1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef __ASM_PREEMPT_H
3#define __ASM_PREEMPT_H
4
5#include <asm/rmwcc.h>
6#include <asm/percpu.h>
7#include <asm/current.h>
8
9#include <linux/static_call_types.h>
10
11/* We use the MSB mostly because its available */
12#define PREEMPT_NEED_RESCHED	0x80000000
13
14/*
15 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
16 * that a decrement hitting 0 means we can and should reschedule.
17 */
18#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)
19
20/*
21 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
22 * that think a non-zero value indicates we cannot preempt.
23 */
24static __always_inline int preempt_count(void)
25{
26	return raw_cpu_read_4(pcpu_hot.preempt_count) & ~PREEMPT_NEED_RESCHED;
27}
28
29static __always_inline void preempt_count_set(int pc)
30{
31	int old, new;
32
33	old = raw_cpu_read_4(pcpu_hot.preempt_count);
34	do {
35		new = (old & PREEMPT_NEED_RESCHED) |
36			(pc & ~PREEMPT_NEED_RESCHED);
37	} while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new));
38}
39
40/*
41 * must be macros to avoid header recursion hell
42 */
43#define init_task_preempt_count(p) do { } while (0)
44
45#define init_idle_preempt_count(p, cpu) do { \
46	per_cpu(pcpu_hot.preempt_count, (cpu)) = PREEMPT_DISABLED; \
47} while (0)
48
49/*
50 * We fold the NEED_RESCHED bit into the preempt count such that
51 * preempt_enable() can decrement and test for needing to reschedule with a
52 * single instruction.
53 *
54 * We invert the actual bit, so that when the decrement hits 0 we know we both
55 * need to resched (the bit is cleared) and can resched (no preempt count).
56 */
57
58static __always_inline void set_preempt_need_resched(void)
59{
60	raw_cpu_and_4(pcpu_hot.preempt_count, ~PREEMPT_NEED_RESCHED);
61}
62
63static __always_inline void clear_preempt_need_resched(void)
64{
65	raw_cpu_or_4(pcpu_hot.preempt_count, PREEMPT_NEED_RESCHED);
66}
67
68static __always_inline bool test_preempt_need_resched(void)
69{
70	return !(raw_cpu_read_4(pcpu_hot.preempt_count) & PREEMPT_NEED_RESCHED);
71}
72
73/*
74 * The various preempt_count add/sub methods
75 */
76
77static __always_inline void __preempt_count_add(int val)
78{
79	raw_cpu_add_4(pcpu_hot.preempt_count, val);
80}
81
82static __always_inline void __preempt_count_sub(int val)
83{
84	raw_cpu_add_4(pcpu_hot.preempt_count, -val);
85}
86
87/*
88 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
89 * a decrement which hits zero means we have no preempt_count and should
90 * reschedule.
91 */
92static __always_inline bool __preempt_count_dec_and_test(void)
93{
94	return GEN_UNARY_RMWcc("decl", __my_cpu_var(pcpu_hot.preempt_count), e,
95			       __percpu_arg([var]));
96}
97
98/*
99 * Returns true when we need to resched and can (barring IRQ state).
100 */
101static __always_inline bool should_resched(int preempt_offset)
102{
103	return unlikely(raw_cpu_read_4(pcpu_hot.preempt_count) == preempt_offset);
104}
105
106#ifdef CONFIG_PREEMPTION
107
108extern asmlinkage void preempt_schedule(void);
109extern asmlinkage void preempt_schedule_thunk(void);
110
111#define preempt_schedule_dynamic_enabled	preempt_schedule_thunk
112#define preempt_schedule_dynamic_disabled	NULL
113
114extern asmlinkage void preempt_schedule_notrace(void);
115extern asmlinkage void preempt_schedule_notrace_thunk(void);
116
117#define preempt_schedule_notrace_dynamic_enabled	preempt_schedule_notrace_thunk
118#define preempt_schedule_notrace_dynamic_disabled	NULL
119
120#ifdef CONFIG_PREEMPT_DYNAMIC
121
122DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
123
124#define __preempt_schedule() \
125do { \
126	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \
127	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
128} while (0)
129
130DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
131
132#define __preempt_schedule_notrace() \
133do { \
134	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \
135	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
136} while (0)
137
138#else /* PREEMPT_DYNAMIC */
139
140#define __preempt_schedule() \
141	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
142
143#define __preempt_schedule_notrace() \
144	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);
145
146#endif /* PREEMPT_DYNAMIC */
147
148#endif /* PREEMPTION */
149
150#endif /* __ASM_PREEMPT_H */
151