Re: [PATCH v8 1/2] kho: fix deferred initialization of scratch areas

[Mike Rapoport <rppt@kernel.org>]

Hi Michal,

On Thu, Apr 16, 2026 at 01:06:53PM +0200, Michal Clapinski wrote:
> Currently, if CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled,
> kho_release_scratch() will initialize the struct pages and set migratetype
> of KHO scratch. Unless the whole scratch fits below first_deferred_pfn,
> some of that will be overwritten either by deferred_init_pages() or
> memmap_init_reserved_range().
> 
> To fix it, make memmap_init_range(), deferred_init_memmap_chunk() and
> memmap_init_reserved_range() recognize KHO scratch regions and set
> migratetype of pageblocks in those regions to MIGRATE_CMA.
> 
> Signed-off-by: Michal Clapinski <mclapinski@google.com>
> Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Your signed-off should be last here :)
https://docs.kernel.org/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by

> ---
>  include/linux/memblock.h           |  7 +++--
>  kernel/liveupdate/kexec_handover.c | 25 ------------------
>  mm/memblock.c                      | 41 ++++++++++++++----------------
>  mm/mm_init.c                       | 27 ++++++++++++++------
>  4 files changed, 43 insertions(+), 57 deletions(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index 6ec5e9ac0699..410f2a399691 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -614,11 +614,14 @@ static inline void memtest_report_meminfo(struct seq_file *m) { }
>  #ifdef CONFIG_MEMBLOCK_KHO_SCRATCH
>  void memblock_set_kho_scratch_only(void);
>  void memblock_clear_kho_scratch_only(void);
> -void memmap_init_kho_scratch_pages(void);
> +bool memblock_is_kho_scratch_memory(phys_addr_t addr);
>  #else
>  static inline void memblock_set_kho_scratch_only(void) { }
>  static inline void memblock_clear_kho_scratch_only(void) { }
> -static inline void memmap_init_kho_scratch_pages(void) {}
> +static inline bool memblock_is_kho_scratch_memory(phys_addr_t addr)
> +{
> +	return false;
> +}
>  #endif
>  
>  #endif /* _LINUX_MEMBLOCK_H */
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 18509d8082ea..a507366a2cf9 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -1576,35 +1576,10 @@ static __init int kho_init(void)
>  }
>  fs_initcall(kho_init);
>  
> -static void __init kho_release_scratch(void)
> -{
> -	phys_addr_t start, end;
> -	u64 i;
> -
> -	memmap_init_kho_scratch_pages();
> -
> -	/*
> -	 * Mark scratch mem as CMA before we return it. That way we
> -	 * ensure that no kernel allocations happen on it. That means
> -	 * we can reuse it as scratch memory again later.
> -	 */
> -	__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> -			     MEMBLOCK_KHO_SCRATCH, &start, &end, NULL) {
> -		ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
> -		ulong end_pfn = pageblock_align(PFN_UP(end));
> -		ulong pfn;
> -
> -		for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages)
> -			init_pageblock_migratetype(pfn_to_page(pfn),
> -						   MIGRATE_CMA, false);
> -	}
> -}
> -
>  void __init kho_memory_init(void)
>  {
>  	if (kho_in.scratch_phys) {
>  		kho_scratch = phys_to_virt(kho_in.scratch_phys);
> -		kho_release_scratch();
>  
>  		if (kho_mem_retrieve(kho_get_fdt()))
>  			kho_in.fdt_phys = 0;
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 4224fdaa8918..fab234f732c3 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -17,6 +17,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/memblock.h>
>  #include <linux/mutex.h>
> +#include <linux/page-isolation.h>
>  
>  #ifdef CONFIG_KEXEC_HANDOVER
>  #include <linux/libfdt.h>
> @@ -959,28 +960,6 @@ __init void memblock_clear_kho_scratch_only(void)
>  {
>  	kho_scratch_only = false;
>  }
> -
> -__init void memmap_init_kho_scratch_pages(void)
> -{
> -	phys_addr_t start, end;
> -	unsigned long pfn;
> -	int nid;
> -	u64 i;
> -
> -	if (!IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT))
> -		return;
> -
> -	/*
> -	 * Initialize struct pages for free scratch memory.
> -	 * The struct pages for reserved scratch memory will be set up in
> -	 * memmap_init_reserved_pages()
> -	 */
> -	__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> -			     MEMBLOCK_KHO_SCRATCH, &start, &end, &nid) {
> -		for (pfn = PFN_UP(start); pfn < PFN_DOWN(end); pfn++)
> -			init_deferred_page(pfn, nid);
> -	}
> -}
>  #endif
>  
>  /**
> @@ -1971,6 +1950,18 @@ bool __init_memblock memblock_is_map_memory(phys_addr_t addr)
>  	return !memblock_is_nomap(&memblock.memory.regions[i]);
>  }
>  
> +#ifdef CONFIG_MEMBLOCK_KHO_SCRATCH
> +bool __init_memblock memblock_is_kho_scratch_memory(phys_addr_t addr)

We already have a block under #ifdef CONFIG_MEMBLOCK_KHO_SCRATCH, please
add this function to that block.

