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

["Huang, Kai" <kai.huang@intel.com>]

On Thu, 2022-09-01 at 14:18 +0800, Gao, Chao wrote:
> 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>
> 
> Isaku, your signed-off-by is missing.
> 
> > Link: https://lore.kernel.org/r/20220216031528.92558-6-chao.gao@intel.com
> > ---
> > include/linux/cpuhotplug.h |  2 +-
> > virt/kvm/kvm_main.c        | 30 ++++++++++++++++++++++--------
> > 2 files changed, 23 insertions(+), 9 deletions(-)
> > 
> > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> > index f61447913db9..7972bd63e0cb 100644
> > --- a/include/linux/cpuhotplug.h
> > +++ b/include/linux/cpuhotplug.h
> > @@ -185,7 +185,6 @@ enum cpuhp_state {
> > 	CPUHP_AP_CSKY_TIMER_STARTING,
> > 	CPUHP_AP_TI_GP_TIMER_STARTING,
> > 	CPUHP_AP_HYPERV_TIMER_STARTING,
> > -	CPUHP_AP_KVM_STARTING,
> > 	CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
> > 	CPUHP_AP_KVM_ARM_VGIC_STARTING,
> > 	CPUHP_AP_KVM_ARM_TIMER_STARTING,
> 
> The movement of CPUHP_AP_KVM_STARTING changes the ordering between
> CPUHP_AP_KVM_STARTING and CPUHP_AP_KVM_ARM_* above [1]. We need
> the patch [2] from Marc to avoid breaking ARM.
> 
> [1] https://lore.kernel.org/lkml/87sfsq4xy8.wl-maz@kernel.org/
> [2] https://lore.kernel.org/lkml/20220216031528.92558-5-chao.gao@intel.com/

How about Isaku just to take your series directly (+his SoB) and add additional
patches?

-- 
Thanks,
-Kai