On Tue, Feb 27, 2018 at 05:34:28PM +0530, bthakur@xxxxxxxxxxxxxx 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, bthakur@xxxxxxxxxxxxxx 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 ? Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
