[PATCH v6 00/20] KVM: x86: Enable APX for guests

[Chang S. Bae]

Hi Paolo,

On 7/21/2026 12:09 AM, Paolo Bonzini wrote:
> please give a read to its comments in case it found something important.

Here is a small follow-up revision addressing Sashiko's comments:

 * Patch02: Fix "register saving" wording in the changelog.
 * Patch17: Add the APX leaf to cpuid_function_is_indexed().

Rerunning Sashiko locally, it still appears to be somewhat confused by
the potential in-kernel usages and a few ordering of changes, so it may
report similar issues again on this posting.

I assume the V5 changes are still under review, so attaching the previous
cover letter and leaving the V5 notes in each patch.

---

One topic worth highlighting first is about how to handle userspace
writes to the APX state through the KVM XSAVE API, following the
discussion here:

  https://lore.kernel.org/CABgObfaocwfLdUBKJYYYEDH8X3n6iEbMsscbaCe_C=8JNnhDBA@xxxxxxxxxxxxxx

So what this revision ended up with is just to keep those copy paths from
userspace and acknowledge the redundant copy to VCPU cache / guest
fpstate. Patch3 has more context on that.

Besides that, this revision has several fixes and improvements. Sean
gave feedbacks. 0-day spotted on an issue. Also, since the preparatory
patches have been merged into the mainline, finally a review bot could
provide some feedbacks as well. The major changes are:

 1. VMX Instruction Information Extension

    During the time of V4, 0-day reported out an issue with patch7.
    Fixing that also revealed patch4 was missing another function.

    With a review bot's feeback, patch7 was also updated to ensure EGPR
    indices for handling debug-register accesses. Also looking at
    associated macros, patch6 was added for further cleanup.

 2. Emulator Register Tracking

    The review bot at hand also found a potential shift-out-bounds issue
    in the register tracking. Patch10 was fixed.

 3. APX Feature Exposure

    As per Sean's feedback, the APX XCR0 and userspace exposure were
    reworked a bit in patch14-18.

Thanks,
Chang

Reference:
 * Repo: git://github.com/intel/apx.git apx-kvm_v6
 * V5: https://lore.kernel.org/20260512011502.53072-1-chang.seok.bae@xxxxxxxxx
 * KVM-unit-test patch: https://lore.kernel.org/20260420212355.507827-1-chang.seok.bae@xxxxxxxxx

Chang S. Bae (19):
  KVM: x86: Extend VCPU registers for EGPRs
  KVM: VMX: Save guest EGPRs in VCPU cache
  KVM: x86: Support APX state for XSAVE ABI
  KVM: VMX: Refactor VMX instruction information access
  KVM: VMX: Refactor instruction information decoding
  KVM: VMX: Remove unused control-register access defines
  KVM: VMX: Refactor register index retrieval from exit qualification
  KVM: VMX: Support instruction information extension
  KVM: nVMX: Propagate extended instruction information
  KVM: x86: Support EGPR accessing and tracking for emulator
  KVM: x86: Handle EGPR index and REX2-incompatible opcodes
  KVM: x86: Support REX2-prefixed opcode decode
  KVM: x86: Reject EVEX-prefixed instructions
  KVM: x86: Guard valid XCR0.APX settings
  KVM: x86: Add APX to supported XCR0
  KVM: x86: Expose APX foundation feature to userspace
  KVM: x86: Expose APX sub-features to userspace
  KVM: x86: selftests: Add APX state and ABI test
  KVM: x86: selftests: Add APX state handling and XCR0 sanity checks

Sean Christopherson (1):
  KVM: x86: Move KVM_SUPPORTED_{XCR0,XSS} into kvm_x86_vendor_init()

 arch/x86/Kconfig.assembler                    |   5 +
 arch/x86/include/asm/cpuid/api.h              |   1 +
 arch/x86/include/asm/kvm_host.h               |  19 ++
 arch/x86/include/asm/kvm_vcpu_regs.h          |  50 +++++
 arch/x86/include/asm/vmx.h                    |  22 +-
 arch/x86/kvm/Kconfig                          |   4 +
 arch/x86/kvm/cpuid.c                          |  27 ++-
 arch/x86/kvm/cpuid.h                          |   2 +
 arch/x86/kvm/emulate.c                        | 121 +++++++----
 arch/x86/kvm/kvm_emulate.h                    |  21 +-
 arch/x86/kvm/reverse_cpuid.h                  |   6 +
 arch/x86/kvm/svm/svm.c                        |   8 +-
 arch/x86/kvm/vmenter.h                        |   1 +
 arch/x86/kvm/vmx/nested.c                     |  75 +++----
 arch/x86/kvm/vmx/nested.h                     |   2 +-
 arch/x86/kvm/vmx/vmcs12.c                     |   1 +
 arch/x86/kvm/vmx/vmcs12.h                     |   3 +-
 arch/x86/kvm/vmx/vmenter.S                    |  31 ++-
 arch/x86/kvm/vmx/vmx.c                        |  28 ++-
 arch/x86/kvm/vmx/vmx.h                        |  77 ++++++-
 arch/x86/kvm/x86.c                            |  92 +++++++--
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../selftests/kvm/include/x86/processor.h     | 120 +++++++++++
 tools/testing/selftests/kvm/x86/apx_test.c    | 191 ++++++++++++++++++
 tools/testing/selftests/kvm/x86/state_test.c  |   3 +
 .../selftests/kvm/x86/xcr0_cpuid_test.c       |  19 ++
 26 files changed, 802 insertions(+), 128 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86/apx_test.c


base-commit: a204badd8432f93b7e862e7dac6db0fe3d65f370
-- 
2.53.0