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1#ifndef _ASM_X86_SPINLOCK_H
2#define _ASM_X86_SPINLOCK_H
3
4#include <linux/jump_label.h>
5#include <linux/atomic.h>
6#include <asm/page.h>
7#include <asm/processor.h>
8#include <linux/compiler.h>
9#include <asm/paravirt.h>
10#include <asm/bitops.h>
11
12/*
13 * Your basic SMP spinlocks, allowing only a single CPU anywhere
14 *
15 * Simple spin lock operations. There are two variants, one clears IRQ's
16 * on the local processor, one does not.
17 *
18 * These are fair FIFO ticket locks, which support up to 2^16 CPUs.
19 *
20 * (the type definitions are in asm/spinlock_types.h)
21 */
22
23#ifdef CONFIG_X86_32
24# define LOCK_PTR_REG "a"
25#else
26# define LOCK_PTR_REG "D"
27#endif
28
29#if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
30/*
31 * On PPro SMP, we use a locked operation to unlock
32 * (PPro errata 66, 92)
33 */
34# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
35#else
36# define UNLOCK_LOCK_PREFIX
37#endif
38
39/* How long a lock should spin before we consider blocking */
40#define SPIN_THRESHOLD (1 << 15)
41
42extern struct static_key paravirt_ticketlocks_enabled;
43static __always_inline bool static_key_false(struct static_key *key);
44
45#ifdef CONFIG_QUEUED_SPINLOCKS
46#include <asm/qspinlock.h>
47#else
48
49#ifdef CONFIG_PARAVIRT_SPINLOCKS
50
51static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
52{
53 set_bit(0, (volatile unsigned long *)&lock->tickets.head);
54}
55
56#else /* !CONFIG_PARAVIRT_SPINLOCKS */
57static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
58 __ticket_t ticket)
59{
60}
61static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
62 __ticket_t ticket)
63{
64}
65
66#endif /* CONFIG_PARAVIRT_SPINLOCKS */
67static inline int __tickets_equal(__ticket_t one, __ticket_t two)
68{
69 return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
70}
71
72static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
73 __ticket_t head)
74{
75 if (head & TICKET_SLOWPATH_FLAG) {
76 arch_spinlock_t old, new;
77
78 old.tickets.head = head;
79 new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
80 old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
81 new.tickets.tail = old.tickets.tail;
82
83 /* try to clear slowpath flag when there are no contenders */
84 cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
85 }
86}
87
88static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
89{
90 return __tickets_equal(lock.tickets.head, lock.tickets.tail);
91}
92
93/*
94 * Ticket locks are conceptually two parts, one indicating the current head of
95 * the queue, and the other indicating the current tail. The lock is acquired
96 * by atomically noting the tail and incrementing it by one (thus adding
97 * ourself to the queue and noting our position), then waiting until the head
98 * becomes equal to the the initial value of the tail.
99 *
100 * We use an xadd covering *both* parts of the lock, to increment the tail and
101 * also load the position of the head, which takes care of memory ordering
102 * issues and should be optimal for the uncontended case. Note the tail must be
103 * in the high part, because a wide xadd increment of the low part would carry
104 * up and contaminate the high part.
