linux-kernel - Re: [PATCHv2 01/29] x86/tdx: Detect running as a TDX guest in early boot

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Date:   Wed, 2 Feb 2022 02:14:59 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 01/29] x86/tdx: Detect running as a TDX guest in early
 boot

On Tue, Feb 01, 2022 at 08:29:55PM +0100, Thomas Gleixner wrote:
> Kirill,
> 
> On Mon, Jan 24 2022 at 18:01, Kirill A. Shutemov wrote:
> 
> Just a nitpick...
> 
> > +static bool tdx_guest_detected __ro_after_init;
> > +
> > +bool is_tdx_guest(void)
> > +{
> > +	return tdx_guest_detected;
> > +}
> > +
> > +void __init tdx_early_init(void)
> > +{
> > +	u32 eax, sig[3];
> > +
> > +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2],  &sig[1]);
> > +
> > +	if (memcmp(TDX_IDENT, sig, 12))
> > +		return;
> > +
> > +	tdx_guest_detected = true;
> > +
> > +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> 
> So with that we have two ways to detect a TDX guest:
> 
>    - tdx_guest_detected
> 
>    - X86_FEATURE_TDX_GUEST
> 
> Shouldn't X86_FEATURE_TDX_GUEST be good enough?

Right. We have only 3 callers of is_tdx_guest() in cc_platform.c
I will replace them with cpu_feature_enabled(X86_FEATURE_TDX_GUEST).

Thanks.

-- 
 Kirill A. Shutemov