Re: [PATCH v11 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Shuai Xue]

On 2024/2/19 17:25, Borislav Petkov wrote:
> On Sun, Feb 04, 2024 at 04:01:42PM +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@xxxxxxxxxxxxxxxxx>
>> ---
>>  drivers/acpi/apei/ghes.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>> index 7b7c605166e0..0892550732d4 100644
>> --- a/drivers/acpi/apei/ghes.c
>> +++ b/drivers/acpi/apei/ghes.c
>> @@ -806,6 +806,15 @@ 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("Sending SIGBUS to current task due to memory error not recovered");
>> +		force_sig(SIGBUS);
>> +	}
> 
> Except that there are a bunch of CXL GUIDs being handled there too and
> this will sigbus those processes now automatically.

Before the CXL GUIDs added, @Tony confirmed that the HEST notifications are always
asynchronous on x86 platform, so only Synchronous External Abort (SEA) on ARM is
delivered as a synchronous notification.

Will the CXL component trigger synchronous events for which we need to terminate the
current process by sending sigbus to process?

> 
> Lemme add the whole bunch from
> 
>   671a794c33c6 ("acpi/ghes: Process CXL Component Events")
> 
> for comment to Cc.
> 

Thank you.

Best Regards,
Shuai