linux-kernel - Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted memory

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Date:   Fri, 24 Jun 2022 10:47:09 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Marc Orr <marcorr@...gle.com>
Cc:     Peter Gonda <pgonda@...gle.com>,
        "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>,
        Ard Biesheuvel <ardb@...nel.org>,
        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>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Marcelo <marcelo.cerri@...onical.com>, tim.gardner@...onical.com,
        Khalid ElMously <khalid.elmously@...onical.com>,
        philip.cox@...onical.com,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted
 memory

On 6/24/22 10:19, Marc Orr wrote:
>> Is this a matter of
>>
>>         can boot from a guest firmware that doesn't pre-validate all the
>>         guest memory?
>>
>> or
>>
>>         can boot from a guest firmware that doesn't pre-validate all the
>>         guest memory ... with access to all of that guest's RAM?
>>
>> In other words, are we talking about "fails to boot" or "can't see all
>> the RAM"?
> Ah... yeah, you're right, Dave -- I guess it's the latter. The guest
> won't have access to all of the memory that the customer is paying
> for. But that's still bad. If the customer buys a 96 GB VM and can
> only see 4GB because they're kernel doesn't have these patches they're
> going to be confused and frustrated.

They'll at least be a _bit_ less angry and frustrated than if they were
staring at a blank screen. ;)  But, yeah, I totally get the point.

How big is the window going to be where we have guests that can have
unaccepted memory, but don't have acceptance support?  For TDX, it's
looking like it'll probably _just_ be 5.19.  Is TDX on 5.19 in shape
that cloud providers can deploy it?  Or, is stuff like lack of
attestation a deal breaker?