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Re: [libvirt] [PATCH 1/2] conf: add crash to hyperv features



On 11/10/2015 06:55 PM, Dmitry Andreev wrote:
Paolo, Jiri, can I do something more for this patch to be accepted?

On 05.11.2015 17:32, Paolo Bonzini wrote:

On 05/11/2015 14:54, Dmitry Andreev wrote:
Add crash CPU feature for Hyper-V. Hyper-V crash MSR's can be used
by Hyper-V based guests to notify about occurred guest crash.

XML:
<features>
    <hyperv>
      <crash state='on'/>
    </hyperv>
</features>
Sounds like this is related to an existing panic device we already
support. So what does enabling hv_crash do in QEMU? Is it an additional
channel to a panic device or is the panic device still needed even if
hv_crash is enabled? In any case, I think we should map this somehow to
the panic device instead of copying 1:1 the way QEMU enables hv_crash.
pvpanic and Hyper-V crash are independent ways for guest to notify about
OS crash. Both ways rise the 'qemu guest panicked' event. Domain can
have both hv_crash and pvpanic enabled at the same time.

pvpanic is in <devices> section in domain configuration because it is an ISA device. Hyper-V crash is a hypervisor's feature, which enables a set
of model-specific registers. Guest can use this registers to send
notification and store additional information about a crash. This is a
part of Microsoft hypervisor interface.

That's why I think hv_crash should be in <features> section.
I agree.

Paolo

Please.

This feature is very interesting for us for guest debugging
especially during guest installation where specific drivers
are not available or not ready or not that easy to supply.

Den


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