On Wed, Oct 18, 2017 at 03:18:43PM +0200, Christoffer Dall wrote: > On Wed, Oct 18, 2017 at 02:13:05PM +0200, Andrew Jones wrote: > > On Sat, Oct 14, 2017 at 09:13:35PM +0200, Christoffer Dall wrote: > > > On Fri, Sep 29, 2017 at 01:30:41PM +0200, Andrew Jones wrote: > > > > When the vPMU is in use if a VCPU's perf event overflow handler > > > > were to fire after the VCPU started waiting, then the wake up > > > > done by the kvm_vcpu_kick() call in the handler would do nothing, > > > > as no "pmu overflow" state is checked in kvm_arch_vcpu_runnable(). > > > > Fix this by checking the IRQ_PENDING VCPU request in runnable(). > > > > Checking the request also sufficiently covers all the cases that > > > > kvm_vgic_vcpu_pending_irq() cover, so we can just replace that. > > > > > > > > Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx> > > > > --- > > > > virt/kvm/arm/arm.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > > > > index 5bc9b0d2fd0f..725527f491e4 100644 > > > > --- a/virt/kvm/arm/arm.c > > > > +++ b/virt/kvm/arm/arm.c > > > > @@ -423,7 +423,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) > > > > return !vcpu_should_sleep(vcpu) && > > > > (vcpu->arch.mp_state != KVM_MP_STATE_HALTED || > > > > (!!vcpu->arch.irq_lines || > > > > - kvm_vgic_vcpu_pending_irq(vcpu))); > > > > + kvm_test_request(KVM_REQ_IRQ_PENDING, vcpu))); > > > > > > So what if a VCPU blocks, a device raises an IRQ, the VCPU loops around, > > > clears the KVM_REQ_IRQ_PENDING flag, enters the VM again, which does > > > another WFI (for fun), and you end up here again with a pending IRQ but > > > no KVM_REQ_IRQ_PENDING flag anymore. Doesn't this end up incorrectly > > > stalling the VCPU? > > > > Hmm, I see what you mean. I'm sorry I missed that. > > > > > > > > I don't think that a transient flag will work for a persistent binary > > > state here. > > > > I think we can fix it by adding > > > > if (kvm_vgic_vcpu_pending_irq(vcpu)) > > kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu); > > > > to kvm_vgic_sync_hwstate(), if the additional overhead would be > > acceptable. Otherwise we need to find some other way to ensure > > vPMU irqs unblock the VCPU. > > > > I think you just need to check > kvm_vgic_vcpu_pending_irq() || > kvm_test_request(KVM_REQ_IRQ_PENDING, vcpu) > > Wouldn't that fix it? It would. I was just hoping to eliminate the lock-taking kvm_vgic_vcpu_pending_irq() call from kvm_arch_vcpu_runnable() though, as kvm_arch_vcpu_runnable() may be called repeatedly during halt polling. Thanks, drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
