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). Jan
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