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
60struct evtchn_fifo_queue {
61 uint32_t head[EVTCHN_FIFO_MAX_QUEUES];
62};
63
64static DEFINE_PER_CPU(struct evtchn_fifo_control_block *, cpu_control_block);
65static DEFINE_PER_CPU(struct evtchn_fifo_queue, cpu_queue);
66static event_word_t *event_array[MAX_EVENT_ARRAY_PAGES] __read_mostly;
67static 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
85static 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
92static unsigned evtchn_fifo_max_channels(void)
93{
94 return EVTCHN_FIFO_NR_CHANNELS;
95}
96
97static unsigned evtchn_fifo_nr_channels(void)
98{
99 return event_array_pages * EVENT_WORDS_PER_PAGE;
100}
101
102static 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(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, arg: &init_control);
119}
120
121static 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
133static 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
141static 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, arg: &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(fmt: "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
188static void evtchn_fifo_bind_to_cpu(evtchn_port_t evtchn, unsigned int cpu,
189 unsigned int old_cpu)
190{
191 /* no-op */
192}
193
194static 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
200static 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
206static 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
212static 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
218static 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 */
227static bool clear_masked_cond(volatile event_word_t *word)
228{
229 event_word_t new, old;
230
231 old = *word;
232
233 do {
234 if (!(old & (1 << EVTCHN_FIFO_MASKED)))
235 return true;
236
237 if (old & (1 << EVTCHN_FIFO_PENDING))
238 return false;
239
240 old = old & ~(1 << EVTCHN_FIFO_BUSY);
241 new = old & ~(1 << EVTCHN_FIFO_MASKED);
242 } while (!sync_try_cmpxchg(word, &old, new));
243
244 return true;
245}
246
247static void evtchn_fifo_unmask(evtchn_port_t port)
248{
249 event_word_t *word = event_word_from_port(port);
250
251 BUG_ON(!irqs_disabled());
252
253 if (!clear_masked_cond(word)) {
254 struct evtchn_unmask unmask = { .port = port };
255 (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, arg: &unmask);
256 }
257}
258
259static uint32_t clear_linked(volatile event_word_t *word)
260{
261 event_word_t new, old;
262
263 old = *word;
264
265 do {
266 new = (old & ~((1 << EVTCHN_FIFO_LINKED)
267 | EVTCHN_FIFO_LINK_MASK));
268 } while (!sync_try_cmpxchg(word, &old, new));
269
270 return old & EVTCHN_FIFO_LINK_MASK;
271}
272
273static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl,
274 struct evtchn_fifo_control_block *control_block,
275 unsigned priority, unsigned long *ready)
276{
277 struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
278 uint32_t head;
279 evtchn_port_t port;
280 event_word_t *word;
281
282 head = q->head[priority];
283
284 /*
285 * Reached the tail last time? Read the new HEAD from the
286 * control block.
287 */
288 if (head == 0) {
289 virt_rmb(); /* Ensure word is up-to-date before reading head. */
290 head = control_block->head[priority];
291 }
292
293 port = head;
294 word = event_word_from_port(port);
295 head = clear_linked(word);
296
297 /*
298 * If the link is non-zero, there are more events in the
299 * queue, otherwise the queue is empty.
300 *
301 * If the queue is empty, clear this priority from our local
302 * copy of the ready word.
303 */
304 if (head == 0)
305 clear_bit(nr: priority, addr: ready);
306
307 if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
308 if (unlikely(!ctrl))
309 pr_warn("Dropping pending event for port %u\n", port);
310 else
311 handle_irq_for_port(port, ctrl);
312 }
313
314 q->head[priority] = head;
315}
316
317static void __evtchn_fifo_handle_events(unsigned cpu,
318 struct evtchn_loop_ctrl *ctrl)
319{
320 struct evtchn_fifo_control_block *control_block;
321 unsigned long ready;
322 unsigned q;
323
324 control_block = per_cpu(cpu_control_block, cpu);
325
326 ready = xchg(&control_block->ready, 0);
327
328 while (ready) {
329 q = find_first_bit(addr: &ready, EVTCHN_FIFO_MAX_QUEUES);
330 consume_one_event(cpu, ctrl, control_block, priority: q, ready: &ready);
331 ready |= xchg(&control_block->ready, 0);
332 }
333}
334
335static void evtchn_fifo_handle_events(unsigned cpu,
336 struct evtchn_loop_ctrl *ctrl)
337{
338 __evtchn_fifo_handle_events(cpu, ctrl);
339}
340
341static void evtchn_fifo_resume(void)
342{
343 unsigned cpu;
344
345 for_each_possible_cpu(cpu) {
346 void *control_block = per_cpu(cpu_control_block, cpu);
347 int ret;
348
349 if (!control_block)
350 continue;
351
352 /*
353 * If this CPU is offline, take the opportunity to
354 * free the control block while it is not being
355 * used.
356 */
357 if (!cpu_online(cpu)) {
358 free_page((unsigned long)control_block);
359 per_cpu(cpu_control_block, cpu) = NULL;
360 continue;
361 }
362
363 ret = init_control_block(cpu, control_block);
364 BUG_ON(ret < 0);
365 }
366
367 /*
368 * The event array starts out as empty again and is extended
369 * as normal when events are bound. The existing pages will
370 * be reused.
371 */
372 event_array_pages = 0;
373}
374
375static int evtchn_fifo_alloc_control_block(unsigned cpu)
376{
377 void *control_block = NULL;
378 int ret = -ENOMEM;
379
380 control_block = (void *)__get_free_page(GFP_KERNEL);
381 if (control_block == NULL)
382 goto error;
383
384 ret = init_control_block(cpu, control_block);
385 if (ret < 0)
386 goto error;
387
388 per_cpu(cpu_control_block, cpu) = control_block;
389
390 return 0;
391
392 error:
393 free_page((unsigned long)control_block);
394 return ret;
395}
396
397static int evtchn_fifo_percpu_init(unsigned int cpu)
398{
399 if (!per_cpu(cpu_control_block, cpu))
400 return evtchn_fifo_alloc_control_block(cpu);
401 return 0;
402}
403
404static int evtchn_fifo_percpu_deinit(unsigned int cpu)
405{
406 __evtchn_fifo_handle_events(cpu, NULL);
407 return 0;
408}
409
410static const struct evtchn_ops evtchn_ops_fifo = {
411 .max_channels = evtchn_fifo_max_channels,
412 .nr_channels = evtchn_fifo_nr_channels,
413 .setup = evtchn_fifo_setup,
414 .bind_to_cpu = evtchn_fifo_bind_to_cpu,
415 .clear_pending = evtchn_fifo_clear_pending,
416 .set_pending = evtchn_fifo_set_pending,
417 .is_pending = evtchn_fifo_is_pending,
418 .mask = evtchn_fifo_mask,
419 .unmask = evtchn_fifo_unmask,
420 .handle_events = evtchn_fifo_handle_events,
421 .resume = evtchn_fifo_resume,
422 .percpu_init = evtchn_fifo_percpu_init,
423 .percpu_deinit = evtchn_fifo_percpu_deinit,
424};
425
426int __init xen_evtchn_fifo_init(void)
427{
428 int cpu = smp_processor_id();
429 int ret;
430
431 ret = evtchn_fifo_alloc_control_block(cpu);
432 if (ret < 0)
433 return ret;
434
435 pr_info("Using FIFO-based ABI\n");
436
437 evtchn_ops = &evtchn_ops_fifo;
438
439 return ret;
440}
441

source code of linux/drivers/xen/events/events_fifo.c