linux-kernel - Re: [PATCH v6 3/8] mm/memfd: Introduce MFD

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Message-ID: <CAGtprH8EMsPMMoOEzjRu0SMVKT0RqmkLk=n+6uXkBA6-wiRtUA@mail.gmail.com>
Date:   Tue, 31 May 2022 12:15:00 -0700
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        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>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jun Nakajima <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
Subject: Re: [PATCH v6 3/8] mm/memfd: Introduce MFD_INACCESSIBLE flag

On Thu, May 19, 2022 at 8:41 AM Chao Peng <chao.p.peng@...ux.intel.com> wrote:
>
> Introduce a new memfd_create() flag indicating the content of the
> created memfd is inaccessible from userspace through ordinary MMU
> access (e.g., read/write/mmap). However, the file content can be
> accessed via a different mechanism (e.g. KVM MMU) indirectly.
>

SEV, TDX, pkvm and software-only VMs seem to have usecases to set up
initial guest boot memory with the needed blobs.
TDX already supports a KVM IOCTL to transfer contents to private
memory using the TDX module but rest of the implementations will need
to invent
a way to do this.

Is there a plan to support a common implementation for either allowing
initial write access from userspace to private fd or adding a KVM
IOCTL to transfer contents to such a file,
as part of this series through future revisions?

Regards,
Vishal