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

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Message-ID: <78B2A649-BF46-4907-86FA-952D6CAD162B@nutanix.com>
Date: Tue, 13 May 2025 02:17:06 +0000
From: Jon Kohler <jon@...anix.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de"
	<tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de"
	<bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...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 May 12, 2025, at 2:14 PM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> !-------------------------------------------------------------------|
>  CAUTION: External Email
> 
> |-------------------------------------------------------------------!
> 
> 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...

42, I think.

> 
>> ---
>> 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.

Yep, will do

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