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
10#define MWAIT_SUBSTATE_MASK 0xf
11#define MWAIT_CSTATE_MASK 0xf
12#define MWAIT_SUBSTATE_SIZE 4
13#define MWAIT_HINT2CSTATE(hint) (((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
14#define MWAIT_HINT2SUBSTATE(hint) ((hint) & MWAIT_CSTATE_MASK)
15
16#define CPUID_MWAIT_LEAF 5
17#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
18#define CPUID5_ECX_INTERRUPT_BREAK 0x2
19
20#define MWAIT_ECX_INTERRUPT_BREAK 0x1
21#define MWAITX_ECX_TIMER_ENABLE BIT(1)
22#define MWAITX_MAX_LOOPS ((u32)-1)
23#define MWAITX_DISABLE_CSTATES 0xf
24
25static inline void __monitor(const void *eax, unsigned long ecx,
26 unsigned long edx)
27{
28 /* "monitor %eax, %ecx, %edx;" */
29 asm volatile(".byte 0x0f, 0x01, 0xc8;"
30 :: "a" (eax), "c" (ecx), "d"(edx));
31}
32
33static inline void __monitorx(const void *eax, unsigned long ecx,
34 unsigned long edx)
35{
36 /* "monitorx %eax, %ecx, %edx;" */
37 asm volatile(".byte 0x0f, 0x01, 0xfa;"
38 :: "a" (eax), "c" (ecx), "d"(edx));
39}
40
41static inline void __mwait(unsigned long eax, unsigned long ecx)
42{
43 /* "mwait %eax, %ecx;" */
44 asm volatile(".byte 0x0f, 0x01, 0xc9;"
45 :: "a" (eax), "c" (ecx));
46}
47
48/*
49 * MWAITX allows for a timer expiration to get the core out a wait state in
50 * addition to the default MWAIT exit condition of a store appearing at a
51 * monitored virtual address.
52 *
53 * Registers:
54 *
55 * MWAITX ECX[1]: enable timer if set
56 * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0
57 * frequency is the same as the TSC frequency.
58 *
59 * Below is a comparison between MWAIT and MWAITX on AMD processors:
60 *
61 * MWAIT MWAITX
62 * opcode 0f 01 c9 | 0f 01 fb
63 * ECX[0] value of RFLAGS.IF seen by instruction
64 * ECX[1] unused/#GP if set | enable timer if set
65 * ECX[31:2] unused/#GP if set
66 * EAX unused (reserve for hint)
67 * EBX[31:0] unused | max wait time (P0 clocks)
68 *
69 * MONITOR MONITORX
70 * opcode 0f 01 c8 | 0f 01 fa
71 * EAX (logical) address to monitor
72 * ECX #GP if not zero
73 */
74static inline void __mwaitx(unsigned long eax, unsigned long ebx,
75 unsigned long ecx)
76{
77 /* "mwaitx %eax, %ebx, %ecx;" */
78 asm volatile(".byte 0x0f, 0x01, 0xfb;"
79 :: "a" (eax), "b" (ebx), "c" (ecx));
80}
81
82static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
83{
84 trace_hardirqs_on();
85 /* "mwait %eax, %ecx;" */
86 asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
87 :: "a" (eax), "c" (ecx));
88}
89
90/*
91 * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
92 * which can obviate IPI to trigger checking of need_resched.
93 * We execute MONITOR against need_resched and enter optimized wait state
94 * through MWAIT. Whenever someone changes need_resched, we would be woken
95 * up from MWAIT (without an IPI).
96 *
97 * New with Core Duo processors, MWAIT can take some hints based on CPU
98 * capability.
99 */
100static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
101{
102 if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) {
103 if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
104 mb();
105 clflush((void *)&current_thread_info()->flags);
106 mb();
107 }
108
109 __monitor((void *)&current_thread_info()->flags, 0, 0);
110 if (!need_resched())
111 __mwait(eax, ecx);
112 }
113 current_clr_polling();
114}
115
116#endif /* _ASM_X86_MWAIT_H */
117