Re: [PATCH] mm/memory_failure: reject unsupported non-folio compound page

[Zi Yan]

On 4 Feb 2026, at 22:25, Miaohe Lin wrote:

> On 2026/2/5 8:56, Zi Yan wrote:
>> When !CONFIG_TRANSPARENT_HUGEPAGE, a non-folio compound page can appear in
>> a userspace mapping via either vm_insert_*() functions or
>> vm_operatios_struct->fault(). They are not folios, thus should not be
>> considered for folio operations like split. Change memory_failure() and
>> soft_offline_page() to reject these non-folio compound pages as
>> EOPNOTSUPP.
>>
>> Add PageNonFolioCompound() helper function. This function is functionally
>> equivalent to folio_test_large() && !folio_test_large_rmappable(), but it
>> is supposed to be used on struct page. So open code it instead.
>>
>> Fixes: 689b8986776c ("mm/memory-failure: improve large block size folio handling")
>> Reported-by: 是参差 <shicenci@xxxxxxxxx>
>> Closes: https://lore.kernel.org/all/PS1PPF7E1D7501F1E4F4441E7ECD056DEADAB98A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> ---
>>  include/linux/page-flags.h | 16 ++++++++++++++++
>>  mm/memory-failure.c        |  9 ++++++---
>>  2 files changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index f7a0e4af0c73..2fe8047f42a3 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -1102,6 +1102,22 @@ static inline bool folio_contain_hwpoisoned_page(struct folio *folio)
>>
>>  bool is_free_buddy_page(const struct page *page);
>>
>> +static inline bool PageNonFolioCompound(const struct page *page)
>> +{
>> +	if (PageCompound(page)) {
>> +		const struct page *head = compound_head(page);
>> +
>> +		/*
>> +		 * Without CONFIG_TRANSPARENT_HUGEPAGE, PG_large_rmappable
>> +		 * should not be set/used.
>> +		 */
>> +		return !IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) ||
>> +		       !test_bit(PG_large_rmappable, &head[1].flags.f);
>> +	}
>> +
>> +	return false;
>> +}
>> +
>>  #ifdef CONFIG_MIGRATION
>>  /*
>>   * This page is migratable through movable_ops (for selected typed pages
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index cf0d526e6d41..8b6b5950bb66 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -2440,9 +2440,12 @@ int memory_failure(unsigned long pfn, int flags)
>>
>>  	folio = page_folio(p);
>>
>> -	/* filter pages that are protected from hwpoison test by users */
>> +	/*
>> +	 * filter pages that are protected from hwpoison test by users or
>> +	 * unsupported non folio compound ones
>> +	 */
>>  	folio_lock(folio);
>> -	if (hwpoison_filter(p)) {
>> +	if (hwpoison_filter(p) || PageNonFolioCompound(p)) {
>>  		ClearPageHWPoison(p);
>>  		folio_unlock(folio);
>>  		folio_put(folio);
>> @@ -2945,7 +2948,7 @@ int soft_offline_page(unsigned long pfn, int flags)
>>  	ret = get_hwpoison_page(page, flags | MF_SOFT_OFFLINE);
>>  	put_online_mems();
>>
>> -	if (hwpoison_filter(page)) {
>> +	if (hwpoison_filter(page) || PageNonFolioCompound(page)) {
>
> There should be no problem in soft_offline_page(). HWPoisonHandlable() check will be used
> by get_hwpoison_page() to reject PageNonFolioCompound folios. Or am I miss something?

I did not know that. Why does memory_failure() not call HWPosonHandlable() to check the input
page? It looks to me that HWPosonHandlable() is more appropriate than PageNonFolioCompound()
here.

--
Best Regards,
Yan, Zi