linux-kernel - [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE

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Date:   Tue,  1 Nov 2016 11:14:47 +0100
From:   Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
To:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Cc:     bp@...e.de, dave.hansen@...ux.intel.com, lukasz.daniluk@...el.com,
        james.h.cownie@...el.com, jacob.jun.pan@...el.com,
        Piotr.Luc@...el.com, linux-kernel@...r.kernel.org,
        Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
Subject: [PATCH v8: 1/4] x86/msr: Add MSR_MISC_FEATURE_ENABLES and PHIR3MWAIT bit

Intel Xeon Phi x200 (codenamed Knights Landing) allows to enable
MONITOR and MWAIT instructions outside of ring 0.

The feature is controlled by MSR MISC_FEATURE_ENABLES (0x140).
Setting bit 1 of this register enables it, so MONITOR and MWAIT
instructions do not cause invalid-opcode exceptions when invoked
outside of ring 0.
The feature MSR is not yet documented in the SDM. Here is
the relevant documentation:

Hex   Dec  Name                    Scope
140H  320  MISC_FEATURE_ENABLES    Thread
           0    Reserved
           1    if set to 1, the MONITOR and MWAIT instructions do not
                cause invalid-opcode exceptions when executed with CPL > 0
                or in virtual-8086 mode. If MWAIT is executed when CPL > 0
                or in virtual-8086 mode, and if EAX indicates a C-state
                other than C0 or C1, the instruction operates as if EAX
                indicated the C-state C1.
           63:2 Reserved

Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>
---
 arch/x86/include/asm/msr-index.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 56f4c66..0fc220d 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -540,6 +540,11 @@
 #define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE_BIT	39
 #define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE		(1ULL << MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE_BIT)
 
+/* Intel Xeon Phi x200 ring 3 MONITOR/MWAIT */
+#define MSR_MISC_FEATURE_ENABLES	0x00000140
+#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT	1
+#define MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT	(1ULL << MSR_MISC_FEATURE_ENABLES_PHIR3MWAIT_BIT)
+
 #define MSR_IA32_TSC_DEADLINE		0x000006E0
 
 /* P4/Xeon+ specific */
-- 
2.5.1