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Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private
 memory
To:     Sean Christopherson <seanjc@google.com>
Cc:     jejb@linux.ibm.com, Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <3b63a5d9-30e4-2ae8-2f01-a92b758e81de@redhat.com>
Date:   Wed, 1 Sep 2021 19:53:50 +0200
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On 01.09.21 19:50, Sean Christopherson wrote:
> On Wed, Sep 01, 2021, David Hildenbrand wrote:
>>>>> Well not necessarily, but it depends how clever we want to get.  If
>>>>> you look over on the OVMF/edk2 list, there's a proposal to do guest
>>>>> migration via a mirror VM that invokes a co-routine embedded in the
>>>>> OVMF binary:
>>>>
>>>> Yes, I heard of that. "Interesting" design.
>>>
>>> Heh, well what other suggestion do you have?  The problem is there
>>> needs to be code somewhere to perform some operations that's trusted by
>>> both the guest and the host.  The only element for a confidential VM
>>> that has this shared trust is the OVMF firmware, so it seems logical to
>>> use it.
>>
>> <offtopic>
>>
>> Let me put it this way: I worked with another architecture that doesn't
>> fault on access of a secure page, but instead automatically exports/encrypts
> 
> I thought s390 does fault on insecure accesses to secure pages, and it's the
> kernel's fault handler that "automatically" converts the page?  E.g. trap 0x3d
> -> do_secure_storage_access() -> arch_make_page_accessible().

"automatic" as in "the kernel can do it easily automatically under the 
hood when accessing such memory", yes that's what I meant :)

-- 
Thanks,

David / dhildenb