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    SubjectRe: [PATCH] kexec: force x86_64 arches to boot kdump kernels on boot cpu
    Date
    Vivek Goyal <vgoyal@redhat.com> writes:

    > Ok. Got it. So in this case we route the interrupts directly through LAPIC
    > and put LVT0 in ExtInt mode and IOAPIC is bypassed.
    >
    > I am looking at Intel Multiprocessor specification v1.4 and as per figure
    > 3-3 on page 3-9, 8259 is connected to LINTIN0 line, which in turn is
    > connected to LINTIN0 pin on all processors. If that is the case, even in
    > this mode, all the CPU should see the timer interrupts (which is coming
    > from 8259)?

    However things are implemented completely differently now. I don't think
    the coherent hypertransport domain of AMD processors actually routes
    ExtINT interrupts to all cpus but instead one (the default route?) is
    picked.

    So I think for the kdump case we pretty much need to use an IOAPIC
    in virtual wire mode for recent AMD systems.

    For current Intel systems I believe either scenario still works.

    > Can you print the LAPIC registers (print_local_APIC) during normal boot
    > and during kdump boot and paste here?

    It's worth a look.

    I still think we need to just use apic mode at kernel startup, and
    be done with it.

    Eric
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