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Date:   Sun, 21 Aug 2022 11:27:44 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Hugh Dickins <hughd@google.com>
Cc:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
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        Paolo Bonzini <pbonzini@redhat.com>,
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        Sean Christopherson <seanjc@google.com>,
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        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>,
        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>,
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        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>,
        "Gupta, Pankaj" <pankaj.gupta@amd.com>
Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM
 guest private memory
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On Thu, Aug 18, 2022 at 08:00:41PM -0700, Hugh Dickins wrote:
> tmpfs and hugetlbfs and page cache are designed around sharing memory:
> TDX is designed around absolutely not sharing memory; and the further
> uses which Sean foresees appear not to need it as page cache either.
> 
> Except perhaps for page migration reasons.  It's somewhat incidental,  
> but of course page migration knows how to migrate page cache, so
> masquerading as page cache will give a short cut to page migration,
> when page migration becomes at all possible.

I haven't read the patch series, and I'm not taking a position one way
or the other on whether this is better implemented as a shmem addition
or a shim that asks shmem for memory.  Page migration can be done for
driver memory by using PageMovable.  I just rewrote how it works, so
the details are top of my mind at the moment if anyone wants something
explained.  Commit 68f2736a8583 is the key one to look at.