105 */
106static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
107{
108 register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
109
110 inc = xadd(&lock->tickets, inc);
111 if (likely(inc.head == inc.tail))
112 goto out;
113
114 for (;;) {
115 unsigned count = SPIN_THRESHOLD;
116
117 do {
118 inc.head = READ_ONCE(lock->tickets.head);
119 if (__tickets_equal(inc.head, inc.tail))
120 goto clear_slowpath;
121 cpu_relax();
122 } while (--count);
123 __ticket_lock_spinning(lock, inc.tail);
124 }
125clear_slowpath:
126 __ticket_check_and_clear_slowpath(lock, inc.head);
127out:
128 barrier(); /* make sure nothing creeps before the lock is taken */
129}
130
131static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
132{
133 arch_spinlock_t old, new;
134
135 old.tickets = READ_ONCE(lock->tickets);
136 if (!__tickets_equal(old.tickets.head, old.tickets.tail))
137 return 0;
138
139 new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
140 new.head_tail &= ~TICKET_SLOWPATH_FLAG;
141
142 /* cmpxchg is a full barrier, so nothing can move before it */
143 return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
144}
145
146static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
147{
148 if (TICKET_SLOWPATH_FLAG &&
149 static_key_false(¶virt_ticketlocks_enabled)) {
150 __ticket_t head;
151
152 BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
153
154 head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
155
156 if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
157 head &= ~TICKET_SLOWPATH_FLAG;
158 __ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
159 }
160 } else
161 __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
162}
163
164static inline int arch_spin_is_locked(arch_spinlock_t *lock)
165{
166 struct __raw_tickets tmp = READ_ONCE(lock->tickets);
167
168 return !__tickets_equal(tmp.tail, tmp.head);
169}
170
171static inline int arch_spin_is_contended(arch_spinlock_t *lock)
172{
173 struct __raw_tickets tmp = READ_ONCE(lock->tickets);
174
175 tmp.head &= ~TICKET_SLOWPATH_FLAG;
176 return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
177}
178#define arch_spin_is_contended arch_spin_is_contended
179
180static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
181 unsigned long flags)
182{
183 arch_spin_lock(lock);
184}
185
186static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
187{
188 __ticket_t head = READ_ONCE(lock->tickets.head);
189
190 for (;;) {
191 struct __raw_tickets tmp = READ_ONCE(lock->tickets);
192 /*
193 * We need to check "unlocked" in a loop, tmp.head == head
194 * can be false positive because of overflow.
195 */
196 if (__tickets_equal(tmp.head, tmp.tail) ||
197 !__tickets_equal(tmp.head, head))
198 break;
199
200 cpu_relax();
201 }
202}
203#endif /* CONFIG_QUEUED_SPINLOCKS */
204
205/*
206 * Read-write spinlocks, allowing multiple readers
207 * but only one writer.
208 *
209 * NOTE! it is quite common to have readers in interrupts
210 * but no interrupt writers. For those circumstances we
211 * can "mix" irq-safe locks - any writer needs to get a
212 * irq-safe write-lock, but readers can get non-irqsafe
213 * read-locks.
214 *
215 * On x86, we implement read-write locks using the generic qrwlock with
216 * x86 specific optimization.
217 */
218
219#include <asm/qrwlock.h>
220
221#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
222#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
223
224#define arch_spin_relax(lock) cpu_relax()
225#define arch_read_relax(lock) cpu_relax()
226#define arch_write_relax(lock) cpu_relax()
227
228#endif /* _ASM_X86_SPINLOCK_H */
1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_X86_SPINLOCK_H
3#define _ASM_X86_SPINLOCK_H
4
5#include <linux/jump_label.h>
6#include <linux/atomic.h>
7#include <asm/page.h>
8#include <asm/processor.h>
9#include <linux/compiler.h>
10#include <asm/paravirt.h>
11#include <asm/bitops.h>
12
13/*
14 * Your basic SMP spinlocks, allowing only a single CPU anywhere
15 *
16 * Simple spin lock operations. There are two variants, one clears IRQ's
17 * on the local processor, one does not.
18 *
19 * These are fair FIFO ticket locks, which support up to 2^16 CPUs.
20 *
21 * (the type definitions are in asm/spinlock_types.h)
22 */
23
24/* How long a lock should spin before we consider blocking */
25#define SPIN_THRESHOLD (1 << 15)
26
27#include <asm/qspinlock.h>
28
29/*
30 * Read-write spinlocks, allowing multiple readers
31 * but only one writer.
32 *
33 * NOTE! it is quite common to have readers in interrupts
34 * but no interrupt writers. For those circumstances we
35 * can "mix" irq-safe locks - any writer needs to get a
36 * irq-safe write-lock, but readers can get non-irqsafe
37 * read-locks.
38 *
39 * On x86, we implement read-write locks using the generic qrwlock with
40 * x86 specific optimization.
41 */
42
43#include <asm/qrwlock.h>
44
45#endif /* _ASM_X86_SPINLOCK_H */