+ kho-add-interfaces-to-unpreserve-folios-and-page-ranges.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kho: add interfaces to unpreserve folios and page ranges
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kho-add-interfaces-to-unpreserve-folios-and-page-ranges.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kho-add-interfaces-to-unpreserve-folios-and-page-ranges.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: kho: add interfaces to unpreserve folios and page ranges
Date: Fri, 24 Oct 2025 12:09:58 -0400

Allow users of KHO to cancel the previous preservation by adding the
necessary interfaces to unpreserve folio and pages.

Link: https://lkml.kernel.org/r/20251024161002.747372-5-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/kexec_handover.h |   12 ++++
 kernel/kexec_handover.c        |   84 ++++++++++++++++++++++++++-----
 2 files changed, 83 insertions(+), 13 deletions(-)

--- a/include/linux/kexec_handover.h~kho-add-interfaces-to-unpreserve-folios-and-page-ranges
+++ a/include/linux/kexec_handover.h
@@ -43,7 +43,9 @@ bool kho_is_enabled(void);
 bool is_kho_boot(void);
 
 int kho_preserve_folio(struct folio *folio);
+int 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);
 int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation);
 struct folio *kho_restore_folio(phys_addr_t phys);
 struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages);
@@ -76,10 +78,20 @@ static inline int kho_preserve_folio(str
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_unpreserve_folio(struct folio *folio)
+{
+	return -EOPNOTSUPP;
+}
+
 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 int kho_preserve_vmalloc(void *ptr,
 				       struct kho_vmalloc *preservation)
--- a/kernel/kexec_handover.c~kho-add-interfaces-to-unpreserve-folios-and-page-ranges
+++ a/kernel/kexec_handover.c
@@ -157,26 +157,33 @@ static void *xa_load_or_alloc(struct xar
 	return no_free_ptr(elm);
 }
 
-static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
-			     unsigned long end_pfn)
+static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned long pfn,
+				   unsigned int order)
 {
 	struct kho_mem_phys_bits *bits;
 	struct kho_mem_phys *physxa;
+	const unsigned long pfn_high = pfn >> order;
 
-	while (pfn < end_pfn) {
-		const unsigned int order =
-			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
-		const unsigned long pfn_high = pfn >> order;
+	physxa = xa_load(&track->orders, order);
+	if (!physxa)
+		return;
+
+	bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
+	if (!bits)
+		return;
 
-		physxa = xa_load(&track->orders, order);
-		if (!physxa)
-			continue;
+	clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+}
+
+static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
+			     unsigned long end_pfn)
+{
+	unsigned int order;
 
-		bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
-		if (!bits)
-			continue;
+	while (pfn < end_pfn) {
+		order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
 
-		clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+		__kho_unpreserve_order(track, pfn, order);
 
 		pfn += 1 << order;
 	}
@@ -746,6 +753,30 @@ int kho_preserve_folio(struct folio *fol
 EXPORT_SYMBOL_GPL(kho_preserve_folio);
 
 /**
+ * kho_unpreserve_folio - unpreserve a folio.
+ * @folio: folio to unpreserve.
+ *
+ * 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)
+{
+	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);
+
+/**
  * kho_preserve_pages - preserve contiguous pages across kexec
  * @page: first page in the list.
  * @nr_pages: number of pages.
@@ -789,6 +820,33 @@ int kho_preserve_pages(struct page *page
 }
 EXPORT_SYMBOL_GPL(kho_preserve_pages);
 
+/**
+ * kho_unpreserve_pages - unpreserve contiguous pages.
+ * @page: first page in the list.
+ * @nr_pages: number of pages.
+ *
+ * Instructs KHO to unpreserve @nr_pages contiguous pages starting from @page.
+ * 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)
+{
+	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);
+
 struct kho_vmalloc_hdr {
 	DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
 };
_

Patches currently in -mm which might be from pasha.tatashin@soleen.com are

liveupdate-kho-warn-and-fail-on-metadata-or-preserved-memory-in-scratch-area.patch
liveupdate-kho-increase-metadata-bitmap-size-to-page_size.patch
liveupdate-kho-allocate-metadata-directly-from-the-buddy-allocator.patch
kho-allow-to-drive-kho-from-within-kernel.patch
kho-make-debugfs-interface-optional.patch
kho-add-interfaces-to-unpreserve-folios-and-page-ranges.patch
kho-dont-unpreserve-memory-during-abort.patch
liveupdate-kho-move-to-kernel-liveupdate.patch
liveupdate-kho-move-kho-debugfs-directory-to-liveupdate.patch
memblock-unpreserve-memory-in-case-of-error.patch