linux-kernel - Re: [PATCH 2/3] mm/madvise: Add MF_ACTION_REQUIRED to madvise(MADV

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Message-ID: <c37e5aac-3bc7-4013-b58a-e29c6bfbfd1f@oracle.com>
Date: Mon, 6 May 2024 12:54:17 -0700
From: Jane Chu <jane.chu@...cle.com>
To: Miaohe Lin <linmiaohe@...wei.com>, nao.horiguchi@...il.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/madvise: Add MF_ACTION_REQUIRED to
 madvise(MADV_HWPOISON)

On 5/5/2024 12:02 AM, Miaohe Lin wrote:

> On 2024/5/2 7:24, Jane Chu wrote:
>> The soft hwpoison injector via madvise(MADV_HWPOISON) operates in
>> a synchrous way in a sense, the injector is also a process under
>> test, and should it have the poisoned page mapped in its address
>> space, it should legitimately get killed as much as in a real UE
>> situation.
> Will it be better to add a method to set MF_ACTION_REQUIRED explicitly when inject soft hwpoison?
> Thanks.

So the first question is: Is there a need to preserve the existing 
behavior of  madvise(MADV_HWPOISON)?

The madvise(2) man page says -

        *MADV_HWPOISON *(since Linux 2.6.32)
               Poison the pages in the range specified by/addr/  and/length/
               and handle subsequent references to those pages like a
               hardware memory corruption.  This operation is available
               only for privileged (*CAP_SYS_ADMIN*) processes.  This
               operation may result in the calling process receiving a
               *SIGBUS *and the page being unmapped.

               This feature is intended for testing of memory error-
               handling code; it is available only if the kernel was
               configured with*CONFIG_MEMORY_FAILURE*.

And the impression from my reading is that: there doesn't seem to be a need.

A couple observations -
- The man page states that the calling process may receive a SIGBUS and the page being unmapped.
But the existing behavior is no SIGBUS unless MCE early kill is elected, so it doesn't quite match
the man page.
- There is 'hwpoison-inject' which behaves similar to the existing madvise(MADV_HWPOISON), that is,
soft inject without MF_ACTION_REQUIRED flag.

thanks,
-jane

> .
>
>> Signed-off-by: Jane Chu <jane.chu@...cle.com>
>> ---
>>   mm/madvise.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/madvise.c b/mm/madvise.c
>> index 1a073fcc4c0c..eaeae5252c02 100644
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -1127,7 +1127,7 @@ static int madvise_inject_error(int behavior,
>>   		} else {
>>   			pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
>>   				 pfn, start);
>> -			ret = memory_failure(pfn, MF_COUNT_INCREASED | MF_SW_SIMULATED);
>> +			ret = memory_failure(pfn, MF_ACTION_REQUIRED | MF_COUNT_INCREASED | MF_SW_SIMULATED);
>>   			if (ret == -EOPNOTSUPP)
>>   				ret = 0;
>>   		}
>>