linux-kernel - Re: [PATCH v4 01/12] mm/shmem: Introduce F_SEAL

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Message-ID: <800a68f8-fbe0-5980-4290-bdc0ed4d05bd@redhat.com>
Date:   Tue, 8 Mar 2022 13:17:02 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Steven Price <steven.price@....com>,
        kvm list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org, Linux API <linux-api@...r.kernel.org>,
        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>,
        the arch/x86 maintainers <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>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE

On 3/7/22 14:26, Chao Peng wrote:
>> In pseudo-Rust, this is the difference between:
>>
>> fn convert_to_private(in: &mut Memfd)
>>
>> and
>>
>> fn convert_to_private(in: Memfd) -> PrivateMemoryFd
>>
>> This doesn't map particularly nicely to the kernel, though.
> I understand this Rust semantics and the difficulty to handle races.
> Probably we should not expose F_SEAL_INACCESSIBLE to userspace, instead
> we can use a new in-kernel flag to indicate the same thing. That flag
> should be set only when the memfd is created with MFD_INACCESSIBLE.

Yes, I like this.

Paolo