On Wed, Feb 16, 2022, Chao Gao wrote: > 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@xxxxxxxxxxxxx> > Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx> > --- For the KVM bits, Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> Someone with more knowledge of the CPU hotplug sequences should really review this too.
