linux-kernel - Re: [RFC PATCH 04/18] KVM: VMX: add cpu_has_vmx

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Message-ID: <aCI6e6KYXmfi_Oqp@google.com>
Date: Mon, 12 May 2025 11:14:19 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jon Kohler <jon@...anix.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	"Mickaël Salaün" <mic@...ikod.net>
Subject: Re: [RFC PATCH 04/18] KVM: VMX: add cpu_has_vmx_mbec helper

On Thu, Mar 13, 2025, Jon Kohler wrote:
> From: Mickaël Salaün <mic@...ikod.net>
> 
> Add 'cpu_has_vmx_mbec' helper to determine whether the cpu based VMCS
> from hardware has Intel Mode Based Execution Control exposed, which is
> secondary execution control bit 22.
> 
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> Co-developed-by: Jon Kohler <jon@...anix.com>
> Signed-off-by: Jon Kohler <jon@...anix.com>

LOL, really?  There's a joke in here about how many SWEs it takes...

> ---
>  arch/x86/kvm/vmx/capabilities.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index cb6588238f46..f83592272920 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -253,6 +253,12 @@ static inline bool cpu_has_vmx_xsaves(void)
>  		SECONDARY_EXEC_ENABLE_XSAVES;
>  }
>  
> +static inline bool cpu_has_vmx_mbec(void)
> +{
> +	return vmcs_config.cpu_based_2nd_exec_ctrl &
> +		SECONDARY_EXEC_MODE_BASED_EPT_EXEC;
> +}

This absolutely doesn't warrant its own patch.  Introduce it whenever its first
used/needed.

> +
>  static inline bool cpu_has_vmx_waitpkg(void)
>  {
>  	return vmcs_config.cpu_based_2nd_exec_ctrl &
> -- 
> 2.43.0
>