kho: allow memory preservation state updates after finalization

Currently, kho_preserve_* and kho_unpreserve_* return -EBUSY if KHO is
finalized.  This enforces a rigid "freeze" on the KHO memory state.

With the introduction of re-entrant finalization, this restriction is no
longer necessary.  Users should be allowed to modify the preservation set
(e.g., adding new pages or freeing old ones) even after an initial
finalization.

The intended workflow for updates is now:
1. Modify state (preserve/unpreserve).
2. Call kho_finalize() again to refresh the serialized metadata.

Remove the kho_out.finalized checks to enable this dynamic behavior.

This also allows to convert kho_unpreserve_* functions to void, as they do
not return any error anymore.

Link: https://lkml.kernel.org/r/20251114190002.3311679-13-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>

Author: soleen

include/linux/kexec_handover.h

@@ -44,11 +44,11 @@ bool kho_is_enabled(void);
 bool is_kho_boot(void);
 
 int kho_preserve_folio(struct folio *folio);
-int kho_unpreserve_folio(struct folio *folio);
+void kho_unpreserve_folio(struct folio *folio);
 int kho_preserve_pages(struct page *page, unsigned int nr_pages);
-int kho_unpreserve_pages(struct page *page, unsigned int nr_pages);
+void kho_unpreserve_pages(struct page *page, unsigned int nr_pages);
 int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);
-int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation);
+void kho_unpreserve_vmalloc(struct kho_vmalloc *preservation);
 void *kho_alloc_preserve(size_t size);
 void kho_unpreserve_free(void *mem);
 void kho_restore_free(void *mem);
@@ -79,31 +79,22 @@ static inline int kho_preserve_folio(struct folio *folio)
 	return -EOPNOTSUPP;
 }
 
-static inline int kho_unpreserve_folio(struct folio *folio)
-{
-	return -EOPNOTSUPP;
-}
+static inline void kho_unpreserve_folio(struct folio *folio) { }
 
 static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages)
 {
 	return -EOPNOTSUPP;
 }
 
-static inline int kho_unpreserve_pages(struct page *page, unsigned int nr_pages)
-{
-	return -EOPNOTSUPP;
-}
+static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { }
 
 static inline int kho_preserve_vmalloc(void *ptr,
 				       struct kho_vmalloc *preservation)
 {
 	return -EOPNOTSUPP;
 }
 
-static inline int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation)
-{
-	return -EOPNOTSUPP;
-}
+static inline void kho_unpreserve_vmalloc(struct kho_vmalloc *preservation) { }
 
 static inline void *kho_alloc_preserve(size_t size)
 {

kernel/liveupdate/kexec_handover.c

@@ -185,10 +185,6 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
 	const unsigned long pfn_high = pfn >> order;
 
 	might_sleep();
-
-	if (kho_out.finalized)
-		return -EBUSY;
-
 	physxa = xa_load(&track->orders, order);
 	if (!physxa) {
 		int err;
@@ -807,20 +803,14 @@ EXPORT_SYMBOL_GPL(kho_preserve_folio);
  * Instructs KHO to unpreserve a folio that was preserved by
  * kho_preserve_folio() before. The provided @folio (pfn and order)
  * must exactly match a previously preserved folio.
- *
- * Return: 0 on success, error code on failure
  */
-int kho_unpreserve_folio(struct folio *folio)
+void kho_unpreserve_folio(struct folio *folio)
 {
 	const unsigned long pfn = folio_pfn(folio);
 	const unsigned int order = folio_order(folio);
 	struct kho_mem_track *track = &kho_out.track;
 
-	if (kho_out.finalized)
-		return -EBUSY;
-
 	__kho_unpreserve_order(track, pfn, order);
-	return 0;
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
 
@@ -877,21 +867,14 @@ EXPORT_SYMBOL_GPL(kho_preserve_pages);
  * This must be called with the same @page and @nr_pages as the corresponding
  * kho_preserve_pages() call. Unpreserving arbitrary sub-ranges of larger
  * preserved blocks is not supported.
- *
- * Return: 0 on success, error code on failure
  */
-int kho_unpreserve_pages(struct page *page, unsigned int nr_pages)
+void kho_unpreserve_pages(struct page *page, unsigned int nr_pages)
 {
 	struct kho_mem_track *track = &kho_out.track;
 	const unsigned long start_pfn = page_to_pfn(page);
 	const unsigned long end_pfn = start_pfn + nr_pages;
 
-	if (kho_out.finalized)
-		return -EBUSY;
-
 	__kho_unpreserve(track, start_pfn, end_pfn);
-
-	return 0;
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_pages);
 
@@ -976,20 +959,6 @@ static void kho_vmalloc_unpreserve_chunk(struct kho_vmalloc_chunk *chunk,
 	}
 }
 
-static void kho_vmalloc_free_chunks(struct kho_vmalloc *kho_vmalloc)
-{
-	struct kho_vmalloc_chunk *chunk = KHOSER_LOAD_PTR(kho_vmalloc->first);
-
-	while (chunk) {
-		struct kho_vmalloc_chunk *tmp = chunk;
-
-		kho_vmalloc_unpreserve_chunk(chunk, kho_vmalloc->order);
-
-		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
-		free_page((unsigned long)tmp);
-	}
-}
-
 /**
  * kho_preserve_vmalloc - preserve memory allocated with vmalloc() across kexec
  * @ptr: pointer to the area in vmalloc address space
@@ -1051,7 +1020,7 @@ int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation)
 	return 0;
 
 err_free:
-	kho_vmalloc_free_chunks(preservation);
+	kho_unpreserve_vmalloc(preservation);
 	return err;
 }
 EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
@@ -1062,17 +1031,19 @@ EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
  *
  * Instructs KHO to unpreserve the area in vmalloc address space that was
  * previously preserved with kho_preserve_vmalloc().
- *
- * Return: 0 on success, error code on failure
  */
-int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation)
+void kho_unpreserve_vmalloc(struct kho_vmalloc *preservation)
 {
-	if (kho_out.finalized)
-		return -EBUSY;
+	struct kho_vmalloc_chunk *chunk = KHOSER_LOAD_PTR(preservation->first);
 
-	kho_vmalloc_free_chunks(preservation);
+	while (chunk) {
+		struct kho_vmalloc_chunk *tmp = chunk;
 
-	return 0;
+		kho_vmalloc_unpreserve_chunk(chunk, preservation->order);
+
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		free_page((unsigned long)tmp);
+	}
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_vmalloc);
 
@@ -1221,7 +1192,7 @@ void kho_unpreserve_free(void *mem)
 		return;
 
 	folio = virt_to_folio(mem);
-	WARN_ON_ONCE(kho_unpreserve_folio(folio));
+	kho_unpreserve_folio(folio);
 	folio_put(folio);
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_free);