linux-kernel - Re: [PATCHv7 02/14] mm: Add support for unaccepted memory

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Message-ID: <Yt6LOD9Ae2NqyG1N@zn.tnic>
Date:   Mon, 25 Jul 2022 14:23:20 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "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>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.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: [PATCHv7 02/14] mm: Add support for unaccepted memory

On Fri, Jul 22, 2022 at 12:30:36PM -0700, Dave Hansen wrote:
> Sure does...  *Something* has to manage the cache coherency so that old
> physical aliases of the converted memory don't write back and clobber
> new data.  But, maybe the hardware is doing that now.

Let's hope.

> Yeah, that two-tier system is the way it's happening today from what
> I understand. This whole conversation is about how to handle the >4GB
> memory.

Would it be possible to pre-accept a bunch of mem - think "pre-fault" -
from userspace?

I.e., I'm thinking some huge process is going to start in the VM, VM
userspace goes and causes a chunk of memory to be pre-accepted and then
the process starts and runs more-or-less smoothly as the majority of its
memory has already been "prepared".

Or does that not make any sense from mm perspective?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette