linux-kernel - [PATCH v5 1/7] kho: allow to drive kho from within kernel

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Message-ID: <20251007033100.836886-2-pasha.tatashin@soleen.com>
Date: Tue,  7 Oct 2025 03:30:54 +0000
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	brauner@...nel.org,
	corbet@....net,
	graf@...zon.com,
	jgg@...pe.ca,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org,
	masahiroy@...nel.org,
	ojeda@...nel.org,
	pasha.tatashin@...een.com,
	pratyush@...nel.org,
	rdunlap@...radead.org,
	rppt@...nel.org,
	tj@...nel.org
Subject: [PATCH v5 1/7] kho: allow to drive kho from within kernel

Allow to do finalize and abort from kernel modules, so LUO could
drive the KHO sequence via its own state machine.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 include/linux/kexec_handover.h | 15 +++++++
 kernel/kexec_handover.c        | 74 ++++++++++++++++++++--------------
 2 files changed, 59 insertions(+), 30 deletions(-)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 25042c1d8d54..04d0108db98e 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -67,6 +67,10 @@ void kho_memory_init(void);
 
 void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys,
 		  u64 scratch_len);
+
+int kho_finalize(void);
+int kho_abort(void);
+
 #else
 static inline bool kho_is_enabled(void)
 {
@@ -139,6 +143,17 @@ static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 				phys_addr_t scratch_phys, u64 scratch_len)
 {
 }
+
+static inline int kho_finalize(void)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int kho_abort(void)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif /* CONFIG_KEXEC_HANDOVER */
 
 #endif /* LINUX_KEXEC_HANDOVER_H */
diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index 76f0940fb485..76c34ea923f0 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -1067,7 +1067,7 @@ static int kho_out_update_debugfs_fdt(void)
 	return err;
 }
 
-static int kho_abort(void)
+static int __kho_abort(void)
 {
 	int err;
 	unsigned long order;
@@ -1100,7 +1100,27 @@ static int kho_abort(void)
 	return err;
 }
 
-static int kho_finalize(void)
+int kho_abort(void)
+{
+	int ret = 0;
+
+	if (!kho_enable)
+		return -EOPNOTSUPP;
+
+	guard(mutex)(&kho_out.lock);
+	if (!kho_out.finalized)
+		return -ENOENT;
+
+	ret = __kho_abort();
+	if (ret)
+		return ret;
+
+	kho_out.finalized = false;
+
+	return kho_out_update_debugfs_fdt();
+}
+
+static int __kho_finalize(void)
 {
 	int err = 0;
 	u64 *preserved_mem_map;
@@ -1143,12 +1163,32 @@ static int kho_finalize(void)
 abort:
 	if (err) {
 		pr_err("Failed to convert KHO state tree: %d\n", err);
-		kho_abort();
+		__kho_abort();
 	}
 
 	return err;
 }
 
+int kho_finalize(void)
+{
+	int ret;
+
+	if (!kho_enable)
+		return -EOPNOTSUPP;
+
+	guard(mutex)(&kho_out.lock);
+	if (kho_out.finalized)
+		return -EEXIST;
+
+	ret = __kho_finalize();
+	if (ret)
+		return ret;
+
+	kho_out.finalized = true;
+
+	return kho_out_update_debugfs_fdt();
+}
+
 static int kho_out_finalize_get(void *data, u64 *val)
 {
 	mutex_lock(&kho_out.lock);
@@ -1160,33 +1200,7 @@ static int kho_out_finalize_get(void *data, u64 *val)
 
 static int kho_out_finalize_set(void *data, u64 _val)
 {
-	int ret = 0;
-	bool val = !!_val;
-
-	mutex_lock(&kho_out.lock);
-
-	if (val == kho_out.finalized) {
-		if (kho_out.finalized)
-			ret = -EEXIST;
-		else
-			ret = -ENOENT;
-		goto unlock;
-	}
-
-	if (val)
-		ret = kho_finalize();
-	else
-		ret = kho_abort();
-
-	if (ret)
-		goto unlock;
-
-	kho_out.finalized = val;
-	ret = kho_out_update_debugfs_fdt();
-
-unlock:
-	mutex_unlock(&kho_out.lock);
-	return ret;
+	return (!!_val) ? kho_finalize() : kho_abort();
 }
 
 DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
-- 
2.51.0.618.g983fd99d29-goog