On 02/12/15 02:40, Shannon Zhao wrote: > > > On 2015/12/2 0:57, Marc Zyngier wrote: >> On 01/12/15 16:26, Shannon Zhao wrote: >>> >>> >>> On 2015/12/1 23:41, Marc Zyngier wrote: >>>>> The reason is that when guest clear the overflow register, it will trap >>>>>> to kvm and call kvm_pmu_sync_hwstate() as you see above. At this moment, >>>>>> the overflow register is still overflowed(that is some bit is still 1). >>>>>> So We need to use some flag to mark we already inject this interrupt. >>>>>> And if during guest handling the overflow, there is a new overflow >>>>>> happening, the pmu->irq_pending will be set ture by >>>>>> kvm_pmu_perf_overflow(), then it needs to inject this new interrupt, right? >>>> I don't think so. This is a level interrupt, so the level should stay >>>> high as long as the guest hasn't cleared all possible sources for that >>>> interrupt. >>>> >>>> For your example, the guest writes to PMOVSCLR to clear the overflow >>>> caused by a given counter. If the status is now 0, the interrupt line >>>> drops. If the status is still non zero, the line stays high. And I >>>> believe that writing a 1 to PMOVSSET would actually trigger an >>>> interrupt, or keep it high if it has already high. >>>> >>> Right, writing 1 to PMOVSSET will trigger an interrupt. >>> >>>> In essence, do not try to maintain side state. I've been bitten. >>> >>> So on VM entry, it check if PMOVSSET is zero. If not, call >>> kvm_vgic_inject_irq to set the level high. If so, set the level low. >>> On VM exit, it seems there is nothing to do. >> >> It is even simpler than that: >> >> - When you get an overflow, you inject an interrupt with the level set to 1. >> - When the overflow register gets cleared, you inject the same interrupt >> with the level set to 0. >> >> I don't think you need to do anything else, and the world switch should >> be left untouched. >> > > On 2015/7/17 23:28, Christoffer Dall wrote:>> > + > kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, >>>> + pmu->irq_num, 1); >> what context is this overflow handler function? kvm_vgic_inject_irq >> grabs a mutex, so it can sleep... >> >> from a quick glance at the perf core code, it looks like this is in >> interrupt context, so that call to kvm_vgic_inject_irq looks bad. >> > > But as Christoffer said before, it's not good to call > kvm_vgic_inject_irq directly in interrupt context. So if we just kick > the vcpu here and call kvm_vgic_inject_irq on VM entry, is this fine? Possibly. I'm slightly worried that inject_irq itself is going to kick the vcpu again for no good reason. I guess we'll find out (and maybe we'll add a kvm_vgic_inject_irq_no_kick_please() helper...). Thanks, M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
