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    SubjectRe: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path
    On Sat, Feb 18, 2012 at 12:49:16AM +0900, HATAYAMA Daisuke wrote:
    > A few days ago I investigted the case where system is reseted due to
    > triple fault caused by the NMI after idt is disabled in
    > machine_kexec. I didn't see the reset when trigering the kdump with
    > NMI since the NMI is masked until next iret instruction executed as
    > described in 6.7.2. Handling Multiple NMIs of Intel Manual Vol.3A.
    > The NMI mask remains untill the first iret execution on the 2nd
    > kernel: just the return path of the first kernel_thread invocation for
    > init process. The exact path is:

    hmm. So even though the local apic was disabled you still got an NMI?
    That could have been from an external NMI. I forget how that is wired up,
    if it goes through the IOAPIC to the Local APIC or directly to the NMI pin
    on the cpu.

    > switch_to
    > -> ret_from_fork
    > -> int_ret_from_sys_call
    > -> retint_restore_args
    > -> irq_return
    > At that phase idt is already set up and kdump works.
    > From the discussion I interpret kdump doesn't assume this behaviour,
    > right?

    probably not.

    > BTW, does anyone know the detail of the NMI mask? I couldn't figure
    > out about it from the Intel spec more than ``certain hardware
    > conditions''... I expect those who look at here are x86 NMI experts.

    I don't understand the question.


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