On 21/05/20 16:08, Paolo Bonzini wrote: > On 21/05/20 14:50, Vitaly Kuznetsov wrote: >> Sorry for reporting this late but I just found out that this commit >> breaks Hyper-V 2016 on KVM on SVM completely (always hangs on boot). I >> haven't investigated it yet (well, this is Windows, you know...) but >> what's usually different about Hyper-V is that unlike KVM/Linux it has >> handlers for some hardware interrupts in the guest and not in the >> hypervisor. > > "Always hangs on boot" is easy. :) At this point I think it's easiest > to debug it on top of the whole pending SVM patches that remove > exit_required completely (and exit_required is not coming back anyway). Ok so there could be two bugs, as the hang seems to happens much earlier later in the series (try "grep int_ctl:.0x.....1.." on the trace). As one could guess from the grep, one thing that is certainly different between KVM and Hyper-V is that Hyper-V injects interrupts using int_ctl; sometimes it also uses eventinj but presumably it's just copying it from exitintinfo). This could cause problems: for example, when L1 wants to inject a virtual interrupt into L2 that has interrupts disabled or V_TPR >= V_INTR_PRIO, and KVM also wants to inject an interrupt to L1, then KVM might end up stomping on Hyper-V's int_ctl. However I cannot think off-hand of a scenario where this could happen in this case, because Hyper-V does set EXIT_INTR and therefore we should never get into enable_irq_window while L2 is running. Still, that's one place where I'd start adding some trace_printk's. Also, if a uniprocessor guest also fails, it might be easier to debug. Paolo
