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;
+}
+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




Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
Ust-ID: DE 365 538 597

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.