1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_X86_MWAIT_H
3#define _ASM_X86_MWAIT_H
4
5#include <linux/sched.h>
6#include <linux/sched/idle.h>
7
8#include <asm/cpufeature.h>
9#include <asm/nospec-branch.h>
10
11#define MWAIT_SUBSTATE_MASK 0xf
12#define MWAIT_CSTATE_MASK 0xf
13#define MWAIT_SUBSTATE_SIZE 4
14#define MWAIT_HINT2CSTATE(hint) (((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
15#define MWAIT_HINT2SUBSTATE(hint) ((hint) & MWAIT_CSTATE_MASK)
16#define MWAIT_C1_SUBSTATE_MASK 0xf0
17
18#define CPUID_MWAIT_LEAF 5
19#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
20#define CPUID5_ECX_INTERRUPT_BREAK 0x2
21
22#define MWAIT_ECX_INTERRUPT_BREAK 0x1
23#define MWAITX_ECX_TIMER_ENABLE BIT(1)
24#define MWAITX_MAX_WAIT_CYCLES UINT_MAX
25#define MWAITX_DISABLE_CSTATES 0xf0
26#define TPAUSE_C01_STATE 1
27#define TPAUSE_C02_STATE 0
28
29static __always_inline void __monitor(const void *eax, unsigned long ecx,
30 unsigned long edx)
31{
32 /* "monitor %eax, %ecx, %edx;" */
33 asm volatile(".byte 0x0f, 0x01, 0xc8;"
34 :: "a" (eax), "c" (ecx), "d"(edx));
35}
36
37static __always_inline void __monitorx(const void *eax, unsigned long ecx,
38 unsigned long edx)
39{
40 /* "monitorx %eax, %ecx, %edx;" */
41 asm volatile(".byte 0x0f, 0x01, 0xfa;"
42 :: "a" (eax), "c" (ecx), "d"(edx));
43}
44
45static __always_inline void __mwait(unsigned long eax, unsigned long ecx)
46{
47 mds_idle_clear_cpu_buffers();
48
49 /* "mwait %eax, %ecx;" */
50 asm volatile(".byte 0x0f, 0x01, 0xc9;"
51 :: "a" (eax), "c" (ecx));
52}
53
54/*
55 * MWAITX allows for a timer expiration to get the core out a wait state in
56 * addition to the default MWAIT exit condition of a store appearing at a
57 * monitored virtual address.
58 *
59 * Registers:
60 *
61 * MWAITX ECX[1]: enable timer if set
62 * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0
63 * frequency is the same as the TSC frequency.
64 *
65 * Below is a comparison between MWAIT and MWAITX on AMD processors:
66 *
67 * MWAIT MWAITX
68 * opcode 0f 01 c9 | 0f 01 fb
69 * ECX[0] value of RFLAGS.IF seen by instruction
70 * ECX[1] unused/#GP if set | enable timer if set
71 * ECX[31:2] unused/#GP if set
72 * EAX unused (reserve for hint)
73 * EBX[31:0] unused | max wait time (P0 clocks)
74 *
75 * MONITOR MONITORX
76 * opcode 0f 01 c8 | 0f 01 fa
77 * EAX (logical) address to monitor
78 * ECX #GP if not zero
79 */
80static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx,
81 unsigned long ecx)
82{
83 /* No MDS buffer clear as this is AMD/HYGON only */
84
85 /* "mwaitx %eax, %ebx, %ecx;" */
86 asm volatile(".byte 0x0f, 0x01, 0xfb;"
87 :: "a" (eax), "b" (ebx), "c" (ecx));
88}
89
90static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx)
91{
92 mds_idle_clear_cpu_buffers();
93 /* "mwait %eax, %ecx;" */
94 asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
95 :: "a" (eax), "c" (ecx));
96}
97
98/*
99 * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
100 * which can obviate IPI to trigger checking of need_resched.
101 * We execute MONITOR against need_resched and enter optimized wait state
102 * through MWAIT. Whenever someone changes need_resched, we would be woken
103 * up from MWAIT (without an IPI).
104 *
105 * New with Core Duo processors, MWAIT can take some hints based on CPU
106 * capability.
107 */
108static __always_inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
109{
110 if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) {
111 if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
112 mb();
113 clflush(p: (void *)&current_thread_info()->flags);
114 mb();
115 }
116
117 __monitor(eax: (void *)&current_thread_info()->flags, ecx: 0, edx: 0);
118 if (!need_resched())
119 __mwait(eax, ecx);
120 }
121 current_clr_polling();
122}
123
124/*
125 * Caller can specify whether to enter C0.1 (low latency, less
126 * power saving) or C0.2 state (saves more power, but longer wakeup
127 * latency). This may be overridden by the IA32_UMWAIT_CONTROL MSR
128 * which can force requests for C0.2 to be downgraded to C0.1.
129 */
130static inline void __tpause(u32 ecx, u32 edx, u32 eax)
131{
132 /* "tpause %ecx, %edx, %eax;" */
133 #ifdef CONFIG_AS_TPAUSE
134 asm volatile("tpause %%ecx\n"
135 :
136 : "c"(ecx), "d"(edx), "a"(eax));
137 #else
138 asm volatile(".byte 0x66, 0x0f, 0xae, 0xf1\t\n"
139 :
140 : "c"(ecx), "d"(edx), "a"(eax));
141 #endif
142}
143
144#endif /* _ASM_X86_MWAIT_H */
145

source code of linux/arch/x86/include/asm/mwait.h