linux-kernel - Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

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Message-ID: <20220816122457.2fjyd4uz5hp5cani@box.shutemov.name>
Date:   Tue, 16 Aug 2022 15:24:57 +0300
From:   "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Gupta, Pankaj" <pankaj.gupta@....com>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>,
        "Nikunj A. Dadhania" <nikunj@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>, luto@...nel.org,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com,
        david@...hat.com, aarcange@...hat.com, ddutile@...hat.com,
        dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>, bharata@....com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory

On Tue, Aug 16, 2022 at 01:33:00PM +0200, Gupta, Pankaj wrote:
> Hi Chao,
> 
> > 
> > Actually the current version allows you to delay the allocation to a
> > later time (e.g. page fault time) if you don't call fallocate() on the
> > private fd. fallocate() is necessary in previous versions because we
> > treat the existense in the fd as 'private' but in this version we track
> > private/shared info in KVM so we don't rely on that fact from memory
> > backstores.
> 
> Does this also mean reservation of guest physical memory with secure
> processor (both for SEV-SNP & TDX) will also happen at page fault time?
> 
> Do we plan to keep it this way?

If you are talking about accepting memory by the guest, it is initiated by
the guest and has nothing to do with page fault time vs fallocate()
allocation of host memory. I mean acceptance happens after host memory
allocation but they are not in lockstep, acceptance can happen much later.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov