1 /*
2  * Xen event channels (FIFO-based ABI)
3  *
4  * Copyright (C) 2013 Citrix Systems R&D ltd.
5  *
6  * This source code is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License as
8  * published by the Free Software Foundation; either version 2 of the
9  * License, or (at your option) any later version.
10  *
11  * Or, when distributed separately from the Linux kernel or
12  * incorporated into other software packages, subject to the following
13  * license:
14  *
15  * Permission is hereby granted, free of charge, to any person obtaining a copy
16  * of this source file (the "Software"), to deal in the Software without
17  * restriction, including without limitation the rights to use, copy, modify,
18  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
19  * and to permit persons to whom the Software is furnished to do so, subject to
20  * the following conditions:
21  *
22  * The above copyright notice and this permission notice shall be included in
23  * all copies or substantial portions of the Software.
24  *
25  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
26  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
27  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
28  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
29  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
30  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
31  * IN THE SOFTWARE.
32  */
33 
34 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
35 
36 #include <linux/linkage.h>
37 #include <linux/interrupt.h>
38 #include <linux/irq.h>
39 #include <linux/smp.h>
40 #include <linux/percpu.h>
41 #include <linux/cpu.h>
42 
43 #include <asm/barrier.h>
44 #include <asm/sync_bitops.h>
45 #include <asm/xen/hypercall.h>
46 #include <asm/xen/hypervisor.h>
47 
48 #include <xen/xen.h>
49 #include <xen/xen-ops.h>
50 #include <xen/events.h>
51 #include <xen/interface/xen.h>
52 #include <xen/interface/event_channel.h>
53 #include <xen/page.h>
54 
55 #include "events_internal.h"
56 
57 #define EVENT_WORDS_PER_PAGE (XEN_PAGE_SIZE / sizeof(event_word_t))
58 #define MAX_EVENT_ARRAY_PAGES (EVTCHN_FIFO_NR_CHANNELS / EVENT_WORDS_PER_PAGE)
59 
60 struct evtchn_fifo_queue {
61 	uint32_t head[EVTCHN_FIFO_MAX_QUEUES];
62 };
63 
64 static DEFINE_PER_CPU(struct evtchn_fifo_control_block *, cpu_control_block);
65 static DEFINE_PER_CPU(struct evtchn_fifo_queue, cpu_queue);
66 static event_word_t *event_array[MAX_EVENT_ARRAY_PAGES] __read_mostly;
67 static unsigned event_array_pages __read_mostly;
68 
69 /*
70  * sync_set_bit() and friends must be unsigned long aligned.
71  */
72 #if BITS_PER_LONG > 32
73 
74 #define BM(w) (unsigned long *)((unsigned long)w & ~0x7UL)
75 #define EVTCHN_FIFO_BIT(b, w) \
76     (((unsigned long)w & 0x4UL) ? (EVTCHN_FIFO_ ##b + 32) : EVTCHN_FIFO_ ##b)
77 
78 #else
79 
80 #define BM(w) ((unsigned long *)(w))
81 #define EVTCHN_FIFO_BIT(b, w) EVTCHN_FIFO_ ##b
82 
83 #endif
84 
event_word_from_port(evtchn_port_t port)85 static inline event_word_t *event_word_from_port(evtchn_port_t port)
86 {
87 	unsigned i = port / EVENT_WORDS_PER_PAGE;
88 
89 	return event_array[i] + port % EVENT_WORDS_PER_PAGE;
90 }
91 
evtchn_fifo_max_channels(void)92 static unsigned evtchn_fifo_max_channels(void)
93 {
94 	return EVTCHN_FIFO_NR_CHANNELS;
95 }
96 
evtchn_fifo_nr_channels(void)97 static unsigned evtchn_fifo_nr_channels(void)
98 {
99 	return event_array_pages * EVENT_WORDS_PER_PAGE;
100 }
101 
init_control_block(int cpu,struct evtchn_fifo_control_block * control_block)102 static int init_control_block(int cpu,
103                               struct evtchn_fifo_control_block *control_block)
104 {
105 	struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
106 	struct evtchn_init_control init_control;
107 	unsigned int i;
108 
