Re: [PATCH v3] x86/speculation/l1tf: Add KConfig for setting the L1D cache flush mode

[Waiman Long <longman@redhat.com>]

On 7/5/20 11:23 AM, Mike Rapoport wrote:
>> Nothing prevents people from continuing to use the command line
>> options if they want, right?  This just allows a different default.
>> So if a distro is security focused and decided that it wanted a slower
>> / more secure default then it could ship that way but individual users
>> could still override, right?
> Well, nothing prevents you from continuing to use the command line as
> well;-)
>
> I can see why whould you want an ability to select compile time default
> for an option, but I'm really not thrilled by the added ifdefery.
>   

It turns out that CONFIG_KVM_VMENTRY_L1D_FLUSH values match the enum 
vmx_l1d_flush_state values. So one way to reduce the ifdefery is to do, 
for example,

+#ifdef CONFIG_KVM_VMENTRY_L1D_FLUSH
+#define VMENTER_L1D_FLUSH_DEFAULT CONFIG_KVM_VMENTRY_L1D_FLUSH
+#else
+#define VMENTER_L1D_FLUSH_DEFAULT      VMENTER_L1D_FLUSH_AUTO
#endif
-enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_DEFAULT;

Of course, we may need to add a comment on enum vmx_l1d_flush_state 
definition to highlight the dependency of CONFIG_KVM_VMENTRY_L1D_FLUSH 
on it to avoid future mismatch.

Cheers,
Longman