Re: [PATCH v4 03/17] x86/acrn: Introduce an API to check if a VM is privileged

[Shuo A Liu]

Hi Boris,

On Wed 30.Sep'20 at 10:09:59 +0200, Borislav Petkov wrote:
> On Tue, Sep 22, 2020 at 07:42:57PM +0800, shuo.a.liu@xxxxxxxxx wrote:
> > +static u32 acrn_cpuid_base(void)
> > +{
> > +	static u32 acrn_cpuid_base;
> > +
> > +	if (!acrn_cpuid_base && boot_cpu_has(X86_FEATURE_HYPERVISOR))
> > +		acrn_cpuid_base = hypervisor_cpuid_base("ACRNACRNACRN", 0);
> > +
> > +	return acrn_cpuid_base;
> > +}
> > +
> > +bool acrn_is_privileged_vm(void)
> > +{
> > +	return cpuid_eax(acrn_cpuid_base() | ACRN_CPUID_FEATURES) &
>
> What's that dance and acrn_cpuid_base static thing needed for? Why not
> simply:
>
> 	cpuid_eax(ACRN_CPUID_FEATURES) & ...
>
> ?

hypervisor_cpuid_base() searches reserved hypervisor cpuid region and
return the base matched the right signature, the base might vary. So i
put it here.

> > +			 ACRN_FEATURE_PRIVILEGED_VM;
> > +}
> > +EXPORT_SYMBOL_GPL(acrn_is_privileged_vm);
>
> Also, if you're going to need more of those bit checkers acrn_is_<something>
> which look at ACRN_CPUID_FEATURES, just stash CPUID_0x40000001_EAX locally and
> use a
>
> 	acrn_has(ACRN_FEATURE_PRIVILEGED_VM)
>
> which does the bit testing.

Thanks. Currently, there is only one feature bit. I will introduce
that you suggested with more feature bits to be tested.

Thanks
shuo