109 	/* Reset the control block and the local HEADs. */
110 	clear_page(control_block);
111 	for (i = 0; i < EVTCHN_FIFO_MAX_QUEUES; i++)
112 		q->head[i] = 0;
113 
114 	init_control.control_gfn = virt_to_gfn(control_block);
115 	init_control.offset      = 0;
116 	init_control.vcpu        = xen_vcpu_nr(cpu);
117 
118 	return HYPERVISOR_event_channel_op(EVTCHNOP_init_control, &init_control);
119 }
120 
free_unused_array_pages(void)121 static void free_unused_array_pages(void)
122 {
123 	unsigned i;
124 
125 	for (i = event_array_pages; i < MAX_EVENT_ARRAY_PAGES; i++) {
126 		if (!event_array[i])
127 			break;
128 		free_page((unsigned long)event_array[i]);
129 		event_array[i] = NULL;
130 	}
131 }
132 
init_array_page(event_word_t * array_page)133 static void init_array_page(event_word_t *array_page)
134 {
135 	unsigned i;
136 
137 	for (i = 0; i < EVENT_WORDS_PER_PAGE; i++)
138 		array_page[i] = 1 << EVTCHN_FIFO_MASKED;
139 }
140 
evtchn_fifo_setup(evtchn_port_t port)141 static int evtchn_fifo_setup(evtchn_port_t port)
142 {
143 	unsigned new_array_pages;
144 	int ret;
145 
146 	new_array_pages = port / EVENT_WORDS_PER_PAGE + 1;
147 
148 	if (new_array_pages > MAX_EVENT_ARRAY_PAGES)
149 		return -EINVAL;
150 
151 	while (event_array_pages < new_array_pages) {
152 		void *array_page;
153 		struct evtchn_expand_array expand_array;
154 
155 		/* Might already have a page if we've resumed. */
156 		array_page = event_array[event_array_pages];
157 		if (!array_page) {
158 			array_page = (void *)__get_free_page(GFP_KERNEL);
159 			if (array_page == NULL) {
160 				ret = -ENOMEM;
161 				goto error;
162 			}
163 			event_array[event_array_pages] = array_page;
164 		}
165 
166 		/* Mask all events in this page before adding it. */
167 		init_array_page(array_page);
168 
169 		expand_array.array_gfn = virt_to_gfn(array_page);
170 
171 		ret = HYPERVISOR_event_channel_op(EVTCHNOP_expand_array, &expand_array);
172 		if (ret < 0)
173 			goto error;
174 
175 		event_array_pages++;
176 	}
177 	return 0;
178 
179   error:
180 	if (event_array_pages == 0)
181 		panic("xen: unable to expand event array with initial page (%d)\n", ret);
182 	else
183 		pr_err("unable to expand event array (%d)\n", ret);
184 	free_unused_array_pages();
185 	return ret;
186 }
187 
evtchn_fifo_bind_to_cpu(evtchn_port_t evtchn,unsigned int cpu,unsigned int old_cpu)188 static void evtchn_fifo_bind_to_cpu(evtchn_port_t evtchn, unsigned int cpu,
189 				    unsigned int old_cpu)
190 {
191 	/* no-op */
192 }
193 
evtchn_fifo_clear_pending(evtchn_port_t port)194 static void evtchn_fifo_clear_pending(evtchn_port_t port)
195 {
196 	event_word_t *word = event_word_from_port(port);
197 	sync_clear_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
198 }
199 
evtchn_fifo_set_pending(evtchn_port_t port)200 static void evtchn_fifo_set_pending(evtchn_port_t port)
201 {
202 	event_word_t *word = event_word_from_port(port);
203 	sync_set_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
204 }
205 
evtchn_fifo_is_pending(evtchn_port_t port)206 static bool evtchn_fifo_is_pending(evtchn_port_t port)
207 {
208 	event_word_t *word = event_word_from_port(port);
209 	return sync_test_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
210 }
211 
evtchn_fifo_mask(evtchn_port_t port)212 static void evtchn_fifo_mask(evtchn_port_t port)
213 {
214 	event_word_t *word = event_word_from_port(port);
215 	sync_set_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
216 }
217 
evtchn_fifo_is_masked(evtchn_port_t port)218 static bool evtchn_fifo_is_masked(evtchn_port_t port)
219 {
220 	event_word_t *word = event_word_from_port(port);
221 	return sync_test_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
222 }
223 /*
224  * Clear MASKED if not PENDING, spinning if BUSY is set.
