kho: introduce KHO FDT ABI header

Introduce the `include/linux/kho/abi/kexec_handover.h` header file, which
defines the stable ABI for the KHO mechanism.  This header specifies how
preserved data is passed between kernels using an FDT.

The ABI contract includes the FDT structure, node properties, and the
"kho-v1" compatible string.  By centralizing these definitions, this
header serves as the foundational agreement for inter-kernel communication
of preserved states, ensuring forward compatibility and preventing
misinterpretation of data across kexec transitions.

Since the ABI definitions are now centralized in the header files, the
YAML files that previously described the FDT interfaces are redundant. 
These redundant files have therefore been removed.

Link: https://lkml.kernel.org/r/20260105165839.285270-5-rppt@kernel.org
Signed-off-by: Jason Miu <jasonmiu@google.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 9 insertions, 10 deletions

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index d4482b6e3cae..8f57d6e040af 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -15,6 +15,7 @@
 #include <linux/count_zeros.h>
 #include <linux/kexec.h>
 #include <linux/kexec_handover.h>
+#include <linux/kho/abi/kexec_handover.h>
 #include <linux/libfdt.h>
 #include <linux/list.h>
 #include <linux/memblock.h>
@@ -33,10 +34,7 @@
 #include "../kexec_internal.h"
 #include "kexec_handover_internal.h"
 
-#define KHO_FDT_COMPATIBLE "kho-v1"
-#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
-#define PROP_SUB_FDT "fdt"
-
+/* The magic token for preserved pages */
 #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */
 
 /*
@@ -378,7 +376,7 @@ 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);
+	ptr = fdt_getprop_w(kho_out.fdt, 0, KHO_FDT_MEMORY_MAP_PROP_NAME, NULL);
 
 	/* Check and discard previous memory map */
 	phys = get_unaligned((u64 *)ptr);
@@ -466,7 +464,7 @@ static phys_addr_t __init kho_get_mem_map_phys(const void *fdt)
 	const void *mem_ptr;
 	int len;
 
-	mem_ptr = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
+	mem_ptr = fdt_getprop(fdt, 0, KHO_FDT_MEMORY_MAP_PROP_NAME, &len);
 	if (!mem_ptr || len != sizeof(u64)) {
 		pr_err("failed to get preserved memory bitmaps\n");
 		return 0;
@@ -727,7 +725,8 @@ int kho_add_subtree(const char *name, void *fdt)
 		goto out_pack;
 	}
 
-	err = fdt_setprop(root_fdt, off, PROP_SUB_FDT, &phys, sizeof(phys));
+	err = fdt_setprop(root_fdt, off, KHO_FDT_SUB_TREE_PROP_NAME,
+			  &phys, sizeof(phys));
 	if (err < 0)
 		goto out_pack;
 
@@ -758,7 +757,7 @@ void kho_remove_subtree(void *fdt)
 		const u64 *val;
 		int len;
 
-		val = fdt_getprop(root_fdt, off, PROP_SUB_FDT, &len);
+		val = fdt_getprop(root_fdt, off, KHO_FDT_SUB_TREE_PROP_NAME, &len);
 		if (!val || len != sizeof(phys_addr_t))
 			continue;
 
@@ -1305,7 +1304,7 @@ int kho_retrieve_subtree(const char *name, phys_addr_t *phys)
 	if (offset < 0)
 		return -ENOENT;
 
-	val = fdt_getprop(fdt, offset, PROP_SUB_FDT, &len);
+	val = fdt_getprop(fdt, offset, KHO_FDT_SUB_TREE_PROP_NAME, &len);
 	if (!val || len != sizeof(*val))
 		return -EINVAL;
 
@@ -1325,7 +1324,7 @@ static __init int kho_out_fdt_setup(void)
 	err |= fdt_finish_reservemap(root);
 	err |= fdt_begin_node(root, "");
 	err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE);
-	err |= fdt_property(root, PROP_PRESERVED_MEMORY_MAP, &empty_mem_map,
+	err |= fdt_property(root, KHO_FDT_MEMORY_MAP_PROP_NAME, &empty_mem_map,
 			    sizeof(empty_mem_map));
 	err |= fdt_end_node(root);
 	err |= fdt_finish(root);