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Date:   Tue, 16 Aug 2022 13:33:00 +0200
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From:   "Gupta, Pankaj" <pankaj.gupta@amd.com>
Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory
To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     "Nikunj A. Dadhania" <nikunj@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>, bharata@amd.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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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?

Thanks,
Pankaj
> 
> Definitely the page will still be pinned once it's allocated, there is
> no way to swap it out for example just with the current code. That kind
> of support, if desirable, can be extended through MOVABLE flag and some
> other callbacks to let feature-specific code to involve.