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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Split spinlock implementation out into its own file, so it can be
4 * compiled in a FTRACE-compatible way.
5 */
6#include <linux/kernel.h>
7#include <linux/spinlock.h>
8#include <linux/slab.h>
9#include <linux/atomic.h>
10
11#include <asm/paravirt.h>
12#include <asm/qspinlock.h>
13
14#include <xen/events.h>
15
16#include "xen-ops.h"
17
18static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
19static DEFINE_PER_CPU(char *, irq_name);
20static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
21static bool xen_pvspin = true;
22
23static void xen_qlock_kick(int cpu)
24{
25 int irq = per_cpu(lock_kicker_irq, cpu);
26
27 /* Don't kick if the target's kicker interrupt is not initialized. */
28 if (irq == -1)
29 return;
30
31 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
32}
33
34/*
35 * Halt the current CPU & release it back to the host
36 */
37static void xen_qlock_wait(u8 *byte, u8 val)
38{
39 int irq = __this_cpu_read(lock_kicker_irq);
40 atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
41
42 /* If kicker interrupts not initialized yet, just spin */
43 if (irq == -1 || in_nmi())
44 return;
45
46 /* Detect reentry. */
47 atomic_inc(nest_cnt);
48
49 /* If irq pending already and no nested call clear it. */
50 if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
51 xen_clear_irq_pending(irq);
52 } else if (READ_ONCE(*byte) == val) {
53 /* Block until irq becomes pending (or a spurious wakeup) */
54 xen_poll_irq(irq);
55 }
56
57 atomic_dec(nest_cnt);
58}
59
60static irqreturn_t dummy_handler(int irq, void *dev_id)
61{
62 BUG();
63 return IRQ_HANDLED;
64}
65
66void xen_init_lock_cpu(int cpu)
67{
68 int irq;
69 char *name;
70
71 if (!xen_pvspin)
72 return;
73
74 WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
75 cpu, per_cpu(lock_kicker_irq, cpu));
76
77 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
78 per_cpu(irq_name, cpu) = name;
79 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
80 cpu,
81 dummy_handler,
82 IRQF_PERCPU|IRQF_NOBALANCING,
83 name,
84 NULL);
85
86 if (irq >= 0) {
87 disable_irq(irq); /* make sure it's never delivered */
88 per_cpu(lock_kicker_irq, cpu) = irq;
89 }
90
91 printk("cpu %d spinlock event irq %d\n", cpu, irq);
92}
93
94void xen_uninit_lock_cpu(int cpu)
95{
96 int irq;
97
98 if (!xen_pvspin)
99 return;
100
101 kfree(per_cpu(irq_name, cpu));
102 per_cpu(irq_name, cpu) = NULL;
103 /*
104 * When booting the kernel with 'mitigations=auto,nosmt', the secondary
105 * CPUs are not activated, and lock_kicker_irq is not initialized.
106 */
107 irq = per_cpu(lock_kicker_irq, cpu);
108 if (irq == -1)
109 return;
110
111 unbind_from_irqhandler(irq, NULL);
112 per_cpu(lock_kicker_irq, cpu) = -1;
113}
114
115PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
116
117/*
118 * Our init of PV spinlocks is split in two init functions due to us
119 * using paravirt patching and jump labels patching and having to do
120 * all of this before SMP code is invoked.
121 *
122 * The paravirt patching needs to be done _before_ the alternative asm code
123 * is started, otherwise we would not patch the core kernel code.
