On Tue, Feb 27, 2018 at 01:46:04PM +0100, Christoffer Dall wrote: > 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 ? > CC'ing Igor and qemu-devel drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
