Re: [PATCH 01/21] qapi/migration: add cpr-luo migration mode

[Markus Armbruster <armbru@redhat.com>]

Dongli Zhang <dongli.zhang@oracle.com> writes:

> On Wed, Oct 14, 2026 12:42:55AM -0700, Markus Armbruster wrote:
>> Dongli Zhang <dongli.zhang@oracle.com> writes:
>> 
>>> Add the cpr-luo migration mode for CPR through the Linux Live Update
>>> Orchestrator (LUO). Subsequent changes preserve CPR state and RAMBlock
>>> backing file descriptors in an LUO session across a host kernel update.
>>>
>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>> ---
>>>  qapi/migration.json | 11 ++++++++++-
>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/qapi/migration.json b/qapi/migration.json
>>> index 889a9b89c2..ab117c3897 100644
>>> --- a/qapi/migration.json
>>> +++ b/qapi/migration.json
>>> @@ -712,9 +712,18 @@
>>>  #     with the '-machine aux-ram-share=on' option.
>>>  #
>>>  #     (since 10.2)
>>> +#
>>> +# @cpr-luo: A CPR mode that preserves guest RAM backing file
>>> +#     descriptors and CPR state through the Linux Live Update
>>> +#     Orchestrator (LUO) across a host kernel update.
>>> +#
>>> +#     This mode requires Linux with LUO support.
>> 
>> Pardon my ignorant question: host or guest kernel?
>> 
> Host KVM kernel.

Suggest something like "This mode requires Linux with LUO support on the
host", or "This mode requires the host to run Linux with LUO support".

> cpr-luo is more similar to cpr-exec (assuming VFIO is not involved).
>
> cpr-exec (same process across exec):
>
> - RAMBlock fds are preserved across exec(). The metadata is transferred to the
> target via a memfd passed through an environment variable.
> - The device state (i.e., virtio) is transferred through the main stream (i.e.,
> a file).
>
> cpr-transfer (two processes):
>
> - RAMBlock fds are preserved and transferred to the target QEMU via a UNIX
> domain socket.
> - The device state (i.e., virtio) is transferred through the main stream (i.e.,
> local TCP).
>
> cpr-reboot (across reboot):
>
> - The RAMBlock is always reconstructed. It is just a matter of whether to
> save/load the memory data, depending on whether x-ignore-shared is enabled.
> - The vmstate (i.e., virtio) is transferred through the main stream (i.e., a file).
>
> New cpr-luo (across kexec/LUO/KHO):
>
> - RAMBlock fds are preserved and transferred across kexec to the target QEMU via
> LUO/KHO, identified by a LUO session and tokens.
> - The device state (i.e., virtio) is transferred through the main stream (i.e.,
> a file).

Is this covered in the documentation?

> Thank you very much!
>
> Dongli Zhang

You're welcome!