124 */
125void __init xen_init_spinlocks(void)
126{
127 /* Don't need to use pvqspinlock code if there is only 1 vCPU. */
128 if (num_possible_cpus() == 1 || nopvspin)
129 xen_pvspin = false;
130
131 if (!xen_pvspin) {
132 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
133 static_branch_disable(&virt_spin_lock_key);
134 return;
135 }
136 printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
137
138 __pv_init_lock_hash();
139 pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
140 pv_ops.lock.queued_spin_unlock =
141 PV_CALLEE_SAVE(__pv_queued_spin_unlock);
142 pv_ops.lock.wait = xen_qlock_wait;
143 pv_ops.lock.kick = xen_qlock_kick;
144 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
145}
146
147static __init int xen_parse_nopvspin(char *arg)
148{
149 pr_notice("\"xen_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
150 xen_pvspin = false;
151 return 0;
152}
153early_param("xen_nopvspin", xen_parse_nopvspin);
154
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
11#include <asm/paravirt.h>
12
13#include <xen/interface/xen.h>
14#include <xen/events.h>
15
16#include "xen-ops.h"
17#include "debugfs.h"
18
19#ifdef CONFIG_XEN_DEBUG_FS
20static struct xen_spinlock_stats
21{
22 u64 taken;
23 u32 taken_slow;
24 u32 taken_slow_nested;
25 u32 taken_slow_pickup;
26 u32 taken_slow_spurious;
27 u32 taken_slow_irqenable;
28
29 u64 released;
30 u32 released_slow;
31 u32 released_slow_kicked;
32
33#define HISTO_BUCKETS 30
34 u32 histo_spin_total[HISTO_BUCKETS+1];
35 u32 histo_spin_spinning[HISTO_BUCKETS+1];
36 u32 histo_spin_blocked[HISTO_BUCKETS+1];
37
38 u64 time_total;
39 u64 time_spinning;
40 u64 time_blocked;
41} spinlock_stats;
42
43static u8 zero_stats;
44
45static unsigned lock_timeout = 1 << 10;
46#define TIMEOUT lock_timeout
47
48static inline void check_zero(void)
49{
50 if (unlikely(zero_stats)) {
51 memset(&spinlock_stats, 0, sizeof(spinlock_stats));
52 zero_stats = 0;
53 }
54}
55
56#define ADD_STATS(elem, val) \
57 do { check_zero(); spinlock_stats.elem += (val); } while(0)
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_spinning(u64 start)
77{
78 u32 delta = xen_clocksource_read() - start;
79
80 __spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
81 spinlock_stats.time_spinning += delta;
82}
83
84static inline void spin_time_accum_total(u64 start)
85{
86 u32 delta = xen_clocksource_read() - start;
87
88 __spin_time_accum(delta, spinlock_stats.histo_spin_total);
89 spinlock_stats.time_total += delta;
90}
91
92static inline void spin_time_accum_blocked(u64 start)
93{
94 u32 delta = xen_clocksource_read() - start;
95
96 __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
97 spinlock_stats.time_blocked += delta;
98}
99#else /* !CONFIG_XEN_DEBUG_FS */
100#define TIMEOUT (1 << 10)
101#define ADD_STATS(elem, val) do { (void)(val); } while(0)
102
103static inline u64 spin_time_start(void)
104{
105 return 0;
106}
107
108static inline void spin_time_accum_total(u64 start)
109{
110}
111static inline void spin_time_accum_spinning(u64 start)
112{
113}
114static inline void spin_time_accum_blocked(u64 start)
115{
116}
117#endif /* CONFIG_XEN_DEBUG_FS */
118
119/*
120 * Size struct xen_spinlock so it's the same as arch_spinlock_t.
121 */
122#if NR_CPUS < 256
123typedef u8 xen_spinners_t;
124# define inc_spinners(xl) \
125 asm(LOCK_PREFIX " incb %0" : "+m" ((xl)->spinners) : : "memory");
126# define dec_spinners(xl) \
127 asm(LOCK_PREFIX " decb %0" : "+m" ((xl)->spinners) : : "memory");
128#else
129typedef u16 xen_spinners_t;
130# define inc_spinners(xl) \
131 asm(LOCK_PREFIX " incw %0" : "+m" ((xl)->spinners) : : "memory");
132# define dec_spinners(xl) \
133 asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : : "memory");
134#endif
135
136struct xen_spinlock {
137 unsigned char lock; /* 0 -> free; 1 -> locked */
138 xen_spinners_t spinners; /* count of waiting cpus */
139};
140
141static int xen_spin_is_locked(struct arch_spinlock *lock)
142{
143 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
144
145 return xl->lock != 0;
146}
147
148static int xen_spin_is_contended(struct arch_spinlock *lock)
149{
150 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
151
152 /* Not strictly true; this is only the count of contended
153 lock-takers entering the slow path. */
154 return xl->spinners != 0;
155}
156
157static int xen_spin_trylock(struct arch_spinlock *lock)
158{
159 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
160 u8 old = 1;
161
162 asm("xchgb %b0,%1"
163 : "+q" (old), "+m" (xl->lock) : : "memory");
164
165 return old == 0;
166}
167
168static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
169static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
170
171/*
172 * Mark a cpu as interested in a lock. Returns the CPU's previous
173 * lock of interest, in case we got preempted by an interrupt.
