From 6dbbf5ec9e1e9f607a4c51266d0f9a63ba754b63 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Wed, 19 Jun 2019 18:33:54 -0700 Subject: [PATCH] x86/cpufeatures: Enumerate user wait instructions umonitor, umwait, and tpause are a set of user wait instructions. umonitor arms address monitoring hardware using an address. The address range is determined by using CPUID.0x5. A store to an address within the specified address range triggers the monitoring hardware to wake up the processor waiting in umwait. umwait instructs the processor to enter an implementation-dependent optimized state while monitoring a range of addresses. The optimized state may be either a light-weight power/performance optimized state (C0.1 state) or an improved power/performance optimized state (C0.2 state). tpause instructs the processor to enter an implementation-dependent optimized state C0.1 or C0.2 state and wake up when time-stamp counter reaches specified timeout. The three instructions may be executed at any privilege level. The instructions provide power saving method while waiting in user space. Additionally, they can allow a sibling hyperthread to make faster progress while this thread is waiting. One example of an application usage of umwait is when waiting for input data from another application, such as a user level multi-threaded packet processing engine. Availability of the user wait instructions is indicated by the presence of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX[5]. Detailed information on the instructions and CPUID feature WAITPKG flag can be found in the latest Intel Architecture Instruction Set Extensions and Future Features Programming Reference and Intel 64 and IA-32 Architectures Software Developer's Manual. Signed-off-by: Fenghua Yu Signed-off-by: Thomas Gleixner Reviewed-by: Ashok Raj Reviewed-by: Andy Lutomirski Cc: "Borislav Petkov" Cc: "H Peter Anvin" Cc: "Peter Zijlstra" Cc: "Tony Luck" Cc: "Ravi V Shankar" Link: https://lkml.kernel.org/r/1560994438-235698-2-git-send-email-fenghua.yu@intel.com --- arch/x86/include/asm/cpufeatures.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 8ecd9fac97c3..998c2cc08363 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -330,6 +330,7 @@ #define X86_FEATURE_UMIP (16*32+ 2) /* User Mode Instruction Protection */ #define X86_FEATURE_PKU (16*32+ 3) /* Protection Keys for Userspace */ #define X86_FEATURE_OSPKE (16*32+ 4) /* OS Protection Keys Enable */ +#define X86_FEATURE_WAITPKG (16*32+ 5) /* UMONITOR/UMWAIT/TPAUSE Instructions */ #define X86_FEATURE_AVX512_VBMI2 (16*32+ 6) /* Additional AVX512 Vector Bit Manipulation Instructions */ #define X86_FEATURE_GFNI (16*32+ 8) /* Galois Field New Instructions */ #define X86_FEATURE_VAES (16*32+ 9) /* Vector AES */ -- 2.25.1