1/*
2 * Split spinlock implementation out into its own file, so it can be
3 * compiled in a FTRACE-compatible way.
4 */
5#include <linux/kernel_stat.h>
6#include <linux/spinlock.h>
7#include <linux/debugfs.h>
8#include <linux/log2.h>
9#include <linux/gfp.h>
10#include <linux/slab.h>
11
12#include <asm/paravirt.h>
13
14#include <xen/interface/xen.h>
15#include <xen/events.h>
16
17#include "xen-ops.h"
18#include "debugfs.h"
19
20enum xen_contention_stat {
21	TAKEN_SLOW,
22	TAKEN_SLOW_PICKUP,
23	TAKEN_SLOW_SPURIOUS,
24	RELEASED_SLOW,
25	RELEASED_SLOW_KICKED,
26	NR_CONTENTION_STATS
27};
28
29
30#ifdef CONFIG_XEN_DEBUG_FS
31#define HISTO_BUCKETS	30
32static struct xen_spinlock_stats
33{
34	u32 contention_stats[NR_CONTENTION_STATS];
35	u32 histo_spin_blocked[HISTO_BUCKETS+1];
36	u64 time_blocked;
37} spinlock_stats;
38
39static u8 zero_stats;
40
41static inline void check_zero(void)
42{
43	u8 ret;
44	u8 old = READ_ONCE(zero_stats);
45	if (unlikely(old)) {
46		ret = cmpxchg(&zero_stats, old, 0);
47		/* This ensures only one fellow resets the stat */
48		if (ret == old)
49			memset(&spinlock_stats, 0, sizeof(spinlock_stats));
50	}
51}
52
53static inline void add_stats(enum xen_contention_stat var, u32 val)
54{
55	check_zero();
56	spinlock_stats.contention_stats[var] += val;
57}
58
59static inline u64 spin_time_start(void)
60{
61	return xen_clocksource_read();
62}
63
64static void __spin_time_accum(u64 delta, u32 *array)
65{
66	unsigned index = ilog2(delta);
67
68	check_zero();
69
70	if (index < HISTO_BUCKETS)
71		array[index]++;
72	else
73		array[HISTO_BUCKETS]++;
74}
75
76static inline void spin_time_accum_blocked(u64 start)
77{
78	u32 delta = xen_clocksource_read() - start;
79
80	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
81	spinlock_stats.time_blocked += delta;
82}
83#else  /* !CONFIG_XEN_DEBUG_FS */
84static inline void add_stats(enum xen_contention_stat var, u32 val)
85{
86}
87
88static inline u64 spin_time_start(void)
89{
90	return 0;
91}
92
93static inline void spin_time_accum_blocked(u64 start)
94{
95}
96#endif  /* CONFIG_XEN_DEBUG_FS */
97
98struct xen_lock_waiting {
99	struct arch_spinlock *lock;
100	__ticket_t want;
101};
102
103static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
104static DEFINE_PER_CPU(char *, irq_name);
105static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
106static cpumask_t waiting_cpus;
107
108static bool xen_pvspin = true;
109__visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
110{
111	int irq = __this_cpu_read(lock_kicker_irq);
112	struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
113	int cpu = smp_processor_id();
114	u64 start;
115	__ticket_t head;
116	unsigned long flags;
117
118	/* If kicker interrupts not initialized yet, just spin */
119	if (irq == -1)
120		return;
121
122	start = spin_time_start();
123
124	/*
125	 * Make sure an interrupt handler can't upset things in a
126	 * partially setup state.
127	 */
128	local_irq_save(flags);
129	/*
130	 * We don't really care if we're overwriting some other
131	 * (lock,want) pair, as that would mean that we're currently
132	 * in an interrupt context, and the outer context had
133	 * interrupts enabled.  That has already kicked the VCPU out
134	 * of xen_poll_irq(), so it will just return spuriously and
135	 * retry with newly setup (lock,want).
136	 *
137	 * The ordering protocol on this is that the "lock" pointer
138	 * may only be set non-NULL if the "want" ticket is correct.
139	 * If we're updating "want", we must first clear "lock".
140	 */
141	w->lock = NULL;
142	smp_wmb();
143	w->want = want;
144	smp_wmb();
145	w->lock = lock;
146
147	/* This uses set_bit, which atomic and therefore a barrier */
148	cpumask_set_cpu(cpu, &waiting_cpus);
149	add_stats(TAKEN_SLOW, 1);
150
151	/* clear pending */
152	xen_clear_irq_pending(irq);
153
154	/* Only check lock once pending cleared */
155	barrier();
156
157	/*
158	 * Mark entry to slowpath before doing the pickup test to make
159	 * sure we don't deadlock with an unlocker.
