> > On 10.07.14 15:10, Christian Borntraeger wrote: > > From: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx> > > > > If a cpu is stopped, it must never be allowed to run and no interrupt may wake it > > up. A cpu also has to be unhalted if it is halted and has work to do - this > > scenario wasn't hit in kvm case yet, as only "disabled wait" is processed within > > QEMU. > > > > Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx> > > Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx> > > Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> > > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> > > This looks like it's something that generic infrastructure should take > care of, no? How does this work for the other archs? They always get an > interrupt on the transition between !has_work -> has_work. Why don't we > get one for s390x? > > > Alex > > Well, we have the special case on s390 as a CPU that is in the STOPPED or the CHECK STOP state may never run - even if there is an interrupt. It's basically like this CPU has been switched off. Imagine that it is tried to inject an interrupt into a stopped vcpu. It will kick the stopped vcpu and thus lead to a call to "kvm_arch_process_async_events()". We have to deny that this vcpu will ever run as long as it is stopped. It's like a way to "suppress" the interrupt for such a transition you mentioned. Later, another vcpu might decide to turn that vcpu back on (by e.g. sending a SIGP START to that vcpu). I am not sure if such a mechanism/scenario is applicable to any other arch. They all seem to reset the cs->halted flag if they know they are able to run (e.g. due to an interrupt) - they have no such thing as "stopped cpus", only "halted/waiting cpus". David -- 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
