linux-kernel - Re: [PATCH v15 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

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Message-ID: <20241030140800.GA1288714@yaz-khff2.amd.com>
Date: Wed, 30 Oct 2024 10:08:00 -0400
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,
	rafael@...nel.org, wangkefeng.wang@...wei.com,
	tanxiaofei@...wei.com, mawupeng1@...wei.com, tony.luck@...el.com,
	linmiaohe@...wei.com, naoya.horiguchi@....com, james.morse@....com,
	tongtiangen@...wei.com, gregkh@...uxfoundation.org, will@...nel.org,
	jarkko@...nel.org, linux-acpi@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-edac@...r.kernel.org, x86@...nel.org, justin.he@....com,
	ardb@...nel.org, ying.huang@...el.com, ashish.kalra@....com,
	baolin.wang@...ux.alibaba.com, tglx@...utronix.de,
	dave.hansen@...ux.intel.com, lenb@...nel.org, hpa@...or.com,
	robert.moore@...el.com, lvying6@...wei.com, xiexiuqi@...wei.com,
	zhuo.song@...ux.alibaba.com
Subject: Re: [PATCH v15 1/3] ACPI: APEI: send SIGBUS to current task if
 synchronous memory error not recovered

On Wed, Oct 30, 2024 at 09:54:00AM +0800, Shuai Xue wrote:
> 
> 
> 在 2024/10/30 04:48, Yazen Ghannam 写道:
> > On Mon, Oct 28, 2024 at 04:11:40PM +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..f2ee28c44d7a 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("%s:%d: hardware memory corruption (SIGBUS)\n",
> > > +			current->comm, task_pid_nr(current));
> > 
> > I think it would help to include the GHES_PFX to indicate where this
> > message is coming from. The pr_fmt() macro could also be introduced
> > instead.
> 
> Yes, GHES_PFX is a effective prefix and will be consistent to other message
> in GHES driver. Will add it in next version.
> 
> What do you mean about pr_fmt()?

This can be used to set a prefix for an entire section of code. The
pr_*() macros will pick it up without needing to include a prefix for
each call.

This is described in "Documentation/core-api/printk-basics.rst".

> 
> > 
> > Also, you may want to include the HW_ERR prefix. Not all kernel messages
> > related to hardware errors have this prefix today. But maybe that should
> > be changed so there is more consistent messaging.
> > 
> 
> Do we really need a HW_ERR prefix? The other case which use HW_ERR prefix
> are for hardware registers. The messages which send SIGBUS does
> not include HW_ERR, e.g. in kill_proc(), kill_procs().
> 
>     pr_err("%#lx: Sending SIGBUS to %s:%d due to hardware memory
> corruption\n",...
>     pr_err("%#lx: forcibly killing %s:%d because of failure to unmap
> corrupted page\n",...
> 
>

Correct, HW_ERR isn't used there. My interpretation is that it can be
used whenever an event is due to a hardware error (real or simulated).
This is a very clear message to a user.

It may be redundant in some cases (like here where the message already
says "hardware memory corruption"). But I think it would be go to use it
anyway for consistency.

I think other relevant places in the kernel should also be updated. But
that is beyond this patch, and I don't expect it to be done here and
now.

Thanks,
Yazen