Re: [PATCH v15 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Shuai Xue <xueshuai@linux.alibaba.com>]

在 2024/10/30 22:08, Yazen Ghannam 写道:
> On Wed, Oct 30, 2024 at 09:54:00AM +0800, Shuai Xue wrote:
>>
>>
>> 在 2024/10/30 04:48, Yazen Ghannam 写道:
>>> On Mon, Oct 28, 2024 at 04:11:40PM +0800, Shuai Xue wrote:
>>>> Synchronous error was detected as a result of user-space process accessing
>>>> a 2-bit uncorrected error. The CPU will take a synchronous error exception
>>>> such as Synchronous External Abort (SEA) on Arm64. The kernel will queue a
>>>> memory_failure() work which poisons the related page, unmaps the page, and
>>>> then sends a SIGBUS to the process, so that a system wide panic can be
>>>> avoided.
>>>>
>>>> However, no memory_failure() work will be queued when abnormal synchronous
>>>> errors occur. These errors can include situations such as invalid PA,
>>>> unexpected severity, no memory failure config support, invalid GUID
>>>> section, etc. In such case, the user-space process will trigger SEA again.
>>>> This loop can potentially exceed the platform firmware threshold or even
>>>> trigger a kernel hard lockup, leading to a system reboot.
>>>>
>>>> Fix it by performing a force kill if no memory_failure() work is queued
>>>> for synchronous errors.
>>>>
>>>> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
>>>> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>>> ---
>>>>    drivers/acpi/apei/ghes.c | 10 ++++++++++
>>>>    1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>>>> index ada93cfde9ba..f2ee28c44d7a 100644
>>>> --- a/drivers/acpi/apei/ghes.c
>>>> +++ b/drivers/acpi/apei/ghes.c
>>>> @@ -801,6 +801,16 @@ static bool ghes_do_proc(struct ghes *ghes,
>>>>    		}
>>>>    	}
>>>> +	/*
>>>> +	 * If no memory failure work is queued for abnormal synchronous
>>>> +	 * errors, do a force kill.
>>>> +	 */
>>>> +	if (sync && !queued) {
>>>> +		pr_err("%s:%d: hardware memory corruption (SIGBUS)\n",
>>>> +			current->comm, task_pid_nr(current));
>>>
>>> I think it would help to include the GHES_PFX to indicate where this
>>> message is coming from. The pr_fmt() macro could also be introduced
>>> instead.
>>
>> Yes, GHES_PFX is a effective prefix and will be consistent to other message
>> in GHES driver. Will add it in next version.
>>
>> What do you mean about pr_fmt()?
> 
> This can be used to set a prefix for an entire section of code. The
> pr_*() macros will pick it up without needing to include a prefix for
> each call.
> 
> This is described in "Documentation/core-api/printk-basics.rst".

Got you point, a pr_fmt is much more convenient, but it is beyond this 
patch. I would like to send a patch to add pr_fmt and then replace each 
call after this patch merged.

> 
>>
>>>
>>> Also, you may want to include the HW_ERR prefix. Not all kernel messages
>>> related to hardware errors have this prefix today. But maybe that should
>>> be changed so there is more consistent messaging.
>>>
>>
>> Do we really need a HW_ERR prefix? The other case which use HW_ERR prefix
>> are for hardware registers. The messages which send SIGBUS does
>> not include HW_ERR, e.g. in kill_proc(), kill_procs().
>>
>>      pr_err("%#lx: Sending SIGBUS to %s:%d due to hardware memory
>> corruption\n",...
>>      pr_err("%#lx: forcibly killing %s:%d because of failure to unmap
>> corrupted page\n",...
>>
>>
> 
> Correct, HW_ERR isn't used there. My interpretation is that it can be
> used whenever an event is due to a hardware error (real or simulated).
> This is a very clear message to a user.
> 
> It may be redundant in some cases (like here where the message already
> says "hardware memory corruption"). But I think it would be go to use it
> anyway for consistency.
> 
> I think other relevant places in the kernel should also be updated. But
> that is beyond this patch, and I don't expect it to be done here and
> now.

Ok, I will add the HW_ERR in next version, if no one else objects.
> 
> Thanks,
> Yazen

Thank you.
Best Regards,
Shuai