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From: | Maran Wilson |
Subject: | Re: [Qemu-arm] VCPU hotplug on KVM/ARM |
Date: | Tue, 24 Jul 2018 11:35:31 -0700 |
User-agent: | Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
Thanks, -Maran On 2/27/2018 5:21 AM, Andrew Jones wrote:
On Tue, Feb 27, 2018 at 01:46:04PM +0100, Christoffer Dall wrote:On Tue, Feb 27, 2018 at 05:34:28PM +0530, address@hidden wrote:Hi Christoffer, Thanks for your reply. On 2018-02-27 16:17, Christoffer Dall wrote:Hi Bhupinder, On Tue, Feb 27, 2018 at 03:01:17PM +0530, address@hidden 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?It should be a feasible solution provided the guest VM is not able to control the onlining/offlining of VCPUs. It should be controlled by the Host.KVM could simply refuse to turn on some of the CPUs unless given permission from host userspace.How does VCPU hotplug work on x86?On x86, you can add a vcpu through libvirt setvcpu command and it shows up in the guest VM as a new CPU if you do lscpu.Sure, but what is the mechanism, does x86 qemu actually call KVM_CREATE_VCPU, or is this also a question of turning on already created vcpus ?CC'ing Igor and qemu-devel drew _______________________________________________ kvmarm mailing list address@hidden https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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