linux-kernel - Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL

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Message-ID: <56c0dffc-5fc4-c337-3e85-a5c9ce619140@redhat.com>
Date:   Mon, 22 Nov 2021 14:35:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...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>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com
Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST

On 22.11.21 14:31, Jason Gunthorpe wrote:
> On Mon, Nov 22, 2021 at 10:26:12AM +0100, David Hildenbrand wrote:
> 
>> I do wonder if we want to support sharing such memfds between processes
>> in all cases ... we most certainly don't want to be able to share
>> encrypted memory between VMs (I heard that the kernel has to forbid
>> that). It would make sense in the use case you describe, though.
> 
> If there is a F_SEAL_XX that blocks every kind of new access, who
> cares if userspace passes the FD around or not?
I was imagining that you actually would want to do some kind of "change
ownership". But yeah, the intended semantics and all use cases we have
in mind are not fully clear to me yet. If it's really "no new access"
(side note: is "access" the right word?) then sure, we can pass the fd
around.

-- 
Thanks,

David / dhildenb