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/thread_info.h>
10#include <linux/static_call_types.h>
11
12/* We use the MSB mostly because its available */
13#define PREEMPT_NEED_RESCHED	0x80000000
14
15/*
16 * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
17 * that a decrement hitting 0 means we can and should reschedule.
18 */
19#define PREEMPT_ENABLED	(0 + PREEMPT_NEED_RESCHED)
20
21/*
22 * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
23 * that think a non-zero value indicates we cannot preempt.
24 */
25static __always_inline int preempt_count(void)
26{
27	return raw_cpu_read_4(pcpu_hot.preempt_count) & ~PREEMPT_NEED_RESCHED;
28}
29
30static __always_inline void preempt_count_set(int pc)
31{
32	int old, new;
33
34	do {
35		old = raw_cpu_read_4(pcpu_hot.preempt_count);
36		new = (old & PREEMPT_NEED_RESCHED) |
37			(pc & ~PREEMPT_NEED_RESCHED);
38	} while (raw_cpu_cmpxchg_4(pcpu_hot.preempt_count, old, new) != old);
39}
40
41/*
42 * must be macros to avoid header recursion hell
43 */
44#define init_task_preempt_count(p) do { } while (0)
45
46#define init_idle_preempt_count(p, cpu) do { \
47	per_cpu(pcpu_hot.preempt_count, (cpu)) = PREEMPT_DISABLED; \
48} while (0)
49
50/*
51 * We fold the NEED_RESCHED bit into the preempt count such that
52 * preempt_enable() can decrement and test for needing to reschedule with a
53 * single instruction.
54 *
55 * We invert the actual bit, so that when the decrement hits 0 we know we both
56 * need to resched (the bit is cleared) and can resched (no preempt count).
57 */
58
59static __always_inline void set_preempt_need_resched(void)
60{
61	raw_cpu_and_4(pcpu_hot.preempt_count, ~PREEMPT_NEED_RESCHED);
62}
63
64static __always_inline void clear_preempt_need_resched(void)
65{
66	raw_cpu_or_4(pcpu_hot.preempt_count, PREEMPT_NEED_RESCHED);
67}
68
69static __always_inline bool test_preempt_need_resched(void)
70{
71	return !(raw_cpu_read_4(pcpu_hot.preempt_count) & PREEMPT_NEED_RESCHED);
72}
73
74/*
75 * The various preempt_count add/sub methods
76 */
77
78static __always_inline void __preempt_count_add(int val)
79{
80	raw_cpu_add_4(pcpu_hot.preempt_count, val);
81}
82
83static __always_inline void __preempt_count_sub(int val)
84{
85	raw_cpu_add_4(pcpu_hot.preempt_count, -val);
86}
87
88/*
89 * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
90 * a decrement which hits zero means we have no preempt_count and should
91 * reschedule.
92 */
93static __always_inline bool __preempt_count_dec_and_test(void)
94{
95	return GEN_UNARY_RMWcc("decl", pcpu_hot.preempt_count, e,
96			       __percpu_arg([var]));
97}
98
99/*
100 * Returns true when we need to resched and can (barring IRQ state).
101 */
102static __always_inline bool should_resched(int preempt_offset)
103{
104	return unlikely(raw_cpu_read_4(pcpu_hot.preempt_count) == preempt_offset);
105}
106
107#ifdef CONFIG_PREEMPTION
108
109extern asmlinkage void preempt_schedule(void);
110extern asmlinkage void preempt_schedule_thunk(void);
111
112#define preempt_schedule_dynamic_enabled	preempt_schedule_thunk
113#define preempt_schedule_dynamic_disabled	NULL
114
115extern asmlinkage void preempt_schedule_notrace(void);
116extern asmlinkage void preempt_schedule_notrace_thunk(void);
117
118#define preempt_schedule_notrace_dynamic_enabled	preempt_schedule_notrace_thunk
119#define preempt_schedule_notrace_dynamic_disabled	NULL
120
121#ifdef CONFIG_PREEMPT_DYNAMIC
122
123DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
124
125#define __preempt_schedule() \
126do { \
127	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule); \
128	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
129} while (0)
130
131DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
132
133#define __preempt_schedule_notrace() \
134do { \
135	__STATIC_CALL_MOD_ADDRESSABLE(preempt_schedule_notrace); \
136	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
137} while (0)
138
139#else /* PREEMPT_DYNAMIC */
140
141#define __preempt_schedule() \
142	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
143
144#define __preempt_schedule_notrace() \
145	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);
146
147#endif /* PREEMPT_DYNAMIC */
148
149#endif /* PREEMPTION */
150
151#endif /* __ASM_PREEMPT_H */
152