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

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Message-ID: <20210812211732.l46uwa5p22s4nsqg@box.shutemov.name>
Date:   Fri, 13 Aug 2021 00:17:32 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        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
Subject: Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory

On Tue, Aug 10, 2021 at 12:19:22PM -0700, Dave Hansen wrote:
> On 8/10/21 12:08 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)?
> > But it's already not user selectable. Note that there's no prompt next to
> > the "bool". The "help" section is just for documentation. I think it can
> > be useful.
> 
> Ahh, gotcha.  I misread it.  Seems like an odd thing to do, but it's
> also fairly widespread in the tree.
> 
> Can you even reach that help text from any of the configuration tools?
> If you're doing an 'oldconfig', you won't get a prompt to do the "?".
> Even in the 'meunconfig' search results, it doesn't display "help" text,
> only the "prompt".

I don't know how get a tool show the text, but my vim sees just fine :P

> BTW, should this text call out that this is for parsing an actual UEFI
> feature along with the spec version?  It's not obvious from the text
> that "unaccepted memory" really is a UEFI thing as opposed to being some
> kernel-only concept.

Okay.

-- 
 Kirill A. Shutemov