Re: [PATCH v2 4/7] KVM: x86: Add a per-vendor callback to setup EFER caps

[Sean Christopherson]

On Mon, Jul 06, 2026, Yosry Ahmed wrote:
> Move handling EFER.SVME and EFER.LMSLE from hardware setup to a new
> optional per-vendor callback invoked from kvm_setup_efer_caps(). This
> centralizes allowed EFER bits handling to kvm_setup_efer_caps(),
> facilitating following changes to move efer_reserved_bits into kvm_caps.
> 
> Move the call to kvm_setup_efer_caps() after per-vendor ops are
> initialized.

Why?

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a0b2c40d93c21..a297a77469b38 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6903,6 +6903,8 @@ static void kvm_setup_efer_caps(void)
>  
>  	if (kvm_cpu_cap_has(X86_FEATURE_AUTOIBRS))
>  		kvm_enable_efer_bits(EFER_AUTOIBRS);
> +
> +	kvm_x86_call(setup_efer_caps)();

I would rather move the togging to kvm_setup_efer_caps(), e.g.

  static void kvm_setup_efer_caps(void)
  {
	/* Enable syscall by default because its emulated by KVM */
	kvm_caps.supported_efer_bits = (u64)EFER_SCE;

	if (kvm_cpu_cap_has(X86_FEATURE_LM))
		kvm_caps.supported_efer_bits |= (EFER_LME | EFER_LMA);

	if (kvm_cpu_cap_has(X86_FEATURE_NX))
		kvm_caps.supported_efer_bits |= EFER_NX;

	if (kvm_cpu_cap_has(X86_FEATURE_FXSR_OPT))
		kvm_caps.supported_efer_bits |= EFER_FFXSR;

	if (kvm_cpu_cap_has(X86_FEATURE_AUTOIBRS))
		kvm_caps.supported_efer_bits |= EFER_AUTOIBRS;

	if (kvm_cpu_cap_has(X86_FEATURE_SVM)) {
		kvm_caps.supported_efer_bits |= EFER_SVME;
		if (!boot_cpu_has(X86_FEATURE_EFER_LMSLE_MBZ))
			kvm_caps.supported_efer_bits |= EFER_LMSLE;
	}
  }