On 11/07/2016 10:56, Yang Zhang wrote: > On 2016/7/11 15:44, Paolo Bonzini wrote: >> >> >> On 11/07/2016 08:06, Yang Zhang wrote: >>>> Changes to MSI addresses follow the format used by interrupt remapping >>>> unit. >>>> The upper address word, that used to be 0, contains upper 24 bits of >>>> the LAPIC >>>> address in its upper 24 bits. Lower 8 bits are reserved as 0. >>>> Using the upper address word is not backward-compatible either as we >>>> didn't >>>> check that userspace zeroed the word. Reserved bits are still not >>>> explicitly >>> >>> Does this means we cannot migrate the VM from KVM_CAP_X2APIC_API enabled >>> host to the disable host even VM doesn't have more than 255 VCPUs? >> >> Yes, but that's why KVM_CAP_X2APIC_API is enabled manually. The idea is >> that QEMU will not use KVM_CAP_X2APIC_API except on the newest machine >> type. > > Thanks for confirmation. And when the KVM_CAP_X2APIC_API will be enabled > in Qemu? It could be 2.7 or 2.8. >> >> If interrupt remapping is on, KVM_CAP_X2APIC_API is needed even with 8 >> VCPUs, I think. Otherwise KVM will believe that 0xff is "broadcast" >> rather than "cluster 0, CPUs 0-7". > > If interrupt remapping is using, what 0xff means is relying on which > mode the destination CPU is in. I think there is no KVM_CAP_X2APIC_API > needed since interrupt remapping table gives all the information. If you have EIM 0xff never means broadcast, but KVM sees a 0xff in the interrupt route or KVM_SIGNAL_MSI argument and translates it into a broadcast. Paolo -- 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