174 */
175static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
176{
177 struct xen_spinlock *prev;
178
179 prev = __this_cpu_read(lock_spinners);
180 __this_cpu_write(lock_spinners, xl);
181
182 wmb(); /* set lock of interest before count */
183
184 inc_spinners(xl);
185
186 return prev;
187}
188
189/*
190 * Mark a cpu as no longer interested in a lock. Restores previous
191 * lock of interest (NULL for none).
192 */
193static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
194{
195 dec_spinners(xl);
196 wmb(); /* decrement count before restoring lock */
197 __this_cpu_write(lock_spinners, prev);
198}
199
200static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
201{
202 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
203 struct xen_spinlock *prev;
204 int irq = __this_cpu_read(lock_kicker_irq);
205 int ret;
206 u64 start;
207
208 /* If kicker interrupts not initialized yet, just spin */
209 if (irq == -1)
210 return 0;
211
212 start = spin_time_start();
213
214 /* announce we're spinning */
215 prev = spinning_lock(xl);
216
217 ADD_STATS(taken_slow, 1);
218 ADD_STATS(taken_slow_nested, prev != NULL);
219
220 do {
221 unsigned long flags;
222
223 /* clear pending */
224 xen_clear_irq_pending(irq);
225
226 /* check again make sure it didn't become free while
227 we weren't looking */
228 ret = xen_spin_trylock(lock);
229 if (ret) {
230 ADD_STATS(taken_slow_pickup, 1);
231
232 /*
233 * If we interrupted another spinlock while it
234 * was blocking, make sure it doesn't block
235 * without rechecking the lock.
236 */
237 if (prev != NULL)
238 xen_set_irq_pending(irq);
239 goto out;
240 }
241
242 flags = arch_local_save_flags();
243 if (irq_enable) {
244 ADD_STATS(taken_slow_irqenable, 1);
245 raw_local_irq_enable();
246 }
247
248 /*
249 * Block until irq becomes pending. If we're
250 * interrupted at this point (after the trylock but
251 * before entering the block), then the nested lock
252 * handler guarantees that the irq will be left
253 * pending if there's any chance the lock became free;
254 * xen_poll_irq() returns immediately if the irq is
255 * pending.
256 */
257 xen_poll_irq(irq);
258
259 raw_local_irq_restore(flags);
260
261 ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
262 } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
263
264 kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
265
266out:
267 unspinning_lock(xl, prev);
268 spin_time_accum_blocked(start);
269
270 return ret;
271}
272
273static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
274{
275 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
276 unsigned timeout;
277 u8 oldval;
278 u64 start_spin;
279
280 ADD_STATS(taken, 1);
281
282 start_spin = spin_time_start();
283
284 do {
285 u64 start_spin_fast = spin_time_start();
286
287 timeout = TIMEOUT;
288
289 asm("1: xchgb %1,%0\n"
290 " testb %1,%1\n"
291 " jz 3f\n"
292 "2: rep;nop\n"
293 " cmpb $0,%0\n"
294 " je 1b\n"
295 " dec %2\n"
296 " jnz 2b\n"
297 "3:\n"
298 : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
299 : "1" (1)
300 : "memory");
301
302 spin_time_accum_spinning(start_spin_fast);
303
304 } while (unlikely(oldval != 0 &&
305 (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
306
307 spin_time_accum_total(start_spin);
308}
309
310static void xen_spin_lock(struct arch_spinlock *lock)
311{
312 __xen_spin_lock(lock, false);
313}
314
315static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
316{
317 __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
318}
319
320static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
321{
322 int cpu;
323
324 ADD_STATS(released_slow, 1);
325
326 for_each_online_cpu(cpu) {
327 /* XXX should mix up next cpu selection */
328 if (per_cpu(lock_spinners, cpu) == xl) {
329 ADD_STATS(released_slow_kicked, 1);
330 xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
331 break;
332 }
333 }
334}
335
336static void xen_spin_unlock(struct arch_spinlock *lock)
337{
338 struct xen_spinlock *xl = (struct xen_spinlock *)lock;
339
340 ADD_STATS(released, 1);
341
342 smp_wmb(); /* make sure no writes get moved after unlock */
343 xl->lock = 0; /* release lock */
344
345 /*
346 * Make sure unlock happens before checking for waiting
347 * spinners. We need a strong barrier to enforce the
348 * write-read ordering to different memory locations, as the
349 * CPU makes no implied guarantees about their ordering.
