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Subject: Re: [PATCH v8 02/11] x86/tdx: Introduce INTEL_TDX_GUEST config option
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>, Deep Shah <sdeep@vmware.com>,
        VMware Inc <pv-drivers@vmware.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
Cc:     Peter H Anvin <hpa@zytor.com>, Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        linux-kernel@vger.kernel.org
References: <20211005025205.1784480-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20211005025205.1784480-3-sathyanarayanan.kuppuswamy@linux.intel.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <cf33750f-615a-1edd-0fee-28e720bb38ce@infradead.org>
Date:   Mon, 4 Oct 2021 21:53:01 -0700
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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