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

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Date:   Mon, 25 Jul 2022 16:00:14 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "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>,
        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 Mon, Jul 25, 2022 at 02:23:20PM +0200, Borislav Petkov wrote:
> 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".

An application in the VM can do mlock() or mmap(..., MAP_POPULATE, ...) and
this will essentially force acceptance of that memory.

But there's no sysctl or something for that.
 
> Or does that not make any sense from mm perspective?
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

-- 
Sincerely yours,
Mike.