350 */
351 mb();
352
353 if (unlikely(xl->spinners))
354 xen_spin_unlock_slow(xl);
355}
356
357static irqreturn_t dummy_handler(int irq, void *dev_id)
358{
359 BUG();
360 return IRQ_HANDLED;
361}
362
363void __cpuinit xen_init_lock_cpu(int cpu)
364{
365 int irq;
366 const char *name;
367
368 name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
369 irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
370 cpu,
371 dummy_handler,
372 IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
373 name,
374 NULL);
375
376 if (irq >= 0) {
377 disable_irq(irq); /* make sure it's never delivered */
378 per_cpu(lock_kicker_irq, cpu) = irq;
379 }
380
381 printk("cpu %d spinlock event irq %d\n", cpu, irq);
382}
383
384void xen_uninit_lock_cpu(int cpu)
385{
386 unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
387}
388
389void __init xen_init_spinlocks(void)
390{
391 BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
392
393 pv_lock_ops.spin_is_locked = xen_spin_is_locked;
394 pv_lock_ops.spin_is_contended = xen_spin_is_contended;
395 pv_lock_ops.spin_lock = xen_spin_lock;
396 pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
397 pv_lock_ops.spin_trylock = xen_spin_trylock;
398 pv_lock_ops.spin_unlock = xen_spin_unlock;
399}
400
401#ifdef CONFIG_XEN_DEBUG_FS
402
403static struct dentry *d_spin_debug;
404
405static int __init xen_spinlock_debugfs(void)
406{
407 struct dentry *d_xen = xen_init_debugfs();
408
409 if (d_xen == NULL)
410 return -ENOMEM;
411
412 d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
413
414 debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
415
416 debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
417
418 debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
419 debugfs_create_u32("taken_slow", 0444, d_spin_debug,
420 &spinlock_stats.taken_slow);
421 debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
422 &spinlock_stats.taken_slow_nested);
423 debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
424 &spinlock_stats.taken_slow_pickup);
425 debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
426 &spinlock_stats.taken_slow_spurious);
427 debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
428 &spinlock_stats.taken_slow_irqenable);
429
430 debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
431 debugfs_create_u32("released_slow", 0444, d_spin_debug,
432 &spinlock_stats.released_slow);
433 debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
434 &spinlock_stats.released_slow_kicked);
435
436 debugfs_create_u64("time_spinning", 0444, d_spin_debug,
437 &spinlock_stats.time_spinning);
438 debugfs_create_u64("time_blocked", 0444, d_spin_debug,
439 &spinlock_stats.time_blocked);
440 debugfs_create_u64("time_total", 0444, d_spin_debug,
441 &spinlock_stats.time_total);
442
443 debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
444 spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
445 debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
446 spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
447 debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
448 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
449
450 return 0;
451}
452fs_initcall(xen_spinlock_debugfs);
453
454#endif /* CONFIG_XEN_DEBUG_FS */