Re: [PATCH v8 3/8] kho: drop notifiers

On Fri, Oct 24, 2025 at 12:09:57PM -0400, Pasha Tatashin wrote:

From: "Mike Rapoport (Microsoft)" rppt@kernel.org

The KHO framework uses a notifier chain as the mechanism for clients to participate in the finalization process. While this works for a single, central state machine, it is too restrictive for kernel-internal components like pstore/reserve_mem or IMA. These components need a simpler, direct way to register their state for preservation (e.g., during their initcall) without being part of a complex, shutdown-time notifier sequence. The notifier model forces all participants into a single finalization flow and makes direct preservation from an arbitrary context difficult. This patch refactors the client participation model by removing the notifier chain and introducing a direct API for managing FDT subtrees.

The core kho_finalize() and kho_abort() state machine remains, but clients now register their data with KHO beforehand.

Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Co-developed-by: Pasha Tatashin pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com

---

include/linux/kexec_handover.h | 28 +----- kernel/kexec_handover.c | 166 +++++++++++++++++-------------- kernel/kexec_handover_debugfs.c | 17 ++-- kernel/kexec_handover_internal.h | 5 +- lib/test_kho.c | 33 +----- mm/memblock.c | 62 +++--------- 6 files changed, 126 insertions(+), 185 deletions(-)

diff --git a/lib/test_kho.c b/lib/test_kho.c index 60cd899ea745..1c6c4ce83666 100644 --- a/lib/test_kho.c +++ b/lib/test_kho.c @@ -120,6 +93,7 @@ static int kho_test_prepare_fdt(struct kho_test_state *state) fdt = folio_address(state->fdt);

• err |= kho_preserve_folio(state->fdt);

We should bail out here, no point creating an fdt if it won't be preserved.

err |= fdt_create(fdt, fdt_size); err |= fdt_finish_reservemap(fdt); @@ -131,6 +105,7 @@ static int kho_test_prepare_fdt(struct kho_test_state *state) err |= fdt_finish(fdt);

• err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt)); if (err) folio_put(state->fdt);

@@ -203,7 +178,7 @@ static int kho_test_save(void) if (err) goto err_free_folios;

• err = register_kho_notifier(&kho_test_nb);

• err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));

This is the second time we add the same subtree, isn't it?

if (err) goto err_free_fdt; @@ -326,7 +301,7 @@ static void kho_test_cleanup(void) static void __exit kho_test_exit(void) {

• unregister_kho_notifier(&kho_test_nb);

• kho_remove_subtree(folio_address(kho_test_state.fdt)); kho_test_cleanup();

} module_exit(kho_test_exit); diff --git a/mm/memblock.c b/mm/memblock.c index e23e16618e9b..e3bef9b35d63 100644 --- a/mm/memblock.c +++ b/mm/memblock.c static int __init prepare_kho_fdt(void) { int err = 0, i;

• struct page *fdt_page; void *fdt;

• kho_fdt = alloc_page(GFP_KERNEL);
• if (!kho_fdt)

• fdt_page = alloc_page(GFP_KERNEL);
• if (!fdt_page) return -ENOMEM;

• fdt = page_to_virt(kho_fdt);

• fdt = page_to_virt(fdt_page);

err |= fdt_create(fdt, PAGE_SIZE); err |= fdt_finish_reservemap(fdt); @@ -2499,7 +2464,10 @@ static int __init prepare_kho_fdt(void) err |= fdt_property_string(fdt, "compatible", MEMBLOCK_KHO_NODE_COMPATIBLE); for (i = 0; i < reserved_mem_count; i++) { struct reserve_mem_table *map = &reserved_mem_table[i];

• struct page *page = phys_to_page(map->start);
  

• unsigned int nr_pages = map->size >> PAGE_SHIFT;
  

• err |= kho_preserve_pages(page, nr_pages);
  

  err |= fdt_begin_node(fdt, map->name); err |= fdt_property_string(fdt, "compatible", RESERVE_MEM_KHO_NODE_COMPATIBLE); err |= fdt_property(fdt, "start", &map->start, sizeof(map->start));

@@ -2507,13 +2475,16 @@ static int __init prepare_kho_fdt(void) err |= fdt_end_node(fdt); } err |= fdt_end_node(fdt);

• err |= fdt_finish(fdt);

• err |= kho_preserve_folio(page_folio(fdt_page));

When looking at the end result after patch 8 it becomes a total mess. Let's move this right after the allocation and make it

err = kho_preserve_folio(page_folio(fdt_page); if (err) goto err_free_fdt;

• if (!err)

• err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt);
  

and replace this pattern with usual kernel

if (err) goto err_free_fdt;

err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt); if (err) goto err_free_fdt;

so that only fdt operations will be a part of

err |= fdt_<function>

sequence.

if (err) { pr_err("failed to prepare memblock FDT for KHO: %d\n", err);

• put_page(kho_fdt);
  

• kho_fdt = NULL;
  

• put_page(fdt_page);
  

  }

return err; @@ -2529,13 +2500,6 @@ static int __init reserve_mem_init(void) err = prepare_kho_fdt(); if (err) return err;

• err = register_kho_notifier(&reserve_mem_kho_nb);
• if (err) {

• put_page(kho_fdt);
  

• kho_fdt = NULL;
  

• }
• return err;

} late_initcall(reserve_mem_init); -- 2.51.1.821.gb6fe4d2222-goog