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

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Message-ID: <f95f35af-4824-2a2a-7cd0-71d1fda6867a@amd.com>
Date:   Tue, 16 Aug 2022 15:03:12 +0200
From:   "Gupta, Pankaj" <pankaj.gupta@....com>
To:     "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.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


>>> 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.

No, I meant reserving guest physical memory range from hypervisor e.g 
with RMPUpdate for SEV-SNP or equivalent at TDX side (PAMTs?).

Thanks,
Pankaj