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Description of problem: If there is one time random hotplug vcpus then other hotplug operation will fail. for example: start guest with -smp 1 and maxcpus=160 option. the first hotplug: (qemu) cpu_set 10 online other hotplug Version-Release number of selected component (if applicable): How reproducible: Steps to Reproduce: 1./usr/libexec/qemu-kvm -M rhel6.3.0 -cpu host --enable-kvm -m 4G -smp 1,maxcpus=161 -name rhel6.3 -uuid ddcbfb49-3411-1701-3c36-6bdbc00bedbb -rtc base=utc,clock=host,driftfix=slew -drive file=/dev/vg-54/lvtest,if=none,id=ide,format=qcow2,cache=none,werror=stop,rerror=stop -device ide-drive,drive=ide,id=drive-ide0-0-0,bootindex=1 -netdev tap,id=hostnet1 -device e1000,netdev=hostnet1,id=net1,mac=86:12:50:a4:32:72 -spice port=5911,disable-ticketing -vga qxl -device sga -chardev socket,id=serial0,path=/var/test1,server,nowait -device isa-serial,chardev=serial0 -balloon virtio -monitor unix:/tmp/monitor2,server,nowait -monitor stdio 2.the first hotplug vcpu (qemu) cpu_set 100 online 3.continue to hotplug vcpus in order (qemu) cpu_set 2 online Actual results: hotplug fail Expected results: hotplug operation is successful within range of maxcpus Additional info: after step 2, use 'top' and 'cat /proc/cpuinfo' cann't get vcpu but 'ls /sys/device/system/cpus/' can see added vcpu in guest.
host info: # uname -r 2.6.32-257.el6.x86_64 qemu vesion: qemu-kvm-0.12.1.2-2.265.el6.x86_64 guest info: rhel6.3 64bit guest kernel version: uname -r 2.6.32-251.el6.x86_64
I'd say it is WONTFIX for 6.3 with high chance of regression if I start touch cpu_index and apic code to fix it. Lets deal with it upstream first, and then maybe rhel7 will have fix for it. For now plug cpus only in consecutive order or use libvirt which does this.