On 20/03/2017 15:21, Herongguang (Stephen) wrote: > > We encountered a problem that when a domain starts, seabios failed to > online a vCPU. > > After investigation, we found that the reason is in kvm-kmod, > KVM_APIC_INIT bit in > vcpu->arch.apic->pending_events was overwritten by qemu, and thus an > INIT IPI sent > to AP was lost. Qemu does this since libvirtd sends a ‘query-cpus’ qmp > command to qemu > on VM start. > > In qemu, qmp_query_cpus-> cpu_synchronize_state-> > kvm_cpu_synchronize_state-> > do_kvm_cpu_synchronize_state, qemu gets registers/vcpu_events from > kvm-kmod and > sets cpu->kvm_vcpu_dirty to true, and vcpu thread in qemu will call > kvm_arch_put_registers if cpu->kvm_vcpu_dirty is true, thus > pending_events is > overwritten by qemu. > > I think there is no need for qemu to set cpu->kvm_vcpu_dirty to true > after ‘query-cpus’, > and kvm-kmod should not clear KVM_APIC_INIT unconditionally. And I am > not sure whether > it is OK for qemu to set cpu->kvm_vcpu_dirty in > do_kvm_cpu_synchronize_state in each caller. > > What’s your opinion? Hi Rongguang, sorry for the late response. Where exactly is KVM_APIC_INIT dropped? kvm_get_mp_state does clear the bit, but the result of the INIT is stored in mp_state. kvm_get_vcpu_events is called after kvm_get_mp_state; it retrieves KVM_APIC_INIT in events.smi.latched_init and kvm_set_vcpu_events passes it back. Maybe it should ignore events.smi.latched_init if not in SMM, but I would like to understand the exact sequence of events. Thanks, paolo
