Re: [PATCH v5 00/20] KVM: x86: Enable APX for guests

[Paolo Bonzini]

On 7/20/26 19:19, Chang S. Bae wrote:
> Hi Paolo and Sean,
>
> Here is another iteration for this enabling series.
>
> 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.
>
> Along with the in-tree KVM x86 selftests, this time I ensured running the
> x86 KVM-unit-test comparing between:
>
>   * Baseline - Paolo's `queue` branch
>   * This series on non-APX systems, and
>   * This series on APX hardware
>
> The full set is also available at:
>
>    git://github.com/intel/apx.git apx-kvm_v5

Thanks, will review.  Sashiko was a bit drunk when doing its thing, but 
please give a read to its comments in case it found something important.

Paolo

> Thanks,
> Chang
>
> Relevant Posting
>   * V4: 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 in 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/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 ++
>   25 files changed, 801 insertions(+), 128 deletions(-)
>   create mode 100644 tools/testing/selftests/kvm/x86/apx_test.c
>
>
> base-commit: a204badd8432f93b7e862e7dac6db0fe3d65f370