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

Shuo A Liu
2020-10-12T08:40:45Z

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@intel.com 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