From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: VCPU hotplug on KVM/ARM Date: Tue, 27 Feb 2018 11:47:08 +0100 Message-ID: <20180227104708.GA11391@cbox> References: <000e01d3afad$b9a13830$2ce3a890$@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1EE0F402C7 for ; Tue, 27 Feb 2018 05:40:42 -0500 (EST) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id uriKG6lTG9oR for ; Tue, 27 Feb 2018 05:40:18 -0500 (EST) Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id B4CB6402B8 for ; Tue, 27 Feb 2018 05:40:18 -0500 (EST) Received: by mail-wm0-f53.google.com with SMTP id w128so17181445wmw.0 for ; Tue, 27 Feb 2018 02:47:11 -0800 (PST) Content-Disposition: inline In-Reply-To: <000e01d3afad$b9a13830$2ce3a890$@codeaurora.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: bthakur@codeaurora.org Cc: kvmarm@lists.cs.columbia.edu List-Id: kvmarm@lists.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