[PATCH v4 00/10] KVM: SEV: Add support for IBPB-on-Entry and BTB Isolation

[Kim Phillips]

IBPB-on-Entry and BTB Isolation are supplemental Spectre V2 mitigations
available to SNP guests.

Patch 1 fixes a misleading no-spectre-v2-mitigation error when the kernel isn't
compiled with retpolines, but a user can still select AutoIBRS, for example.

Patch 2 fixes a longstanding bug where users weren't able
to force Automatic IBRS on SNP enabled machines using spectre_v2=eibrs.

Patch 3 allows AutoIBRS to be used on a kernel compiled without retpolines.

Patch 4 fixes another longstanding bug where users couldn't
select legacy / toggling SPEC_CTRL[IBRS] on AMD systems.  Users of
the BTB Isolation feature may use IBRS to mitigate possible
performance degradation caused by BTB Isolation.

Patches 5, 6, 7 and 8 deal with code refactoring as a result of
Sean's review of the v2 IBPB-on-Entry series: an SNP-only feature
mask.

Patch 9 adds support for IBPB-on-Entry.

Patch 10 adds support for BTB Isolation.

Based on tip/master (currently fd0ece3c0826):
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

This v4 series now also available here:

https://github.com/AMDESE/linux/tree/btb-isol-latest

Advance qemu bits (to add feature on/off switches) available here:

https://github.com/AMDESE/qemu/tree/btb-isol-latest

Qemu bits will be posted upstream once kernel bits are merged.
They depend on Naveen Rao's "target/i386: SEV: Add support for
enabling VMSA SEV features":

https://lore.kernel.org/qemu-devel/cover.1761648149.git.naveen@xxxxxxxxxx/

v4:
   - Ran Sashiko in a loop until all(?) its comments were addressed (Boris)

v3:
   - https://lore.kernel.org/kvm/20260402202558.195005-1-kim.phillips@xxxxxxx/
   - Merged IBPB-on-Entry and BTB Isolation into single patchseries
   - Addressed comments from Sean Christopherson, Pawan Gupta, kernel test robot
   - Simplified unnecessarily complicated logic in spectre_v2=eibrs-with-SNP fix
   - Reworded, rebased features on top of new SNP_ONLY_MASK etc. changes

v2:
[IBPB-on-Entry]
     - https://lore.kernel.org/kvm/20260203222405.4065706-1-kim.phillips@xxxxxxx/
     - Change first patch's title (Nikunj)
     - Add reviews-by (Nikunj, Tom)
     - Change second patch's description to more generally explain what the patch does (Boris)
     - Add new, third patch renaming SNP_FEATURES_PRESENT->SNP_FEATURES_IMPL
[BTB Isolation]
     - https://lore.kernel.org/kvm/20260311130611.2201214-1-kim.phillips@xxxxxxx/
     - Patch 1/3:
       - Address Dave Hansen's comment to adhere to using the IBRS_ENHANCED
         Intel feature flag also for AutoIBRS.

v1:
[IBPB-on-Entry] https://lore.kernel.org/kvm/20260126224205.1442196-1-kim.phillips@xxxxxxx/
[BTB Isolation] https://lore.kernel.org/kvm/20260224180157.725159-1-kim.phillips@xxxxxxx/

Kim Phillips (10):
  x86/bugs: Only log missing retpoline when it's actually the missing
    mitigation
  cpu/bugs: Allow forcing Automatic IBRS with SNP active using
    spectre_v2=eibrs
  cpu/bugs: Fall back to AutoIBRS when retpoline unavailable on SNP CPUs
  cpu/bugs: Allow spectre_v2=ibrs on x86 vendors other than Intel
  KVM: SEV: Define SVM_SEV_FEAT_* flags using BIT_ULL()
  KVM: selftests: sev_init2: Use BIT_ULL for VMSA feature bit definition
  KVM: SEV: Disallow setting SNP-only features for non-SNP guests via a
    single mask
  KVM: SEV: Advertise SVM_SEV_FEAT_SNP_ACTIVE
  KVM: SEV: Add support for IBPB-on-Entry
  KVM: SEV: Add support for SNP BTB Isolation

 arch/x86/Kconfig                              |  7 +-
 arch/x86/include/asm/cpufeatures.h            |  1 +
 arch/x86/include/asm/svm.h                    | 17 +++--
 arch/x86/kernel/cpu/bugs.c                    | 71 ++++++++++++++-----
 arch/x86/kernel/cpu/common.c                  |  6 +-
 arch/x86/kvm/svm/sev.c                        | 18 ++++-
 tools/arch/x86/include/asm/cpufeatures.h      |  1 +
 .../selftests/kvm/x86/sev_init2_tests.c       | 20 ++++--
 8 files changed, 103 insertions(+), 38 deletions(-)


base-commit: fd0ece3c082632334ded22076932b302a048c7de
-- 
2.43.0