Re: [PATCH 1/2] mm/compaction: skip folios containing hwpoisoned pages

[David Hildenbrand (Arm)]

On 10/20/26 13:27, Kaitao Cheng wrote:
> 
> 
> 在 2026/10/11 21:14, Huang, Ying 写道:
>> Yuanhe Shu <xiangzao@xxxxxxxxxxxxxxxxx> writes:
>>
>>>
>>> Agreed, and nothing here replaces copy_mc.  Two things the check adds
>>> while that work is pending: on archs without copy_mc the plain copy
>>> does not fail, it consumes the poison - the same poison consumption
>>> commit 841a8bfcbad9 ("mm: prevent poison consumption when splitting
>>> THP") refused to risk on the split path, at your suggestion; and the
>>> refusal happens before the copy is attempted at all, while copy_mc
>>> recovers only during the read.  The check and copy_mc compose.
>>>
>>
>> Is it good to implement the trick in copy_mc_user_highpage() and
>> copy_mc_highpage() if the macro copy_mc_to_kernel is undefined?
> 
> On architectures with hardware error correction and exception recovery
> support, accessing faulty memory automatically triggers an exception,
> which itself guarantees atomicity.
> 
> On architectures without such support, even if we implement this logic
> in copy_mc_user_highpage() and copy_mc_highpage(), checking the hwpoison
> flag and copying the data remain two separate operations. They cannot
> be performed atomically, so there is still a race window between them,
> however small.

Yes. And you need proper architecture support to fix it?

> 
> Moving the hwpoison check after the copy might address this issue.
> Is there anything wrong with my understanding?

Will architectures that are not prepared for copy_mc_user_highpage() not simply
crash if they trigger an MCE during an access?

-- 
Cheers,

David