Re: [PATCH v2 05/19] KVM: Rename and move CPUHP_AP_KVM_STARTING to ONLINE section

Chao Gao
2022-09-01T06:00:22Z

On Tue, Aug 30, 2022 at 05:01:20AM -0700, isaku.yamahata@intel.com wrote:
>From: Chao Gao <chao.gao@intel.com>
>
>The CPU STARTING section doesn't allow callbacks to fail. Move KVM's
>hotplug callback to ONLINE section so that it can abort onlining a CPU in
>certain cases to avoid potentially breaking VMs running on existing CPUs.
>For example, when kvm fails to enable hardware virtualization on the
>hotplugged CPU.
>
>Place KVM's hotplug state before CPUHP_AP_SCHED_WAIT_EMPTY as it ensures
>when offlining a CPU, all user tasks and non-pinned kernel tasks have left
>the CPU, i.e. there cannot be a vCPU task around. So, it is safe for KVM's
>CPU offline callback to disable hardware virtualization at that point.
>Likewise, KVM's online callback can enable hardware virtualization before
>any vCPU task gets a chance to run on hotplugged CPUs.
>
>KVM's CPU hotplug callbacks are renamed as well.
>
>Suggested-by: Thomas Gleixner <tglx@linutronix.de>
>Signed-off-by: Chao Gao <chao.gao@intel.com>
>Link: https://lore.kernel.org/r/20220216031528.92558-6-chao.gao@intel.com

Note that Sean gave his Reviewed-by for KVM changes.