[PATCH 0/3] x86/speculation: Support Automatic IBRS

[Kim Phillips]

The AMD Zen4 core supports a new feature called Automatic IBRS.
(Indirect Branch Restricted Speculation).

Enable Automatic IBRS by default if the CPU feature is present.
It typically provides greater performance over the incumbent
generic retpolines mitigation.

Patch 1 adds support for the CPUID_8000_0021_EAX leaf
that has the bit that identifies X86_FEATURE_AUTOIBRS.

Patch 2 adds support for Auto IBRS.

Patch 3 makes the Auto IBRS feature available for VM guests.

Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Babu Moger <Babu.Moger@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx

Kim Phillips (3):
  x86/cpufeatures: Add support for cpuid leaf 80000021/EAX
    (FeatureExt2Eax)
  x86/speculation: Support Automatic IBRS
  x86/speculation: Support Automatic IBRS under virtualization

 .../admin-guide/kernel-parameters.txt         |  1 +
 arch/x86/include/asm/cpufeature.h             |  7 ++--
 arch/x86/include/asm/cpufeatures.h            |  5 ++-
 arch/x86/include/asm/disabled-features.h      |  3 +-
 arch/x86/include/asm/msr-index.h              |  2 ++
 arch/x86/include/asm/nospec-branch.h          |  1 +
 arch/x86/include/asm/required-features.h      |  3 +-
 arch/x86/kernel/cpu/bugs.c                    | 34 +++++++++++++++++--
 arch/x86/kernel/cpu/common.c                  |  3 ++
 arch/x86/kvm/cpuid.c                          |  5 ++-
 arch/x86/kvm/reverse_cpuid.h                  |  1 +
 arch/x86/kvm/svm/svm.c                        |  3 ++
 arch/x86/kvm/x86.c                            |  3 ++
 13 files changed, 62 insertions(+), 9 deletions(-)

-- 
2.34.1