[PATCH v2 08/13] kho: Remove global preserved_mem_map and store state in FDT

Pasha Tatashin
2025-11-14T19:00:16Z

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.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
---
kernel/liveupdate/kexec_handover.c | 43 ++++++++++++++++++------------
1 file 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:
--
2.52.0.rc1.455.g30608eb744-goog