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    SubjectRe: [PATCH 1/2] boot: ignore early NMIs
    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.

    > 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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