linux-kernel - [PATCH v2 1/3] x86/cpufeatures: Enumerate user wait instructions

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Message-Id: <1547673522-226408-2-git-send-email-fenghua.yu@intel.com>
Date:   Wed, 16 Jan 2019 13:18:36 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Borislav Petkov" <bp@...en8.de>, "Ingo Molnar" <mingo@...hat.com>,
        "H Peter Anvin" <hpa@...or.com>,
        "Andy Lutomirski" <luto@...capital.net>,
        "Andrew Cooper" <andrew.cooper3@...rix.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v2 1/3] 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. 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).

The UMONITOR and UMWAIT operate together to provide power saving
in idle.

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.

Availability of the user wait instructions is indicated by the presence
of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX[5].

Please check the latest Intel Architecture Instruction Set Extensions
and Future Features Programming Reference for more details on the
instructions and CPUID feature WAITPKG flag.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.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 6d6122524711..344874df5dc3 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -322,6 +322,7 @@
 #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 */
-- 
2.19.1