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. 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
