Re: [PATCH v12 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Jarkko Sakkinen]

On Mon Sep 2, 2024 at 6:00 AM EEST, 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 unless all bellow
> preconditions check passed:
>
> - `if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))` in ghes_handle_memory_failure()
> - `if (flags == -1)` in ghes_handle_memory_failure()
> - `if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))` in ghes_do_memory_failure()
> - `if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) ` in ghes_do_memory_failure()
>
> 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.
>
> Suggested-by: Xiaofei Tan <tanxiaofei@xxxxxxxxxx>
> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>
> ---
>  drivers/acpi/apei/ghes.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 623cc0cb4a65..b0b20ee533d9 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -801,6 +801,16 @@ 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 %s:%d due to hardware memory corruption\n",
> +			current->comm, task_pid_nr(current));

Hmm... doest this need "hardware" or would "memory corruption" be
enough?

Also, does this need to say that it is sending SIGBUS when the signal
itself tells that already?

I.e. could "%s:%d has memory corruption" be enough information?

> +		force_sig(SIGBUS);
> +	}
> +
>  	return queued;
>  }
>  

BR, Jarkko