linux-kernel - Re: [PATCH v8 02/11] x86/tdx: Introduce INTEL_TDX

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Date:   Mon, 4 Oct 2021 21:53:01 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     Peter H Anvin <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 02/11] x86/tdx: Introduce INTEL_TDX_GUEST config option

On 10/4/21 7:51 PM, Kuppuswamy Sathyanarayanan wrote:
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 2b2a9639d8ae..c42dd8a2d1f4 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -865,6 +865,20 @@ config ACRN_GUEST
>   	  IOT with small footprint and real-time features. More details can be
>   	  found inhttps://projectacrn.org/.
>   
> +config INTEL_TDX_GUEST
> +	bool "Intel Trusted Domain eXtensions Guest Support"
> +	depends on X86_64 && CPU_SUP_INTEL && PARAVIRT
> +	depends on SECURITY
> +	select X86_X2APIC

Apparently some Intel CPUs don't have the x2apic feature, since the
Kconfig help text for X86_X2APIC says:

	  This enables x2apic support on CPUs that have this feature.

so how is it safe to set/enable/select that kconfig symbol?

Will the x2apic code just safely not work if the h/w feature is
missing?

> +	select SECURITY_LOCKDOWN_LSM
> +	help
> +	  Provide support for running in a trusted domain on Intel processors
> +	  equipped with Trusted Domain eXtensions. TDX is a Intel technology
> +	  that extends VMX and Memory Encryption with a new kind of virtual
> +	  machine guest called Trust Domain (TD). A TD is designed to run in
> +	  a CPU mode that protects the confidentiality of TD memory contents
> +	  and the TD’s CPU state from other software, including VMM.


thanks.
-- 
~Randy