linux-kernel - Re: [PATCH v5 05/22] liveupdate: kho: when live update add KHO image during kexec load

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Message-ID: <CA+CK2bA=cQkibx4dSxJQTVxVxqkAsZPfFoPJip6rx8DqX62aEA@mail.gmail.com>
Date: Mon, 10 Nov 2025 10:31:23 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
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Subject: Re: [PATCH v5 05/22] liveupdate: kho: when live update add KHO image
 during kexec load

On Mon, Nov 10, 2025 at 7:47 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Fri, Nov 07, 2025 at 04:03:03PM -0500, Pasha Tatashin wrote:
> > In case KHO is driven from within kernel via live update, finalize will
> > always happen during reboot, so add the KHO image unconditionally.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> > ---
> >  kernel/liveupdate/kexec_handover.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> > index 9f0913e101be..b54ca665e005 100644
> > --- a/kernel/liveupdate/kexec_handover.c
> > +++ b/kernel/liveupdate/kexec_handover.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/kexec_handover.h>
> >  #include <linux/libfdt.h>
> >  #include <linux/list.h>
> > +#include <linux/liveupdate.h>
> >  #include <linux/memblock.h>
> >  #include <linux/page-isolation.h>
> >  #include <linux/vmalloc.h>
> > @@ -1489,7 +1490,7 @@ int kho_fill_kimage(struct kimage *image)
> >       int err = 0;
> >       struct kexec_buf scratch;
> >
> > -     if (!kho_out.finalized)
> > +     if (!kho_out.finalized && !liveupdate_enabled())
> >               return 0;
>
> This feels backwards, I don't think KHO should call liveupdate methods.

It is backward, but it is a requirement until KHO becomes stateless.
LUO does not have dependencies on userspace state of when kexec is
loaded. In fact the next kernel must be loaded before the brownout as
it is an expensive operation. The sequence of events should:

1. Load the next kernel in memory
2. Preserve resources via LUO
3. Do Kexec reboot

Pasha