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

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Date:   Wed, 30 Sep 2020 10:09:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     shuo.a.liu@...el.com
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

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) & ...

?

> +			 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.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette