On Thu, Sep 01, 2022 at 07:17:42PM -0700, isaku.yamahata@xxxxxxxxx wrote: > From: Chao Gao <chao.gao@xxxxxxxxx> > > 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> > Link: https://lore.kernel.org/r/20220216031528.92558-6-chao.gao@xxxxxxxxx > Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> > --- > 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 7337414e4947..de45be38dd27 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, > /* Must be the last timer callback */ > CPUHP_AP_DUMMY_TIMER_STARTING, > CPUHP_AP_ARM_XEN_STARTING, > @@ -200,6 +199,7 @@ enum cpuhp_state { > > /* Online section invoked on the hotplugged CPU from the hotplug thread */ > CPUHP_AP_ONLINE_IDLE, > + CPUHP_AP_KVM_ONLINE, > CPUHP_AP_SCHED_WAIT_EMPTY, > CPUHP_AP_SMPBOOT_THREADS, > CPUHP_AP_X86_VDSO_VMA_ONLINE, > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 278eb6cc7cbe..db1303e2abc9 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -5011,13 +5011,27 @@ static void hardware_enable_nolock(void *caller_name) > } > } > > -static int kvm_starting_cpu(unsigned int cpu) > +static int kvm_online_cpu(unsigned int cpu) > { > + int ret = 0; > + > raw_spin_lock(&kvm_count_lock); > - if (kvm_usage_count) > + /* > + * Abort the CPU online process if hardware virtualization cannot > + * be enabled. Otherwise running VMs would encounter unrecoverable > + * errors when scheduled to this CPU. > + */ > + if (kvm_usage_count) { > + WARN_ON_ONCE(atomic_read(&hardware_enable_failed)); Reviewed-by: Yuan Yao <yuan.yao@xxxxxxxxx> > + > hardware_enable_nolock((void *)__func__); > + if (atomic_read(&hardware_enable_failed)) { > + atomic_set(&hardware_enable_failed, 0); > + ret = -EIO; > + } > + } > raw_spin_unlock(&kvm_count_lock); > - return 0; > + return ret; > } > > static void hardware_disable_nolock(void *junk) > @@ -5030,7 +5044,7 @@ static void hardware_disable_nolock(void *junk) > kvm_arch_hardware_disable(); > } > > -static int kvm_dying_cpu(unsigned int cpu) > +static int kvm_offline_cpu(unsigned int cpu) > { > raw_spin_lock(&kvm_count_lock); > if (kvm_usage_count) > @@ -5841,8 +5855,8 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align, > goto out_free_2; > } > > - r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_STARTING, "kvm/cpu:starting", > - kvm_starting_cpu, kvm_dying_cpu); > + r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online", > + kvm_online_cpu, kvm_offline_cpu); > if (r) > goto out_free_2; > register_reboot_notifier(&kvm_reboot_notifier); > @@ -5903,7 +5917,7 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align, > kmem_cache_destroy(kvm_vcpu_cache); > out_free_3: > unregister_reboot_notifier(&kvm_reboot_notifier); > - cpuhp_remove_state_nocalls(CPUHP_AP_KVM_STARTING); > + cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); > out_free_2: > kvm_arch_hardware_unsetup(); > out_free_1: > @@ -5929,7 +5943,7 @@ void kvm_exit(void) > kvm_async_pf_deinit(); > unregister_syscore_ops(&kvm_syscore_ops); > unregister_reboot_notifier(&kvm_reboot_notifier); > - cpuhp_remove_state_nocalls(CPUHP_AP_KVM_STARTING); > + cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); > on_each_cpu(hardware_disable_nolock, NULL, 1); > kvm_arch_hardware_unsetup(); > kvm_arch_exit(); > -- > 2.25.1 >
