kho: expose kho_scratch_overlap() to kexec_handover.h

Support for discovering memory blocks with no preserved memory will be
added in coming patches. These areas will also be marked as scratch to
allow allocations from them. Memblock will switch to looking through the
scratch array to decide the right migratetype.

Expose kho_scratch_overlap() to KHO users. Since it is now used by
non-debug code, move it out of kexec_handover_debug.c and into
kexec_handover.c. Gate the overlap checks in kho_preserve_folio() and
kho_preserve_pages() by IS_ENABLED(CONFIG_KEXEC_HANDOVER_DEBUG) instead.

Since kexec_handover_debug.c is now empty, delete it.

Add a stub for kho_scratch_overlap() to memblock tests to make sure it
compiles. It will be used in memblock by a coming commit.

No functional changes.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Link: https://patch.msgid.link/20260801084833.1897543-14-pratyush@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

include/linux/kexec_handover.h

@@ -36,6 +36,8 @@ void kho_memory_init(void);
 
 void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys,
 		  u64 scratch_len);
+
+bool kho_scratch_overlap(phys_addr_t phys, size_t size);
 #else
 static inline bool kho_is_enabled(void)
 {
@@ -112,6 +114,11 @@ static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 				phys_addr_t scratch_phys, u64 scratch_len)
 {
 }
+
+static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size)
+{
+	return false;
+}
 #endif /* CONFIG_KEXEC_HANDOVER */
 
 #endif /* LINUX_KEXEC_HANDOVER_H */

kernel/liveupdate/Makefile

@@ -8,7 +8,6 @@ luo-y :=								\
 		luo_session.o
 
 obj-$(CONFIG_KEXEC_HANDOVER)		+= kexec_handover.o
-obj-$(CONFIG_KEXEC_HANDOVER_DEBUG)	+= kexec_handover_debug.o
 obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS)	+= kexec_handover_debugfs.o
 
 obj-$(CONFIG_LIVEUPDATE)		+= luo.o

kernel/liveupdate/kexec_handover.c

@@ -767,6 +767,22 @@ static phys_addr_t __init scratch_size_node(int nid)
 	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
 }
 
+bool kho_scratch_overlap(phys_addr_t phys, size_t size)
+{
+	phys_addr_t scratch_start, scratch_end;
+	unsigned int i;
+
+	for (i = 0; i < kho_scratch_cnt; i++) {
+		scratch_start = kho_scratch[i].addr;
+		scratch_end = kho_scratch[i].addr + kho_scratch[i].size;
+
+		if (phys < scratch_end && (phys + size) > scratch_start)
+			return true;
+	}
+
+	return false;
+}
+
 /**
  * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
  *
@@ -964,7 +980,8 @@ int kho_preserve_folio(struct folio *folio)
 	const unsigned long pfn = folio_pfn(folio);
 	const unsigned int order = folio_order(folio);
 
-	if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
+	if (IS_ENABLED(CONFIG_KEXEC_HANDOVER_DEBUG) &&
+	    WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
 		return -EINVAL;
 
 	return kho_radix_add_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
@@ -1041,7 +1058,8 @@ int kho_preserve_pages(struct page *page, unsigned long nr_pages)
 	unsigned long failed_pfn = 0;
 	int err = 0;
 
-	if (WARN_ON(kho_scratch_overlap(start_pfn << PAGE_SHIFT,
+	if (IS_ENABLED(CONFIG_KEXEC_HANDOVER_DEBUG) &&
+	    WARN_ON(kho_scratch_overlap(start_pfn << PAGE_SHIFT,
 					nr_pages << PAGE_SHIFT))) {
 		return -EINVAL;
 	}

kernel/liveupdate/kexec_handover_debug.c

@@ -1,25 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * kexec_handover_debug.c - kexec handover optional debug functionality
- * Copyright (C) 2025 Google LLC, Pasha Tatashin <pasha.tatashin@soleen.com>
- */
-
-#define pr_fmt(fmt) "KHO: " fmt
-
-#include "kexec_handover_internal.h"
-
-bool kho_scratch_overlap(phys_addr_t phys, size_t size)
-{
-	phys_addr_t scratch_start, scratch_end;
-	unsigned int i;
-
-	for (i = 0; i < kho_scratch_cnt; i++) {
-		scratch_start = kho_scratch[i].addr;
-		scratch_end = kho_scratch[i].addr + kho_scratch[i].size;
-
-		if (phys < scratch_end && (phys + size) > scratch_start)
-			return true;
-	}
-
-	return false;
-}

kernel/liveupdate/kexec_handover_internal.h

@@ -41,13 +41,4 @@ static inline void kho_debugfs_blob_remove(struct kho_debugfs *dbg,
 					   void *blob) { }
 #endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */
 
-#ifdef CONFIG_KEXEC_HANDOVER_DEBUG
-bool kho_scratch_overlap(phys_addr_t phys, size_t size);
-#else
-static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size)
-{
-	return false;
-}
-#endif /* CONFIG_KEXEC_HANDOVER_DEBUG */
-
 #endif /* LINUX_KEXEC_HANDOVER_INTERNAL_H */

tools/testing/memblock/internal.h

@@ -66,4 +66,9 @@ static inline void init_deferred_page(unsigned long pfn, int nid)
 
 #define __SetPageReserved(p)	((void)(p))
 
+static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size)
+{
+	return false;
+}
+
 #endif