On 22/06/20 18:08, Igor Mammedov wrote: > Guest fails to online hotplugged CPU with error > smpboot: do_boot_cpu failed(-1) to wakeup CPU#4 > > It's caused by the fact that kvm_apic_set_state(), which used to call > recalculate_apic_map() unconditionally and pulled hotplugged CPU into > apic map, is updating map conditionally [1] on state change which doesn't > happen in this case and apic map update is skipped. > > Note: > new CPU during kvm_arch_vcpu_create() is not visible to > kvm_recalculate_apic_map(), so all related update calls endup > as NOP and only follow up kvm_apic_set_state() used to trigger map > update that counted in hotplugged CPU. > Fix issue by forcing unconditional update from kvm_apic_set_state(), > like it used to be. > > 1) > Fixes: (4abaffce4d25a KVM: LAPIC: Recalculate apic map in batch) > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx> > --- > PS: > it's alternative to full revert of [1], I've posted earlier > https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg2205600.html > so fii free to pick up whatever is better by now > --- > arch/x86/kvm/lapic.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 34a7e0533dad..5696831d4005 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -2556,6 +2556,7 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s) > struct kvm_lapic *apic = vcpu->arch.apic; > int r; > > + apic->vcpu->kvm->arch.apic_map_dirty = true; > kvm_lapic_set_base(vcpu, vcpu->arch.apic_base); > /* set SPIV separately to get count of SW disabled APICs right */ > apic_set_spiv(apic, *((u32 *)(s->regs + APIC_SPIV))); > Queued, but it's better to set apic_map_dirty just before the call to kvm_recalculate_apic_map, or you can have a variant of the race that you pointed out. Paolo
