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[Xen-devel] [PATCH for-4.11 00/10] x86: Improvements and fixes to Spectre handling

In hindsight, the end result of the Spectre mitigations aren't as great as I'd
hoped, and have several inefficiencies.  Also, the `bti=` command line option
isn't as flexible as intended.

This series does four things:

  1) Some internal cleanup, for clarity and to help the other features
  2) Introduce `spec-ctrl=no-pv` mode.  XenServer's performance measurements
     see a 10% net/disk performance improvement in some production scenarios.
  3) Introduce the ability to use IBPB-only mode for guests.  This was
     discussed by Amazon during the Spectre work, but I don't have any
     performance numbers to hand.
  4) Avoid imposing IBRS mode while dom0 is booting.  This was reported by
     Oracle on the list, and speeds up boot time on some servers by 50s.

I know this series is rather late for 4.11, but seeing as I've managed to
complete it before 4.12 opens, it should be considered at this point, as all
of the Spectre code is new in 4.11.

Andrew Cooper (10):
  x86/spec_ctrl: Read MSR_ARCH_CAPABILITIES only once
  x86/spec_ctrl: Express Xen's choice of MSR_SPEC_CTRL value as a variable
  x86/spec_ctrl: Merge bti_ist_info and use_shadow_spec_ctrl into 
  x86/spec_ctrl: Fold the XEN_IBRS_{SET,CLEAR} ALTERNATIVES together
  x86/spec_ctrl: Rename bits of infrastructure to avoid NATIVE and VMEXIT
  x86/spec_ctrl: Split X86_FEATURE_SC_MSR into PV and HVM variants
  x86/spec_ctrl: Explicitly set Xen's default MSR_SPEC_CTRL value
  x86/cpuid: Improvements to guest policies for speculative sidechannel features
  x86/spec_ctrl: Introduce a new `spec-ctrl=` command line argument to replace 
  x86/spec_ctrl: Elide MSR_SPEC_CTRL handling in idle context when possible

 docs/misc/xen-command-line.markdown |  49 +++++++
 xen/arch/x86/acpi/power.c           |   4 +-
 xen/arch/x86/cpuid.c                |  60 +++++----
 xen/arch/x86/hvm/svm/entry.S        |   4 +-
 xen/arch/x86/hvm/vmx/entry.S        |   4 +-
 xen/arch/x86/setup.c                |   7 +
 xen/arch/x86/smpboot.c              |   8 ++
 xen/arch/x86/spec_ctrl.c            | 258 ++++++++++++++++++++++++++++--------
 xen/arch/x86/x86_64/asm-offsets.c   |   4 +-
 xen/arch/x86/x86_64/compat/entry.S  |   2 +-
 xen/arch/x86/x86_64/entry.S         |   2 +-
 xen/include/asm-x86/cpufeatures.h   |   9 +-
 xen/include/asm-x86/current.h       |   4 +-
 xen/include/asm-x86/spec_ctrl.h     |  20 +--
 xen/include/asm-x86/spec_ctrl_asm.h | 131 +++++++++---------
 15 files changed, 396 insertions(+), 170 deletions(-)


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