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Date:   Tue, 16 Aug 2022 15:03:12 +0200
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Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory
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To:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>,
        "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>, 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,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
        qemu-devel@nongnu.org, linux-fsdevel@vger.kernel.org
References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com>
 <b21f41e5-0322-bbfb-b9c2-db102488592d@amd.com>
 <9e86daea-5619-a216-fe02-0562cf14c501@amd.com>
 <9dc91ce8-4cb6-37e6-4c25-27a72dc11dd0@amd.com>
 <422b9f97-fdf5-54bf-6c56-3c45eff5e174@amd.com>
 <1407c70c-0c0b-6955-10bb-d44c5928f2d9@amd.com>
 <1136925c-2e37-6af4-acac-be8bed9f6ed5@amd.com>
 <1b02db9d-f2f1-94dd-6f37-59481525abff@amd.com>
 <20220815130411.GA1073443@chaop.bj.intel.com>
 <f0094f31-9669-47b5-eb52-6754a13ce757@amd.com>
 <20220816122457.2fjyd4uz5hp5cani@box.shutemov.name>
From:   "Gupta, Pankaj" <pankaj.gupta@amd.com>
In-Reply-To: <20220816122457.2fjyd4uz5hp5cani@box.shutemov.name>
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>>> 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