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

[Shuai Xue]

On 2024/2/23 20:17, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 12:08:13 +0000
> Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:
> 
>> On Thu, 22 Feb 2024 21:26:43 -0800
>> Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>>
>>> Shuai Xue wrote:  
>>>>
>>>>
>>>> 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?    
>>>
>>> None of the CXL component errors should be handled as synchronous
>>> events. They are either asynchronous protocol errors, or effectively
>>> equivalent to CPER_SEC_PLATFORM_MEM notifications.  
>>
>> Not a good example, CPER_SEC_PLATFORM_MEM is sometimes signaled via SEA.
>>
> 
> Premature send.:(
> 
> One example I can point at is how we do signaling of memory
> errors detected by the host into a VM on arm64.
> https://elixir.bootlin.com/qemu/latest/source/hw/acpi/ghes.c#L391
> CPER_SEC_PLATFORM_MEM via ARM Synchronous External Abort (SEA).
> 
> Right now we've only used async in QEMU for proposed CXL error
> CPER records signalling but your reference to them being similar
> to CPER_SEC_PLATFORM_MEM is valid so 'maybe' they will be
> synchronous in some physical systems as it's one viable way to
> provide rich information for synchronous reception of poison.
> For the VM case my assumption today is we don't care about providing the
> VM with rich data, so CPER_SEC_PLATFORM_MEM is fine as a path for
> errors whether from CXL CPER records or not.
> 
> Jonathan

Thank you for your confirmation and explanation.

So I think the condition:

- `sync` for synchronous event,
- `!queued` for CPER_SEC_PLATFORM_MEM notifications which do not handle memory failures.

is fine.

@Borislav, do you have any other concerns?

Best Regards,
Shuai