linux-kernel - Re: [PATCH v16 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

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Message-ID: <20241105150945.GE916505@yaz-khff2.amd.com>
Date: Tue, 5 Nov 2024 10:09:45 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: Shuai Xue <xueshuai@...ux.alibaba.com>
Cc: mark.rutland@....com, catalin.marinas@....com, mingo@...hat.com,
	robin.murphy@....com, Jonathan.Cameron@...wei.com, bp@...en8.de,
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	tongtiangen@...wei.com, gregkh@...uxfoundation.org, will@...nel.org,
	jarkko@...nel.org, linux-acpi@...r.kernel.org, linux-mm@...ck.org,
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	zhuo.song@...ux.alibaba.com
Subject: Re: [PATCH v16 1/3] ACPI: APEI: send SIGBUS to current task if
 synchronous memory error not recovered

On Mon, Nov 04, 2024 at 09:54:28AM +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@...ux.alibaba.com>
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>  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 ada93cfde9ba..af3339dd3817 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(HW_ERR GHES_PFX "%s:%d: hardware memory corruption (SIGBUS)\n",

Is this always a memory error? The code flow above implies that an
unrecoverable ARM processor error can all be !queued. So should the
message be more generic like "synchronous unrecoverable error" or
similar?

In any case, this is just a minor nit if this is not an issue in
practice.

Reviewed-by: Yazen Ghannam <yazen.ghannam@....com>

Thanks,
Yazen