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Date: Fri, 23 Feb 2024 12:08:13 +0000
From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Dan Williams <dan.j.williams@intel.com>
CC: 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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Subject: Re: [PATCH v11 1/3] ACPI: APEI: send SIGBUS to current task if
 synchronous memory error not recovered
Message-ID: <20240223120813.00005d1f@Huawei.com>
In-Reply-To: <65d82c9352e78_24f3f294d5@dwillia2-mobl3.amr.corp.intel.com.notmuch>
References: <20221027042445.60108-1-xueshuai@linux.alibaba.com>
	<20240204080144.7977-2-xueshuai@linux.alibaba.com>
	<20240219092528.GTZdMeiDWIDz613VeT@fat_crate.local>
	<bdf15819-46e0-498f-97e1-a0183f257086@linux.alibaba.com>
	<65d82c9352e78_24f3f294d5@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Organization: Huawei Technologies Research and Development (UK) Ltd.
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On Thu, 22 Feb 2024 21:26:43 -0800
Dan Williams <dan.j.williams@intel.com> wrote:

> 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.

Not a good example, CPER_SEC_PLATFORM_MEM is sometimes signaled via SEA.