Message-ID: <ebe07977-8840-ebe2-57ce-9126a4081bb4@redhat.com>
Date:   Tue, 23 Nov 2021 16:20:02 +0100
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Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST
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To:     Paolo Bonzini <pbonzini@redhat.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Chao Peng <chao.p.peng@linux.intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        qemu-devel@nongnu.org, 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>
 <6de78894-8269-ea3a-b4ee-a5cc4dad827e@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <6de78894-8269-ea3a-b4ee-a5cc4dad827e@redhat.com>
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Precedence: bulk

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