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? Thanks, -- 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
