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

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Message-ID: <ebe07977-8840-ebe2-57ce-9126a4081bb4@redhat.com>
Date:   Tue, 23 Nov 2021 16:20:02 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        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,
        qemu-devel@...gnu.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>,
        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 23.11.21 10:06, Paolo Bonzini wrote:
> On 11/19/21 16:39, David Hildenbrand wrote:
>>> If qmeu can put all the guest memory in a memfd and not map it, then
>>> I'd also like to see that the IOMMU can use this interface too so we
>>> can have VFIO working in this configuration.
>>
>> In QEMU we usually want to (and must) be able to access guest memory
>> from user space, with the current design we wouldn't even be able to
>> temporarily mmap it -- which makes sense for encrypted memory only. The
>> corner case really is encrypted memory. So I don't think we'll see a
>> broad use of this feature outside of encrypted VMs in QEMU. I might be
>> wrong, most probably I am:)
> 
> It's not _that_ crazy an idea, but it's going to be some work to teach 
> KVM that it has to kmap/kunmap around all memory accesses.

I'm also concerned about userspace access. But you sound like you have a
plan :)

-- 
Thanks,

David / dhildenb