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(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
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, &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
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, &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(priority, 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(&ready, EVTCHN_FIFO_MAX_QUEUES);
330		consume_one_event(cpu, ctrl, control_block, q, &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