On Mon, Aug 27, 2018 at 04:02:39PM +0200, Greg Kurz wrote: > On Mon, 27 Aug 2018 13:07:10 +0200 > Igor Mammedov <imamm...@redhat.com> wrote: > > > The first cpu unplug wasn't ever supported and corresponding > > monitor/qmp commands refuse to unplug it. However guest is able > > to issue eject request either using following command: > > # echo 1 >/sys/devices/system/cpu/cpu0/firmware_node/eject > > I can't reproduce the issue with a pc guest and current master... > > All I seem to get is an error in dmesg: > > [ 97.435446] processor cpu0: Offline failed. > > > or directly writing to cpu hotplug registers, which makes > > qemu crash with SIGSEGV following back trace: > > > > kvm_flush_coalesced_mmio_buffer () > > while (ring->first != ring->last) > > ... > > qemu_flush_coalesced_mmio_buffer > > prepare_mmio_access > > flatview_read_continue > > flatview_read > > address_space_read_full > > address_space_rw > > kvm_cpu_exec(cpu!0) > > qemu_kvm_cpu_thread_fn > > > > the reason for which is that ring == KVMState::coalesced_mmio_ring > > happens to be a part of 1st CPU that was uplugged by guest. > > > > Fix it by forbidding 1st cpu unplug from guest side and in addition > > remove CPU0._EJ0 ACPI method to make clear that unplug of the first > > CPU is not supported. > > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > --- > > CCing spapr and s390x folks in case targets need to prevent 1st CPU unplug > > as well > > > > A spapr guest can _release_ the first cpu by doing something like: > > # echo -n "/cpus/PowerPC,POWER8@0" > /sys/devices/system/cpu/release > > But AFAIK, this doesn't unplug the cpu from a QEMU standpoint.
Unplugging CPU 0 with device_del should be ok too.
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David Gibson | I'll have my music baroque, and my code
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