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 CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1 19 #define CPUID5_ECX_INTERRUPT_BREAK 0x2 20 21 #define MWAIT_ECX_INTERRUPT_BREAK 0x1 22 #define MWAITX_ECX_TIMER_ENABLE BIT(1) 23 #define MWAITX_MAX_WAIT_CYCLES UINT_MAX 24 #define MWAITX_DISABLE_CSTATES 0xf0 25 #define TPAUSE_C01_STATE 1 26 #define TPAUSE_C02_STATE 0 27 28 static __always_inline void __monitor(const void *eax, u32 ecx, u32 edx) 29 { 30 /* 31 * Use the instruction mnemonic with implicit operands, as the LLVM 32 * assembler fails to assemble the mnemonic with explicit operands: 33 */ 34 asm volatile("monitor" :: "a" (eax), "c" (ecx), "d" (edx)); 35 } 36 37 static __always_inline void __monitorx(const void *eax, u32 ecx, u32 edx) 38 { 39 /* "monitorx %eax, %ecx, %edx" */ 40 asm volatile(".byte 0x0f, 0x01, 0xfa" 41 :: "a" (eax), "c" (ecx), "d"(edx)); 42 } 43 44 static __always_inline void __mwait(u32 eax, u32 ecx) 45 { 46 /* 47 * Use the instruction mnemonic with implicit operands, as the LLVM 48 * assembler fails to assemble the mnemonic with explicit operands: 49 */ 50 asm volatile("mwait" :: "a" (eax), "c" (ecx)); 51 } 52 53 /* 54 * MWAITX allows for a timer expiration to get the core out a wait state in 55 * addition to the default MWAIT exit condition of a store appearing at a 56 * monitored virtual address. 57 * 58 * Registers: 59 * 60 * MWAITX ECX[1]: enable timer if set 61 * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0 62 * frequency is the same as the TSC frequency. 63 * 64 * Below is a comparison between MWAIT and MWAITX on AMD processors: 65 * 66 * MWAIT MWAITX 67 * opcode 0f 01 c9 | 0f 01 fb 68 * ECX[0] value of RFLAGS.IF seen by instruction 69 * ECX[1] unused/#GP if set | enable timer if set 70 * ECX[31:2] unused/#GP if set 71 * EAX unused (reserve for hint) 72 * EBX[31:0] unused | max wait time (P0 clocks) 73 * 74 * MONITOR MONITORX 75 * opcode 0f 01 c8 | 0f 01 fa 76 * EAX (logical) address to monitor 77 * ECX #GP if not zero 78 */ 79 static __always_inline void __mwaitx(u32 eax, u32 ebx, u32 ecx) 80 { 81 /* No need for TSA buffer clearing on AMD */ 82 83 /* "mwaitx %eax, %ebx, %ecx" */ 84 asm volatile(".byte 0x0f, 0x01, 0xfb" 85 :: "a" (eax), "b" (ebx), "c" (ecx)); 86 } 87 88 /* 89 * Re-enable interrupts right upon calling mwait in such a way that 90 * no interrupt can fire _before_ the execution of mwait, ie: no 91 * instruction must be placed between "sti" and "mwait". 92 * 93 * This is necessary because if an interrupt queues a timer before 94 * executing mwait, it would otherwise go unnoticed and the next tick 95 * would not be reprogrammed accordingly before mwait ever wakes up. 96 */ 97 static __always_inline void __sti_mwait(u32 eax, u32 ecx) 98 { 99 100 asm volatile("sti; mwait" :: "a" (eax), "c" (ecx)); 101 } 102 103 /* 104 * This uses new MONITOR/MWAIT instructions on P4 processors with PNI, 105 * which can obviate IPI to trigger checking of need_resched. 106 * We execute MONITOR against need_resched and enter optimized wait state 107 * through MWAIT. Whenever someone changes need_resched, we would be woken 108 * up from MWAIT (without an IPI). 109 * 110 * New with Core Duo processors, MWAIT can take some hints based on CPU 111 * capability. 112 */ 113 static __always_inline void mwait_idle_with_hints(u32 eax, u32 ecx) 114 { 115 if (need_resched()) 116 return; 117 118 x86_idle_clear_cpu_buffers(); 119 120 if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) { 121 const void *addr = ¤t_thread_info()->flags; 122 123 alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr)); 124 __monitor(addr, 0, 0); 125 126 if (need_resched()) 127 goto out; 128 129 if (ecx & 1) { 130 __mwait(eax, ecx); 131 } else { 132 __sti_mwait(eax, ecx); 133 raw_local_irq_disable(); 134 } 135 } 136 137 out: 138 current_clr_polling(); 139 } 140 141 /* 142 * Caller can specify whether to enter C0.1 (low latency, less 143 * power saving) or C0.2 state (saves more power, but longer wakeup 144 * latency). This may be overridden by the IA32_UMWAIT_CONTROL MSR 145 * which can force requests for C0.2 to be downgraded to C0.1. 146 */ 147 static inline void __tpause(u32 ecx, u32 edx, u32 eax) 148 { 149 /* "tpause %ecx" */ 150 asm volatile(".byte 0x66, 0x0f, 0xae, 0xf1" 151 :: "c" (ecx), "d" (edx), "a" (eax)); 152 } 153 154 #endif /* _ASM_X86_MWAIT_H */ 155