Re: [Xen-devel] live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Olaf Hering <olaf@xxxxxxxxx>]

As a followup to the issue below, and the one which "just" popped in in
qemu-2.6+:

Why is the machine description for xen not fixed?

Shouldnt the be some sort of verification of old and new 'xenfv' when a
new qemu rc1 is done?
Is there a way to dump the machine description in text form?

Olaf

On Fri, May 13, Stefano Stabellini wrote:

> On Thu, 12 May 2016, Olaf Hering wrote:
> > On Thu, May 12, Olaf Hering wrote:
> > 
> > > One thing to fix it in staging-4.5 is to introduce a dummy device which
> > > handles a section named "kvm-tpr-opt". I already have a hack which does
> > > that, and the migration proceeds. I will propose a patch to deal with
> > > this part of the bug.
> > 
> > Something like shown below.
> 
> Thanks for looking into this. I don't think that adding a dummy device
> in QEMU is acceptable. This kind of problems is usually solved with
> versioning the PC machine in QEMU, see all the pc_machine_* in
> hw/i386/pc_piix.c. One specific version of the machine is supposed to
> remain identical over multiple QEMU releases. In this case xenfv (or the
> pc machine you are using, if you are not using xenfv) has to be always
> identical. That's why I think we need to add kvmapic back to it for
> compatibility. I know it sucks. But we can choose a different PC machine
> with accel=xen for new VMs.

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