Re: [PATCH v2 25/49] KVM: x86: Harden CPU capabilities processing against out-of-scope features

[Maxim Levitsky]

On Tue, 2024-07-09 at 11:11 -0700, Sean Christopherson wrote:
> On Thu, Jul 04, 2024, Maxim Levitsky wrote:
> > On Fri, 2024-05-17 at 10:39 -0700, Sean Christopherson wrote:
> > > +/*
> > > + * For kernel-defined leafs, mask the boot CPU's pre-populated value.  For KVM-
> > > + * defined leafs, explicitly set the leaf, as KVM is the one and only authority.
> > > + */
> > > +#define kvm_cpu_cap_init(leaf, mask)					\
> > > +do {									\
> > > +	const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);	\
> > > +	const u32 __maybe_unused kvm_cpu_cap_init_in_progress = leaf;	\
> > 
> > Why not to #define the kvm_cpu_cap_init_in_progress as well instead of a variable?
> 
> Macros can't #define new macros.  A macro could be used, but it would require the
> caller to #define and #undef the macro, e.g.

Oh, I somehow forgot about this, of course this is how C processor works.


> 	#define kvm_cpu_cap_init_in_progress CPUID_1_ECX
> 	kvm_cpu_cap_init(CPUID_1_ECX, ...)
> 	#undef kvm_cpu_cap_init_in_progress
> 
Yes, this is much uglier.

> but, stating the obvious, that's ugly and is less robust than automatically
> "defining" the in-progress leaf in kvm_cpu_cap_init().
> 

Best regards,
	Maxim Levitsky