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    SubjectRe: [PATCH] kvm: notify host when guest paniced
    At 02/29/2012 06:39 PM, Avi Kivity Wrote:
    > On 02/29/2012 12:17 PM, Wen Congyang wrote:
    >>>>>
    >>>> Yes, crash can be so severe that it is not even detected by a kernel
    >>>> itself, so not OOPS message even printed. But in most cases if kernel is
    >>>> functional enough to print OOPS it is functional enough to call single
    >>>> hypercall instruction.
    >>>
    >>> Why not print the oops to virtio-serial? Or even just a regular serial
    >>> port? That's what bare metal does.
    >>
    >> If virtio-serial's driver has bug or the guest doesn't have such device...
    >
    > We have the same issue with the hypercall; and virtio-serial is
    > available on many deployed versions.

    virtio-serial is available, but it is an optional device. If the guest does
    not have this device, the guest cannot tell the host that is is paniced. So
    I still prefer to touch the hypervisor.

    Thanks
    Wen Congyang

    >
    >>>
    >>>>>> Having special kdump
    >>>>>> kernel that transfers dump to a host via virtio-serial channel though
    >>>>>> sounds interesting. May be that's what you mean.
    >>>>>
    >>>>> Yes. The "panic, starting dump" signal should be initiated by the
    >>>>> panicking kernel though, in case the dump fails.
    >>>>>
    >>>> Then panic hypercall sounds like a reasonable solution.
    >>>
    >>> It is, but I'm trying to see if we can get away with doing nothing.
    >>>
    >>
    >> If we have a reliable way with doing nothing, it is better. But I donot
    >> find such way.
    >
    > We won't have a 100% reliable way. But I think a variant of the driver
    > that doesn't use interrupts, or just using the ordinary serial driver,
    > should be reliable enough.
    >



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