Virtualization has been widely used as a key technology in cloud computing. Although facilitating the deployment of applications, virtualization introduces huge processing overheads, among which is network I/O virtualization that has become a critical bottleneck of a virtual system. DPDK-vhost is currently the fastest para-virtualized network I/O backend, however it performs poorly when exchanging large packets between virtual machines. Its inefficiency comes from packet copying involved in packet transmission. A zero-copy solution was proposed in the literature to eliminate packet copying by use of shared memory, but it violates the isolation principle of virtual machines. This paper presents a zero-copy vhost design that eliminates packet copying by modifying the extended page tables (EPTs), and meanwhile keeps virtual machines isolated. A prototype adapted from DPDK-vhost is implemented in QEMU/KVM environment, and its performance is verified by experiments to be much higher than that of DPDK-vhost when large packets are transmitted.