linux-kernel - Re: [PATCH 01/26] x86/tdx: Detect running as a TDX guest in early boot

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Date:   Tue, 14 Dec 2021 19:18:14 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, 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: [PATCH 01/26] x86/tdx: Detect running as a TDX guest in early
 boot

On Tue, Dec 14, 2021 at 06:02:39PM +0300, Kirill A. Shutemov wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> cc_platform_has() API is used in the kernel to enable confidential
> computing features. Since TDX guest is a confidential computing
> platform, it also needs to use this API.
> 
> In preparation of extending cc_platform_has() API to support TDX guest,
> use CPUID instruction to detect for TDX guests support in the early

" ... to detect support for TDX guests... "

> boot code (via tdx_early_init()). Since copy_bootdata() is the first
> user of cc_platform_has() API, detect the TDX guest status before it.

...

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 793e9b42ace0..a61ac6f8821a 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -872,6 +872,19 @@ config ACRN_GUEST
>  	  IOT with small footprint and real-time features. More details can be
>  	  found in https://projectacrn.org/.
>  
> +# TDX guest uses X2APIC for interrupt management.

For whom is that comment and who's going to see it? Is that comment
supposed to explain the "depends on X86_X2APIC" below?

> +config INTEL_TDX_GUEST
> +	bool "Intel TDX (Trust Domain Extensions) - Guest Support"
> +	depends on X86_64 && CPU_SUP_INTEL
> +	depends on X86_X2APIC
> +	help
> +	  Support running as a guest under Intel TDX.  Without this support,
> +	  the guest kernel can not boot or run under TDX.
> +	  TDX includes memory encryption and integrity capabilities
> +	  which protect the confidentiality and integrity of guest
> +	  memory contents and CPU state. TDX guests are protected from
> +	  potential attacks from the VMM.
> +

-- 
Regards/Gruss,
    Boris.

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