Re: [PATCH RFC 1/1] mm/ksm: Add recovery mechanism for memory failures

[Miaohe Lin <linmiaohe@huawei.com>]

On 2025/10/11 17:38, Lance Yang wrote:
> 
> 
> On 2025/10/11 17:23, Miaohe Lin wrote:
>> On 2025/10/11 15:52, Lance Yang wrote:
>>> @Miaohe
>>>
>>> I'd like to raise a concern about a potential hardware failure :)
>>
>> Thanks for your thought.
>>
>>>
>>> My tests show that if the shared zeropage (or huge zeropage) gets marked
>>> with HWpoison, the kernel continues to install it for new mappings.
>>> Surprisingly, it does not kill the accessing process ...
>>
>> Have you investigated the cause? If user space writes to shared zeropage,
>> it will trigger COW and a new page will be installed. After that, reading
>> the newly allocated page won't trigger memory error. In this scene, it does
>> not kill the accessing process.
> 
> Not write just read :)
> 
>>
>>>
>>> The concern is, once the page is no longer zero-filled due to the hardware
>>> failure, what will happen? Would this lead to silent data corruption for
>>> applications that expect to read zeros?
>>
>> IMHO, once the page is no longer zero-filled due to the hardware failure, later
>> any read will trigger memory error and memory_failure should handle that.
> 
> I've only tested injecting an error on the shared zeropage using corrupt-pfn:
> 
> echo $PFN > /sys/kernel/debug/hwpoison/corrupt-pfn
> 
> But no memory error was triggered on a subsequent read ...

It's because corrupt-pfn only provides a software error injection mechanism.
If you want to trigger memory error on read, you need use hardware error injection
mechanism e.g.APEI Error INJection [1].

[1] https://www.kernel.org/doc/html/v5.8/firmware-guide/acpi/apei/einj.html

Thanks.
.