linux-kernel - Re: [PATCHv6 02/15] mm: Add support for unaccepted memory

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Message-ID: <20220519115527.jqzrvsqk4o225m6d@black.fi.intel.com>
Date:   Thu, 19 May 2022 14:55:27 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Gupta, Pankaj" <pankaj.gupta@....com>
Cc:     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>,
        Dave Hansen <dave.hansen@...el.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: [PATCHv6 02/15] mm: Add support for unaccepted memory

On Thu, May 19, 2022 at 12:43:15PM +0200, Gupta, Pankaj wrote:
> If both Intel TDX and AMD SEV-SNP requires the memory to be accepted before
> it can be used by the guest. In what other use cases (apart from memory
> hotplug), the lazy memory acceptance will be useful?

It is nothing to do with hotplug.

Any memory has to be accepted before it can be used inside the TDX or
SEV-SNP guest. It can happen upfront, before kernel gets control (like by
firmware) or by kernel. The idea is to accept small portion of the memory
upfront and leave the rest to the kernel. The reason why delaying
acceptance make sense is boot time. We want the guest to start doing
useful stuff as fast as possible.

-- 
 Kirill A. Shutemov