Re: [PATCH 6.18.y 1/2] kho: add interfaces to unpreserve folios, page ranges, and vmalloc

[Greg KH <greg@kroah.com>]

On Thu, Jul 30, 2026 at 02:33:30PM +0200, Greg KH wrote:
> On Sat, Jul 25, 2026 at 06:54:32AM -0400, Sasha Levin wrote:
> > From: Pasha Tatashin <pasha.tatashin@soleen.com>
> > 
> > [ Upstream commit 36f8f7ef7fd2f238922e9d217e86c69838319d8c ]
> > 
> > Allow users of KHO to cancel the previous preservation by adding the
> > necessary interfaces to unpreserve folio, pages, and vmallocs.
> > 
> > Link: https://lkml.kernel.org/r/20251101142325.1326536-4-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: Changyuan Lyu <changyuanl@google.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: Simon Horman <horms@kernel.org>
> > Cc: Tejun Heo <tj@kernel.org>
> > Cc: Zhu Yanjun <yanjun.zhu@linux.dev>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > Stable-dep-of: 0e39380a7316 ("kho: make sure scratch size is always aligned by CMA_MIN_ALIGNMENT_BYTES")
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> >  include/linux/kexec_handover.h |  18 ++++++
> >  kernel/kexec_handover.c        | 104 ++++++++++++++++++++++++++++-----
> >  2 files changed, 109 insertions(+), 13 deletions(-)
> > 
> > diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> > index 25042c1d8d54af..e1af332a262fba 100644
> > --- a/include/linux/kexec_handover.h
> > +++ b/include/linux/kexec_handover.h
> > @@ -52,8 +52,11 @@ bool kho_is_enabled(void);
> >  bool is_kho_boot(void);
> >  
> >  int kho_preserve_folio(struct folio *folio);
> > +int kho_unpreserve_folio(struct folio *folio);
> >  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);
> > +int kho_unpreserve_vmalloc(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);
> >  void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
> > @@ -83,17 +86,32 @@ 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)
> >  {
> >  	return -EOPNOTSUPP;
> >  }
> >  
> > +static inline int kho_unpreserve_vmalloc(struct kho_vmalloc *preservation)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >  static inline struct folio *kho_restore_folio(phys_addr_t phys)
> >  {
> >  	return NULL;
> > diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> > index c13b99f7c9891e..37e6048118e8b7 100644
> > --- a/kernel/kexec_handover.c
> > +++ b/kernel/kexec_handover.c
> > @@ -153,26 +153,33 @@ 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 (WARN_ON_ONCE(!physxa))
> > +		return;
> >  
> > -		physxa = xa_load(&track->orders, order);
> > -		if (WARN_ON_ONCE(!physxa))
> > -			return;
> > +	bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
> > +	if (WARN_ON_ONCE(!bits))
> > +		return;
> > +
> > +	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 (WARN_ON_ONCE(!bits))
> > -			return;
> > +	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;
> >  	}
> > @@ -739,6 +746,30 @@ 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.
> > @@ -783,6 +814,33 @@ 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 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 *);
> >  };
> > @@ -944,6 +1002,26 @@ int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation)
> >  }
> >  EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
> >  
> > +/**
> > + * kho_unpreserve_vmalloc - unpreserve memory allocated with vmalloc()
> > + * @preservation: preservation metadata returned by 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)
> > +{
> > +	if (kho_out.finalized)
> > +		return -EBUSY;
> > +
> > +	kho_vmalloc_free_chunks(preservation);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(kho_unpreserve_vmalloc);
> > +
> >  /**
> >   * kho_restore_vmalloc - recreates and populates an area in vmalloc address
> >   * space from the preserved memory.
> > -- 
> > 2.53.0
> > 
> > 
> 
> Oops, nope, dropped this and patch 2/2 as this causes a build error :(
> 
> 

Actually patch 2/2 works just fine on it's own, so I've kept that.