225  * Return true if mask was cleared.
226  */
clear_masked_cond(volatile event_word_t * word)227 static bool clear_masked_cond(volatile event_word_t *word)
228 {
229 	event_word_t new, old, w;
230 
231 	w = *word;
232 
233 	do {
234 		if (!(w & (1 << EVTCHN_FIFO_MASKED)))
235 			return true;
236 
237 		if (w & (1 << EVTCHN_FIFO_PENDING))
238 			return false;
239 
240 		old = w & ~(1 << EVTCHN_FIFO_BUSY);
241 		new = old & ~(1 << EVTCHN_FIFO_MASKED);
242 		w = sync_cmpxchg(word, old, new);
243 	} while (w != old);
244 
245 	return true;
246 }
247 
evtchn_fifo_unmask(evtchn_port_t port)248 static void evtchn_fifo_unmask(evtchn_port_t port)
249 {
250 	event_word_t *word = event_word_from_port(port);
251 
252 	BUG_ON(!irqs_disabled());
253 
254 	if (!clear_masked_cond(word)) {
255 		struct evtchn_unmask unmask = { .port = port };
256 		(void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
257 	}
258 }
259 
clear_linked(volatile event_word_t * word)260 static uint32_t clear_linked(volatile event_word_t *word)
261 {
262 	event_word_t new, old, w;
263 
264 	w = *word;
265 
266 	do {
267 		old = w;
268 		new = (w & ~((1 << EVTCHN_FIFO_LINKED)
269 			     | EVTCHN_FIFO_LINK_MASK));
270 	} while ((w = sync_cmpxchg(word, old, new)) != old);
271 
272 	return w & EVTCHN_FIFO_LINK_MASK;
273 }
274 
consume_one_event(unsigned cpu,struct evtchn_loop_ctrl * ctrl,struct evtchn_fifo_control_block * control_block,unsigned priority,unsigned long * ready)275 static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl,
276 			      struct evtchn_fifo_control_block *control_block,
277 			      unsigned priority, unsigned long *ready)
278 {
279 	struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
280 	uint32_t head;
281 	evtchn_port_t port;
282 	event_word_t *word;
283 
284 	head = q->head[priority];
285 
286 	/*
287 	 * Reached the tail last time?  Read the new HEAD from the
288 	 * control block.
289 	 */
290 	if (head == 0) {
291 		virt_rmb(); /* Ensure word is up-to-date before reading head. */
292 		head = control_block->head[priority];
293 	}
294 
295 	port = head;
296 	word = event_word_from_port(port);
297 	head = clear_linked(word);
298 
299 	/*
300 	 * If the link is non-zero, there are more events in the
301 	 * queue, otherwise the queue is empty.
302 	 *
303 	 * If the queue is empty, clear this priority from our local
304 	 * copy of the ready word.
