linux-kernel - Re: [PATCH -v2 6/7] x86, NMI, Add support to notify hardware error with unknown NMI

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Date:	Mon, 27 Sep 2010 15:38:16 +0200
From:	Robert Richter <robert.richter@....com>
To:	huang ying <huang.ying.caritas@...il.com>
CC:	Huang Ying <ying.huang@...el.com>, Don Zickus <dzickus@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v2 6/7] x86, NMI, Add support to notify hardware error
 with unknown NMI

On 27.09.10 08:47:53, huang ying wrote:

> >>  arch/x86/kernel/hwerr.c    |   55 +++++++++++++++++++++++++++++++++++++++++++++
> >
> > Instead of creating this file the code should be implemented in
> >
> >  arch/x86/kernel/cpu/intel.c
> >
> > Similar AMD NB code is implemented in amd.c and k8.c.
> 
> Why? This file is not vendor specific.

No, it only implements an Intel specific PCI device, nothing else.

> >> +late_initcall(check_unknown_nmi_for_hwerr);
> >
> > Maybe you can use early pci functions like read_pci_config() to avoid
> > late init.
> 
> I don't think late init is a big issue. Hardware error is rare after all.

Just want to let you know this as an option.

> >> --- a/arch/x86/kernel/traps.c
> >> +++ b/arch/x86/kernel/traps.c
> >> @@ -83,6 +83,8 @@ EXPORT_SYMBOL_GPL(used_vectors);
> >>
> >>  static int ignore_nmis;
> >>
> >> +int unknown_nmi_for_hwerr;
> >
> > If it is an nmi for hwerr, it is no longer an unknown nmi. So we
> > should drop 'unknow' in the naming.
> 
> I think unkown NMI is the one we can not identify the source.
> Something like anonymous.
> 
> >> +
> >>  /*
> >>   * Prevent NMI reason port (0x61) being accessed simultaneously, can
> >>   * only be used in NMI handler.
> >> @@ -360,6 +362,14 @@ io_check_error(unsigned char reason, str
> >>  static notrace __kprobes void
> >>  unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
> >>  {
> >> +     /*
> >> +      * On some platforms, hardware errors may be notified via
> >> +      * unknown NMI
> >> +      */
> >> +     if (unknown_nmi_for_hwerr)
> >> +             panic("NMI for hardware error without error record: "
> >> +                   "Not continuing");
> >> +
> >
> > Instead of checking this flag you should implement and register an nmi
> > handler for this case.
> 
> I think explicit function calls have better readability than notifier chains.

What is different to unknown_nmi() then?

So no, in your case you want to catch unknown nmis for a certain
hardware and then throw a panic. This should be clearly implemented in
a separate handler for this piece of hardware.

We want to cleanup this code and throw out all hardware specific
snippets, and not introduce new special cases here.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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