Re: [PATCH] mm/memory-failure: teach kill_accessing_process to accept hugetlb tail page pfn

[Miaohe Lin <linmiaohe@huawei.com>]

On 2025/12/19 16:06, jane.chu@oracle.com wrote:
> 
> 
> On 12/19/2025 12:01 AM, Miaohe Lin wrote:
>> On 2025/12/19 14:28, Jane Chu wrote:
>>> When a hugetlb folio is being poisoned again, try_memory_failure_hugetlb()
>>> passed head pfn to kill_accessing_process(), that is not right.
>>> The precise pfn of the poisoned page should be used in order to
>>> determine the precise vaddr as the SIGBUS payload.
>>>
>>> This issue has already been taken care of in the normal path, that is,
>>> hwpoison_user_mappings(), see [1][2].  Further more, for [3] to work
>>> correctly in the hugetlb repoisoning case, it's essential to inform
>>> VM the precise poisoned page, not the head page.
>>>
>>> [1] https://lkml.kernel.org/r/20231218135837.3310403-1-willy@infradead.org
>>> [2] https://lkml.kernel.org/r/20250224211445.2663312-1-jane.chu@oracle.com
>>> [3] https://lore.kernel.org/lkml/20251116013223.1557158-1-jiaqiyan@google.com/
>>>
>>
>> Thanks for your patch.
>>
>>> Cc: <stable@vger.kernel.org>
>>> Signed-off-by: Jane Chu <jane.chu@oracle.com>
>>> ---
>>>   mm/memory-failure.c | 22 ++++++++++++----------
>>>   1 file changed, 12 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>> index 3edebb0cda30..c9d87811b1ea 100644
>>> --- a/mm/memory-failure.c
>>> +++ b/mm/memory-failure.c
>>> @@ -681,9 +681,11 @@ static void set_to_kill(struct to_kill *tk, unsigned long addr, short shift)
>>>   }
>>>     static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
>>> -                unsigned long poisoned_pfn, struct to_kill *tk)
>>> +                unsigned long poisoned_pfn, struct to_kill *tk,
>>> +                int pte_nr)
>>>   {
>>>       unsigned long pfn = 0;
>>> +    unsigned long hwpoison_vaddr;
>>>         if (pte_present(pte)) {
>>>           pfn = pte_pfn(pte);
>>> @@ -694,10 +696,11 @@ static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
>>>               pfn = swp_offset_pfn(swp);
>>>       }
>>>   -    if (!pfn || pfn != poisoned_pfn)
>>> +    if (!pfn || (pfn > poisoned_pfn || (pfn + pte_nr - 1) < poisoned_pfn))
>>>           return 0;
>>
>> Can we get pte_nr from @shift? I.e. something like "pte_nr = 1UL << (shift - PAGE_SHIFT);"?
> 
> Why?  Is there any concern with using the macro pages_per_huge_page(h) ?

No, I was trying to get rid of new @pte_nr parameter. Something like below:

 static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
-                               unsigned long poisoned_pfn, struct to_kill *tk,
-                               int pte_nr)
+                               unsigned long poisoned_pfn, struct to_kill *tk)
 {
        unsigned long pfn = 0;
        unsigned long hwpoison_vaddr;
+       int pte_nr;

        if (pte_present(pte)) {
                pfn = pte_pfn(pte);
@@ -701,7 +701,8 @@ static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
                        pfn = softleaf_to_pfn(entry);
        }

-       if (!pfn || (pfn > poisoned_pfn || (pfn + pte_nr - 1) < poisoned_pfn))
+       pte_nr = 1UL << (shift - PAGE_SHIFT);
+       if (!pfn || (pfn > poisoned_pfn || (pfn +  pte_nr - 1) < poisoned_pfn))
                return 0;

        hwpoison_vaddr = addr + ((poisoned_pfn - pfn) << PAGE_SHIFT);

So we don't have to pass in pte_nr from all callers. But that's trivial.

Thanks.
.