {
287 	const u_int id = pcu->pcu_id;
288 	struct cpu_info *ci;
289 	uint64_t where;
290 	int s;
291 
292 	/*
293 	 * Caller should have re-checked if there is any state to manage.
294 	 * Block the interrupts and inspect again, since cross-call sent
295 	 * by remote CPU could have changed the state.
296 	 */
297 	s = splsoftclock();
298 	ci = l->l_pcu_cpu[id];
299 	if (ci == curcpu()) {
300 		/*
301 		 * State is on the current CPU - just perform the operations.
302 		 */
303 		KASSERT((flags & PCU_CLAIM) == 0);
304 		KASSERTMSG(ci->ci_pcu_curlwp[id] == l,
305 		    "%s: cpu%u: pcu_curlwp[%u] (%p) != l (%p)",
306 		     __func__, cpu_index(ci), id, ci->ci_pcu_curlwp[id], l);
307 		pcu_do_op(pcu, l, flags);
308 		splx(s);
309 		return;
310 	}
311 
312 	if (__predict_false(ci == NULL)) {
313 		if (flags & PCU_CLAIM) {
314 			pcu_do_op(pcu, l, flags);
315 		}
316 		/* Cross-call has won the race - no state to manage. */
317 		splx(s);
318 		return;
319 	}
320 
321 	splx(s);
322 
323 	/*
324 	 * State is on the remote CPU - perform the operations there.
325 	 * Note: there is a race condition; see description in the top.
326 	 */
327 	where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op,
328 	    __UNCONST(pcu), (void *)(uintptr_t)flags, ci);
329 	xc_wait(where);
330 
331 	KASSERT((flags & PCU_RELEASE) == 0 || l->l_pcu_cpu[id] == NULL);
332 }
333 
334 /*
335  * pcu_load: load/initialize the PCU state of current LWP on current CPU.
336  */
337 void
338 pcu_load(const pcu_ops_t *pcu)
339 {
340 	const u_int id = pcu->pcu_id;
341 	struct cpu_info *ci, *curci;
342 	lwp_t * const l = curlwp;
343 	uint64_t where;
344 	int s;
345 
346 	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
347 
348 	s = splsoftclock();
349 	curci = curcpu();
350 	ci = l->l_pcu_cpu[id];
351 
352 	/* Does this CPU already have our PCU state loaded? */
353 	if (ci == curci) {
354 		KASSERT(curci->ci_pcu_curlwp[id] == l);
355 		pcu->pcu_state_load(l, PCU_ENABLE);	/* Re-enable */
356 		splx(s);
357 		return;
358 	}
359 
360 	/* If PCU state of this LWP is on the remote CPU - save it there. */
361 	if (ci) {
362 		splx(s);
363 		/* Note: there is a race; see description in the top. */
364 		where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op,
365 		    __UNCONST(pcu), (void *)(PCU_SAVE | PCU_RELEASE), ci);
366 		xc_wait(where);
367 
368 		/* Enter IPL_SOFTCLOCK and re-fetch the current CPU. */
369 		s = splsoftclock();
370 		curci = curcpu();
371 	}
372 	KASSERT(l->l_pcu_cpu[id] == NULL);
373 
374 	/* Save the PCU state on the current CPU, if there is any. */
375 	pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE);
376 	KASSERT(curci->ci_pcu_curlwp[id] == NULL);
377 
378 	/*
379 	 * Finally, load the state for this LWP on this CPU.  Indicate to
380 	 * load function whether PCU was used before.  Note the usage.
381 	 */
382 	pcu_do_op(pcu, l, PCU_CLAIM | PCU_ENABLE | PCU_RELOAD);
383 	splx(s);
384 }
385 
386 /*
387  * pcu_discard: discard the PCU state of current LWP.
388  */
389 void
390 pcu_discard(const pcu_ops_t *pcu)
391 {
392 	const u_int id = pcu->pcu_id;
393 	lwp_t * const l = curlwp;
394 
395 	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
396 
397 	if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
398 		return;
399 	}
400 	pcu_lwp_op(pcu, l, PCU_RELEASE);
401 	l->l_pcu_used[PCU_USER] &= ~(1 << id);
402 }
403 
404 /*
405  * pcu_save_lwp: save PCU state to the given LWP.
406  */
407 void
408 pcu_save(const pcu_ops_t *pcu)
409 {
410 	const u_int id = pcu->pcu_id;
411 	lwp_t * const l = curlwp;
412 
413 	KASSERT(!cpu_intr_p() && !cpu_softintr_p());
414 
415 	if (__predict_true(l->l_pcu_cpu[id] == NULL)) {
416 		return;
417 	}
418 	pcu_lwp_op(pcu, l, PCU_SAVE | PCU_RELEASE);
419 }
420 
421 /*
422  * pcu_used: return true if PCU was used (pcu_load() case) by the LWP.
423  */
424 bool
425 pcu_used_p(const pcu_ops_t *pcu)
426 {
427 	const u_int id = pcu->pcu_id;
428 	lwp_t * const l = curlwp;
429 
430 	return l->l_pcu_used[0] & (1 << id);
431 }
432 
433 void
434 pcu_kernel_acquire(const pcu_ops_t *pcu)
435 {
436 	struct cpu_info * const ci = curcpu();
437 	lwp_t * const l = curlwp;
438 	const u_int id = pcu->pcu_id;
439 
440 	/*
441 	 * If we own the PCU, save our user state.
442 	 */
443 	if (ci == l->l_pcu_cpu[id]) {
444 		pcu_lwp_op(pcu, l, PCU_KERNEL);
445 		return;
446 	}
447 	if (ci->ci_data.cpu_pcu_curlwp[id] != NULL) {
448 		/*
449 		 * The PCU is owned by another LWP so save its state.
450 		 */
451 		pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE);
452 	}
453 	/*
454 	 * Mark the PCU as hijacked and take ownership of it.
455 	 */
456 	pcu_lwp_op(pcu, l, PCU_KERNEL | PCU_CLAIM | PCU_ENABLE | PCU_RELOAD);
457 }
458 
459 void
460 pcu_kernel_release(const pcu_ops_t *pcu)
461 {
462 	lwp_t * const l = curlwp;
463 
464 	KASSERT(l->l_pcu_used[PCU_KERNEL] & (1 << pcu->pcu_id));
465 
466 	/*
467 	 * Release the PCU, if the curlwp wants to use it, it will have incur
468 	 * a trap to reenable it.
469 	 */
470 	pcu_lwp_op(pcu, l, PCU_KERNEL | PCU_RELEASE);
471 }
472 
473 #endif /* PCU_UNIT_COUNT > 0 */
474