linux-kernel - [PATCH v2 1/2] kexec: introduce is_kho

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Message-ID: <7043f4da31390c58bb7721a3774c30998997df44.1755643201.git.epetron@amazon.de>
Date: Tue, 19 Aug 2025 23:22:45 +0000
From: Evangelos Petrongonas <epetron@...zon.de>
To: Ard Biesheuvel <ardb@...nel.org>, Mike Rapoport <rppt@...nel.org>
CC: Evangelos Petrongonas <epetron@...zon.de>, Alexander Graf
	<graf@...zon.com>, Changyuan Lyu <changyuanl@...gle.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
	<kexec@...ts.infradead.org>, <linux-mm@...ck.org>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nh-open-source@...zon.com>
Subject: [PATCH v2 1/2] kexec: introduce is_kho_boot()

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@...zon.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




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