qemu 2.1.0 fails to start if number of cores is greater than 1. qemu (kvm) 2.1.0 (built from sources) fails to start if number of cores is greater than 1. relevant part of commandline arguments: /usr/bin/qemu-system-x86_64 -name test3 -S -machine pc-i440fx-2.1,accel=kvm,usb=off -cpu Westmere -m 4096 -realtime mlock=off -smp 1,maxcpus=4,sockets=1,cores=4,threads=1 the error reported is: qemu-system-x86_64: /home/asavah/pkgbuild/qemu-2.1.0/hw/i386/smbios.c:825: smbios_get_tables: Assertion `smbios_smp_sockets >= 1' failed. 2014-08-05 21:45:35.825+0000: shutting down however setting 4 sockets with 1 core each allows me to start the machine just fine. the system is debian wheezy Linux hostname 3.16.0-hostname2 #2 SMP Mon Aug 4 17:02:16 EEST 2014 x86_64 GNU/Linux libvirt 1.2.7 (built from sources) -smp 1,maxcpus=4,sockets=1,cores=4,threads=1 should be -smp 4,maxcpus=4,sockets=1,cores=4,threads=1 although more human-friendly error is more appropriate there (better than a silent fallback to either 1- or 4- core topology) I forgot to mention that VM was created and managed remotely via virt-manager 0.9.5 from another host. I used custom cpu topology. however this config worked fine on qemu 2.0.0 with virt-manager 0.9.5 just tried virt-manager 1.0.1 - it creates the proper argument -smp 4,maxcpus=4,sockets=1,cores=4,threads=1 so this was a virt-manager bug already fixed upstream. this bug can be closed :)