KVM: VMX: Introduce Intel Mode-Based Execute Control (MBEC)

[RFC PATCH 04/18] KVM: VMX: add cpu_has_vmx_mbec helper

Posted by Jon Kohler 9 months, 1 week ago

From: Mickaël Salaün <mic@digikod.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@digikod.net>
Co-developed-by: Jon Kohler <jon@nutanix.com>
Signed-off-by: Jon Kohler <jon@nutanix.com>

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

Re: [RFC PATCH 04/18] KVM: VMX: add cpu_has_vmx_mbec helper

Posted by Sean Christopherson 7 months, 1 week ago

On Thu, Mar 13, 2025, Jon Kohler wrote:
> From: Mickaël Salaün <mic@digikod.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@digikod.net>
> Co-developed-by: Jon Kohler <jon@nutanix.com>
> Signed-off-by: Jon Kohler <jon@nutanix.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
>

Re: [RFC PATCH 04/18] KVM: VMX: add cpu_has_vmx_mbec helper

Posted by Jon Kohler 7 months, 1 week ago


> On May 12, 2025, at 2:14 PM, Sean Christopherson <seanjc@google.com> wrote:
> 
> !-------------------------------------------------------------------|
>  CAUTION: External Email
> 
> |-------------------------------------------------------------------!
> 
> On Thu, Mar 13, 2025, Jon Kohler wrote:
>> From: Mickaël Salaün <mic@digikod.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@digikod.net>
>> Co-developed-by: Jon Kohler <jon@nutanix.com>
>> Signed-off-by: Jon Kohler <jon@nutanix.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