cpu on vm

I have a application I am getting ready to install that runs on sql server 2008 r2 express. I have a server with 2 quad core 2.8 ghz processors. How will this work if I run the sql 2008 r2 express server in a VM. i read 1 cpu is supported so if I give that vm 4 cores will all 4 cores work with sql since each physical cpu is quad core?

Thanks