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Date: Sat, 24 Feb 2024 11:40:19 -0800
From: Dan Williams <dan.j.williams@intel.com>
To: Borislav Petkov <bp@alien8.de>, Shuai Xue <xueshuai@linux.alibaba.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: <65da4623b6287_2bce9294be@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>
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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.
> 
> Lemme add the whole bunch from
> 
>   671a794c33c6 ("acpi/ghes: Process CXL Component Events")
> 
> for comment to Cc.

BTW, I am about to revert all the CXL GUIDs for v6.8 to try again for
v6.9:

http://lore.kernel.org/r/170820177849.631006.8893584762602010898.stgit@dwillia2-xfh.jf.intel.com