Re: [PATCHv7 4/7] kho: add interfaces to unpreserve folios and page ranges

On Tue, Oct 21, 2025 at 08:57:16PM -0400, Pasha Tatashin wrote:

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

Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com

Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org

---

include/linux/kexec_handover.h | 12 +++++ kernel/kexec_handover.c | 85 ++++++++++++++++++++++++++++------ 2 files changed, 84 insertions(+), 13 deletions(-)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 2faf290803ce..4ba145713838 100644 --- a/include/linux/kexec_handover.h +++ b/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); @@ -76,11 +78,21 @@ static inline int kho_preserve_folio(struct folio *folio) 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) { diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 0a4234269fe5..8412897385ad 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -157,26 +157,33 @@ static void *xa_load_or_alloc(struct xarray *xa, unsigned long index) 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; } @@ -749,6 +756,30 @@ int kho_preserve_folio(struct folio *folio) } 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.

@@ -793,6 +824,34 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages) } 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 contigious pages starting from @page.
• • This call must exactly match a granularity at which memory was originally
• • preserved by kho_preserve_pages, call with the same @page and
• • @nr_pages). 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 *); }; -- 2.51.0.915.g61a8936c21-goog