Message-ID: <d2b46b84-8930-4304-2946-4d4a16698b24@redhat.com>
Date:   Mon, 22 Nov 2021 15:57:17 +0100
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Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST
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To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, qemu-devel@nongnu.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        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>,
        Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, john.ji@intel.com, susie.li@intel.com,
        jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com
References: <20211119134739.20218-1-chao.p.peng@linux.intel.com>
 <20211119134739.20218-2-chao.p.peng@linux.intel.com>
 <20211119151943.GH876299@ziepe.ca>
 <df11d753-6242-8f7c-cb04-c095f68b41fa@redhat.com>
 <20211119160023.GI876299@ziepe.ca>
 <4efdccac-245f-eb1f-5b7f-c1044ff0103d@redhat.com>
 <20211122133145.GQ876299@ziepe.ca>
 <56c0dffc-5fc4-c337-3e85-a5c9ce619140@redhat.com>
 <20211122140148.GR876299@ziepe.ca>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20211122140148.GR876299@ziepe.ca>
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On 22.11.21 15:01, Jason Gunthorpe wrote:
> On Mon, Nov 22, 2021 at 02:35:49PM +0100, David Hildenbrand wrote:
>> 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.
> 
> What is "ownership" in a world with kvm and iommu are reading pages
> out of the same fd?

In the world of encrypted memory / TDX, KVM somewhat "owns" that memory
IMHO (for example, only it can migrate or swap out these pages; it's
might be debatable if the TDX module or KVM actually "own" these pages ).

-- 
Thanks,

David / dhildenb