Re: [PATCH v2 1/2] kexec: introduce is_kho_boot()

[Mike Rapoport <rppt@kernel.org>]

On Tue, Aug 19, 2025 at 11:22:45PM +0000, Evangelos Petrongonas wrote:
> During early initialisation, after a kexec, other components, like EFI
> need to know if a KHO enabled kexec is performed. The `kho_is_enabled`
> function is not enough as in the early stages, it only reflects
> whether the cmdline has KHO enabled, not if an actual KHO FDT exists.
> 
> Extend the KHO API with `is_kho_boot()` to provide a way for components
> to check if a KHO enabled kexec is performed.
> 
> Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
> ---
>  include/linux/kexec_handover.h |  6 ++++++
>  kernel/kexec_handover.c        | 20 ++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index 348844cffb13..559d13a3bc44 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -40,6 +40,7 @@ struct kho_serialization;
>  
>  #ifdef CONFIG_KEXEC_HANDOVER
>  bool kho_is_enabled(void);
> +bool is_kho_boot(void);
>  
>  int kho_preserve_folio(struct folio *folio);
>  int kho_preserve_phys(phys_addr_t phys, size_t size);
> @@ -60,6 +61,11 @@ static inline bool kho_is_enabled(void)
>  	return false;
>  }
>  
> +static inline bool is_kho_boot(void)
> +{
> +	return false;
> +}
> +
>  static inline int kho_preserve_folio(struct folio *folio)
>  {
>  	return -EOPNOTSUPP;
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index 69b953551677..a1a4e76e0ff1 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -925,6 +925,26 @@ static const void *kho_get_fdt(void)
>  	return kho_in.fdt_phys ? phys_to_virt(kho_in.fdt_phys) : NULL;
>  }
>  
> +/**
> + * is_kho_boot - check if current kernel was booted via KHO-enabled
> + * kexec
> + *
> + * This function checks if the current kernel was loaded through a kexec
> + * operation with KHO enabled, by verifying both that KHO is enabled via
> + * cmdline AND that a valid KHO FDT was passed.
> + *
> + * Note: This function returns reliable results only after
> + * kho_populate() has been called during early boot. Before that,
> + * it may return false even if KHO data is present.
> + *
> + * Return: true if booted via KHO-enabled kexec, false otherwise
> + */
> +bool is_kho_boot(void)
> +{
> +	return !!kho_get_fdt() && kho_enable;

Let's drop '&& kho_enable' and presume that a kernel that booted with KHO
FDT goes through KHO revival.

With that change feel free to add

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> +}
> +EXPORT_SYMBOL_GPL(is_kho_boot);
> +
>  /**
>   * kho_retrieve_subtree - retrieve a preserved sub FDT by its name.
>   * @name: the name of the sub FDT passed to kho_add_subtree().
> -- 
> 2.47.3

-- 
Sincerely yours,
Mike.