kho: remove global preserved_mem_map and store state in FDT

Currently, the serialized memory map is tracked via
kho_out.preserved_mem_map and copied to the FDT during finalization.  This
double tracking is redundant.

Remove preserved_mem_map from kho_out.  Instead, maintain the physical
address of the head chunk directly in the preserved-memory-map FDT
property.

Introduce kho_update_memory_map() to manage this property. This function
handles:
1. Retrieving and freeing any existing serialized map (handling the
   abort/retry case).
2. Updating the FDT property with the new chunk address.

This establishes the FDT as the single source of truth for the handover
state.

Link: https://lkml.kernel.org/r/20251114190002.3311679-9-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Dave Vasilevsky <dave@vasilevsky.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 26 insertions, 17 deletions

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 297136054f75..63800f63551f 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -119,9 +119,6 @@ struct kho_out {
 	struct mutex fdts_lock;
 
 	struct kho_mem_track track;
-	/* First chunk of serialized preserved memory map */
-	struct khoser_mem_chunk *preserved_mem_map;
-
 	struct kho_debugfs dbg;
 };
 
@@ -382,6 +379,27 @@ static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk)
 	}
 }
 
+/*
+ *  Update memory map property, if old one is found discard it via
+ *  kho_mem_ser_free().
+ */
+static void kho_update_memory_map(struct khoser_mem_chunk *first_chunk)
+{
+	void *ptr;
+	u64 phys;
+
+	ptr = fdt_getprop_w(kho_out.fdt, 0, PROP_PRESERVED_MEMORY_MAP, NULL);
+
+	/* Check and discard previous memory map */
+	phys = get_unaligned((u64 *)ptr);
+	if (phys)
+		kho_mem_ser_free((struct khoser_mem_chunk *)phys_to_virt(phys));
+
+	/* Update with the new value */
+	phys = first_chunk ? (u64)virt_to_phys(first_chunk) : 0;
+	put_unaligned(phys, (u64 *)ptr);
+}
+
 static int kho_mem_serialize(struct kho_out *kho_out)
 {
 	struct khoser_mem_chunk *first_chunk = NULL;
@@ -422,7 +440,7 @@ static int kho_mem_serialize(struct kho_out *kho_out)
 		}
 	}
 
-	kho_out->preserved_mem_map = first_chunk;
+	kho_update_memory_map(first_chunk);
 
 	return 0;
 
@@ -1223,8 +1241,7 @@ int kho_abort(void)
 	if (!kho_out.finalized)
 		return -ENOENT;
 
-	kho_mem_ser_free(kho_out.preserved_mem_map);
-	kho_out.preserved_mem_map = NULL;
+	kho_update_memory_map(NULL);
 	kho_out.finalized = false;
 
 	return 0;
@@ -1234,21 +1251,15 @@ static int __kho_finalize(void)
 {
 	void *root = kho_out.fdt;
 	struct kho_sub_fdt *fdt;
-	u64 *preserved_mem_map;
+	u64 empty_mem_map = 0;
 	int err;
 
 	err = fdt_create(root, PAGE_SIZE);
 	err |= fdt_finish_reservemap(root);
 	err |= fdt_begin_node(root, "");
 	err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE);
-	/**
-	 * Reserve the preserved-memory-map property in the root FDT, so
-	 * that all property definitions will precede subnodes created by
-	 * KHO callers.
-	 */
-	err |= fdt_property_placeholder(root, PROP_PRESERVED_MEMORY_MAP,
-					sizeof(*preserved_mem_map),
-					(void **)&preserved_mem_map);
+	err |= fdt_property(root, PROP_PRESERVED_MEMORY_MAP, &empty_mem_map,
+			    sizeof(empty_mem_map));
 	if (err)
 		goto err_exit;
 
@@ -1271,8 +1282,6 @@ static int __kho_finalize(void)
 	if (err)
 		goto err_exit;
 
-	*preserved_mem_map = (u64)virt_to_phys(kho_out.preserved_mem_map);
-
 	return 0;
 
 err_exit: