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From: Jim Mattson <jmattson@google.com>
Date: Fri, 2 Nov 2018 09:44:54 -0700
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Subject: Re: [Qemu-devel] [QEMU PATCH v2 0/2]: KVM: i386: Add support for
 save and restore nested state
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To: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, kvm list <kvm@vger.kernel.org>, mtosatti@redhat.com, rth@twiddle.net, qemu-devel@nongnu.org

On Fri, Nov 2, 2018 at 5:59 AM, Liran Alon <liran.alon@oracle.com> wrote:
>

>>> Therefore, I don't think that we want this versioning to be based on KVM_CAP at all.
>>> It seems that we would want the process to behave as follows:
>>> 1) Mgmt-layer at dest queries dest host max supported nested_state size.
>>>   (Which should be returned from kvm_check_extension(KVM_CAP_NESTED_STATE))
>>> 2) Mgmt-layer at source initiate migration to dest with requesting QEMU to send nested_state
>>>   matching dest max supported nested_state size.
>>>   When saving nested state using KVM_GET_NESTED_STATE IOCTL, QEMU will specify in nested_state->size
>>>   the *requested* size to be saved and KVM should be able to save only the information which matches
>>>   the version that worked with that size.
>>> 3) After some sanity checks on received migration stream, dest host use KVM_SET_NESTED_STATE IOCTL.
>>>   This IOCTL should deduce which information it should deploy based on given nested_state->size.

I have to object to any proposal which requires the management later
to communicate with the source and the destination to determine what
should be done.