arch/x86/include/asm/mwait.h

   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
  17 #define CPUID_MWAIT_LEAF                5
  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_LOOPS                ((u32)-1)
  24 #define MWAITX_DISABLE_CSTATES          0xf0
  25
  26 static inline void __monitor(const void *eax, unsigned long ecx,
  27                              unsigned long edx)
  28 {
  29         /* "monitor %eax, %ecx, %edx;" */
  30         asm volatile(".byte 0x0f, 0x01, 0xc8;"
  31                      :: "a" (eax), "c" (ecx), "d"(edx));
  32 }
  33
  34 static inline void __monitorx(const void *eax, unsigned long ecx,
  35                               unsigned long edx)
  36 {
  37         /* "monitorx %eax, %ecx, %edx;" */
  38         asm volatile(".byte 0x0f, 0x01, 0xfa;"
  39                      :: "a" (eax), "c" (ecx), "d"(edx));
  40 }
  41
  42 static inline void __mwait(unsigned long eax, unsigned long ecx)
  43 {
  44         mds_idle_clear_cpu_buffers();
  45
  46         /* "mwait %eax, %ecx;" */
  47         asm volatile(".byte 0x0f, 0x01, 0xc9;"
  48                      :: "a" (eax), "c" (ecx));
  49 }
  50
  51 /*
  52  * MWAITX allows for a timer expiration to get the core out a wait state in
  53  * addition to the default MWAIT exit condition of a store appearing at a
  54  * monitored virtual address.
  55  *
  56  * Registers:
  57  *
  58  * MWAITX ECX[1]: enable timer if set
  59  * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0
  60  * frequency is the same as the TSC frequency.
  61  *
  62  * Below is a comparison between MWAIT and MWAITX on AMD processors:
  63  *
  64  *                 MWAIT                           MWAITX
  65  * opcode          0f 01 c9           |            0f 01 fb
  66  * ECX[0]                  value of RFLAGS.IF seen by instruction
  67  * ECX[1]          unused/#GP if set  |            enable timer if set
  68  * ECX[31:2]                     unused/#GP if set
  69  * EAX                           unused (reserve for hint)
  70  * EBX[31:0]       unused             |            max wait time (P0 clocks)
  71  *
  72  *                 MONITOR                         MONITORX
  73  * opcode          0f 01 c8           |            0f 01 fa
  74  * EAX                     (logical) address to monitor
  75  * ECX                     #GP if not zero
  76  */
  77 static inline void __mwaitx(unsigned long eax, unsigned long ebx,
  78                             unsigned long ecx)
  79 {
  80         /* No MDS buffer clear as this is AMD/HYGON only */
  81
  82         /* "mwaitx %eax, %ebx, %ecx;" */
  83         asm volatile(".byte 0x0f, 0x01, 0xfb;"
  84                      :: "a" (eax), "b" (ebx), "c" (ecx));
  85 }
  86
  87 static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
  88 {
  89         trace_hardirqs_on();
  90
  91         mds_idle_clear_cpu_buffers();
  92         /* "mwait %eax, %ecx;" */
  93         asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
  94                      :: "a" (eax), "c" (ecx));
  95 }
  96
  97 /*
  98  * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
  99  * which can obviate IPI to trigger checking of need_resched.
 100  * We execute MONITOR against need_resched and enter optimized wait state
 101  * through MWAIT. Whenever someone changes need_resched, we would be woken
 102  * up from MWAIT (without an IPI).
 103  *
 104  * New with Core Duo processors, MWAIT can take some hints based on CPU
 105  * capability.
 106  */
 107 static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
 108 {
 109         if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) {
 110                 if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
 111                         mb();
 112                         clflush((void *)&current_thread_info()->flags);
 113                         mb();
 114                 }
 115
 116                 __monitor((void *)&current_thread_info()->flags, 0, 0);
 117                 if (!need_resched())
 118                         __mwait(eax, ecx);
 119         }
 120         current_clr_polling();
 121 }
 122
 123 #endif /* _ASM_X86_MWAIT_H */