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.andrejc...@intel.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..c95da90 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_RING3MWAIT_BIT 1
+#define MSR_MISC_FEATURE_ENABLES_RING3MWAIT (1ULL <<
MSR_MISC_FEATURE_ENABLES_RING3MWAIT_BIT)
+
#define MSR_IA32_TSC_DEADLINE 0x000006E0
/* P4/Xeon+ specific */
--
2.5.1
