Re: [PATCH v5 02/22] liveupdate: luo_core: integrate with KHO

[Mike Rapoport <rppt@kernel.org>]

On Fri, Nov 07, 2025 at 04:03:00PM -0500, Pasha Tatashin wrote:
> Integrate the LUO with the KHO framework to enable passing LUO state
> across a kexec reboot.
> 
> When LUO is transitioned to a "prepared" state, it tells KHO to
> finalize, so all memory segments that were added to KHO preservation
> list are getting preserved. After "Prepared" state no new segments
> can be preserved. If LUO is canceled, it also tells KHO to cancel the
> serialization, and therefore, later LUO can go back into the prepared
> state.
> 
> This patch introduces the following changes:
> - During the KHO finalization phase allocate FDT blob.
> - Populate this FDT with a LUO compatibility string ("luo-v1").
> 
> LUO now depends on `CONFIG_KEXEC_HANDOVER`. The core state transition
> logic (`luo_do_*_calls`) remains unimplemented in this patch.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---

...

> @@ -69,7 +197,22 @@ early_param("liveupdate", early_liveupdate_param);
>   */
>  int liveupdate_reboot(void)
>  {
> -	return 0;
> +	int err;
> +
> +	if (!liveupdate_enabled())
> +		return 0;
> +
> +	err = kho_finalize();

kho_finalize() should be really called from kernel_kexec().

We avoided it because of the concern that memory allocations that late in
reboot could be an issue. But I looked at hibernate() and it does
allocations on reboot->hibernate path, so adding kho_finalize() as the
first step of kernel_kexec() seems fine.

And if we prioritize stateless memory tracking in KHO, it won't be a
concern at all.

> +	if (err) {
> +		pr_err("kho_finalize failed %d\n", err);
> +		/*
> +		 * kho_finalize() may return libfdt errors, to aboid passing to
> +		 * userspace unknown errors, change this to EAGAIN.
> +		 */
> +		err = -EAGAIN;
> +	}
> +
> +	return err;
>  }
>  
>  /**

-- 
Sincerely yours,
Mike.