305 	 */
306 	if (head == 0)
307 		clear_bit(priority, ready);
308 
309 	if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
310 		if (unlikely(!ctrl))
311 			pr_warn("Dropping pending event for port %u\n", port);
312 		else
313 			handle_irq_for_port(port, ctrl);
314 	}
315 
316 	q->head[priority] = head;
317 }
318 
__evtchn_fifo_handle_events(unsigned cpu,struct evtchn_loop_ctrl * ctrl)319 static void __evtchn_fifo_handle_events(unsigned cpu,
320 					struct evtchn_loop_ctrl *ctrl)
321 {
322 	struct evtchn_fifo_control_block *control_block;
323 	unsigned long ready;
324 	unsigned q;
325 
326 	control_block = per_cpu(cpu_control_block, cpu);
327 
328 	ready = xchg(&control_block->ready, 0);
329 
330 	while (ready) {
331 		q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
332 		consume_one_event(cpu, ctrl, control_block, q, &ready);
333 		ready |= xchg(&control_block->ready, 0);
334 	}
335 }
336 
evtchn_fifo_handle_events(unsigned cpu,struct evtchn_loop_ctrl * ctrl)337 static void evtchn_fifo_handle_events(unsigned cpu,
338 				      struct evtchn_loop_ctrl *ctrl)
339 {
340 	__evtchn_fifo_handle_events(cpu, ctrl);
341 }
342 
evtchn_fifo_resume(void)343 static void evtchn_fifo_resume(void)
344 {
345 	unsigned cpu;
346 
347 	for_each_possible_cpu(cpu) {
348 		void *control_block = per_cpu(cpu_control_block, cpu);
349 		int ret;
350 
351 		if (!control_block)
352 			continue;
353 
354 		/*
355 		 * If this CPU is offline, take the opportunity to
356 		 * free the control block while it is not being
357 		 * used.
358 		 */
359 		if (!cpu_online(cpu)) {
360 			free_page((unsigned long)control_block);
361 			per_cpu(cpu_control_block, cpu) = NULL;
362 			continue;
363 		}
364 
365 		ret = init_control_block(cpu, control_block);
366 		BUG_ON(ret < 0);
367 	}
368 
369 	/*
370 	 * The event array starts out as empty again and is extended
371 	 * as normal when events are bound.  The existing pages will
372 	 * be reused.
373 	 */
374 	event_array_pages = 0;
375 }
376 
evtchn_fifo_alloc_control_block(unsigned cpu)377 static int evtchn_fifo_alloc_control_block(unsigned cpu)
378 {
379 	void *control_block = NULL;
380 	int ret = -ENOMEM;
381 
382 	control_block = (void *)__get_free_page(GFP_KERNEL);
383 	if (control_block == NULL)
384 		goto error;
385 
386 	ret = init_control_block(cpu, control_block);
387 	if (ret < 0)
388 		goto error;
389 
390 	per_cpu(cpu_control_block, cpu) = control_block;
391 
392 	return 0;
393 
394   error:
395 	free_page((unsigned long)control_block);
396 	return ret;
397 }
398 
evtchn_fifo_percpu_init(unsigned int cpu)399 static int evtchn_fifo_percpu_init(unsigned int cpu)
400 {
401 	if (!per_cpu(cpu_control_block, cpu))
402 		return evtchn_fifo_alloc_control_block(cpu);
403 	return 0;
404 }
405 
evtchn_fifo_percpu_deinit(unsigned int cpu)406 static int evtchn_fifo_percpu_deinit(unsigned int cpu)
407 {
408 	__evtchn_fifo_handle_events(cpu, NULL);
409 	return 0;
410 }
411 
412 static const struct evtchn_ops evtchn_ops_fifo = {
413 	.max_channels      = evtchn_fifo_max_channels,
414 	.nr_channels       = evtchn_fifo_nr_channels,
415 	.setup             = evtchn_fifo_setup,
416 	.bind_to_cpu       = evtchn_fifo_bind_to_cpu,
417 	.clear_pending     = evtchn_fifo_clear_pending,
418 	.set_pending       = evtchn_fifo_set_pending,
419 	.is_pending        = evtchn_fifo_is_pending,
420 	.mask              = evtchn_fifo_mask,
421 	.unmask            = evtchn_fifo_unmask,
422 	.handle_events     = evtchn_fifo_handle_events,
423 	.resume            = evtchn_fifo_resume,
424 	.percpu_init       = evtchn_fifo_percpu_init,
425 	.percpu_deinit     = evtchn_fifo_percpu_deinit,
426 };
427 
xen_evtchn_fifo_init(void)428 int __init xen_evtchn_fifo_init(void)
429 {
430 	int cpu = smp_processor_id();
431 	int ret;
432 
433 	ret = evtchn_fifo_alloc_control_block(cpu);
434 	if (ret < 0)
435 		return ret;
436 
437 	pr_info("Using FIFO-based ABI\n");
438 
439 	evtchn_ops = &evtchn_ops_fifo;
440 
441 	return ret;
442 }
443