Re: [PATCH v4 12/12] x86/traps: Fix up invalid PASID

[Luck, Tony]

On Fri, Jun 26, 2020 at 11:44:50AM +0200, Peter Zijlstra wrote:
> On Thu, Jun 25, 2020 at 01:17:22PM -0700, Fenghua Yu wrote:
> 
> > +static bool fixup_pasid_exception(void)
> > +{
> > +	if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> > +		return false;
> > +	if (!static_cpu_has(X86_FEATURE_ENQCMD))
> > +		return false;
> 
> elsewhere you had another variation:
> 
> +       if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> +               return;
> +
> +       if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> +               return;
> 
> Which is it, and why do we need the CONFIG thing when combined with the
> enabled thing?

Do we have a standard way of coding for a feature that depends on multiple
other features?  For this case the system needs to both suport the ENQCMD
instruction, and also have kernel code that programs the IOMMU.

And/or guidance on when to use each of the very somewhat simlar looking
	boot_cpu_has()
	static_cpu_has()
	IS_ENABLED()
	cpu_feature_enabled()
options?

-Tony