Merge branch 'overlayfs-next' of git://git.kernel.org/pub/scm/linux/kernel/git/mszere...
[firefly-linux-kernel-4.4.55.git] / arch / x86 / xen / spinlock.c
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
20 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
21 static DEFINE_PER_CPU(char *, irq_name);
22 static bool xen_pvspin = true;
23
24 #ifdef CONFIG_QUEUED_SPINLOCKS
25
26 #include <asm/qspinlock.h>
27
28 static void xen_qlock_kick(int cpu)
29 {
30         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
31 }
32
33 /*
34  * Halt the current CPU & release it back to the host
35  */
36 static void xen_qlock_wait(u8 *byte, u8 val)
37 {
38         int irq = __this_cpu_read(lock_kicker_irq);
39
40         /* If kicker interrupts not initialized yet, just spin */
41         if (irq == -1)
42                 return;
43
44         /* clear pending */
45         xen_clear_irq_pending(irq);
46         barrier();
47
48         /*
49          * We check the byte value after clearing pending IRQ to make sure
50          * that we won't miss a wakeup event because of the clearing.
51          *
52          * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
53          * So it is effectively a memory barrier for x86.
54          */
55         if (READ_ONCE(*byte) != val)
56                 return;
57
58         /*
59          * If an interrupt happens here, it will leave the wakeup irq
60          * pending, which will cause xen_poll_irq() to return
61          * immediately.
62          */
63
64         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
65         xen_poll_irq(irq);
66 }
67
68 #else /* CONFIG_QUEUED_SPINLOCKS */
69
70 enum xen_contention_stat {
71         TAKEN_SLOW,
72         TAKEN_SLOW_PICKUP,
73         TAKEN_SLOW_SPURIOUS,
74         RELEASED_SLOW,
75         RELEASED_SLOW_KICKED,
76         NR_CONTENTION_STATS
77 };
78
79
80 #ifdef CONFIG_XEN_DEBUG_FS
81 #define HISTO_BUCKETS   30
82 static struct xen_spinlock_stats
83 {
84         u32 contention_stats[NR_CONTENTION_STATS];
85         u32 histo_spin_blocked[HISTO_BUCKETS+1];
86         u64 time_blocked;
87 } spinlock_stats;
88
89 static u8 zero_stats;
90
91 static inline void check_zero(void)
92 {
93         u8 ret;
94         u8 old = READ_ONCE(zero_stats);
95         if (unlikely(old)) {
96                 ret = cmpxchg(&zero_stats, old, 0);
97                 /* This ensures only one fellow resets the stat */
98                 if (ret == old)
99                         memset(&spinlock_stats, 0, sizeof(spinlock_stats));
100         }
101 }
102
103 static inline void add_stats(enum xen_contention_stat var, u32 val)
104 {
105         check_zero();
106         spinlock_stats.contention_stats[var] += val;
107 }
108
109 static inline u64 spin_time_start(void)
110 {
111         return xen_clocksource_read();
112 }
113
114 static void __spin_time_accum(u64 delta, u32 *array)
115 {
116         unsigned index = ilog2(delta);
117
118         check_zero();
119
120         if (index < HISTO_BUCKETS)
121                 array[index]++;
122         else
123                 array[HISTO_BUCKETS]++;
124 }
125
126 static inline void spin_time_accum_blocked(u64 start)
127 {
128         u32 delta = xen_clocksource_read() - start;
129
130         __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
131         spinlock_stats.time_blocked += delta;
132 }
133 #else  /* !CONFIG_XEN_DEBUG_FS */
134 static inline void add_stats(enum xen_contention_stat var, u32 val)
135 {
136 }
137
138 static inline u64 spin_time_start(void)
139 {
140         return 0;
141 }
142
143 static inline void spin_time_accum_blocked(u64 start)
144 {
145 }
146 #endif  /* CONFIG_XEN_DEBUG_FS */
147
148 struct xen_lock_waiting {
149         struct arch_spinlock *lock;
150         __ticket_t want;
151 };
152
153 static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
154 static cpumask_t waiting_cpus;
155
156 __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
157 {
158         int irq = __this_cpu_read(lock_kicker_irq);
159         struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
160         int cpu = smp_processor_id();
161         u64 start;
162         __ticket_t head;
163         unsigned long flags;
164
165         /* If kicker interrupts not initialized yet, just spin */
166         if (irq == -1)
167                 return;
168
169         start = spin_time_start();
170
171         /*
172          * Make sure an interrupt handler can't upset things in a
173          * partially setup state.
174          */
175         local_irq_save(flags);
176         /*
177          * We don't really care if we're overwriting some other
178          * (lock,want) pair, as that would mean that we're currently
179          * in an interrupt context, and the outer context had
180          * interrupts enabled.  That has already kicked the VCPU out
181          * of xen_poll_irq(), so it will just return spuriously and
182          * retry with newly setup (lock,want).
183          *
184          * The ordering protocol on this is that the "lock" pointer
185          * may only be set non-NULL if the "want" ticket is correct.
186          * If we're updating "want", we must first clear "lock".
187          */
188         w->lock = NULL;
189         smp_wmb();
190         w->want = want;
191         smp_wmb();
192         w->lock = lock;
193
194         /* This uses set_bit, which atomic and therefore a barrier */
195         cpumask_set_cpu(cpu, &waiting_cpus);
196         add_stats(TAKEN_SLOW, 1);
197
198         /* clear pending */
199         xen_clear_irq_pending(irq);
200
201         /* Only check lock once pending cleared */
202         barrier();
203
204         /*
205          * Mark entry to slowpath before doing the pickup test to make
206          * sure we don't deadlock with an unlocker.
