Re: VCPU hotplug on KVM/ARM

[Christoffer Dall <cdall@cs.columbia.edu>]

Hi Bhupinder,

On Tue, Feb 27, 2018 at 03:01:17PM +0530, bthakur@codeaurora.org wrote:
> I hope it is the right forum to post my query.
> 
>  
> 
> I am currently looking at the possibility of adding a new VCPU to a running
> guest VM in KVM/ARM. I see that currently, it is not allowed to add a new
> VCPU to a guest VM, if it is already initialized. The first check in
> kvm_arch_vcpu_create() returns failure if it is already initialized.
> 

This would require a major rework of a lot of logic surrounding the GIC
and other parts of KVM initialization.

>  
> 
> There was some work done in QEMU to add support for VCPU hotplug:
> https://lists.gnu.org/archive/html/qemu-arm/2017-05/msg00404.html
> 
>  
> 
> But I am looking at the KVM side for enabling adding a new VCPU. If you can
> point me to any relevant work/resources, which I can refer to then it will
> help me.
> 

I don't have any specific pointers, but I was always told that the way
we were going to do CPU hotplug would be to instantiate a large number
of VCPUs, and hotplug would be equivalent to turning on a VCPU which was
previously powered off.

Is this not still a feasible solution?

How does VCPU hotplug work on x86?

Thanks,
-Christoffer