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

[Oliver Sang <oliver.sang@intel.com>]

hi, Chang,

On Mon, Jul 20, 2026 at 05:19:29PM +0000, 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@mail.gmail.com
> 
> 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.

thanks for mentioning us 0-day.

for previous version, we captured a regression in ltp.kvm_vmx01 test, now we
tested upon this version again and confirmed the test passes now. thanks!

Tested-by: kernel test robot <oliver.sang@intel.com>


> 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,
> Chang
> 
> Relevant Posting
>  * V4: https://lore.kernel.org/20260512011502.53072-1-chang.seok.bae@intel.com
>  * KVM-unit-test patch: https://lore.kernel.org/20260420212355.507827-1-chang.seok.bae@intel.com
> 
> 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
> -- 
> 2.53.0
>