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). Jan
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