Re: [PATCH v2 11/13] kho: Allow kexec load before KHO finalization

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

On Thu, Dec 18, 2025 at 07:26:19PM -0500, Pasha Tatashin wrote:
> On Thu, Dec 18, 2025 at 4:49 PM Ricardo Neri
> <ricardo.neri-calderon@linux.intel.com> wrote:
> >
> > On Fri, Nov 14, 2025 at 02:00:00PM -0500, Pasha Tatashin wrote:
> > > Currently, kho_fill_kimage() checks kho_out.finalized and returns
> > > early if KHO is not yet finalized. This enforces a strict ordering where
> > > userspace must finalize KHO *before* loading the kexec image.
> > >
> > > This is restrictive, as standard workflows often involve loading the
> > > target kernel early in the lifecycle and finalizing the state (FDT)
> > > only immediately before the reboot.
> > >
> > > Since the KHO FDT resides at a physical address allocated during boot
> > > (kho_init), its location is stable. We can attach this stable address
> > > to the kimage regardless of whether the content has been finalized yet.
> > >
> > > Relax the check to only require kho_enable, allowing kexec_file_load
> > > to proceed at any time.
> > >
> > > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > > Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > > Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
> > > ---
> > >  kernel/liveupdate/kexec_handover.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> > > index 461d96084c12..4596e67de832 100644
> > > --- a/kernel/liveupdate/kexec_handover.c
> > > +++ b/kernel/liveupdate/kexec_handover.c
> > > @@ -1550,7 +1550,7 @@ int kho_fill_kimage(struct kimage *image)
> > >       int err = 0;
> > >       struct kexec_buf scratch;
> > >
> > > -     if (!kho_out.finalized)
> > > +     if (!kho_enable)
> > >               return 0;
> >
> > Hi Pasha,
> >
> > Using v6.19-rc1 (which has this changeset) and with:
> >
> > CONFIG_KEXEC_HANDOVER=y
> > CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
> > CONFIG_LIVEUPDATE=n (i.e., nobody calling kho_finalize())
> > no reserve_mem= entries in the kernel command line
> >
> > I omit doing
> >
> > echo 1 > /sys/kernel/debug/kho/out/finalize
> >
> > before doing
> >
> > kexec -l <kernel> --initrd=<initrd> --commandline="$(cat /proc/cmdline)"
> > kexec -e
> 
> Hi Ricardo,
> 
> Thank you for reporting this bug. I created a fix here:
> https://lore.kernel.org/lkml/20251219002355.3323896-1-pasha.tatashin@soleen.com
> 
> Please let me know if it works.

Thanks for the quick reply, Pasha. Your patch does work for me (I saw you
will post a v2).

From this patchset, I gather that kho_finalize() can be called multiple
times and in-kernel users of KHO should call it when done preparing their
subrees. Is that correct?