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    SubjectRe: [PATCH 1/2] boot: ignore early NMIs
    On Tue, Mar 13, 2012 at 09:33:50AM -0400, Don Zickus wrote:
    > On Tue, Mar 13, 2012 at 11:11:49AM +0900, Fernando Luis Vázquez Cao wrote:
    > > On 03/13/2012 05:16 AM, H. Peter Anvin wrote:
    > > >On 03/12/2012 01:04 PM, H. Peter Anvin wrote:
    > > >>On 03/12/2012 01:01 PM, Eric W. Biederman wrote:
    > > >>>The basic problem is which source do we block this at? How many
    > > >>>sources are their? And architecturally last I looked x86 no longer
    > > >>>has a NMI disable EFI and similar systems want to get away without
    > > >>>a CMOS legacy clock because designers so often get them wrong.
    > > >>>
    > > >>On all processors which have an LAPIC you can block all NMI sources at
    > > >>the LAPIC. I think it's safe to assume that if you don't have an LAPIC
    > > >>-- an ancient system by now -- you have port 70h.
    > > >>
    > > >One thing: *disabling* the LAPIC will allow external NMIs coming in on
    > > >LINT1 through, since the LAPIC in the disabled state tries to mimic the
    > > >no-LAPIC configuration. So I don't think you want to disable LAPIC as
    > > >much as disable the interrupt vectors within.
    > >
    > > Does this sound like a plan to get the ball rolling?:
    > >
    > > 1.- Merge Don's patch to disable the LAPIC in kdump reboot path (this
    > > fixes a real issue seen in the field, is a net win and certainly not a
    > > regression - indeed it makes the code simpler because the I/O
    > > APICs are left untouched).
    >
    > I think you mean my patch to stop disabling the I/O APIC. That patch
    > hasn't seen any new issues. It was the piece that stopped disabling the
    > LAPIC that opened the doors for NMIs to fault the system.
    >
    > >
    > > 2.- Merge my patch set to ignore early NMIs (this brings the behavior
    > > of the boot code in line with what we do in the rest of the kernel
    > > a we can avoid situations were a spurious NMI causes the kernel
    > > to halt). The early NMI handler is temporary and the final NMI
    > > handler installed shortly afterwards will take care of subsequent
    > > NMIs.
    > >
    > > 3.- Make sure that spurious NMIs (i.e. NMIs that for whatever reason
    > > could not be stopped at the source) received during the reboot
    > > path to the kdump kernel do not cause a triple fault or a system
    > > lockup. This is under testing.
    >
    > This will require changes in kexec-tools as the purgatory code zaps the
    > GDT I believe. This is going to make a 'complete solution' dependent on
    > a version of kexec-tools. Not sure what we want to do there.

    Ouch. I guess that in the event that purgatory needs to be modified
    some backwards-compatibility will need to be provided, possibly
    by allowing purgatory to switch between two behaviours based on
    e.g. a command line parameter.

    > > 4.- Identify all the NMI sources and keep them from reaching the CPU
    > > when it can be done in a race-free way.
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