linux-kernel - Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory

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Date:   Tue, 10 Aug 2021 11:30:42 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory

On 8/9/21 11:26 PM, Kirill A. Shutemov wrote:
> +config UNACCEPTED_MEMORY
> +	bool
> +	depends on EFI_STUB
> +	help
> +	   Some Virtual Machine platforms, such as Intel TDX, introduce
> +	   the concept of memory acceptance, requiring memory to be accepted
> +	   before it can be used by the guest. This protects against a class of
> +	   attacks by the virtual machine platform.
> +
> +	   This option adds support for unaccepted memory and makes such memory
> +	   usable by kernel.

Do we really need a full-blown user-visible option here?  If we, for
instance, just did:

config UNACCEPTED_MEMORY
	bool
	depends on EFI_STUB

it could be 'select'ed from the TDX Kconfig and no users would ever be
bothered with it.  Would a user *ever* turn this on if they don't have
TDX (or equivalent)?