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Date: Thu, 22 Feb 2024 21:26:43 -0800
From: Dan Williams <dan.j.williams@intel.com>
To: Shuai Xue <xueshuai@linux.alibaba.com>, Borislav Petkov <bp@alien8.de>,
	Ira Weiny <ira.weiny@intel.com>, "Luck, Tony" <tony.luck@intel.com>,
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	<Jonathan.Cameron@huawei.com>, Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v11 1/3] ACPI: APEI: send SIGBUS to current task if
 synchronous memory error not recovered
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References: <20221027042445.60108-1-xueshuai@linux.alibaba.com>
 <20240204080144.7977-2-xueshuai@linux.alibaba.com>
 <20240219092528.GTZdMeiDWIDz613VeT@fat_crate.local>
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Shuai Xue wrote:
> 
> 
> On 2024/2/19 17:25, Borislav Petkov wrote:
> > On Sun, Feb 04, 2024 at 04:01:42PM +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@linux.alibaba.com>
> >> ---
> >>  drivers/acpi/apei/ghes.c | 9 +++++++++
> >>  1 file changed, 9 insertions(+)
> >>
> >> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> >> index 7b7c605166e0..0892550732d4 100644
> >> --- a/drivers/acpi/apei/ghes.c
> >> +++ b/drivers/acpi/apei/ghes.c
> >> @@ -806,6 +806,15 @@ 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 current task due to memory error not recovered");
> >> +		force_sig(SIGBUS);
> >> +	}
> > 
> > Except that there are a bunch of CXL GUIDs being handled there too and
> > this will sigbus those processes now automatically.
> 
> Before the CXL GUIDs added, @Tony confirmed that the HEST notifications are always
> asynchronous on x86 platform, so only Synchronous External Abort (SEA) on ARM is
> delivered as a synchronous notification.
> 
> Will the CXL component trigger synchronous events for which we need to terminate the
> current process by sending sigbus to process?

None of the CXL component errors should be handled as synchronous
events. They are either asynchronous protocol errors, or effectively
equivalent to CPER_SEC_PLATFORM_MEM notifications.