Re: [PATCH RFC v1 08/20] KVM: VMX: Support extended register index in exit handling

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/10/25 19:01, Chang S. Bae wrote:
> Support to 5-bit register indices in VMCS fields when EGPRs are enabled.
> 
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> ---
> RFC note:
> The "chicken bit" (XCR0.APX) checker is intentionally deferred, as the
> emulator in the next series will do a similar check. Consolidating the
> XCR0 handling at the end keeps the logic clearer during the feature
> exposition.
> ---
>   arch/x86/kvm/vmx/vmx.h | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index b8da6ebc35dc..6cf1eb739caf 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -374,12 +374,17 @@ struct vmx_insn_info {
>   
>   static inline bool vmx_egpr_enabled(struct kvm_vcpu *vcpu __maybe_unused) { return false; }
>   
> -static inline struct vmx_insn_info vmx_get_insn_info(struct kvm_vcpu *vcpu __maybe_unused)
> +static inline struct vmx_insn_info vmx_get_insn_info(struct kvm_vcpu *vcpu)
>   {
>   	struct vmx_insn_info insn;
>   
> -	insn.extended  = false;
> -	insn.info.word = vmcs_read32(VMX_INSTRUCTION_INFO);
> +	if (vmx_egpr_enabled(vcpu)) {
> +		insn.extended   = true;
> +		insn.info.dword = vmcs_read64(EXTENDED_INSTRUCTION_INFO);
> +	} else {
> +		insn.extended  = false;
> +		insn.info.word = vmcs_read32(VMX_INSTRUCTION_INFO);
> +	}

Could this use static_cpu_has(X86_FEATURE_APX) instead, which is more 
efficient (avoids a runtime test)?

>   	return insn;
>   }
> @@ -415,7 +420,10 @@ static __always_inline unsigned long vmx_get_exit_qual(struct kvm_vcpu *vcpu)
>   
>   static inline int vmx_get_exit_qual_gpr(struct kvm_vcpu *vcpu)
>   {
> -	return (vmx_get_exit_qual(vcpu) >> 8) & 0xf;
> +	if (vmx_egpr_enabled(vcpu))
> +		return (vmx_get_exit_qual(vcpu) >> 8) & 0x1f;
> +	else
> +		return (vmx_get_exit_qual(vcpu) >> 8) & 0xf;

Can this likewise mask against 0x1f, unconditionally?

Paolo

>   }
>   
>   static __always_inline u32 vmx_get_intr_info(struct kvm_vcpu *vcpu)