Re: [RESEND PATCH v18 1/2] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Hanjun Guo <guohanjun@huawei.com>]

On 2025/4/18 20:35, Shuai Xue wrote:
> 
> 
> 在 2025/4/18 15:48, Hanjun Guo 写道:
>> On 2025/4/14 23:02, Shuai Xue wrote:
>>>
>>>
>>> 在 2025/4/14 22:37, Hanjun Guo 写道:
>>>> On 2025/4/4 19:20, 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>
>>>>> Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
>>>>> Reviewed-by: Jane Chu <jane.chu@oracle.com>
>>>>> ---
>>>>>   drivers/acpi/apei/ghes.c | 11 +++++++++++
>>>>>   1 file changed, 11 insertions(+)
>>>>>
>>>>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>>>>> index b72772494655..50e4d924aa8b 100644
>>>>> --- a/drivers/acpi/apei/ghes.c
>>>>> +++ b/drivers/acpi/apei/ghes.c
>>>>> @@ -799,6 +799,17 @@ 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) {
>>>>> +        dev_err(ghes->dev,
>>>>> +            HW_ERR GHES_PFX "%s:%d: synchronous unrecoverable 
>>>>> error (SIGBUS)\n",
>>>>> +            current->comm, task_pid_nr(current));
>>>>> +        force_sig(SIGBUS);
>>>>> +    }
>>>>
>>>> I think it's reasonable to send a force kill to the task when the
>>>> synchronous memory error is not recovered.
>>>>
>>>> But I hope this code will not trigger some legacy firmware issues,
>>>> let's be careful for this, so can we just introduce arch specific
>>>> callbacks for this?
>>>
>>> Sorry, can you give more details? I am not sure I got your point.
>>>
>>> For x86, Tony confirmed that ghes will not dispatch x86 synchronous 
>>> errors
>>> (a.k.a machine check exception), in previous vesion.
>>> Sync is only used in arm64 platform, see is_hest_sync_notify().
>>
>> Sorry for the late reply, from the code I can see that x86 will reuse
>> ghes_do_proc(), if Tony confirmed that x86 is OK, it's OK to me as well.
> 
> Hi, Hanjun,
> 
> Glad to hear that.
> 
> I copy and paste in the original disscusion with @Tony from mailist.[1]
> 
>> On x86 the "action required" cases are signaled by a synchronous 
>> machine check
>> that is delivered before the instruction that is attempting to consume 
>> the uncorrected
>> data retires. I.e., it is guaranteed that the uncorrected error has 
>> not been propagated
>> because it is not visible in any architectural state.
> 
>> APEI signaled errors don't fall into that category on x86 ... the 
>> uncorrected data
>> could have been consumed and propagated long before the signaling used 
>> for
>> APEI can alert the OS.
> 
> I also add comments in the code.
> 
> /*
>   * A platform may describe one error source for the handling of 
> synchronous
>   * errors (e.g. MCE or SEA), or for handling asynchronous errors (e.g. SCI
>   * or External Interrupt). On x86, the HEST notifications are always
>   * asynchronous, so only SEA on ARM is delivered as a synchronous
>   * notification.
>   */
> static inline bool is_hest_sync_notify(struct ghes *ghes)
> {
>      u8 notify_type = ghes->generic->notify.type;
> 
>      return notify_type == ACPI_HEST_NOTIFY_SEA;
> }
> 
> 
> If you are happy with code, please explictly give me your reviewed-by 
> tags :)

Call force_sig(SIGBUS) directly in ghes_do_proc() is not my favourite,
but I can bear that, please add

Reviewed-by: Hanjun Guo <guohanjun@huawei.com>

Thanks
Hanjun