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Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel

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Olaf Hering <olaf@aepfle.de> writes:

> KY,
>
> if a hyperv VM crashes alot of work must be done to prepare the
> environment for the kdump kernel. This approach is different compared to
> all the other VM types, or baremetal. Since the just crashed kernel is
> per definition unreliable all that work should be done within the kdump
> kernel because I think a reliable environment exists only there.
>
> Was it ever considered to do the CHANNELMSG_UNLOAD /
> CHANNELMSG_UNLOAD_RESPONSE work during boot, instead of doing it before
> starting the kexec/kdump kernel?

Sorry guys I missed the discussion, I was on vacation.

I see a number of minor but at least one major issue against such move:
At least for some Hyper-V versions (2012R2 for example)
CHANNELMSG_UNLOAD_RESPONSE is delivered to the CPU which initially sent 
CHANNELMSG_REQUESTOFFERS and on kdump we may not have this CPU up as
we usually do kdump with nr_cpus=1 (and on the CPU which crashed). 

Minor issue is the necessity preserve the information about
message/events pages across kexec.

>
> What would it take to prepare the runtime environment during boot?
> Does the newly booted kernel need any info from the previous kernel,
> something that cant be determined during boot? If yes, how can such info
> be passed from the old kernel to the new kernel?
>
> Olaf
>

-- 
  Vitaly

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Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 11:40 +0100
  Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 11:40 +0100
    Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 11:40 +0100
      Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 12:00 +0100
    Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 12:00 +0100
      Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 14:00 +0100
        Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 14:30 +0100
          Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 15:00 +0100
            Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 15:40 +0100
              RE: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel KY Srinivasan <kys@microsoft.com> - 2016-12-16 02:00 +0100
          Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 16:20 +0100

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