Re: [PATCH v7 1/3] kho: make kho_scratch_overlap usable outside debugging

[Mike Rapoport <rppt@kernel.org>]

Hi Michal,

On Tue, Mar 17, 2026 at 03:15:32PM +0100, Michal Clapinski wrote:
> Also return false if kho_scratch is NULL.
> 
> Signed-off-by: Michal Clapinski <mclapinski@google.com>
> ---
>  include/linux/kexec_handover.h              |  6 +++++
>  kernel/liveupdate/Makefile                  |  1 -
>  kernel/liveupdate/kexec_handover.c          | 28 ++++++++++++++++++---
>  kernel/liveupdate/kexec_handover_debug.c    | 25 ------------------
>  kernel/liveupdate/kexec_handover_internal.h |  7 ++++--
>  5 files changed, 35 insertions(+), 32 deletions(-)
>  delete mode 100644 kernel/liveupdate/kexec_handover_debug.c
> 
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index ac4129d1d741..6a0e572c3adc 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -35,6 +35,7 @@ void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
>  int kho_add_subtree(const char *name, void *fdt);
>  void kho_remove_subtree(void *fdt);
>  int kho_retrieve_subtree(const char *name, phys_addr_t *phys);
> +bool kho_scratch_overlap(phys_addr_t phys, size_t size);
>  
>  void kho_memory_init(void);
>  
> @@ -109,6 +110,11 @@ static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys)
>  	return -EOPNOTSUPP;
>  }
>  
> +static inline bool kho_scratch_overlap(phys_addr_t phys, size_t size)
> +{
> +	return false;
> +}
> +
>  static inline void kho_memory_init(void) { }
>  
>  static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
> diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile
> index d2f779cbe279..dc352839ccf0 100644
> --- a/kernel/liveupdate/Makefile
> +++ b/kernel/liveupdate/Makefile
> @@ -7,7 +7,6 @@ luo-y :=								\
>  		luo_session.o
>  
>  obj-$(CONFIG_KEXEC_HANDOVER)		+= kexec_handover.o
> -obj-$(CONFIG_KEXEC_HANDOVER_DEBUG)	+= kexec_handover_debug.o
>  obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS)	+= kexec_handover_debugfs.o
>  
>  obj-$(CONFIG_LIVEUPDATE)		+= luo.o
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 532f455c5d4f..c9b982372d6e 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -820,7 +820,8 @@ int kho_preserve_folio(struct folio *folio)
>  	const unsigned long pfn = folio_pfn(folio);
>  	const unsigned int order = folio_order(folio);
>  
> -	if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
> +	if (WARN_ON(kho_scratch_overlap_debug(pfn << PAGE_SHIFT,
> +					      PAGE_SIZE << order)))

Can't say I'm fond of kho_scratch_overlap_debug(). How about we make it

	if (IS_ENABLED(CONFIG_KEXEC_HANDOVER_DEBUG) &&
	    WARN_ON(kho_scratch_overlap(...)) 

>  		return -EINVAL;
>  
>  	return kho_radix_add_page(tree, pfn, order);
> @@ -864,10 +865,9 @@ int kho_preserve_pages(struct page *page, unsigned long nr_pages)
>  	unsigned long failed_pfn = 0;
>  	int err = 0;
>  
> -	if (WARN_ON(kho_scratch_overlap(start_pfn << PAGE_SHIFT,
> -					nr_pages << PAGE_SHIFT))) {
> +	if (WARN_ON(kho_scratch_overlap_debug(start_pfn << PAGE_SHIFT,
> +					      nr_pages << PAGE_SHIFT)))

Ditto.

>  		return -EINVAL;
> -	}
>  
>  	while (pfn < end_pfn) {
>  		unsigned int order =
> @@ -1327,6 +1327,26 @@ int kho_retrieve_subtree(const char *name, phys_addr_t *phys)
>  }
>  EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
>  
> +bool kho_scratch_overlap(phys_addr_t phys, size_t size)
> +{
> +	phys_addr_t scratch_start, scratch_end;
> +	unsigned int i;
> +
> +	if (!kho_scratch)
> +		return false;
> +
> +	for (i = 0; i < kho_scratch_cnt; i++) {
> +		scratch_start = kho_scratch[i].addr;
> +		scratch_end = kho_scratch[i].addr + kho_scratch[i].size;
> +
> +		if (phys < scratch_end && (phys + size) > scratch_start)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(kho_scratch_overlap);

I don't think we need to EXPORT_SYMBOL() it and it'd better grouped with
scratch allocation functions.

> +
>  static int __init kho_mem_retrieve(const void *fdt)
>  {
>  	struct kho_radix_tree tree;

-- 
Sincerely yours,
Mike.