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

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Message-ID: <CAA03e5HxiLkOUbOrsgbzVdAUNZvnnryuNcqrz1ZWECtWLwKMXA@mail.gmail.com>
Date:   Fri, 24 Jun 2022 10:19:07 -0700
From:   Marc Orr <marcorr@...gle.com>
To:     Dave Hansen <dave.hansen@...el.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 Fri, Jun 24, 2022 at 10:10 AM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 6/24/22 10:06, Marc Orr wrote:
> > I think Peter's point is a little more nuanced than that. Once lazy
> > accept goes into the guest firmware -- without the feature negotiation
> > that Peter is suggesting -- cloud providers now have a bookkeeping
> > problem. Which images have kernels that can boot from a guest firmware
> > that doesn't pre-validate all the guest memory?
>
> Hold on a sec though...
>
> 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.