160	 */
161	__ticket_enter_slowpath(lock);
162
163	/* make sure enter_slowpath, which is atomic does not cross the read */
164	smp_mb__after_atomic();
165
166	/*
167	 * check again make sure it didn't become free while
168	 * we weren't looking
169	 */
170	head = READ_ONCE(lock->tickets.head);
171	if (__tickets_equal(head, want)) {
172		add_stats(TAKEN_SLOW_PICKUP, 1);
173		goto out;
174	}
175
176	/* Allow interrupts while blocked */
177	local_irq_restore(flags);
178
179	/*
180	 * If an interrupt happens here, it will leave the wakeup irq
181	 * pending, which will cause xen_poll_irq() to return
182	 * immediately.
183	 */
184
185	/* Block until irq becomes pending (or perhaps a spurious wakeup) */
186	xen_poll_irq(irq);
187	add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
188
189	local_irq_save(flags);
190
191	kstat_incr_irq_this_cpu(irq);
192out:
193	cpumask_clear_cpu(cpu, &waiting_cpus);
194	w->lock = NULL;
195
196	local_irq_restore(flags);
197
198	spin_time_accum_blocked(start);
199}
200PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
201
202static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
203{
204	int cpu;
205
206	add_stats(RELEASED_SLOW, 1);
207
208	for_each_cpu(cpu, &waiting_cpus) {
209		const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
210
211		/* Make sure we read lock before want */
212		if (READ_ONCE(w->lock) == lock &&
213		    READ_ONCE(w->want) == next) {
214			add_stats(RELEASED_SLOW_KICKED, 1);
215			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
216			break;
217		}
218	}
219}
220
221static irqreturn_t dummy_handler(int irq, void *dev_id)
222{
223	BUG();
224	return IRQ_HANDLED;
225}
226
227void xen_init_lock_cpu(int cpu)
228{
229	int irq;
230	char *name;
231
232	if (!xen_pvspin)
233		return;
234
235	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
236	     cpu, per_cpu(lock_kicker_irq, cpu));
237
238	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
239	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
240				     cpu,
241				     dummy_handler,
242				     IRQF_PERCPU|IRQF_NOBALANCING,
243				     name,
244				     NULL);
245
246	if (irq >= 0) {
247		disable_irq(irq); /* make sure it's never delivered */
248		per_cpu(lock_kicker_irq, cpu) = irq;
249		per_cpu(irq_name, cpu) = name;
250	}
251
252	printk("cpu %d spinlock event irq %d\n", cpu, irq);
253}
254
255void xen_uninit_lock_cpu(int cpu)
256{
257	if (!xen_pvspin)
258		return;
259
260	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
261	per_cpu(lock_kicker_irq, cpu) = -1;
262	kfree(per_cpu(irq_name, cpu));
263	per_cpu(irq_name, cpu) = NULL;
264}
265
266
267/*
268 * Our init of PV spinlocks is split in two init functions due to us
269 * using paravirt patching and jump labels patching and having to do
270 * all of this before SMP code is invoked.
271 *
272 * The paravirt patching needs to be done _before_ the alternative asm code
273 * is started, otherwise we would not patch the core kernel code.
274 */
275void __init xen_init_spinlocks(void)
276{
277
278	if (!xen_pvspin) {
279		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
280		return;
281	}
282	printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
283	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
284	pv_lock_ops.unlock_kick = xen_unlock_kick;
285}
286
287/*
288 * While the jump_label init code needs to happend _after_ the jump labels are
289 * enabled and before SMP is started. Hence we use pre-SMP initcall level
290 * init. We cannot do it in xen_init_spinlocks as that is done before
291 * jump labels are activated.
292 */
293static __init int xen_init_spinlocks_jump(void)
294{
295	if (!xen_pvspin)
296		return 0;
297
298	if (!xen_domain())
299		return 0;
300
301	static_key_slow_inc(&paravirt_ticketlocks_enabled);
302	return 0;
303}
304early_initcall(xen_init_spinlocks_jump);
305
306static __init int xen_parse_nopvspin(char *arg)
307{
308	xen_pvspin = false;
309	return 0;
310}
311early_param("xen_nopvspin", xen_parse_nopvspin);
312
313#ifdef CONFIG_XEN_DEBUG_FS
314
315static struct dentry *d_spin_debug;
316
317static int __init xen_spinlock_debugfs(void)
318{
319	struct dentry *d_xen = xen_init_debugfs();
320
321	if (d_xen == NULL)
322		return -ENOMEM;
323
324	if (!xen_pvspin)
325		return 0;
326
327	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
328
329	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
330
331	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
332			   &spinlock_stats.contention_stats[TAKEN_SLOW]);
333	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
334			   &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
335	debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
336			   &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
337
338	debugfs_create_u32("released_slow", 0444, d_spin_debug,
339			   &spinlock_stats.contention_stats[RELEASED_SLOW]);
340	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
341			   &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
342
343	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
344			   &spinlock_stats.time_blocked);
345
346	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
347				spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
348
349	return 0;
350}
351fs_initcall(xen_spinlock_debugfs);
352
353#endif	/* CONFIG_XEN_DEBUG_FS */
354