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Date:   Wed, 06 Apr 2022 11:42:17 -0700
From:   "Andy Lutomirski" <luto@kernel.org>
To:     "Sean Christopherson" <seanjc@google.com>
Cc:     "Quentin Perret" <qperret@google.com>,
        "Steven Price" <steven.price@arm.com>,
        "Chao Peng" <chao.p.peng@linux.intel.com>,
        "kvm list" <kvm@vger.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        "Linux API" <linux-api@vger.kernel.org>, qemu-devel@nongnu.org,
        "Paolo Bonzini" <pbonzini@redhat.com>,
        "Jonathan Corbet" <corbet@lwn.net>,
        "Vitaly Kuznetsov" <vkuznets@redhat.com>,
        "Wanpeng Li" <wanpengli@tencent.com>,
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        "Joerg Roedel" <joro@8bytes.org>,
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        "J . Bruce Fields" <bfields@fieldses.org>,
        "Andrew Morton" <akpm@linux-foundation.org>,
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        "Nakajima, Jun" <jun.nakajima@intel.com>,
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        "Andi Kleen" <ak@linux.intel.com>,
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Subject: Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM guest
 private memory
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Precedence: bulk


On Tue, Apr 5, 2022, at 11:30 AM, Sean Christopherson wrote:
> On Tue, Apr 05, 2022, Andy Lutomirski wrote:

>
>> resume guest
>> *** host -> hypervisor -> guest ***
>> Guest unshares the page.
>> *** guest -> hypervisor ***
>> Hypervisor removes PTE.  TLBI.
>> *** hypervisor -> guest ***
>> 
>> Obviously considerable cleverness is needed to make a virt IOMMU like this
>> work well, but still.
>> 
>> Anyway, my suggestion is that the fd backing proposal get slightly modified
>> to get it ready for multiple subtypes of backing object, which should be a
>> pretty minimal change.  Then, if someone actually needs any of this
>> cleverness, it can be added later.  In the mean time, the
>> pread()/pwrite()/splice() scheme is pretty good.
>
> Tangentially related to getting private-fd ready for multiple things, 
> what about
> implementing the pread()/pwrite()/splice() scheme in pKVM itself?  I.e. 
> read() on
> the VM fd, with the offset corresponding to gfn in some way.
>

Hmm, could make sense.