Re: [PATCH v2] mm/migrate: Avoid copying hwpoisoned folios during migration

[Huang, Ying]

"David Hildenbrand (Arm)" <david@xxxxxxxxxx> writes:

> On 7/7/26 11:01, Kaitao Cheng wrote:
>> From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
>> 
>> The generic folio migration path can copy the source folio after it has
>> been unmapped.  For normal and THP folios this goes through
>> move_to_new_folio(), then the filesystem or anonymous migration callback,
>> and commonly reaches folio_mc_copy().
>> 
>> folio_mc_copy() uses copy_mc_highpage(), but architectures without
>> copy_mc_to_kernel support fall back to copy_highpage().  If the source
>> folio already contains a hwpoisoned page, a normal copy can consume the
>> poisoned memory and trigger a synchronous machine check.
>
> Well, but the code can still race with memory_failure() IIUC, so it's not really
> safe either?

Yes.  So the better way to fix this is to implement copy_mc_to_kernel()
for the target architectures, or to implement the trick in the fallback?

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Best Regards,
Huang, Ying