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

Isaku Yamahata
2022-09-01T16:52:47Z

On Thu, Sep 01, 2022 at 10:58:04AM +0000,
"Huang, Kai" <kai.huang@intel.com> wrote:

> 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?

Ok will do. Although I hoped to slim it down, I've ended up to take most of it.
four out of six. Now why not two more.
--
Isaku Yamahata <isaku.yamahata@gmail.com>