207          */
208         __ticket_enter_slowpath(lock);
209
210         /* make sure enter_slowpath, which is atomic does not cross the read */
211         smp_mb__after_atomic();
212
213         /*
214          * check again make sure it didn't become free while
215          * we weren't looking
216          */
217         head = READ_ONCE(lock->tickets.head);
218         if (__tickets_equal(head, want)) {
219                 add_stats(TAKEN_SLOW_PICKUP, 1);
220                 goto out;
221         }
222
223         /* Allow interrupts while blocked */
224         local_irq_restore(flags);
225
226         /*
227          * If an interrupt happens here, it will leave the wakeup irq
228          * pending, which will cause xen_poll_irq() to return
229          * immediately.
230          */
231
232         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
233         xen_poll_irq(irq);
234         add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
235
236         local_irq_save(flags);
237
238         kstat_incr_irq_this_cpu(irq);
239 out:
240         cpumask_clear_cpu(cpu, &waiting_cpus);
241         w->lock = NULL;
242
243         local_irq_restore(flags);
244
245         spin_time_accum_blocked(start);
246 }
247 PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
248
249 static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
250 {
251         int cpu;
252
253         add_stats(RELEASED_SLOW, 1);
254
255         for_each_cpu(cpu, &waiting_cpus) {
256                 const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
257
258                 /* Make sure we read lock before want */
259                 if (READ_ONCE(w->lock) == lock &&
260                     READ_ONCE(w->want) == next) {
261                         add_stats(RELEASED_SLOW_KICKED, 1);
262                         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
263                         break;
264                 }
265         }
266 }
267 #endif /* CONFIG_QUEUED_SPINLOCKS */
268
269 static irqreturn_t dummy_handler(int irq, void *dev_id)
270 {
271         BUG();
272         return IRQ_HANDLED;
273 }
274
275 void xen_init_lock_cpu(int cpu)
276 {
277         int irq;
278         char *name;
279
280         if (!xen_pvspin)
281                 return;
282
283         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
284              cpu, per_cpu(lock_kicker_irq, cpu));
285
286         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
287         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
288                                      cpu,
289                                      dummy_handler,
290                                      IRQF_PERCPU|IRQF_NOBALANCING,
291                                      name,
292                                      NULL);
293
294         if (irq >= 0) {
295                 disable_irq(irq); /* make sure it's never delivered */
296                 per_cpu(lock_kicker_irq, cpu) = irq;
297                 per_cpu(irq_name, cpu) = name;
298         }
299
300         printk("cpu %d spinlock event irq %d\n", cpu, irq);
301 }
302
303 void xen_uninit_lock_cpu(int cpu)
304 {
305         if (!xen_pvspin)
306                 return;
307
308         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
309         per_cpu(lock_kicker_irq, cpu) = -1;
310         kfree(per_cpu(irq_name, cpu));
311         per_cpu(irq_name, cpu) = NULL;
312 }
313
314
315 /*
316  * Our init of PV spinlocks is split in two init functions due to us
317  * using paravirt patching and jump labels patching and having to do
318  * all of this before SMP code is invoked.
319  *
320  * The paravirt patching needs to be done _before_ the alternative asm code
321  * is started, otherwise we would not patch the core kernel code.
322  */
323 void __init xen_init_spinlocks(void)
324 {
325
326         if (!xen_pvspin) {
327                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
328                 return;
329         }
330         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
331 #ifdef CONFIG_QUEUED_SPINLOCKS
332         __pv_init_lock_hash();
333         pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
334         pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
335         pv_lock_ops.wait = xen_qlock_wait;
336         pv_lock_ops.kick = xen_qlock_kick;
337 #else
338         pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
339         pv_lock_ops.unlock_kick = xen_unlock_kick;
340 #endif
341 }
342
343 /*
344  * While the jump_label init code needs to happend _after_ the jump labels are
345  * enabled and before SMP is started. Hence we use pre-SMP initcall level
346  * init. We cannot do it in xen_init_spinlocks as that is done before
347  * jump labels are activated.
348  */
349 static __init int xen_init_spinlocks_jump(void)
350 {
351         if (!xen_pvspin)
352                 return 0;
353
354         if (!xen_domain())
355                 return 0;
356
357         static_key_slow_inc(&paravirt_ticketlocks_enabled);
358         return 0;
359 }
360 early_initcall(xen_init_spinlocks_jump);
361
362 static __init int xen_parse_nopvspin(char *arg)
363 {
364         xen_pvspin = false;
365         return 0;
366 }
367 early_param("xen_nopvspin", xen_parse_nopvspin);
368
369 #if defined(CONFIG_XEN_DEBUG_FS) && !defined(CONFIG_QUEUED_SPINLOCKS)
370
371 static struct dentry *d_spin_debug;
372
373 static int __init xen_spinlock_debugfs(void)
374 {
375         struct dentry *d_xen = xen_init_debugfs();
376
377         if (d_xen == NULL)
378                 return -ENOMEM;
379
380         if (!xen_pvspin)
381                 return 0;
382
383         d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
384
385         debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
386
387         debugfs_create_u32("taken_slow", 0444, d_spin_debug,
388                            &spinlock_stats.contention_stats[TAKEN_SLOW]);
389         debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
390                            &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
391         debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
392                            &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
393
394         debugfs_create_u32("released_slow", 0444, d_spin_debug,
395                            &spinlock_stats.contention_stats[RELEASED_SLOW]);
396         debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
397                            &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
398
399         debugfs_create_u64("time_blocked", 0444, d_spin_debug,
400                            &spinlock_stats.time_blocked);
401
402         debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
403                                 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
404
405         return 0;
406 }
407 fs_initcall(xen_spinlock_debugfs);
408
409 #endif  /* CONFIG_XEN_DEBUG_FS */