Re: [PATCH v2 0/2] ACPI: APEI: handle synchronous exceptions with proper si_code

[Shuai Xue]

Gentle ping.

On 2023/2/27 PM1:03, Shuai Xue wrote:
> 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.
> 
> [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 | 134 ++++++++++++++++++++++++---------------
>  include/acpi/ghes.h      |   3 -
>  mm/memory-failure.c      |  13 ----
>  3 files changed, 82 insertions(+), 68 deletions(-)
>