On 2015/12/2 16:45, Marc Zyngier wrote: > 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. Yes, this will introduce a extra kick. What's the impact of kicking a kicked vcpu? > I guess we'll find out (and maybe > we'll add a kvm_vgic_inject_irq_no_kick_please() helper...). And add a parameter "bool kick" for vgic_update_irq_pending ? -- Shannon -- 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
