Re: [PATCH v3 0/2] ACPI: APEI: handle synchronous exceptions with proper si_code

[Shuai Xue]

On 2023/3/21 PM3:17, mawupeng wrote:
> Test-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> 
> I have test this on arm64 with following steps:
>   1. make memory failure return EBUSY
>   2. force a UCE with einj
> 
> Without this patchset, user task will not be kill since memory_failure can
> not handle this UCE properly and user task is in D state. The stack can
> be found in the end.
> With this patchset, user task can be killed even memory_failure return
> -EBUSY without doing anything.
> 
> Here is the stack of user task with D state:
> 
>   # cat /proc/7001/stack
>   [<0>] __flush_work.isra.0+0x80/0xa8
>   [<0>] __cancel_work_timer+0x144/0x1c8
>   [<0>] cancel_work_sync+0x1c/0x30
>   [<0>] memory_failure_queue_kick+0x3c/0x88
>   [<0>] ghes_kick_task_work+0x28/0x78
>   [<0>] task_work_run+0xb8/0x188
>   [<0>] do_notify_resume+0x1e0/0x280
>   [<0>] el0_da+0x130/0x138
>   [<0>] el0t_64_sync_handler+0x68/0xc0
>   [<0>] el0t_64_sync+0x188/0x190

Thank you :)

Cheers,
Shuai

> 
> On 2023/3/17 15:24, Shuai Xue wrote:
>> changes since v2 by addressing comments from Naoya:
>> - rename mce_task_work to sync_task_work
>> - drop ACPI_HEST_NOTIFY_MCE case in is_hest_sync_notify()
>> - add steps to reproduce this problem in cover letter
>> - Link: https://lore.kernel.org/lkml/1aa0ca90-d44c-aa99-1e2d-bd2ae610b088@xxxxxxxxxxxxxxxxx/T/#mb3dede6b7a6d189dc8de3cf9310071e38a192f8e
>>
>> changes since v1:
>> - synchronous events by notify type
>> - Link: https://lore.kernel.org/lkml/20221206153354.92394-3-xueshuai@xxxxxxxxxxxxxxxxx/
>>
>> Currently, both synchronous and asynchronous error are queued and handled
>> by a dedicated kthread in workqueue. And Memory failure for synchronous
>> error is synced by a cancel_work_sync trick which ensures that the
>> corrupted page is unmapped and poisoned. And after returning to user-space,
>> the task starts at current instruction which triggering a page fault in
>> which kernel will send SIGBUS to current process due to VM_FAULT_HWPOISON.
>>
>> However, the memory failure recovery for hwpoison-aware mechanisms does not
>> work as expected. For example, hwpoison-aware user-space processes like
>> QEMU register their customized SIGBUS handler and enable early kill mode by
>> seting PF_MCE_EARLY at initialization. Then the kernel will directy notify
>> the process by sending a SIGBUS signal in memory failure with wrong
>> si_code: BUS_MCEERR_AO si_code to the actual user-space process instead of
>> BUS_MCEERR_AR.
>>
>> To address this problem:
>>
>> - PATCH 1 sets mf_flags as MF_ACTION_REQUIRED on synchronous events which
>>   indicates error happened in current execution context
>> - PATCH 2 separates synchronous error handling into task work so that the
>>   current context in memory failure is exactly belongs to the task
>>   consuming poison data.
>>
>> Then, kernel will send SIGBUS with proper si_code in kill_proc().
>>
>> Lv Ying and XiuQi also proposed to address similar problem and we discussed
>> about new solution to add a new flag(acpi_hest_generic_data::flags bit 8) to
>> distinguish synchronous event. [2][3] The UEFI community still has no response.
>> After a deep dive into the SDEI TRM, the SDEI notification should be used for
>> asynchronous error. As SDEI TRM[1] describes "the dispatcher can simulate an
>> exception-like entry into the client, **with the client providing an additional
>> asynchronous entry point similar to an interrupt entry point**". The client
>> (kernel) lacks complete synchronous context, e.g. systeam register (ELR, ESR,
>> etc). So notify type is enough to distinguish synchronous event.
>>
>> To reproduce this problem:
>>
>> 	# STEP1: enable early kill mode
>> 	#sysctl -w vm.memory_failure_early_kill=1
>> 	vm.memory_failure_early_kill = 1
>>
>> 	# STEP2: inject an UCE error and consume it to trigger a synchronous error
>> 	#einj_mem_uc single
>> 	0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
>> 	injecting ...
>> 	triggering ...
>> 	signal 7 code 5 addr 0xffffb0d75000
>> 	page not present
>> 	Test passed
>>
>> The si_code (code 5) from einj_mem_uc indicates that it is BUS_MCEERR_AO error
>> and it is not fact.
>>
>> After this patch set:
>>
>> 	# STEP1: enable early kill mode
>> 	#sysctl -w vm.memory_failure_early_kill=1
>> 	vm.memory_failure_early_kill = 1
>>
>> 	# STEP2: inject an UCE error and consume it to trigger a synchronous error
>> 	#einj_mem_uc single
>> 	0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
>> 	injecting ...
>> 	triggering ...
>> 	signal 7 code 4 addr 0xffffb0d75000
>> 	page not present
>> 	Test passed
>>
>> The si_code (code 4) from einj_mem_uc indicates that it is BUS_MCEERR_AR error
>> as we expected.
>>
>> [1] https://developer.arm.com/documentation/den0054/latest/
>> [2] https://lore.kernel.org/linux-arm-kernel/20221205160043.57465-4-xiexiuqi@xxxxxxxxxx/T/
>> [3] https://lore.kernel.org/lkml/20221209095407.383211-1-lvying6@xxxxxxxxxx/
>>
>> Shuai Xue (2):
>>   ACPI: APEI: set memory failure flags as MF_ACTION_REQUIRED on
>>     synchronous events
>>   ACPI: APEI: handle synchronous exceptions in task work
>>
>>  drivers/acpi/apei/ghes.c | 135 ++++++++++++++++++++++++---------------
>>  include/acpi/ghes.h      |   3 -
>>  mm/memory-failure.c      |  13 ----
>>  3 files changed, 83 insertions(+), 68 deletions(-)
>>