On 05.06.2011, at 19:56, Jan Kiszka wrote: > On 2011-06-05 19:54, Alexander Graf wrote: >> >> On 05.06.2011, at 19:48, Jan Kiszka wrote: >> >>> On 2011-06-05 19:19, Alexander Graf wrote: >>>> >>>> On 05.06.2011, at 18:33, Avi Kivity wrote: >>>> >>>>> On 06/05/2011 07:30 PM, Alexander Graf wrote: >>>>>>>> >>>>>>>> Could you elaborate what you mean here? I'm not really following. Are >>>>>>>> you suggesting a new arch-generic interface? (Pardon my ignorance). >>>>>>> >>>>>>> Using KVM_IRQ_LINE everywhere except s390, not just in x86 and ARM. >>>>>> >>>>>> An in-kernel MPIC implementation is coming for PPC, so I don't see any reason to switch from something that works now. >>>>> >>>>> Right, this is spilled milk. >>>>> >>>>> Does the ppc qemu implementation raise KVM_INTERRUPT solely from the vcpu thread? >>>> >>>> Well, without iothread it used to obviously. Now that we have an iothread, it calls ioctl(KVM_INTERRUPT) from a separate thread. The code also doesn't forcefully wake up the vcpu thread, so yes, I think here's a chance for at least delaying interrupt delivery. Chances are pretty slim we don't get out of the vcpu thread at all :). >>> >>> There are good chances to run into a deadlock when calling a per-vcpu >>> IOCTL over a foreign context: calling thread holds qemu_mutex and blocks >>> on kvm_mutex inside the kernel, target vcpu is running endless guest >>> loop, holding kvm_mutex, all other qemu threads will sooner or later >>> block on the global lock. That's at least one pattern you can get on x86 >>> (we had a few of such bugs in the past). >> >> Any recommendations? Should we just signal the main thread when we want to inject an interrupt? > > Yep. That's also what x86 does (when using user space irqchips). Hrm, ok :). I guess the main reason we don't see major issues is that 1) people don't use iothread too often yet - is it even enabled by default? 2) the decrementor interrupt happens in-kernel, so timer interrupts still arrive properly Alex -- 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
