On Mon, 22 Jun 2020 18:47:57 +0200 Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > 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. Here I was worried about failure path as well that is just before normal kvm_recalculate_apic_map(), and has its own kvm_recalculate_apic_map(). but I'm not sure if we should force map update in that case. > > Paolo >
