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    SubjectRe: [PATCH 0/2 v3] kvm: notify host when guest panicked
    On 2012-03-15 11:39, Gleb Natapov wrote:
    > On Wed, Mar 14, 2012 at 11:46:08AM -0700, Eric Northup wrote:
    >> On Wed, Mar 14, 2012 at 6:25 AM, Gleb Natapov <> wrote:
    >>> On Wed, Mar 14, 2012 at 03:16:05PM +0200, Avi Kivity wrote:
    >>>> On 03/14/2012 03:14 PM, Gleb Natapov wrote:
    >>>>> On Wed, Mar 14, 2012 at 03:07:46PM +0200, Avi Kivity wrote:
    >>>>>> On 03/14/2012 01:11 PM, Wen Congyang wrote:
    >>>>>>>> I don't think we want to use the driver. Instead, have a small
    >>> piece of
    >>>>>>>> code that resets the device and pushes out a string (the panic
    >>> message?)
    >>>>>>>> without any interrupts etc.
    >>>>>>>> It's still going to be less reliable than a hypercall, I agree.
    >>>>>>> Do you still want to use complicated and less reliable way?
    >>>>>> Are you willing to try it out and see how complicated it really is?
    >>>>>> While it's more complicated, it's also more flexible. You can
    >>>>>> communicate the panic message, whether the guest is attempting a
    >>> kdump
    >>>>>> and its own recovery or whether it wants the host to do it, etc., you
    >>>>>> can communicate less severe failures like oopses.
    >>>>> hypercall can take arguments to achieve the same.
    >>>> It has to be designed in advance; and every time we notice something's
    >>>> missing we have to update the host kernel.
    >>> We and in the designed stage now. Not to late to design something flexible
    >>> :) Panic hypercall can take GPA of a buffer where host puts panic info
    >>> as a parameter. This buffer can be read by QEMU and passed to management.
    >> If a host kernel change is in the works, I think it might be cleanest to
    >> have the host kernel export a new kind of VCPU exit for unhandled-by-KVM
    >> hypercalls. Then usermode can respond to the hypercall as appropriate.
    >> This would permit adding or changing future hypercalls without host kernel
    >> changes.
    > There was such vm exit (KVM_EXIT_HYPERCALL), but it was deemed to be a
    > bad idea.

    BTW, this would help a lot in emulating hypercalls of other hypervisors
    (or of KVM's VAPIC in the absence of in-kernel irqchip - I had to jump
    through hoops therefore) in user space. Not all those hypercall handlers
    actually have to reside in the KVM module.


    Siemens AG, Corporate Technology, CT T DE IT 1
    Corporate Competence Center Embedded Linux

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