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

Yazen Ghannam
2024-10-30T14:08:16Z

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@linux.alibaba.com>
> > > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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