> Il 28/07/2014 17:03, David Hildenbrand ha scritto: > > Well the difference is, that a STOPPED vcpu can be woken up by non-interrupt > > like things (SIGP START) AND a special interrupt (SIGP RESTART - which is like > > a "SIPI"++ as it performs a psw exchange - "NMI"). So we basically have two > > paths that can lead to a state change. All interrupt bits may be in any > > combination (SIGP RESTART interrupts can't be masked out, nor can SIGP START be > > denied). > > > > The other thing may be that on s390, each vcpu (including itself) can put > > another vcpu into the STOPPED state - I assume that this is different for x86 " > > INIT_RECEIVED". For this reason we have to watch out for bad race conditions > > (e.g. multiple vcpus working on another vcpu)... > > You can do that in x86 by sending an INIT inter-processor interrupt. A > SIPI is ignored if the CPU is not in INIT_RECEIVED state. > > Commit 66450a21f99636af4fafac2afd33f1a40631bc3a introduced the current > implementation. > > - an INIT cancels a previous SIPI; > > - if both INIT and SIPI are sent, on real hardware you need to have a > few hundred microseconds between them, but KVM will reliably process > INIT before SIPI. > > See commit 299018f44ac553dce3caf84df1d14c4764faa279 for an example of > the races that can happen. > > Note that x86 has KVM_MP_STATE_SIPI_RECEIVED state but it is obsolete, > we go straight from KVM_MP_STATE_INIT_RECEIVED to KVM_MP_STATE_RUNNABLE. > Thanks for the explanation Paolo! Looks like from an interrupt point of view, the states have a lot in common. The major thing that differs on s390 is probably the way these interrupts are generated and what else they influence (all the power of the SIGP facility :) + special check-stop state that can't be left by an interrupt, only by SIGP CPU resets). 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
