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

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Date:   Fri, 24 Jun 2022 11:13:30 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     Marc Orr <marcorr@...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 11:10, Peter Gonda wrote:
>> 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?
> This is complicated because distros don't run upstream linux versions.
> If I understand correctly (I see some distro emails on here so please
> correct me) distros normally maintain forks which they backport things
> into. So I cannot answer this question. It is possible that a
> hypothetical distro backports only the SNP/TDX initial patches and
> doesn't take these for many releases.

Distros could also backport a bare-bones version of this set that
doesn't do anything fancy and just synchronously accepts the memory at
boot.  No bitmap, no page allocator changes.  It'll slow boot down, but
is better than having no RAM.