> +{
> +	int i = memblock_search(&memblock.memory, addr);
> +
> +	if (i == -1)
> +		return false;
> +
> +	return memblock_is_kho_scratch(&memblock.memory.regions[i]);
> +}
> +#endif
> +
>  int __init_memblock memblock_search_pfn_nid(unsigned long pfn,
>  			 unsigned long *start_pfn, unsigned long *end_pfn)
>  {
> @@ -2262,6 +2253,12 @@ static void __init memmap_init_reserved_range(phys_addr_t start,
>  		 * access it yet.
>  		 */
>  		__SetPageReserved(page);
> +
> +#ifdef CONFIG_MEMBLOCK_KHO_SCRATCH

No need for #ifdef here, there's a stub returning false for
CONFIG_MEMBLOCK_KHO_SCRATCH=n case.

> +		if (memblock_is_kho_scratch_memory(PFN_PHYS(pfn)) &&
> +		    pageblock_aligned(pfn))
> +			init_pageblock_migratetype(page, MIGRATE_CMA, false);
> +#endif
>  	}
>  }
>  
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f9f8e1af921c..890c3ae21ba0 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -916,8 +916,15 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
>  		 * over the place during system boot.
>  		 */
>  		if (pageblock_aligned(pfn)) {
> -			init_pageblock_migratetype(page, migratetype,
> -					isolate_pageblock);
> +			int mt = migratetype;
> +
> +#ifdef CONFIG_MEMBLOCK_KHO_SCRATCH

Ditto.

> +			if (memblock_is_kho_scratch_memory(page_to_phys(page)))
> +				mt = MIGRATE_CMA;
> +#endif

memmap_init_zone_range() is called each time for a region in
memblock.memory. This means either entire range will be KHO_SCRATHC or not
and we can check for memblock_is_kho_scratch_memory() once for every region
in memmap_init_zone_range().

> +
> +			init_pageblock_migratetype(page, mt,
> +						   isolate_pageblock);
>  			cond_resched();
>  		}
>  		pfn++;
> @@ -1970,7 +1977,7 @@ unsigned long __init node_map_pfn_alignment(void)
>  
>  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>  static void __init deferred_free_pages(unsigned long pfn,
> -		unsigned long nr_pages)
> +		unsigned long nr_pages, enum migratetype mt)
>  {
>  	struct page *page;
>  	unsigned long i;
> @@ -1983,8 +1990,7 @@ static void __init deferred_free_pages(unsigned long pfn,
>  	/* Free a large naturally-aligned chunk if possible */
>  	if (nr_pages == MAX_ORDER_NR_PAGES && IS_MAX_ORDER_ALIGNED(pfn)) {
>  		for (i = 0; i < nr_pages; i += pageblock_nr_pages)
> -			init_pageblock_migratetype(page + i, MIGRATE_MOVABLE,
> -					false);
> +			init_pageblock_migratetype(page + i, mt, false);
>  		__free_pages_core(page, MAX_PAGE_ORDER, MEMINIT_EARLY);
>  		return;
>  	}
> @@ -1994,8 +2000,7 @@ static void __init deferred_free_pages(unsigned long pfn,
>  
>  	for (i = 0; i < nr_pages; i++, page++, pfn++) {
>  		if (pageblock_aligned(pfn))
> -			init_pageblock_migratetype(page, MIGRATE_MOVABLE,
> -					false);
> +			init_pageblock_migratetype(page, mt, false);
>  		__free_pages_core(page, 0, MEMINIT_EARLY);
>  	}
>  }
> @@ -2051,6 +2056,7 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
>  	u64 i = 0;
>  
>  	for_each_free_mem_range(i, nid, 0, &start, &end, NULL) {
> +		enum migratetype mt = MIGRATE_MOVABLE;
>  		unsigned long spfn = PFN_UP(start);
>  		unsigned long epfn = PFN_DOWN(end);
>  
> @@ -2060,12 +2066,17 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
>  		spfn = max(spfn, start_pfn);
>  		epfn = min(epfn, end_pfn);
>  
> +#ifdef CONFIG_MEMBLOCK_KHO_SCRATCH

No need for #ifdef here as well.

> +		if (memblock_is_kho_scratch_memory(PFN_PHYS(spfn)))
> +			mt = MIGRATE_CMA;
> +#endif
> +
>  		while (spfn < epfn) {
>  			unsigned long mo_pfn = ALIGN(spfn + 1, MAX_ORDER_NR_PAGES);
>  			unsigned long chunk_end = min(mo_pfn, epfn);
>  
>  			nr_pages += deferred_init_pages(zone, spfn, chunk_end);
> -			deferred_free_pages(spfn, chunk_end - spfn);
> +			deferred_free_pages(spfn, chunk_end - spfn, mt);
>  
>  			spfn = chunk_end;
>  
> -- 
> 2.54.0.rc1.555.g9c883467ad-goog
> 

-- 
Sincerely yours,
Mike.