linux-kernel - Re: [RFC v2 00/16] Live Update Orchestrator

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Message-ID: <CA+CK2bBhe4zcxxgqE2X1OeWrWHr1qP_BQGzE7dRhtr1Rs+0S+w@mail.gmail.com>
Date: Fri, 23 May 2025 14:07:45 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
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Subject: Re: [RFC v2 00/16] Live Update Orchestrator

On Tue, May 20, 2025 at 3:25 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> Hi Pasha,
>
> On Thu, May 15, 2025 at 06:23:04PM +0000, Pasha Tatashin wrote:
> > This v2 series introduces the LUO, a kernel subsystem designed to
> > facilitate live kernel updates with minimal downtime,
> > particularly in cloud delplyoments aiming to update without fully
> > disrupting running virtual machines.
> >
> > This series builds upon KHO framework [1] by adding programmatic
> > control over KHO's lifecycle and leveraging KHO for persisting LUO's
> > own metadata across the kexec boundary. The git branch for this series
> > can be found at:
> > https://github.com/googleprodkernel/linux-liveupdate/tree/luo/rfc-v2
> >
> > What is Live Update?
> > Live Update is a specialized reboot process where selected kernel
> > resources (memory, file descriptors, and eventually devices) are kept
> > operational or their state preserved across a kernel transition (e.g.,
> > via kexec). For certain resources, DMA and interrupt activity might
> > continue with minimal interruption during the kernel reboot.
> >
> > LUO v2 Overview:
> > LUO v2 provides a framework for coordinating live updates. It features:
> > State Machine: Manages the live update process through states:
> > NORMAL, PREPARED, FROZEN, UPDATED.
> >
> > KHO Integration:
> >
> > LUO programmatically drives KHO's finalization and abort sequences.
> > KHO's debugfs interface is now optional configured via
> > CONFIG_KEXEC_HANDOVER_DEBUG.
> >
> > LUO preserves its own metadata via KHO's kho_add_subtree and
> > kho_preserve_phys() mechanisms.
>
> I've only had time to skip through the patches, one thing that came to mind
> was that since LUO is quite tightly coupled with KHO maybe we'll put them
> together in, say, kernel/liveupdate?

Thank you Mike, yes, a good idea, I also thought that it would make
sense for them to be in the same place, but initially I thought
perhaps KHO should be moved to misc/liveupdate/, but since it is
already landing in kernel/kexec_*, and it works with a bunch of core
kernel subsystems it makes sense to move LUO and KHO together under
kernel/liveupdate/

Pasha