Avi Kivity wrote: > Jan Kiszka wrote: >>> The nmi handler could change the tpr to mask the preempted interrupt; >>> but the code would not notice that. Once the interrupt was injected the >>> guest would see an interrupt at a higher priority than it has programmed >>> the hardware to allow. >>> >> >> I consider this a bit far fetch. What sane NMI handler would fiddle with >> the APIC? It would be fairly tricky to properly synchronize this with >> the rest of the OS. >> > > Sure, this is not a realistic guest. > >>> Basically, once we commit to an interrupt via kvm_cpu_get_interrupt(), >>> we must inject it before the any instruction gets executed. >>> >>> I don't think any real guest would notice, though. >>> >>> >> >> Well, I have no problems with your approach (when also applied on the >> user space irqchip path) of keeping the order *if* we can ensure that >> only the first instruction of the IRQ handler is executed and we will >> then inject the NMI. Otherwise this opens a prio inversion between IRQs >> and NMIs. The point is that, unless I'm overseeing some detail right >> now, your approach will inject the pending NMI only once the guest >> /happens/ to exit the VM, right? If yes, then it's a no-go IMHO, also >> for keeping this property with the queue approach. >> > > enable_nmi_window() should cause an exit once the interrupt has been > injected (likely before the first interrupt handler instruction was > executed, but after the stack frame was created). So the nmi will not > be delayed.
Right now, you only call enable_nmi_window() if that window is currently closed - and that's not the common case I'm worried about. > > But I think I see a bigger issue - if we inject an regular interrupt > while another is pending, then we will encounter this problem. Looks > like we have to enable the interrupt window after injecting an interrupt > if there are still pending interrupts. Yeah, probably. I'm just wondering now if we can set exit-on-interrupt-window while the vcpu state is interruptible (ie. _before_ the injection). There is some entry check like this for NMIs, but maybe no for interrupts. Need to check. Jan -- Siemens AG, Corporate Technology, CT SE 2 ES-OS Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
