diff options
| -rw-r--r-- | arch/x86/include/asm/mwait.h | 1 | ||||
| -rw-r--r-- | arch/x86/kernel/process.c | 35 |
2 files changed, 26 insertions, 10 deletions
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index 29dd27b5a339..3a8fdf881313 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -13,6 +13,7 @@ #define MWAIT_SUBSTATE_SIZE 4 #define MWAIT_HINT2CSTATE(hint) (((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) #define MWAIT_HINT2SUBSTATE(hint) ((hint) & MWAIT_CSTATE_MASK) +#define MWAIT_C1_SUBSTATE_MASK 0xf0 #define CPUID_MWAIT_LEAF 5 #define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1 diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index dca2e5e2fae2..5cbfbe566270 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -813,28 +813,43 @@ static void amd_e400_idle(void) } /* - * Intel Core2 and older machines prefer MWAIT over HALT for C1. - * We can't rely on cpuidle installing MWAIT, because it will not load - * on systems that support only C1 -- so the boot default must be MWAIT. + * Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf + * exists and whenever MONITOR/MWAIT extensions are present there is at + * least one C1 substate. * - * Some AMD machines are the opposite, they depend on using HALT. - * - * So for default C1, which is used during boot until cpuidle loads, - * use MWAIT-C1 on Intel HW that has it, else use HALT. + * Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait + * is passed to kernel commandline parameter. */ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c) { + u32 eax, ebx, ecx, edx; + /* User has disallowed the use of MWAIT. Fallback to HALT */ if (boot_option_idle_override == IDLE_NOMWAIT) return 0; - if (c->x86_vendor != X86_VENDOR_INTEL) + /* MWAIT is not supported on this platform. Fallback to HALT */ + if (!cpu_has(c, X86_FEATURE_MWAIT)) return 0; - if (!cpu_has(c, X86_FEATURE_MWAIT) || boot_cpu_has_bug(X86_BUG_MONITOR)) + /* Monitor has a bug. Fallback to HALT */ + if (boot_cpu_has_bug(X86_BUG_MONITOR)) return 0; - return 1; + cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx); + + /* + * If MWAIT extensions are not available, it is safe to use MWAIT + * with EAX=0, ECX=0. + */ + if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) + return 1; + + /* + * If MWAIT extensions are available, there should be at least one + * MWAIT C1 substate present. + */ + return (edx & MWAIT_C1_SUBSTATE_MASK); } /* |