linux-kernel - [PATCH] x86/asm: Fix MWAITX C-state hint value

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Date:   Mon, 7 Oct 2019 19:00:22 +0000
From:   "Natarajan, Janakarajan" <Janakarajan.Natarajan@....com>
To:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, Jon Masters <jcm@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        "Natarajan, Janakarajan" <Janakarajan.Natarajan@....com>
Subject: [PATCH] x86/asm: Fix MWAITX C-state hint value

As per "AMD64 Architecture Programmer's Manual Volume 3: General-Purpose
and System Instructions", MWAITX EAX[7:4]+1 specifies the optional hint
of the optimized C-state. For C0 state, EAX[7:4] should be set to 0xf.

Currently, a value of 0xf is set for EAX[3:0] instead of EAX[7:4]. Fix
this by changing MWAITX_DISABLE_CSTATES from 0xf to 0xf0.

Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
---
 arch/x86/include/asm/mwait.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index e28f8b723b5c..9d5252c9685c 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -21,7 +21,7 @@
 #define MWAIT_ECX_INTERRUPT_BREAK	0x1
 #define MWAITX_ECX_TIMER_ENABLE		BIT(1)
 #define MWAITX_MAX_LOOPS		((u32)-1)
-#define MWAITX_DISABLE_CSTATES		0xf
+#define MWAITX_DISABLE_CSTATES		0xf0
 
 static inline void __monitor(const void *eax, unsigned long ecx,
 			     unsigned long edx)
-- 
2.17.1