Why does my Windows 7 VM running under Linux' KVM not use all the virtual processors?

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I've had a problem on my server since I migrated one of my VM's from Windows 2008 Server to Windows 7 (ultimate): though I've assigned four cores to the VM and it even seems to see them, it seems to think it has two cores!

Can anyone tell me what's going on here? I thought it could have been some incompatibility between KVM and Windows 7 but since it sees the virtual processors I'm beginning to think not...any clues?

Here's a screenshot of process manager showing only two cores on the same box:

I suspect the processors are being presented as single core processors in separate sockets. Windows 7 ultimate supports up to 2 socket systems, so it will use 2 processors.

I don't know if you can configure KVM to present the processors as either a single quad core CPU or 2 dual core CPUs, which should resolve the problem.

On libvirt 0.8.3, if you type:

virsh capabilities | grep topology

it will list the topology of the host:

<topology sockets='1' cores='4' threads='1'/>

The numbers refer to sockets, cores per socket, and threads per core. Add this line to the cpu entry in the xml file to allow windows to use all 4 cores, e.g.:

 <vcpu>4</vcpu>
 <cpu>
     <topology sockets='1' cores='4' threads='1'/>
 </cpu>