[PATCH v9 0/4] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

[Grzegorz Andrejczuk]

These patches enable Intel Xeon Phi x200 feature to use MONITOR/MWAIT
instruction in ring 3 (userspace) Patches set MSR 0x140 for all logical CPUs.
Then expose it as CPU feature and introduces elf HWCAP capability for x86.
Reference:
https://software.intel.com/en-us/blogs/2016/10/06/intel-xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait

v9:
Removed PHI from defines

v8:
Fixed commit messages
Removed logging
Used msr_set/clear_bit functions instesd of wrmsrl
Fixed documentation
Renamed HWCAP2_PHIR3MWAIT to HWCAP2_RING3MWAIT

v7:
Change order of the patches, with this code looks cleaner.
Changed the name of MSR to MSR_MISC_FEATURE_ENABLES.
Used Word 3 25th bit to expose feature.

v6: 

v5:
When phir3mwait=disable is cmdline switch off r3 mwait feature
Fix typos

v4:
Wrapped the enabling code by CONFIG_X86_64
Add documentation for phir3mwait=disable cmdline switch
Move probe_ function call from early_intel_init to intel_init
Fixed commit messages

v3:
Included Daves and Thomas comments

v2:
Check MSR before wrmsrl
Shortened names
Used Word 3 for feature init_scattered_cpuid_features()
Fixed commit messages

Grzegorz Andrejczuk (4):
  x86/msr: Add MSR_MISC_FEATURE_ENABLES and RING3MWAIT bit
  x86/elf: Use HWCAP2 to expose ring 3 MWAIT
  x86/cpufeature: Add RING3MWAIT to CPU features
  x86/cpufeatures: Handle RING3MWAIT on Xeon Phi models

 Documentation/kernel-parameters.txt       |  5 ++++
 Documentation/x86/x86_64/boot-options.txt |  5 ++++
 arch/x86/include/asm/cpufeatures.h        |  2 +-
 arch/x86/include/asm/elf.h                |  9 +++++++
 arch/x86/include/asm/msr-index.h          |  5 ++++
 arch/x86/include/uapi/asm/hwcap2.h        |  7 ++++++
 arch/x86/kernel/cpu/common.c              |  3 +++
 arch/x86/kernel/cpu/intel.c               | 39 +++++++++++++++++++++++++++++++
 8 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/include/uapi/asm/hwcap2.h

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2.5.1