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

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

On 2023/3/21 AM2:03, Rafael J. Wysocki wrote:
> On Fri, Mar 17, 2023 at 8:25 AM Shuai Xue <xueshuai@linux.alibaba.com> 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@linux.alibaba.com/T/#mb3dede6b7a6d189dc8de3cf9310071e38a192f8e
>>
>> changes since v1:
>> - synchronous events by notify type
>> - Link: https://lore.kernel.org/lkml/20221206153354.92394-3-xueshuai@linux.alibaba.com/
>>
>> 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@huawei.com/T/
>> [3] https://lore.kernel.org/lkml/20221209095407.383211-1-lvying6@huawei.com/
>>
>> 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(-)
>>
>> --
> 
> I really need the designated APEI reviewers to give their feedback on this.

Gentle ping.

Best Regards.
Shuai