Re: [PATCH] arm64: hwpoison: add VM_FAULT_HWPOISON[_LARGE] handling

[Punit Agrawal <punit.agrawal@arm.com>]

On 06/02/17 22:21, Baicar, Tyler wrote:
> Hello Punit,
>
>
> On 2/3/2017 9:17 AM, Punit Agrawal wrote:
>> Tyler Baicar <tbaicar@codeaurora.org> writes:
>>
>>> From: "Jonathan (Zhixiong) Zhang" <zjzhang@codeaurora.org>
>>>
>>> Add VM_FAULT_HWPOISON[_LARGE] handling to the arm64 page fault
>>> handler. Handling of VM_FAULT_HWPOISON[_LARGE] is very similar
>>> to VM_FAULT_OOM, the only difference is that a different si_code
>>> (BUS_MCEERR_AR) is passed to user space and si_addr_lsb field is
>>> initialized.
>>>
>>> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@codeaurora.org>
>>> Signed-off-by: Tyler Baicar <tbaicar@codeaurora.org>
>>> ---
>>>  arch/arm64/mm/fault.c | 31 +++++++++++++++++++++++++++----
>>>  1 file changed, 27 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> [...]
>>
>>> @@ -426,7 +439,17 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>>>              */
>>>             sig = SIGBUS;
>>>             code = BUS_ADRERR;
>>> -   } else {
>>> +   }
>>> +#ifdef CONFIG_MEMORY_FAILURE
>>> +   else if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
>> Please add spaces around '|'.
> Will do!
>>
>>> +           pr_err(
>>> +   "Killing %s:%d due to hardware memory corruption fault at %lx\n",
>>> +                   tsk->comm, tsk->pid, addr);
>> The message is misleading as we're not really killing a task but
>> delivering a signal (SIGBUS) which might not always lead to the receiver
>> being killed.
>>
>> But considering that we don't print any message for the other faults,
>> I'd prefer that we drop this pr_err.
> Yes, I'll drop the pr_err.
>>> +           sig = SIGBUS;
>>> +           code = BUS_MCEERR_AR;
>>> +   }
>>> +#endif
>> Although to get a HWPOISON fault CONFIG_MEMORY_FAILURE is needed, the
>> handling seems safe even when it is not enabled. Can the ifdeffery be
>> dropped?
> Yes, I can drop the ifdef. The handling would be fine either way.
>>
>> Also, I was wondering how this code was tested? Did you by any chance
>> try using hwpoison inject debugfs interface?
> This was originally tested using proprietary error injection that we have.
>
> I just tried the hwpoison inject interface and it didn't result in
> hitting this code path.
>
> [   70.747697] Injecting memory failure at pfn 0x400340
>
> [   70.748547] Memory failure: 0x400340: Unknown page state
>
> [   70.752911] Memory failure: 0x400340: unknown page still referenced
> by 1 users
>
> [   70.760167] Memory failure: 0x400340: recovery action for unknown
> page: Failed
>
>
> I've never used hwpoison inject though, so maybe I'm doing something
> wrong :)

No worries. Writing the pfn an executable is loaded at
/sys/kernel/debug/hwpoison/corrupt-pfn triggered the code for me. On my
system the program dies after printing "Bus error" - probably what the
default handler from glibc is configured to do in this situation. :)

>
> Thanks,
> Tyler
>
> --
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project.
>
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