On Wed, Dec 02, 2015 at 10:22:04AM +0000, Marc Zyngier wrote: > On 02/12/15 09:49, Shannon Zhao wrote: > > > > > > 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? > > As long as you only kick yourself, it shouldn't be much (trying to > decipher vcpu_kick). > The behavior of vcpu_kick really depends on a number of things: - If you're kicking yourself, nothing happens. - If you're kicking a sleeping vcpu, wake it up - If you're kicking a running vcpu, send it a physical IPI - If the vcpu is not running, and not sleeping (so still runnable) don't do anything, just wait until it gets scheduled. -Christoffer -- 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
