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

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Date:   Mon, 12 Oct 2020 16:40:36 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH v4 03/17] x86/acrn: Introduce an API to check if a VM is
 privileged

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@...el.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