Re: [PATCH v5 7/9] drivers/base/memory: count inherited poisoned frames into the block

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/15/26 14:53, Breno Leitao wrote:
> A frame a kexec handed over is flagged as it reaches the allocator, long
> before its memory block exists, so memblk_nr_poison_inc() had nowhere to
> count it. Walk the block once when it is created and take the count from
> the page flag instead.
> 
> Without it an unpoison later subtracts from a counter that was never
> incremented and wraps it, which then refuses memory_block_online() for
> good.
> 
> Only a block created online needs the walk. A hotplugged one is created
> before its pages are, so there is nothing to find, and its frames are
> counted by num_poisoned_pages_inc() as they are flagged.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  drivers/base/memory.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 5eead3346f1e32..49a33ddbb2e717 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -220,11 +220,16 @@ int memory_notify(enum memory_block_state state, void *v)
>  
>  #if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_MEMORY_HOTPLUG)
>  static unsigned long memblk_nr_poison(struct memory_block *mem);
> +static void memblk_nr_poison_init(struct memory_block *mem);
>  #else
>  static inline unsigned long memblk_nr_poison(struct memory_block *mem)
>  {
>  	return 0;
>  }
> +
> +static inline void memblk_nr_poison_init(struct memory_block *mem)
> +{
> +}
>  #endif
>  
>  /*
> @@ -807,6 +812,7 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
>  	mem->state = state;
>  	mem->nid = nid;
>  	INIT_LIST_HEAD(&mem->group_next);
> +	memblk_nr_poison_init(mem);
>  
>  #ifndef CONFIG_NUMA
>  	if (state == MEM_ONLINE)
> @@ -1251,4 +1257,33 @@ static unsigned long memblk_nr_poison(struct memory_block *mem)
>  {
>  	return atomic_long_read(&mem->nr_hwpoison);
>  }
> +
> +/*
> + * Frames a kexec handed over are flagged as they reach the allocator, long
> + * before this block exists, so memblk_nr_poison_inc() had nowhere to count
> + * them. Take them from the page flag instead.
> + */
> +static void memblk_nr_poison_init(struct memory_block *mem)
> +{
> +	unsigned long pfn = section_nr_to_pfn(mem->start_section_nr);
> +	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
> +	unsigned long i, nr_poison = 0;
> +
> +	/* A hotplugged block is created before its pages are online. */
> +	if (mem->state != MEM_ONLINE)
> +		return;
> +
> +	if (!range_contains_poisoned_memory(PFN_PHYS(pfn),
> +					    nr_pages << PAGE_SHIFT))
> +		return;
> +
> +	for (i = 0; i < nr_pages; i++) {
> +		struct page *page = pfn_to_online_page(pfn + i);
> +
> +		if (page && PageHWPoison(page))
> +			nr_poison++;
> +	}

That just slows down boot unnecessarily on 99.9999999999999999999% of all
systems out there.

-- 
Cheers,

David