linux-kernel - Re: [PATCHv4 1/8] mm: Add support for unaccepted memory

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Date:   Mon, 11 Apr 2022 09:27:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        Brijesh Singh <brijesh.singh@....com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCHv4 1/8] mm: Add support for unaccepted memory

On 4/11/22 08:55, Borislav Petkov wrote:
> On Sun, Apr 10, 2022 at 11:41:57PM -0700, Dave Hansen wrote:
>> Let's just call out the possible (probable?) need for new ABI here.
>> Maybe it will cue folks who care to speak up.
> Err, why would you teach the user to go poke at some arbitrary sysfs
> nodes when the accepting code can simply issue a printk from time to
> time
> 
>   "Guest unnaccepted memory progress: XX%. This slows down operations at the moment."

I guess that's not a horrible place to start.  It's also not *horribly*
different from how guests work today.  If hosts lazily allocate RAM,
they'll see largely the same kind of behavior.

What ends up determining how much memory is pre-accepted versus being
done from the guest?  Is that just a normal part of setting up a TDX
guest, like from the qemu cmdline?  Or, is there some convention with
the virtual firmware?